Science.gov

Sample records for shear velocity ratio

  1. Variable aspect ratio method in the Xu-White model for shear-wave velocity estimation

    NASA Astrophysics Data System (ADS)

    Bai, Jun-Yu; Yue, Cheng-Qi; Liang, Yi-Qiang; Song, Zhi-Xiang; Ling, Su; Zhang, Yang; Wu, Wei

    2013-06-01

    Shear-wave velocity logs are useful for various seismic interpretation applications, including bright spot analyses, amplitude-versus-offset analyses and multicomponent seismic interpretations. This paper presents a method for predicting the shear-wave velocity of argillaceous sandstone from conventional log data and experimental data, based on Gassmann's equations and the Xu-White model. This variable aspect ratio method takes into account all the influences of the matrix nature, shale content, porosity size and pore geometry, and the properties of pore fluid of argillaceous sandstone, replacing the fixed aspect ratio assumption in the conventional Xu-White model. To achieve this, we first use the Xu-White model to derive the bulk and shear modulus of dry rock in a sand-clay mixture. Secondly, we use Gassmann's equations to calculate the fluid-saturated elastic properties, including compressional and shear-wave velocities. Finally, we use the variable aspect ratio method to estimate the shear-wave velocity. The numerical results indicate that the variable aspect ratio method provides an important improvement in the application of the Xu-White model for sand-clay mixtures and allows for a variable aspect ratio log to be introduced into the Xu-White model instead of the constant aspect ratio assumption. This method shows a significant improvement in predicting velocities over the conventional Xu-White model.

  2. Effect of velocity ratio on coherent-structure dynamics in turbulent free shear layers

    NASA Astrophysics Data System (ADS)

    Suryanarayanan, Saikishan; Narasimha, Roddam

    2014-11-01

    The relevance of the vortex-gas model to the large scale dynamics of temporally evolving turbulent free shear layers has been established by extensive simulations (Phys. Rev. E 89, 013009 (2014)). The effects of velocity ratio (r =U2 /U1) on shear layer dynamics are revealed by spatially evolving vortex-gas shear-layer simulations using a computational model based on Basu et al. (Appl. Math. Modelling 19, (1995)), but with a crucial improvement that ensures conservation of global circulation. The simulations show that the initial conditions and downstream boundaries can significantly affect the flow over substantial part of the domain, but the equilibrium spread rate is a universal function of r, and is within the experimental scatter. The spread in the r = 0 limit is higher than Galilean-transformed temporal value. The present 2D simulations at r = 0 show continuous growth of structures, while merger-dominated evolution is observed for r = 0 . 23 (and higher). These two mechanisms were observed across the same two values of r in the experiments of D'Ovidio & Coats (J. Fluid Mech. 737, 2013), but the continuous growth was instead attributed to mixing-transition and 3D. The 2D mechanisms responsible for the observed continuous growth of structures are analyzed in detail. Supported in part by RN/Intel/4288 and RN/DRDO/4124.

  3. System and method to estimate compressional to shear velocity (VP/VS) ratio in a region remote from a borehole

    DOEpatents

    Vu, Cung; Nihei, Kurt T; Schmitt, Denis P; Skelt, Christopher; Johnson, Paul A; Guyer, Robert; TenCate, James A; Le Bas, Pierre-Yves

    2012-10-16

    In some aspects of the disclosure, a method for creating three-dimensional images of non-linear properties and the compressional to shear velocity ratio in a region remote from a borehole using a conveyed logging tool is disclosed. In some aspects, the method includes arranging a first source in the borehole and generating a steered beam of elastic energy at a first frequency; arranging a second source in the borehole and generating a steerable beam of elastic energy at a second frequency, such that the steerable beam at the first frequency and the steerable beam at the second frequency intercept at a location away from the borehole; receiving at the borehole by a sensor a third elastic wave, created by a three wave mixing process, with a frequency equal to a difference between the first and second frequencies and a direction of propagation towards the borehole; determining a location of a three wave mixing region based on the arrangement of the first and second sources and on properties of the third wave signal; and creating three-dimensional images of the non-linear properties using data recorded by repeating the generating, receiving and determining at a plurality of azimuths, inclinations and longitudinal locations within the borehole. The method is additionally used to generate three dimensional images of the ratio of compressional to shear acoustic velocity of the same volume surrounding the borehole.

  4. System and method for investigating sub-surface features and 3D imaging of non-linear property, compressional velocity VP, shear velocity VS and velocity ratio VP/VS of a rock formation

    DOEpatents

    Vu, Cung Khac; Skelt, Christopher; Nihei, Kurt; Johnson, Paul A.; Guyer, Robert; Ten Cate, James A.; Le Bas, Pierre-Yves; Larmat, Carene S.

    2015-06-02

    A system and a method for generating a three-dimensional image of a rock formation, compressional velocity VP, shear velocity VS and velocity ratio VP/VS of a rock formation are provided. A first acoustic signal includes a first plurality of pulses. A second acoustic signal from a second source includes a second plurality of pulses. A detected signal returning to the borehole includes a signal generated by a non-linear mixing process from the first and second acoustic signals in a non-linear mixing zone within an intersection volume. The received signal is processed to extract the signal over noise and/or signals resulting from linear interaction and the three dimensional image of is generated.

  5. Velocity ratio and its application to predicting velocities

    USGS Publications Warehouse

    Lee, Myung W.

    2003-01-01

    The velocity ratio of water-saturated sediment derived from the Biot-Gassmann theory depends mainly on the Biot coefficient?a property of dry rock?for consolidated sediments with porosity less than the critical porosity. With this theory, the shear moduli of dry sediments are the same as the shear moduli of water-saturated sediments. Because the velocity ratio depends on the Biot coefficient explicitly, Biot-Gassmann theory accurately predicts velocity ratios with respect to differential pressure for a given porosity. However, because the velocity ratio is weakly related to porosity, it is not appropriate to investigate the velocity ratio with respect to porosity (f). A new formulation based on the assumption that the velocity ratio is a function of (1?f)n yields a velocity ratio that depends on porosity, but not on the Biot coefficient explicitly. Unlike the Biot-Gassmann theory, the shear moduli of water-saturated sediments depend not only on the Biot coefficient but also on the pore fluid. This nonclassical behavior of the shear modulus of water-saturated sediment is speculated to be an effect of interaction between fluid and the solid matrix, resulting in softening or hardening of the rock frame and an effect of velocity dispersion owing to local fluid flow. The exponent n controls the degree of softening/hardening of the formation. Based on laboratory data measured near 1 MHz, this theory is extended to include the effect of differential pressure on the velocity ratio by making n a function of differential pressure and consolidation. However, the velocity dispersion and anisotropy are not included in the formulation.

  6. Crustal structure beneath seismic stations deployed on rock in West Antarctica: New constrains on crustal shear wave velocities, Poisson's ratios and Moho depths

    NASA Astrophysics Data System (ADS)

    Ramirez, C.; Nyblade, A.; Wiens, D.; Aster, R. C.; Anandakrishnan, S.; Huerta, A. D.; Winberry, J. P.; Wilson, T. J.

    2016-12-01

    Over the past two decades there have been a number of broadband seismic networks deployed in Antarctica for investigating the deep earth structure and elucidating the nature of the crust and upper mantle beneath major tectonic features such as the Transantarctic Mountains, the Gamburtsev Subglacial Mountains, the West Antarctic Rift System, and the Marie Byrd Land Dome. Seismic data recorded by these networks have been analyzed to obtain estimates of crustal structure, such as Moho depth and Possion's ratio, leading to an improved understanding of Antarctic crustal structure. However, data from the different networks have been analyzed separately with a variety of modeling methods, resulting in non-uniform information on crustal properties. In this paper, we address the non-uniformity of available crustal parameters by modeling P wave receiver functions and Rayleigh wave velocities for all broadband stations in West Antarctica and the Transantarctic Mountains deployed on rock. Using the H-k stacking and a joint inversion methods and applying them to data from the 2000-2003 TAMSEIS and 2009-2015 POLENET networks, in addition to three permanent stations, we have obtained new estimates of Moho depth, crustal shear wave velocities and crustal Poisson's ratio. In addition, we report results for two new stations in West Antarctica. The ensemble of information on crustal thickness, crustal Poisson's ratio, and crustal shear wave velocity enables us to examine more comprehensively than previous studies the composition and structure of the crust beneath several tectonic blocks within the West Antarctica and the Transantarctic Mountains, and to comment further on their origin.

  7. Shear wave velocities in the earth's mantle.

    NASA Technical Reports Server (NTRS)

    Robinson, R.; Kovach, R. L.

    1972-01-01

    Direct measurement of the travel time gradient for S waves together with travel time data are used to derive a shear velocity model for the earth's mantle. In order to satisfy the data it is necessary to discard the usual assumption of lateral homogeneity below shallow depths. A shear velocity differential is proposed for a region between western North America and areas of the Pacific Ocean. Distinctive features of the velocity model for the upper mantle beneath western North America are a low-velocity zone centered at 100 km depth and zones of high velocity gradient beginning at 400, 650, and 900 km.

  8. Shear wave velocity measurements in marine sediments

    NASA Astrophysics Data System (ADS)

    Matthews, J. E.

    1982-09-01

    Pulsed ultrasonic techniques for the measurement of sound speed are reliable and well documented. Extension of these techniques to the measurement of shear wave velocities in marine sediments, generally was unsuccessful. Recently developed shear wave transducers, based upon piezoelectric benders operated at sonic frequencies, provide significantly improved transducer-sample mechanical coupling. This improved coupling allows the application of pulsed techniques to the measurement of shear wave velocities in marine sediments, and the rapid determination of sediment dynamic elastic properties. Two types of bender-based shear wave transducer and preliminary data are described: 1) a probe configuration for box core samples, and 2) a modification to the Hamilton Frame Velocimeter for cut samples.

  9. Gyrokinetic Simulation of Residual Stress from Diamagnetic Velocity Shears

    NASA Astrophysics Data System (ADS)

    Waltz, R. E.; Staebler, G. M.; Solomon, W. M.

    2010-11-01

    Residual stress refers to the remaining toroidal angular momentum (TAM) flux (divided by major radius) when the shear in the parallel velocity (and parallel velocity itself) vanishes. Previously [1] we demonstrated with gyrokinetic (GYRO) simulations that TAM pinching from the diamagnetic level shear in the ExB velocity could provide the residual stress needed for spontaneous toroidal rotation. Here we show that the shear in the diamagnetic velocities themselves provide comparable residual stress (and level of stabilization). The sign of the residual stress, quantified by the ratio of TAM flow to ion power flow (M/P), depends on the signs of the various velocity shears as well as ion (ITG) versus electron (TEM) mode directed turbulence. The residual stress from these temperature and density gradient diamagnetic velocity shears is demonstrated in global gyrokinetic simulation of ``null'' rotation DIIID discharges by matching M/P profiles within experimental error. 8pt [1] R.E. Waltz, G.M. Staebler, J. Candy, and F.L. Hinton, Phys. Plasmas 14, 122507 (2007); errata 16, 079902 (2009).

  10. Global horizontal shear velocity structure

    NASA Astrophysics Data System (ADS)

    Ho, T. M.; Priestley, K. F.; Debayle, E.; Chapman, C. H.

    2013-12-01

    Rayleigh wave data have been used extensively to produce various SV-wave tomographic models of the upper mantle. Love wave data are more difficult to deal with resulting in fewer SH-wave tomographic models. The models also do not incorporate higher mode information which can place better constraints on the model. We have assembled a large, horizontal component data set and have inverted these seismogram in the 4-13 mHz band including higher mode information. We use a version of the automated waveform inversion technique modified for Love waves. We have explored the effects of various crustal models and because of the greater sensitivity of Love waves to the crustal structure, at present, we limit our inversion to this lower frequency band. Due to the higher mode Love waves having similar group velocities between the periods of 50-100 s for oceanic paths, interference occurs which partition techniques have difficulties dealing with. The modified technique used here does not require partitioning the data and can help extract the data more easily at these period bands. We present a new VSH and Xi model for the upper mantle. High VSH extending to about 250 km depth occurs beneath the cratons and Tibet; Low VSH occurs beneath the mid-ocean ridges, the back arc basins and beneath the Afar hotspot. The Xi model shows that VSH is greater by approximately 3% at 100km and rapidly drops to zero at around 300 km depth where the mantle becomes isotropic. At 250 km depth, there are regions where SV is greater than SH, suggesting more vertical flow beneath mid-ocean ridges at these depths.

  11. Observations of velocity shear driven plasma turbulence

    NASA Technical Reports Server (NTRS)

    Kintner, P. M., Jr.

    1976-01-01

    Electrostatic and magnetic turbulence observations from HAWKEYE-1 during the low altitude portion of its elliptical orbit over the Southern Hemisphere are presented. The magnetic turbulence is confined near the auroral zone and is similar to that seen at higher altitudes by HEOS-2 in the polar cusp. The electrostatic turbulence is composed of a background component with a power spectral index of 1.89 + or - .26 and an intense component with a power spectral index of 2.80 + or - .34. The intense electrostatic turbulence and the magnetic turbulence correlate with velocity shears in the convective plasma flow. Since velocity shear instabilities are most unstable to wave vectors perpendicular to the magnetic field, the shear correlated turbulence is anticipated to be two dimensional in character and to have a power spectral index of 3 which agrees with that observed in the intense electrostatic turbulence.

  12. Shear velocity criterion for incipient motion of sediment

    USGS Publications Warehouse

    Simoes, Francisco J.

    2014-01-01

    The prediction of incipient motion has had great importance to the theory of sediment transport. The most commonly used methods are based on the concept of critical shear stress and employ an approach similar, or identical, to the Shields diagram. An alternative method that uses the movability number, defined as the ratio of the shear velocity to the particle’s settling velocity, was employed in this study. A large amount of experimental data were used to develop an empirical incipient motion criterion based on the movability number. It is shown that this approach can provide a simple and accurate method of computing the threshold condition for sediment motion.

  13. Electrostatic ion cyclotron velocity shear instability

    SciTech Connect

    Lemons, D.S.; Winske, D.; Gary, S.P. )

    1992-12-01

    An electrostatic ion cyclotron instability driven by sheared velocity flow perpendicular to a uniform magnetic field is investigated in the local approximation. The dispersion equation, which includes all kinetic effects and involves only one important parameter, is cast in the form of Gordeyev integrals and solved numerically. The instability occurs roughly at multiples of the ion cyclotron frequency (but modified by the shear) with the growth rate of the individual harmonics overlapping in wavenumber. At small values of the shear parameter, the instability exists in two branches, one at long wavelength, [kappa][rho][sub i] [approximately] 0.5, and one at short wavelength, [kappa][rho][sub i] > 1.5 ([kappa][rho][sub i] is the wavenumber normalized to the ion gyroradius). At larger values of the shear parameter only the longer wavelength branch persists. The growth rate of the long wavelength mode, maximized over wavenumber and frequency, increases monotonically with the shear parameter. Properties of the instability are compared to those of Ganguli et al. obtained in the nonlocal limit.

  14. Drift-wave transport in the velocity shear layer

    NASA Astrophysics Data System (ADS)

    Rosalem, K. C.; Roberto, M.; Caldas, I. L.

    2016-07-01

    Particle drift driven by electrostatic wave fluctuations is numerically computed to describe the transport in a gradient velocity layer at the tokamak plasma edge. We consider an equilibrium plasma in large aspect ratio approximation with E × B flow and specified toroidal plasma velocity, electric field, and magnetic field profiles. A symplectic map, previously derived for infinite coherent time modes, is used to describe the transport dependence on the electric, magnetic, and plasma velocity shears. We also show that resonant perturbations and their correspondent islands in the Poincaré maps are much affected by the toroidal velocity profiles. Moreover, shearless transport barriers, identified by extremum values of the perturbed rotation number profiles of the invariant curves, allow chaotic trajectories trapped into the plasma. We investigate the influence of the toroidal plasma velocity profile on these shearless transport barriers.

  15. The Influence of Shearing Velocity on Shear Behavior of Artificial Joints

    NASA Astrophysics Data System (ADS)

    Atapour, Hadi; Moosavi, Mahdi

    2014-09-01

    In this paper, the effects of shear velocity on the shearing behavior of artificial joints have been studied at different normal stress levels. Here, artificial joints with planar and rough surfaces were prepared with the plaster (simulating soft rock joints) and concrete (medium-hard rock joints) materials. The rough joints had triangular shaped asperities with 10° and 20° inclination angles. Direct shear tests were performed on these joints under various shear velocities in the range of 0.3-30 mm/min. The planar plaster-plaster and planer concrete-concrete joints were sheared at three levels of normal stress under constant normal load boundary condition. Also, the rough plaster-plaster and concrete-concrete joints were sheared at one level of normal stress under constant normal stiffness boundary condition. The results of the shear tests show that the shearing parameters of joints, such as shear strength, shear stiffness and friction angle, are related to the shear velocity. Shear strength of planar and rough plaster-plaster joints were decreased when the shear velocity was increased. Shear strength of concrete joints, except for rough joints with 10° inclination, increased with increasing shear velocity. Regardless of the normal stress level, shear stiffness of both planar plaster-plaster and concrete-concrete joints were decreased when the shear velocity was increased.

  16. Single-fluid stability of stationary plasma equilibria with velocity shear and magnetic shear

    SciTech Connect

    Miura, Akira

    2009-10-15

    By using incompressible single-fluid equations with a generalized Ohm's law neglecting the electron inertia, a linear eigenmode equation for a magnetic field perturbation is derived for stationary equilibria in a slab geometry with velocity and magnetic shears. The general eigenmode equation contains a fourth-order derivative of the perturbation in the highest order and contains Alfven and whistler mode components for a homogeneous plasma. The ratio of the characteristic ion inertia length to the characteristic inhomogeneity scale length is chosen as a small parameter for expansion. Neglecting whistler mode in the lowest order, the eigenmode equation becomes a second-order differential equation similar to the ideal magnetohydrodynamic eigenmode equation except for the fact that the unperturbed perpendicular velocity contains both electric and ion diamagnetic drifts. A sufficient condition for stability against the Kelvin-Helmholtz instability driven by shear in the ion diamagnetic drift velocity is derived and then applied to tokamaks.

  17. Hydrodynamic lubrication in nanoscale bearings under high shear velocity

    NASA Astrophysics Data System (ADS)

    Chen, Yunfei; Li, Deyu; Jiang, Kai; Yang, Juekuan; Wang, Xiaohui; Wang, Yujuan

    2006-08-01

    The setting up process in a nanoscale bearing has been modeled by molecular dynamics simulation. Contrary to the prediction from the classical Reynolds' theory, simulation results show that the load capacity of the nanoscale bearing does not increase monotonically with the operation speed. This is attributed to the change of the local shear rate, which will decrease with the shear velocity of the bearing as the shear velocity exceeds a critical value, i.e., the local shear rate has an upper limit. A simple nonlinear dynamic model indicates that the momentum exchange between the liquid and the solid wall is reduced with the shear velocity when the shear velocity is above a critical value. The weak momentum exchange results in a decrease of the local shear rate, which in turn causes a sharp increase of the slip length.

  18. Angular velocity of a spheroid log rolling in a simple shear at small Reynolds number

    NASA Astrophysics Data System (ADS)

    Meibohm, Jan; Candelier, Fabien; Rosen, Tomas; Einarsson, Jonas; Lundell, Fredrik; Mehlig, Bernhard

    2016-11-01

    We analyse the angular velocity of a small neutrally buoyant spheroid log rolling in a simple shear. When the effect of fluid inertia is negligible the angular velocity ω -> equals half the fluid vorticity. We compute by singular perturbation theory how weak fluid inertia reduces the angular velocity in an unbounded shear, and how this reduction depends upon the shape of the spheroid (on its aspect ratio). In addition we determine the angular velocity by direct numerical simulations. The results are in excellent agreement with the theory at small but not too small values of the shear Reynolds number, for all aspect ratios considered. For the special case of a sphere we find ω / s = - 1 / 2 + 0 . 0540Re 3 / 2 where s is the shear rate and Re is the shear Reynolds number. This result differs from that derived by Lin et al. who obtained a numerical coefficient roughly three times larger.

  19. Shear wave velocity structures of the Arabian Peninsula

    NASA Astrophysics Data System (ADS)

    Mokhtar, Talal A.; Al-Saeed, Mohammed M.

    1994-02-01

    The shear velocity structures of the different tectonic provinces of the Arabian Peninsula has been studied using surface wave data recorded by the RYD (Riyadh) station. The inversion of Rayleigh wave group velocities indicates that the Arabian shield can be modeled by two layers, each of which is 20 km thick with a shear velocity of 3.61 km/s in the upper crust and 3.88 km/s in the lower crust. The underlying upper mantle velocity is 4.61 km/s. Inversion of both Love and Rayleigh waves group velocities shows that the Arabian platform upper and lower crusts are comparable in their thicknesses to those of the shield, but with shear velocities of 3.4 and 4 km/s, respectively. The upper mantle velocity beneath the platform is 4.4 km/s and the average total thickness of the crust is 45 km.

  20. Electrostatic ion cyclotron velocity shear instability

    NASA Technical Reports Server (NTRS)

    Lemons, D. S.; Winske, D.; Gary, S. P.

    1992-01-01

    A local electrostatic dispersion equation is derived for a shear flow perpendicular to an ambient magnetic field, which includes all kinetic effects and involves only one important parameter. The dispersion equation is cast in the form of Gordeyev integrals and is solved numerically. Numerical solutions indicate that an ion cyclotron instability is excited. The instability occurs roughly at multiples of the ion cyclotron frequency (modified by the shear), with the growth rate or the individual harmonics overlapping in the wavenumber. At large values of the shear parameter, the instability is confined to long wavelengths, but at smaller shear, a second distinct branch at shorter wavelengths also appears. The properties of the instability obtained are compared with those obtained in the nonlocal limit by Ganguli et al. (1985, 1988).

  1. Shear velocity structure of the northern California lithosphere

    SciTech Connect

    Levander, A.R. ); Kovach, R.L. )

    1990-11-10

    The authors have determined the regional shear velocity structure of the lithosphere beneath the Coast Ranges and the Great Valley in northern California from inversion of three fundamental mode Rayleigh wave phase velocity curves. The dispersion measurements were made along three different paths crossing the Coast Ranges and Great Valley roughly perpendicular to the North American-Pacific plate boundary. The three dispersion curves diverge at periods greater than about 20 s; phase velocities are systematically higher from the northwest to the southeast along the transform margin. Inverting the phase velocities for crustal and upper mantle structure shows that this divergence is indicative of a 3-5% increase in the upper mantle shear velocity from the Napa-Great Valley region to the Diablo Range-Great Valley region. Crustal shear velocities are consistent with the lithologies expected in the middle and lower crust. The increase in mantle shear velocity from northwest to southeast is anticipated by a tectonic model for the development of the California transform margin in which asthenospheric material is emplaced at the base of the North American crust in the slab gap south of the Mendocino triple junction. Adjacent to the plate boundary, this process creates a subcrustal corridor of cooling asthenosphere which is gradually incorporated in the lithosphere lid. They suggest that this causes the observed increase in upper mantle shear velocity away from the triple junction. Finite difference simulations of Rayleigh wave propagation across asthenosphere corridor models produce synthetic phase velocity curves which are similar to the field observations.

  2. P1138Cardiac shear wave velocity in healthy individuals.

    PubMed

    Strachinaru, M; Geleijnse, M L; Bosch, J G; De Jong, N; Van Der Steen, Afw; Van Dalen, B M; Vos, H J

    2016-12-01

    The closure of the valves generates shear waves in the heart walls. The propagation velocity of shear waves relates to stiffness. This could potentially be used to estimate the stiffness of the myocardium, with huge potential implications in pathologies characterized by a deterioration of the diastolic properties of the left ventricle. In an earlier phantom study we already validated shear wave tracking with a clinical ultrasound system in cardiac mode. In this study we aimed to measure the shear waves velocity in normal individuals. 12 healthy volunteers, mean age=37±10, 33% females, were investigated using a clinical scanner (Philips iE33), equipped with a S5-1 probe, using a clinical tissue Doppler (TDI) application. ECG and phonocardiogram (PCG) were synchronously recorded. We achieved a TDI frame rate of >500Hz by carefully tuning normal system settings. Data were processed offline in Philips Qlab 8 to extract tissue velocity along a virtual M-mode line in the basal third of the interventricular septum, in parasternal long axis view. This tissue velocity showed a propagating wave pattern after closure of the valves. The slope of the wave front velocity in a space-time panel was measured to obtain the shear wave propagation velocity. The velocity of the shear waves induced by the closure of the mitral valve (1st heart sound) and aortic valve (2nd heart sound) was averaged over 4 heartbeats for every subject. Shear waves were visible after each closure of the heart valves, synchronous to the heart sounds. The figure shows one heart cycle of a subject, with the mean velocity along a virtual M-mode line in the upper panel, synchronous to the ECG signal (green line) and phonocardiogram (yellow line) in the lower panel. The slope of the shear waves is marked with dotted lines and the onset of the heart sounds with white lines. In our healthy volunteer group the mean velocity of the shear wave induced by mitral valve closure was 4.8±0.7m/s, standard error of 0.14 m

  3. ML shear wave velocity tomography for the Iranian Plateau

    NASA Astrophysics Data System (ADS)

    Maheri-Peyrov, Mehdi; Ghods, Abdolreza; Abbasi, Madjid; Bergman, Eric; Sobouti, Farhad

    2016-04-01

    Iranian Plateau reflects several different tectonic styles of collision, and large-scale strike-slip faults. We calculate a high-resolution 2-D ML shear velocity map for the Iranian Plateau to detect lateral crustal thickness changes associated with different tectonic boundaries. The ML velocity is very sensitive to strong lateral variations of crustal thickness and varies between the velocity of Lg and Sn phases. Our data set consists of 65 795 ML amplitude velocity measurements from 2531 precisely relocated events recorded by Iranian networks in the period 1996-2014. Using a constrained least-squares inversion scheme, we inverted the ML velocities for a 2-D shear velocity map of Iran. Our results show that the Zagros and South Caspian Basin (SCB) have shear wave velocities close to the Sn phase, and are thus Lg-blocking regions. High velocities in the High Zagros and the Simply Folded Belt imply significant crustal undulations within these zones. We note that in the central and south Zagros, the velocity border between the Zagros and central Iran is not coincident with the Zagros suture line that marks underthrusting of the Arabian plate beneath central Iran. The low plains of Gilan and Gorgan to the south of the Caspian Sea show high shear velocities similar to the SCB, implying that they are either underlain by an oceanic type crust or a transitional crust with a strong lateral crustal thickness gradient. The Lut block is an Lg-passing block implying that it is not surrounded by any sudden crustal thickness changes along its borders with central Iran. In the Alborz, NW Iran, Kopeh-Dagh, Binalud and most of the central Iran, low shear velocity near the Lg velocity is attributed to smooth or minor Moho undulations within these regions.

  4. Gyrokinetic simulation of momentum transport with residual stress from diamagnetic level velocity shears

    SciTech Connect

    Waltz, R. E.; Staebler, G. M.; Solomon, W. M.

    2011-04-15

    Residual stress refers to the remaining toroidal angular momentum (TAM) flux (divided by major radius) when the shear in the equilibrium fluid toroidal velocity (and the velocity itself) vanishes. Previously [Waltz et al., Phys. Plasmas 14, 122507 (2007); errata 16, 079902 (2009)], we demonstrated with GYRO [Candy and Waltz, J. Comp. Phys. 186, 545 (2003)] gyrokinetic simulations that TAM pinching from (ion pressure gradient supported or diamagnetic level) equilibrium ExB velocity shear could provide some of the residual stress needed to support spontaneous toroidal rotation against normal diffusive loss. Here we show that diamagnetic level shear in the intrinsic drift wave velocities (or ''profile shear'' in the ion and electron density and temperature gradients) provides a comparable residual stress. The individual signed contributions of these small (rho-star level) ExB and profile velocity shear rates to the turbulence level and (rho-star squared) ion energy transport stabilization are additive if the rates are of the same sign. However because of the additive stabilization effect, the contributions to the small (rho-star cubed) residual stress is not always simply additive. If the rates differ in sign, the residual stress from one can buck out that from the other (and in some cases reduce the stabilization.) The residual stress from these diamagnetic velocity shear rates is quantified by the ratio of TAM flow to ion energy (power) flow (M/P) in a global GYRO core simulation of a ''null'' toroidal rotation DIII-D [Mahdavi and Luxon, Fusion Sci. Technol. 48, 2 (2005)] discharge by matching M/P profiles within experimental uncertainty. Comparison of global GYRO (ion and electron energy as well as particle) transport flow balance simulations of TAM transport flow in a high-rotation DIII-D L-mode quantifies and isolates the ExB shear and parallel velocity (Coriolis force) pinching components from the larger ''diffusive'' parallel velocity shear driven component and

  5. Lithology and shear-wave velocity in Memphis, Tennessee

    USGS Publications Warehouse

    Gomberg, J.; Waldron, B.; Schweig, E.; Hwang, H.; Webbers, A.; Van Arsdale, R.; Tucker, K.; Williams, R.; Street, R.; Mayne, P.; Stephenson, W.; Odum, J.; Cramer, C.; Updike, R.; Hutson, S.; Bradley, M.

    2003-01-01

    We have derived a new three-dimensional model of the lithologic structure beneath the city of Memphis, Tennessee, and examined its correlation with measured shear-wave velocity profiles. The correlation is sufficiently high that the better-constrained lithologic model may be used as a proxy for shear-wave velocities, which are required to calculate site-amplification for new seismic hazard maps for Memphis. The lithologic model and its uncertainties are derived from over 1200 newly compiled well and boring logs, some sampling to 500 m depth, and a moving-least-squares algorithm. Seventy-six new shear-wave velocity profiles have been measured and used for this study, most sampling to 30 m depth or less. All log and velocity observations are publicly available via new web sites.

  6. Prediction of the Shear Wave Velocity from Compressional Wave Velocity for Gachsaran Formation

    NASA Astrophysics Data System (ADS)

    Parvizi, Saeed; Kharrat, Riyaz; Asef, Mohammad R.; Jahangiry, Bijan; Hashemi, Abdolnabi

    2015-10-01

    Shear and compressional wave velocities, coupled with other petrophysical data, are very important for hydrocarbon reservoir characterization. In situ shear wave velocity ( Vs) is measured by some sonic logging tools. Shear velocity coupled with compressional velocity is vitally important in determining geomechanical parameters, identifying the lithology, mud weight design, hydraulic fracturing, geophysical studies such as VSP, etc. In this paper, a correlation between compressional and shear wave velocity is obtained for Gachsaran formation in Maroon oil field. Real data were used to examine the accuracy of the prediction equation. Moreover, the genetic algorithm was used to obtain the optimal value for constants of the suggested equation. Furthermore, artificial neural network was used to inspect the reliability of this method. These investigations verify the notion that the suggested equation could be considered as an efficient, fast, and cost-effective method for predicting Vs from Vp.

  7. Molybdenum Sound Velocity and Shear Strength Softening

    NASA Astrophysics Data System (ADS)

    Nguyen, Jeffrey; Akin, Minta; Chau, Ricky; Fratandouno, Dayne; Ambrose, Pat; Fat'yanov, Oleg; Asimow, Paul; Holmes, Neil

    2013-06-01

    We recently carried out a series of light-gas gun experiments to measure molybdenum acoustic sound speed up to 5 Mbars on the Hugoniot. Our measured sound speeds increase linearly with pressure up to 2.6 Mbars and taper off near the melting pressure. The gradual leveling off of sound speed suggests a possible loss of shear strength near the melt. A linear extrapolation of our data to zero pressure is in good agreement with the sound speed measured at ambient condition. The results indicate that molybdenum remains in the bcc phase on the Hugoniot up to the melting pressure. There is no bcc solid phase transition on the Hugoniot as previously reported. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

  8. Vorticity structuring and velocity rolls triggered by gradient shear bands.

    PubMed

    Fielding, Suzanne M

    2007-07-01

    We suggest a mechanism by which vorticity structuring and velocity rolls can form in complex fluids, triggered by the linear instability of one-dimensional gradient shear banded flow. We support this with a numerical study of the diffusive Johnson-Segalman model. In the steady vorticity structured state, the thickness of the interface between the bands remains finite in the limit of zero stress diffusivity, presenting a possible challenge to the accepted theory of shear banding.

  9. Escaping radio emission from pulsars: Possible role of velocity shear

    SciTech Connect

    Mahajan, S.M. |; Machabeli, G.Z.; Rogava, A.D. |

    1997-01-01

    It is demonstrated that the velocity shear, intrinsic to the e{sup +}e{sup {minus}} plasma present in the pulsar magnetosphere, can efficiently convert the nonescaping longitudinal Langmuir waves (produced by some kind of a beam or stream instability) into propagating (escaping) electromagnetic waves. It is suggested that this shear induced transformation may be the basic mechanism needed for the eventual generation of the observed pulsar radio emission.

  10. Influence of Velocity Shear on the Rayleigh-Taylor Instability

    DTIC Science & Technology

    1981-12-16

    Agency and the O~ffice of Naval Research. 111 _ _ _ _ _ _ _ _ _ _ 44 References Chandresekhar, S., Hydrodynamic and Hydromagnetic Stabililty (Int. Ser...recovered. However I , ’ 0 for V I 0 the velocity shear term is clearly stabilizing . 0 0 Moreover, the stabilizing influence is k dependent and we expect...Observations of the development of striations in large barium clouds, Planet. Space Sci., 22, 67, 1974. TDrazin, P.C., The stability of a shear layer in an

  11. A strongly negative shear velocity gradient and lateral variability in the lowermost mantle beneath the Pacific

    NASA Astrophysics Data System (ADS)

    Ritsema, Jeroen; Garnero, Edward; Lay, Thorne

    1997-01-01

    A new approach for constraining the seismic shear velocity structure above the core-mantle boundary is introduced, whereby SH-SKS differential travel times, amplitude ratios of SV/SKS, and Sdiff waveshapes are simultaneously modeled. This procedure is applied to the lower mantle beneath the central Pacific using da.ta from numerous deep-focus southwest Pacific earthquakes recorded in North America. We analyze 90 broadband and 248 digitized analog recordings for this source-receiver geometry. SH-SKS times are highly variable and up to 10 s larger than standard reference model predictions, indicating the presence of laterally varying low shear velocities in the study area. The travel times, however, do not constrain the depth extent or velocity gradient of the low-velocity region. SV/SKS amplitude ratios and SH waveforms are sensitive to the radial shear velocity profile, and when analyzed simultaneously with SH-SKS times, rnveal up to 3% shear velocity reductions restricted to the lowermost 190±50 km of the mantle. Our preferred model for the central-eastern Pacific region (Ml) has a strong negative gradient (with 0.5% reduction in velocity relative to the preliminary reference Earth model (PREM) at 2700 km depth and 3% reduction at 2891 km depth) and slight velocity reductions from 2000 to 2700 km depth (0-0.5% lower than PREM). Significant small-scale (100-500 km) shear velocity heterogeneity (0.5%-1%) is required to explain scatter in the differential times and amplitude ratios.

  12. Structure of the velocity gradient tensor in turbulent shear flows

    NASA Astrophysics Data System (ADS)

    Pumir, Alain

    2017-07-01

    The expected universality of small-scale properties of turbulent flows implies isotropic properties of the velocity gradient tensor in the very large Reynolds number limit. Using direct numerical simulations, we determine the tensors formed by n =2 and 3 velocity gradients at a single point in turbulent homogeneous shear flows and in the log-layer of a turbulent channel flow, and we characterize the departure of these tensors from the corresponding isotropic prediction. Specifically, we separate the even components of the tensors, invariant under reflexion with respect to all axes, from the odd ones, which identically vanish in the absence of shear. Our results indicate that the largest deviation from isotropy comes from the odd component of the third velocity gradient correlation function, especially from the third moment of the derivative along the normal direction of the streamwise velocity component. At the Reynolds numbers considered (Reλ≈140 ), we observe that these second- and third-order correlation functions are significantly larger in turbulent channel flows than in homogeneous shear flow. Overall, our work demonstrates that a mean shear leads to relatively simple structure of the velocity gradient tensor. How isotropy is restored in the very large Reynolds limit remains to be understood.

  13. Cardiac Shear Wave Velocity Detection in the Porcine Heart.

    PubMed

    Vos, Hendrik J; van Dalen, Bas M; Heinonen, Ilkka; Bosch, Johan G; Sorop, Oana; Duncker, Dirk J; van der Steen, Antonius F W; de Jong, Nico

    2017-04-01

    Cardiac muscle stiffness can potentially be estimated non-invasively with shear wave elastography. Shear waves are present on the septal wall after mitral and aortic valve closure, thus providing an opportunity to assess stiffness in early systole and early diastole. We report on the shear wave recordings of 22 minipigs with high-frame-rate echocardiography. The waves were captured with 4000 frames/s using a programmable commercial ultrasound machine. The wave pattern was extracted from the data through a local tissue velocity estimator based on one-lag autocorrelation. The wave propagation velocity was determined with a normalized Radon transform, resulting in median wave propagation velocities of 2.2 m/s after mitral valve closure and 4.2 m/s after aortic valve closure. Overall the velocities ranged between 0.8 and 6.3 m/s in a 95% confidence interval. By dispersion analysis we found that the propagation velocity only mildly increased with shear wave frequency. Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.

  14. The velocity shear tensor: tracer of halo alignment

    NASA Astrophysics Data System (ADS)

    Libeskind, Noam I.; Hoffman, Yehuda; Forero-Romero, Jaime; Gottlöber, Stefan; Knebe, Alexander; Steinmetz, Matthias; Klypin, Anatoly

    2013-01-01

    The alignment of dark matter (DM) haloes and the surrounding large-scale structure (LSS) is examined in the context of the cosmic web. Halo spin, shape and the orbital angular momentum of subhaloes are investigated relative to the LSS using the eigenvectors of the velocity shear tensor evaluated on a grid with a scale of 1 Mpc h-1, deep within the non-linear regime. Knots, filaments, sheets and voids are associated with regions that are collapsing along 3, 2, 1 or 0 principal directions simultaneously. Each halo is tagged with a web classification (i.e. knot halo, filament halo, etc.) according to the nature of the collapse at the halo position. The full distribution of shear eigenvalues is found to be substantially different from that tagged to haloes, indicating that the observed velocity shear is significantly biased. We find that larger mass haloes live in regions where the shear is more isotropic, namely the expansion or collapse is more spherical. A correlation is found between the halo shape and the eigenvectors of the shear tensor, with the longest (shortest) axis of the halo shape being aligned with the slowest (fastest) collapsing eigenvector. This correlation is web independent, suggesting that the velocity shear is a fundamental tracer of the halo alignment. A similar result is found for the alignment of halo spin with the cosmic web. It has been shown that high-mass haloes exhibit a spin flip with respect to the LSS: we find that the mass at which this spin flip occurs is web dependent and not universal as suggested previously. Although weaker than haloes, subhalo orbits too exhibit an alignment with the LSS, providing a possible insight into the highly correlated corotation of the Milky Way's satellite system. The present study suggests that the velocity shear tensor constitutes the natural framework for studying the directional properties of the non-linear LSS and those of haloes and galaxies.

  15. Estimation of seabed shear-wave velocity profiles using shear-wave source data.

    PubMed

    Dong, Hefeng; Nguyen, Thanh-Duong; Duffaut, Kenneth

    2013-07-01

    This paper estimates seabed shear-wave velocity profiles and their uncertainties using interface-wave dispersion curves extracted from data generated by a shear-wave source. The shear-wave source generated a seismic signature over a frequency range between 2 and 60 Hz and was polarized in both in-line and cross-line orientations. Low-frequency Scholte- and Love-waves were recorded. Dispersion curves of the Scholte- and Love-waves for the fundamental mode and higher-order modes are extracted by three time-frequency analysis methods. Both the vertically and horizontally polarized shear-wave velocity profiles in the sediment are estimated by the Scholte- and Love-wave dispersion curves, respectively. A Bayesian approach is utilized for the inversion. Differential evolution, a global search algorithm is applied to estimate the most-probable shear-velocity models. Marginal posterior probability profiles are computed by Metropolis-Hastings sampling. The estimated vertically and horizontally polarized shear-wave velocity profiles fit well with the core and in situ measurements.

  16. Pumping velocity in homogeneous helical turbulence with shear.

    PubMed

    Rogachevskii, Igor; Kleeorin, Nathan; Käpylä, Petri J; Brandenburg, Axel

    2011-11-01

    Using different analytical methods (the quasilinear approach, the path-integral technique, and the tau-relaxation approximation) we develop a comprehensive mean-field theory for a pumping effect of the mean magnetic field in homogeneous nonrotating helical turbulence with imposed large-scale shear. The effective pumping velocity is proportional to the product of α effect and large-scale vorticity associated with the shear, and causes a separation of the toroidal and poloidal components of the mean magnetic field along the direction of the mean vorticity. We also perform direct numerical simulations of sheared turbulence in different ranges of hydrodynamic and magnetic Reynolds numbers and use a kinematic test-field method to determine the effective pumping velocity. The results of the numerical simulations are in agreement with the theoretical predictions.

  17. Influence of velocity shear on the Rayleigh-Taylor instability

    SciTech Connect

    Guzdar, P.N.; Satyanarayana, P.; Huba, J.D.; Ossakow, S.L.

    1982-05-01

    The influence of a transverse velocity shear on the Rayleigh-Taylor instability is investigated. It is found that a sheared velocity flow can substantially reduce the growth rate of the Rayleigh-Taylor instability in short wavelength regime (i.e., kL>1 where L is the scale length of the density inhomogeneity), and causes the growth rate to maximize at kL<1.0. Applications of this result to ionospheric phenomena (equatorial spread F (ESF) and ionospheric plasma clouds) are discussed. In particular, the effect of shear could account for, at times, the 100's of km modulation observed on the bottomside of the ESF ionosphere and the km scale size wavelengths observed in barium cloud prompt striation phenomena.

  18. Complex Shear Wave Velocity Structure Imaged Beneath Africa and Iceland.

    PubMed

    Ritsema; van Heijst HJ; Woodhouse

    1999-12-03

    A model of three-dimensional shear wave velocity variations in the mantle reveals a tilted low velocity anomaly extending from the core-mantle boundary (CMB) region beneath the southeastern Atlantic Ocean into the upper mantle beneath eastern Africa. This anomaly suggests that Cenozoic flood basalt volcanism in the Afar region and active rifting beneath the East African Rift is linked to an extensive thermal anomaly at the CMB more than 45 degrees away. In contrast, a low velocity anomaly beneath Iceland is confined to the upper mantle.

  19. Shear-wave velocity variation in jointed rock: an attempt to measure tide-induced variations

    SciTech Connect

    Beem, L.I.

    1987-08-01

    The use of the perturbation of seismic wave velocities by solid earth tides as a possible method of exploration for fractured media is discussed. Velocity of compressional seismic waves in fractured homogeneous rock has been observed to vary through solid earth tide cycles by a significant 0.5-0.9%. This variation of seismic velocities may be attributed to the opening and closing of joints by tidal stresses. In an attempt to see if shear-wave velocities show a similar velocity variation, a pneumatic shear-wave generator was used for the source. The 5 receivers, 3-component, 2.0 Hz, moving-coil geophones, were connected to a GEOS digital recorder. The two receivers located 120 m and 110 m from the source showed large shear-to-compression amplitude ratio and a high signal-to-noise ratio. A glaciated valley was chosen for the experiment site, since topography is flat and the granodiorite is jointed by a set of nearly orthogonal vertical joints, with superimposed horizontal sheeting joints. A slight velocity variation was noted in the first 200 consecutive firings; after which, the amplitude of the shear-wave begun to increase. This increase has been attributed to the compacting of the soil beneath the shear-wave generator (SWG). In the future, the soil will be compacted prior to placing the SWG or the SWG will be coupled directly to the rock to alleviate the amplitude fluctuation problem. This research may have application in exploration for fracture permeability in the rock mass between existing wells, by measuring seismic velocities from well to well through the tidal cycle.

  20. Residual turbulence from velocity shear stabilized interchange instabilities

    SciTech Connect

    Hung, C. P.; Hassam, A. B.

    2013-01-15

    The stabilizing effect of velocity shear on the macroscopic, broad bandwidth, ideal interchange instability is studied in linear and nonlinear regimes. A 2D dissipative magnetohydrodynamic (MHD) code is employed to simulate the system. For a given flow shear, V Prime , linear growth rates are shown to be suppressed to below the shear-free level at both the small and large wavelengths. With increasing V Prime , the unstable band in wavenumber-space shrinks so that the peak growth results for modes that correspond to relatively high wavenumbers, on the scale of the density gradient. In the nonlinear turbulent steady state, a similar turbulent spectrum obtains, and the convection cells are roughly circular. In addition, the density fluctuation level and the degree of flattening of the initial inverted density profile are found to decrease as V Prime increases; in fact, unstable modes are almost completely stabilized and the density profile reverts to laminar when V Prime is a few times the classic interchange growth rate. Moreover, the turbulent particle flux diminishes with increasing velocity shear such that all the flux is carried by the classical diffusive flux in the asymptotic limit. The simulations are compared with measurements of magnetic fluctuations from the Maryland Centrifugal Experiment, MCX, which investigated interchange modes in the presence of velocity shear. The experimental spectral data, taken in the plasma edge, are in general agreement with the numerical data obtained in higher viscosity simulations for which the level of viscosity is chosen consistent with MCX Reynolds numbers at the edge. In particular, the residual turbulence in both cases is dominated by elongated convection cells. Finally, concomitant Kelvin-Helmholtz instabilities in the system are also examined. Complete stability to interchanges is obtained only in the parameter space wherein the generalized Rayleigh inflexion theorem is satisfied.

  1. Gyrokinetic simulation of momentum transport with residual stress from diamagnetic level velocity shears

    NASA Astrophysics Data System (ADS)

    Waltz, R. E.; Staebler, G. M.; Solomon, W. M.

    2011-04-01

    Residual stress refers to the remaining toroidal angular momentum (TAM) flux (divided by major radius) when the shear in the equilibrium fluid toroidal velocity (and the velocity itself) vanishes. Previously [Waltz et al., Phys. Plasmas 14, 122507 (2007); errata 16, 079902 (2009)], we demonstrated with GYRO [Candy and Waltz, J. Comp. Phys. 186, 545 (2003)] gyrokinetic simulations that TAM pinching from (ion pressure gradient supported or diamagnetic level) equilibrium E ×B velocity shear could provide some of the residual stress needed to support spontaneous toroidal rotation against normal diffusive loss. Here we show that diamagnetic level shear in the intrinsic drift wave velocities (or "profile shear" in the ion and electron density and temperature gradients) provides a comparable residual stress. The individual signed contributions of these small (rho-star level) E ×B and profile velocity shear rates to the turbulence level and (rho-star squared) ion energy transport stabilization are additive if the rates are of the same sign. However because of the additive stabilization effect, the contributions to the small (rho-star cubed) residual stress is not always simply additive. If the rates differ in sign, the residual stress from one can buck out that from the other (and in some cases reduce the stabilization.) The residual stress from these diamagnetic velocity shear rates is quantified by the ratio of TAM flow to ion energy (power) flow (M/P) in a global GYRO core simulation of a "null" toroidal rotation DIII-D [Mahdavi and Luxon, Fusion Sci. Technol. 48, 2 (2005)] discharge by matching M/P profiles within experimental uncertainty. Comparison of global GYRO (ion and electron energy as well as particle) transport flow balance simulations of TAM transport flow in a high-rotation DIII-D L-mode quantifies and isolates the E ×B shear and parallel velocity (Coriolis force) pinching components from the larger "diffusive" parallel velocity shear driven component and

  2. An empirical method to estimate shear wave velocity of soils in the New Madrid seismic zone

    USGS Publications Warehouse

    Wei, B.-Z.; Pezeshk, S.; Chang, T.-S.; Hall, K.H.; Liu, Huaibao P.

    1996-01-01

    In this study, a set of charts are developed to estimate shear wave velocity of soils in the New Madrid seismic zone (NMSZ), using the standard penetration test (SPT) N values and soil depths. Laboratory dynamic test results of soil samples collected from the NMSZ showed that the shear wave velocity of soils is related to the void ratio and the effective confining pressure applied to the soils. The void ratio of soils can be estimated from the SPT N values and the effective confining pressure depends on the depth of soils. Therefore, the shear wave velocity of soils can be estimated from the SPT N value and the soil depth. To make the methodology practical, two corrections should be made. One is that field SPT N values of soils must be adjusted to an unified SPT N??? value to account the effects of overburden pressure and equipment. The second is that the effect of water table to effective overburden pressure of soils must be considered. To verify the methodology, shear wave velocities of five sites in the NMSZ are estimated and compared with those obtained from field measurements. The comparison shows that our approach and the field tests are consistent with an error of less than of 15%. Thus, the method developed in this study is useful for dynamic study and practical designs in the NMSZ region. Copyright ?? 1996 Elsevier Science Limited.

  3. Support vector machine for evaluating seismic-liquefaction potential using shear wave velocity

    NASA Astrophysics Data System (ADS)

    Samui, Pijush; Kim, Dookie; Sitharam, T. G.

    2011-01-01

    The use of the shear wave velocity data as a field index for evaluating the liquefaction potential of sands is receiving increased attention because both shear wave velocity and liquefaction resistance are similarly influenced by many of the same factors such as void ratio, state of stress, stress history and geologic age. In this paper, the potential of support vector machine (SVM) based classification approach has been used to assess the liquefaction potential from actual shear wave velocity data. In this approach, an approximate implementation of a structural risk minimization (SRM) induction principle is done, which aims at minimizing a bound on the generalization error of a model rather than minimizing only the mean square error over the data set. Here SVM has been used as a classification tool to predict liquefaction potential of a soil based on shear wave velocity. The dataset consists the information of soil characteristics such as effective vertical stress (σ‧v0), soil type, shear wave velocity (Vs) and earthquake parameters such as peak horizontal acceleration (amax) and earthquake magnitude (M). Out of the available 186 datasets, 130 are considered for training and remaining 56 are used for testing the model. The study indicated that SVM can successfully model the complex relationship between seismic parameters, soil parameters and the liquefaction potential. In the model based on soil characteristics, the input parameters used are σ‧v0, soil type, Vs, amax and M. In the other model based on shear wave velocity alone uses Vs, amax and M as input parameters. In this paper, it has been demonstrated that Vs alone can be used to predict the liquefaction potential of a soil using a support vector machine model.

  4. Hammering Yucca Flat, Part Two: Shear-Wave Velocity

    NASA Astrophysics Data System (ADS)

    Finlay, T. S.; Abbott, R. E.; Knox, H. A.; Tang, D. G.; James, S. R.; Haney, M. M.; Hampshire, J. B., II

    2015-12-01

    In preparation for the next phase of the Source Physics Experiment (SPE), we conducted an active-source seismic survey of Yucca Flat, Nevada, on the Nevada National Security Site. Results from this survey will be used to inform the geologic models associated with the SPE project. For this study, we used a novel 13,000 kilogram weight-drop seismic source to interrogate an 18-km North-South transect of Yucca Flat. Source points were spaced every 200 meters and were recorded by 350 to 380 3-component 2-Hz geophones with variable spacings of 10, 20, and 100 meters. We utilized the Refraction-Microtremor (ReMi) technique to create multiple 1D dispersion curves, which were then inverted for shear-wave velocity profiles using the Dix inversion method (Tsai and Haney, 2015). Each of these 1D velocity models was subsequently stitched together to create a 2D profile over the survey area. The dispersion results indicate a general decrease in surface-wave phase velocity to the south. This result is supported by slower shear-wave velocity sediments and increasing basin depth towards the survey's southern extent. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  5. Non-gyrotropic pressure anisotropy induced by velocity shear.

    NASA Astrophysics Data System (ADS)

    Tenerani, A.; Del Sarto, D.; Pegoraro, F.; Califano, F.

    2015-12-01

    We discuss how, in a collisionless magnetized plasma, a sheared velocity field may lead to the anisotropization of an initial Maxwellian state. By including the full pressure tensor dynamics in a fluid plasma model, we show, analytically and numerically, that a sheared velocity field makes an initial isotropic state anisotropic and non-gyrotropic [1], i.e., makes the plasma pressure tensor anisotropic also in the plane perpendicular to the magnetic field. The propagation of transverse magneto-elastic waves in the anisotropic plasma affects the process of formation of a non-gyrotropic pressure and can lead to its spatial filamentation. This plasma dynamics implies in particular that isotropic MHD equilibria cease to be equilibria in presence of a stationary sheared flow. Similarly, in the case of turbulence, where small-scale spatial inhomogeneities are naturally developed during the direct cascade, we may expect that isotropic turbulent states are not likely to exist whenever a full pressure tensor evolution is accounted for. These results may be relevant to understanding the agyrotropic pressure configurations which are well documented in solar wind measurements and possibly correlated to plasma flows (see e.g. Refs.[2,3]), and which have also been measured in Vlasov simulations of Alfvenic turbulence [4]. [1] D. Del Sarto, F. Pegoraro, F. Califano, "Pressure anisotropy and small spatial scales induced by a velocity shear", http://arxiv.org/abs/1507.04895 [2] H.F. Astudillo, E. Marsch, S. Livi, H. Rosenbauer, "TAUS measurements of non-gyrotropic distribution functions of solar wind alpha particles", AIP Conf. Proc. 328, 289 (1996). [3] A. Posner, M.W. Liemhon, T.H. Zurbuchen, "Upstream magnetospheric ion flux tube within a magnetic cloud: Wind/STICS", Geophys. Res. Lett. 30, (2003). [4] S. Servidio, F. Valentini, F. Califano, P. Veltri, "Local kinetic effects in Two-Dimensional Plasma Turbulence", Phys. Rev. Lett. 108, 045001 (2012).

  6. Anomalous shear wave delays and surface wave velocities at Yellowstone Caldera, Wyoming

    SciTech Connect

    Daniel, R.G.; Boore, D.M.

    1982-04-10

    To investigate the effects of a geothermal area on the propagation of intermediate-period (1--30 s) teleseismic body waves and surface waves, a specially designed portable seismograph system was operated in Yellowstone Caldera, Wyoming. Travel time residuals, relative to a station outside the caldera, of up to 2 s for compressional phases are in agreement with short-period residuals for P phases measured by other investigators. Travel time delays for shear arrivals in the intermediate-period band range from 2 to 9 s and decrease with increasing dT/d..delta... Measured Rayleigh wave phase velocities are extremely low, ranging from 3.2 km/s at 27-s period to 2.0 km/s at 7-s period; the estimated uncertainty associated with these values is 15%. We propose a model for compressional and shear velocities and Poisson's ratio beneath the Yellowstone caldera which fits the teleseismic body and surface wave data: it consists of a highly anomalous crust with an average shear velocity of 3.0 km/s overlying an upper mantle with average velocity of 4.1 km/s. The high average value of Poisson's ratio in the crust (0.34) suggests the presence of fluids there; Poisson's ratio in the mantle between 40 and approximately 200 km is more nearly normal (0.29) than in the crust. A discrepancy between normal values of Poisson's ratio in the crust calculated from short-period data and high values calculated from teleseismic data can be resolved by postulating a viscoelastic crustal model with frequency-dependent shear velocity and attenuation.

  7. Pressure anisotropy and small spatial scales induced by velocity shear

    NASA Astrophysics Data System (ADS)

    Del Sarto, D.; Pegoraro, F.; Califano, F.

    2016-05-01

    By including the full pressure tensor dynamics in a fluid plasma model, we show that a sheared velocity field can provide an effective mechanism that makes the initial isotropic pressure nongyrotropic. This is distinct from the usual gyrotropic anisotropy related to the fluid compressibility and usually accounted for in double-adiabatic models. We determine the time evolution of the pressure agyrotropy and discuss how the propagation of "magnetoelastic perturbations" can affect the pressure tensor anisotropization and its spatial filamentation, which are due to the action of both the magnetic field and the flow strain tensor. We support this analysis with a numerical integration of the nonlinear equations describing the pressure tensor evolution.

  8. 3D anisotropic surface wave and shear wave velocity structure beneath Eastern Tibet

    NASA Astrophysics Data System (ADS)

    Ceylan, S.; Ni, J. F.; Chen, Y. J.; Tilmann, F. J.; Sandvol, E. A.

    2011-12-01

    Recent studies have suggested that uplift of the northern Tibetan plateau may be related to removal of lithospheric mantle, resulting in emplacement of hotter, less dense asthenosphere. Other studies propose that plateau uplift and crustal thickening have occurred through a process of lateral mid-crustal flow or coherent deformation between crust and lithospheric mantle. Some authors attribute the geophysical properties of upper mantle beneath the plateau to either delamination of thickened lithosphere, or asthenospheric counterflow associated with subduction of continental Indian lithosphere beneath central Tibet. In order to study the evolution and dynamics of the Tibetan plateau, we deployed 74 broadband seismic stations throughout northeastern Tibet within the scope of ASCENT/INDEPTH-IV experiment. In conjunction with Namche Barwa data, we have calculated fundamental mode Rayleigh wave phase velocities utilizing two-plane wave approach, for periods between 20-143 seconds. We also obtained preliminary phase velocities using Love waves. To invert for shear wave velocities, we use partial derivatives from Saito (1988), assuming a constant Poisson's ratio. Our azimuthal anisotropy measurements agree well with SKS splitting results; both indicate significant (>2%) average azimuthal anisotropy throughout the upper mantle down to depths exceeding 250 km, with a dominantly EW fast directions. Although we observe variations of fast directions with depth, they are generally consistent (i.e., within 15 degrees) up to ~200 km, indicative of vertically coherent deformation. Furthermore at crustal depths, azimuthal fast directions tend be sub-parallel to the strikes of major strike slip faults, suggesting that shearing is the dominant deformation mechanism in eastern Tibet. Our tomographic models show an uppermost mantle low velocity anomaly north of Bangong-Nujiang Suture (BNS) in northeastern Tibet, and a high velocity anomaly extending ~200 km centered on the BNS. We

  9. Compressional and Shear Wave Velocities for Artificial Granular Media Under Simulated Near Surface Conditions

    SciTech Connect

    Bonner, B.P.; Berge, P.A.; Wildenschild, D.

    2001-09-09

    Laboratory ultrasonic experiments were made on artificial soil samples in order to observe the effects of slight overburden, sand/clay ratio and pore fluid saturation on compressional and shear wave velocities. Up to several meters of overburden were simulated by applying low uniaxial stress of about 0.1 MPa to a restrained sample. Samples were fabricated from Ottawa sand mixed with a swelling clay (Wyoming bentonite). The amount of clay added was 1 to 40 percent by mass. Most measurements were made under room-dry conditions, but some measurements were made for fully-saturated sand-clay mixtures and for partially-saturated sand samples. For the dry sand-clay samples, compressional (P) velocities were low, ranging from about 200 to 500 m/s for the mixtures at low stress. Shear (S) velocities were about half of the compressional velocity, about 70 to 250 m/s. Dramatic increases in all velocities occurred with small uniaxial loads, indicating strong nonlinearity. Composition and grain packing control the mechanical response at grain contacts and the resulting nonlinear response at low stresses. P and S velocities are sensitive to the amount of clay added, even at low concentrations. At these low equivalent overburden conditions, adhesion and capillarity at grain contacts affect wave amplitudes, velocities, and frequency content in the partial saturation case.

  10. Shear velocity of the Rotokawa geothermal field using ambient noise

    NASA Astrophysics Data System (ADS)

    Civilini, F.; Savage, M. K.; Townend, J.

    2014-12-01

    Ambient noise correlation is an increasingly popular seismological technique that uses the ambient seismic noise recorded at two stations to construct an empirical Green's function. Applications of this technique include determining shear velocity structure and attenuation. An advantage of ambient noise is that it does not rely on external sources of seismic energy such as local or teleseismic earthquakes. This method has been used in the geothermal industry to determine the depths at which magmatic processes occur, to distinguish between production and non-production areas, and to observe seismic velocity perturbations associated with fluid extraction. We will present a velocity model for the Rotokawa geothermal field near Taupo, New Zealand, produced from ambient noise cross correlations. Production at Rotokawa is based on the "Rotokawa A" combined cycle power station established in 1997 and the "Nga Awa Purua" triple flash power plant established in 2010. Rotokawa Joint Venture, a partnership between Mighty River Power and Tauhara North No. 2 Trust currently operates 174 MW of generation at Rotokawa. An array of short period seismometers was installed in 2008 and occupies an area of roughly 5 square kilometers around the site. Although both cultural and natural noise sources are recorded at the stations, the instrument separation distance provides a unique challenge for analyzing cross correlations produced by both signal types. The inter-station spacing is on the order of a few kilometers, so waves from cultural sources generally are not coherent from one station to the other, while the wavelength produced by natural noise is greater than the station separation. Velocity models produced from these two source types will be compared to known geological models of the site. Depending on the amount of data needed to adequately construct cross-correlations, a time-dependent model of velocity will be established and compared with geothermal production processes.

  11. Deep Mantle Large Low Shear-Wave Velocity Provinces: Principally Thermal Structures?

    NASA Astrophysics Data System (ADS)

    Davies, R.; Goes, S. D. B.

    2014-12-01

    The two large low shear-wave velocity provinces (LLSVPs) that dominate lower-mantle structure may hold key information on Earth's thermal and chemical evolution. It is generally accepted that these provinces are hotter than background mantle and are likely the main source of mantle plumes. Increasingly, it is also proposed that they hold a dense (primitive and/or recycled) compositional component. The principle evidence that LLSVPs may represent thermo-chemical `piles' comes from seismic constraints, including: (i) their long-wavelength nature; (ii) sharp gradients in shear-wave velocity at their margins; (iii) non-Gaussian distributions of deep mantle shear-wave velocity anomalies; (iv) anti-correlated shear-wave and bulk-sound velocity anomalies (and elevated ratios between shear- and compressional-wave velocity anomalies); (v) anti-correlated shear-wave and density anomalies; and (vi) 1-D/radial profiles of seismic velocity that deviate from those expected for an isochemical, well-mixed mantle. In addition, it has been proposed that hotspots and the reconstructed eruption sites of large igneous provinces correlate in location with LLSVP margins. Here, we review recent results, which indicate that the majority of these constraints do not require thermo-chemical piles: they are equally well (or poorly) explained by thermal heterogeneity alone. Our analyses and conclusions are largely based on comparisons between imaged seismic structure and synthetic seismic structures from a set of thermal and thermo-chemical mantle convection models, which are constrained by 300 Myr of plate motion histories. Modelled physical structure (temperature, pressure and composition) is converted into seismic velocities via a thermodynamic approach that accounts for elastic, anelastic and phase contributions and, subsequently, a tomographic resolution filter is applied to account for the damping and geographic bias inherent to seismic imaging. Our results indicate that, in terms of

  12. Shear wave velocities from noise correlation at local scale

    SciTech Connect

    De Nisco, G.; Nunziata, C.; Vaccari, F.; Panza, G. F.

    2008-07-08

    Cross correlations of ambient seismic noise recordings have been studied to infer shear seismic velocities with depth. Experiments have been done in the crowded and noisy historical centre of Napoli over inter-station distances from 50 m to about 400 m, whereas active seismic spreadings are prohibitive, even for just one receiver. Group velocity dispersion curves have been extracted with FTAN method from the noise cross correlations and then the non linear inversion of them has resulted in Vs profiles with depth. The information of near by stratigraphies and the range of Vs variability for samples of Neapolitan soils and rocks confirms the validity of results obtained with our expeditious procedure. Moreover, the good comparison of noise H/V frequency of the first main peak with 1D and 2D spectral amplifications encourages to continue experiments of noise cross-correlation. If confirmed in other geological settings, the proposed approach could reveal a low cost methodology to obtain reliable and detailed Vs velocity profiles.

  13. The influence of void ratio on small strain shear modulus of granular materials: A micromechanical perspective

    NASA Astrophysics Data System (ADS)

    Xu, Xiaomin; Cheng, Yipik; Ling, Dongsheng

    2013-06-01

    The small strain shear modulus Gmax of granular materials is highly dependent on their current void ratio and stress state, generally expressed as the famous Hardin and Richart equation. Various forms of void ratio functions have been proposed, either based on experimental or theoretical research. It is noted that each of them can be applied for a certain soil within a limited void ratio range. Micromechanical studies on the influence of void ratio on Gmax are conducted in this paper, using Discrete Element Method. After each sample being isotropically consolidated, shear wave velocity is measured by applying a velocity pulse to the transmitter in a certain direction, and monitoring the corresponding average velocity of the receiver. The capabilities of various existing void ratio functions are examined, together with the relationship between coordination number and void ratio, distribution of coordination number, as well as the contact force network. The void ratio effect on Gmax is further explained in terms of the wave travel length and the travel time for different contact connectivity networks.

  14. Imbalanced magnetohydrodynamic turbulence modified by velocity shear in the solar wind

    NASA Astrophysics Data System (ADS)

    Gogoberidze, G.; Voitenko, Y. M.

    2016-11-01

    We study incompressible imbalanced magnetohydrodynamic turbulence in the presence of background velocity shears. Using scaling arguments, we show that the turbulent cascade is significantly accelerated when the background velocity shear is stronger than the velocity shears in the subdominant Alfvén waves at the injection scale. The spectral transport is then controlled by the background shear rather than the turbulent shears and the Tchen spectrum with spectral index -1 is formed. This spectrum extends from the injection scale to the scale of the spectral break where the subdominant wave shear becomes equal to the background shear. The estimated spectral breaks and power spectra are in good agreement with those observed in the fast solar wind. The proposed mechanism can contribute to enhanced turbulent cascades and modified -1 spectra observed in the fast solar wind with strong velocity shears. This mechanism can also operate in many other astrophysical environments where turbulence develops on top of non-uniform plasma flows.

  15. Seismic Radiation in High-Velocity Shear Experiments

    NASA Astrophysics Data System (ADS)

    Zu, X.; Carpenter, B. M.; Reches, Z.

    2016-12-01

    High-speed rotary shear experiments allow to monitor co-seismic weakening along experimental faults, and to observe near source fault behavior. We used a system of 3D accelerometers during high-velocity shear experiments, and present our preliminary observations of the seismic radiation. The experimental faults were composed of solid igneous (diorite, gabbro) and sedimentary rocks (dolomite, sandstone), and slip area is a ring-shaped zone. The faults were loaded under constant velocity, and under controlled power density, in which slip occurs spontaneously and is controlled by the properties of the fault. The four 3D accelerometers were mounted 2 cm away from the experimental fault, recorded waveforms at 1 MHz, and accelerations up to 500 g.Preliminary results show hundreds of acoustic emission (AE) events in a single slip event with varied amplitudes, up to 500 g, and durations of up to 100 milliseconds. The hypocenter location in a given experiment revealed that AE initiated at two sites that are interpreted as strong asperities which were broken first to facilitate slip of the entire fault. Spectrograms of the AEs show multi-component patterns with the influence of both rock attributes and machine artifact. We also ran bi-material fault experiments (Carpenter et al, this meeting) in which the fault was composed of contrasting rock types. In a sandstone/gabbro fault, the arrival of the AEs was emergent, i.e., it had a low acceleration phase before a more impulsive acceleration. In contrast, the diorite/diorite fault displayed only the impulsive acceleration phase without a preceding low acceleration. Future analyses will focus on refinement of event source location patterns, spectral analysis, and the relationship between acoustic and mechanical properties of the faults.

  16. The lithospheric shear-wave velocity structure of Saudi Arabia: Young volcanism in an old shield

    NASA Astrophysics Data System (ADS)

    Tang, Zheng; Julià, Jordi; Mai, P. Martin

    2016-04-01

    We are utilizing receiver function and surface wave dispersion data to investigate the lithospheric shear-wave velocity structure of Saudi Arabia. The Arabian plate consists of the western Arabian shield and the eastern Arabian platform. The Arabian shield is a complicated mélange of several Proterozoic terrains, separated by ophiolite-bearing suture zones and dotted by outcropping Cenozoic volcanic rocks (so-called harrats). The Arabian platform is covered by thick Paleozoic, Mesozoic and Cenozoic sedimentary rocks. To understand the geo-dynamics and present-day geology in western Saudi Arabia, the origin and activity of the harrats needs to be investigated: are they controlled primarily by a local mantle plume underneath western Saudi Arabia or by lateral mantle flow from the Afar and (perhaps) Jordan hotspots? In our study, we first estimate Vp/Vs ratios by applying the H-κ stacking technique and construct local shear-wave velocity-depth profiles by jointly inverting teleseismic P-receiver functions and Rayleigh wave group velocities at 56 broadband stations deployed by the Saudi Geological Survey (SGS). Our results reveal significant lateral variations in crustal thickness, S-velocity, and bulk Vp/Vs ratio. The Arabian shield has, on average a ~34 km thick crust with Vs ~3.72 km/s and Vp/Vs ~1.73. Thinner crust (~25 - 32 km thick) with strong lateral variations is present along the Red Sea coast. In contrast, the Arabian platform reveals a ~41 km thick crust with Vs ~3.52 km/s and Vp/Vs ~1.77. We find anomalously high Vp/Vs ratios at Harrat Lunayyir, interpreted as solidified magma intrusions. Slow shear-velocities in the upper-mantle lid throughout the southernmost and northernmost Arabian shield suggest lateral heating from hot mantle upwellings centered beneath Afar and (perhaps) Jordan. Our findings on crustal S-velocity structures, Vp/Vs ratios, and upper-mantle lid velocities support the hypothesis of lateral mantle flow from the Afar and (perhaps

  17. Shear wave velocity structure of Reed Bank, southern continental margin of the South China Sea

    NASA Astrophysics Data System (ADS)

    Wei, Xiaodong; Ruan, Aiguo; Zhao, Minghui; Qiu, Xuelin; Wu, Zhenli; Niu, Xiongwei

    2015-03-01

    The shear wave velocity structure of a wide angle seismic profile (OBS973-2) across Reed Bank in the southern continental margin of the South China Sea (SCS) is simulated by 2-D ray-tracing method, based on its previous P-wave model. This profile is 369-km-long and consists of fifteen three-component ocean bottom seismometers (OBS). The main results are as follows.(1) The model consists of seven layers and the shear wave velocity increases from 0.7 km/s at the top of sediment layer to 4.0 km/s in the lower crust. (2) The Moho depth decreases from 20-22 km at the Reed Bank to 9-11 km at the deep oceanic basin with the shear wave velocity of 4.2 km/s below the Moho. (3) The Vp/Vs ratio decreases with depth through the sedimentary layers, attributed to increased compaction and consolidation of the rocks. (4) In the continental upper crust (at model distance 90-170 km), S-wave velocity (2.5-3.2 km/s) is relatively low and Vp/Vs ratio (1.75-1.82) is relatively high compared with the other parts of the crust, corresponding to the lower P-wave velocity in the previous P-wave model and normal faults revealed by MCS data, indicating that a strong regional extensional movement had occurred during the formation process of the SCS at the Reed Bank area. (5) The S-wave structures indicate that Reed Bank crust has different rock compositions from that in the east section of the northern margin, denying the presence of conjugate relationship of Reed Bank with Dongsha islands. According to P-wave models and other data, we inferred that Reed Bank and Macclesfield were separated from the same continental crust during the rifting and break-up process.

  18. Transition from velocity weakening to strong velocity strengthening friction in dense granular shear experiments

    NASA Astrophysics Data System (ADS)

    Kuwano, O.; Ando, R.; Hatano, T.

    2009-12-01

    In a "microscopic" view, natural faults generally consist of gouge layers, the frictional properties of which are much richer than the celebrated rate- and state-dependent friction law. One of such examples is intermediate-to-high slip velocity (mm/sec-m/sec) regime, where anomalous weakening and, at the same time, strengthening are reported; the results differ from experiments to experiments. In order to understand such a complicated phenomenon, one must carefully control the physical processes that potentially affect the frictional properties. We seek the nature of granular friction from many-body interaction. Toward this end, experiments are done on dry glass beads layer under low normal stress to exclude the possible effect of melting, comminution, silica gel formation, thermal decomposition, moisture, and so on. In this study, friction experiments of the glass-beads layers at slip rate of 10μm/s-1m/s were conducted. Experiments were performed at constant normal stresses of 10-50kPa using a ring shear apparatus with inner/outer diameters of 15mm/25mm. We used spherical soda-lime glass beads of diameter 200-300μm. The thickness of beads layer is about 2mm. Temperature beneath the lower plate was set to 25 degrees C and kept constant with Peltier Plate. It is found that the power-law dependence of the friction coefficient on slip velocity overwhelms the logarithmic rate dependence which originates from the rate-state friction law. Friction coefficient decreases with increasing slip velocity in low slip velocity regime (10μm/s~1cm/s) with velocity dependence of about -0.01 per decade of slip velocity. In high slip velocity regime (1cm/s~1m/s) it becomes velocity strengthening. This velocity strengthening regime is consistent with the power-law friction in closely-packed granular materials found by one of the authors (Hatano, 2007) by a numerical experiment using the discrete element method. Granular layer dilates with increasing slip velocity in higher velocity

  19. Shear wave anisotropy from aligned inclusions: ultrasonic frequency dependence of velocity and attenuation

    NASA Astrophysics Data System (ADS)

    de Figueiredo, J. J. S.; Schleicher, J.; Stewart, R. R.; Dayur, N.; Omoboya, B.; Wiley, R.; William, A.

    2013-04-01

    To understand their influence on elastic wave propagation, anisotropic cracked media have been widely investigated in many theoretical and experimental studies. In this work, we report on laboratory ultrasound measurements carried out to investigate the effect of source frequency on the elastic parameters (wave velocities and the Thomsen parameter γ) and shear wave attenuation) of fractured anisotropic media. Under controlled conditions, we prepared anisotropic model samples containing penny-shaped rubber inclusions in a solid epoxy resin matrix with crack densities ranging from 0 to 6.2 per cent. Two of the three cracked samples have 10 layers and one has 17 layers. The number of uniform rubber inclusions per layer ranges from 0 to 100. S-wave splitting measurements have shown that scattering effects are more prominent in samples where the seismic wavelength to crack aperture ratio ranges from 1.6 to 1.64 than in others where the ratio varied from 2.72 to 2.85. The sample with the largest cracks showed a magnitude of scattering attenuation three times higher compared with another sample that had small inclusions. Our S-wave ultrasound results demonstrate that elastic scattering, scattering and anelastic attenuation, velocity dispersion and crack size interfere directly in shear wave splitting in a source-frequency dependent manner, resulting in an increase of scattering attenuation and a reduction of shear wave anisotropy with increasing frequency.

  20. Spatial correlation of shear-wave velocity within San Francisco Bay Sediments

    USGS Publications Warehouse

    Thompson, E.M.; Baise, L.G.; Kayen, R.E.

    2006-01-01

    Sediment properties are spatially variable at all scales, and this variability at smaller scales influences high frequency ground motions. We show that surface shear-wave velocity is highly correlated within San Francisco Bay Area sediments using shear-wave velocity measurements from 210 seismic cone penetration tests. We use this correlation to estimate the surface sediment velocity structure using geostatistics. We find that the variance of the estimated shear-wave velocity is reduced using ordinary kriging, and that including this velocity structure in 2D ground motion simulations of a moderate sized earthquake improves the accuracy of the synthetics. Copyright ASCE 2006.

  1. Determination of shallow shear wave velocity profiles in the Cologne, Germany area using ambient vibrations

    NASA Astrophysics Data System (ADS)

    Scherbaum, Frank; Hinzen, Klaus-G.; Ohrnberger, Matthias

    2003-03-01

    We have used both single-station and array methods to determine shallow shear velocity site profiles in the vicinity of the city of Cologne, Germany from ambient vibration records. Based on fk-analysis we assume that fundamental-mode Rayleigh waves dominate the analysed wavefield in the frequency range of 0.7-2.2 Hz. According to this view a close relation exists between H/V spectral ratios and the ellipticity of the contributing Rayleigh waves. The inversion of the shape of H/V spectral ratios then provides quantitative information concerning the local shear wave velocity structure. However, based on tests with synthetic data believed to represent a typical situation in the Lower Rhine Embayment, dispersion curves were found to provide stronger constraints on the absolute values of the velocity-depth model than the ellipticities. The shape of the ellipticities was found to be subject to a strong trade-off between the layer thickness and the average layer velocity. We have made use of this observation by combining the inversion schemes for dispersion curves and ellipticities such that the velocity-depth dependence is essentially constrained by the dispersion curves while the layer thickness is constrained by the ellipticities. In order to test this method in practice, we have used array recordings of ambient vibrations from three sites where the subsurface geology is fairly well known and geotechnical information is at least partially available. In order to keep the parameter space as simple as possible we attempted to fit only a single layer over a half-space model. However, owing to earlier studies from the region, we assume a power-law depth dependence for sediment velocities. For all three sites investigated, the inversion resulted in models for which the shear wave velocity within the sediment layer both in absolute value at the surface and in depth dependence are found to be remarkably similar to the results obtained by Budny from downhole measurements. This

  2. Three-Dimensional Shear Wave Velocity Structure of the Peru Flat Slab Subduction Segment

    NASA Astrophysics Data System (ADS)

    Knezevic Antonijevic, S.; Wagner, L. S.; Beck, S. L.; Zandt, G.; Long, M. D.

    2012-12-01

    Recent studies focused on flat slab subduction segments in central Chile (L. S. Wagner, 2006) and Alaska (B. R. Hacker and G. A. Aber, 2012) suggest significant differences in seismic velocity structures, and hence, composition in the mantle wedge between flat and normal "steep" subducting slabs. Instead of finding the low velocities and high Vp/Vs ratios common in normal subduction zones, these studies find low Vp, high Vs, and very low Vp/Vs above flat slabs. This may indicate the presence of dry, cold material in the mantle wedge. In order to investigate the seismic velocities of the upper mantle above the Peruvian flat segment, we have inverted for 2D Rayleigh wave phase velocity maps using data from the currently deployed 40 station PULSE seismic network and some adjacent stations from the CAUGHT seismic network. We then used the sensitivity of surface waves to shear wave velocity structure with depth to develop a 3D shear wave velocity model. This model will allow us to determine the nature of the mantle lithosphere above the flat slab, and how this may have influenced the development of local topography. For example, dry conditions (high Vs velocities) above the flat slab would imply greater strength of this material, possibly making it capable of causing further inland overthrusting, while wet conditions (low Vs) would imply weaker material. This could provide some insight into the ongoing debate over whether the Fitzcarrald arch (along the northern most flank of the Altiplano) could be a topographical response to the subducted Nazca ridge hundred kilometers away from the trench (N. Espurt, 2012, P. Baby, 2005, V. A. Ramos, 2012) or not (J. Martinod, 2005, M. Wipf, 2008, T. Gerya, 2008).

  3. Shear wave velocities of unconsolidated shallow sediments in the Gulf of Mexico

    USGS Publications Warehouse

    Lee, Myung W.

    2013-01-01

    Accurate shear-wave velocities for shallow sediments are important for a variety of seismic applications such as inver-sion and amplitude versus offset analysis. During the U.S. Department of Energy-sponsored Gas Hydrate Joint Industry Project Leg II, shear-wave velocities were measured at six wells in the Gulf of Mexico using the logging-while-drilling SonicScope acoustic tool. Because the tool measurement point was only 35 feet from the drill bit, the adverse effect of the borehole condition, which is severe for the shallow unconsolidated sediments in the Gulf of Mexico, was mini-mized and accurate shear-wave velocities of unconsolidated sediments were measured. Measured shear-wave velocities were compared with the shear-wave velocities predicted from the compressional-wave velocities using empirical formulas and the rock physics models based on the Biot-Gassmann theory, and the effectiveness of the two prediction methods was evaluated. Although the empirical equation derived from measured shear-wave data is accurate for predicting shear-wave velocities for depths greater than 500 feet in these wells, the three-phase Biot-Gassmann-theory -based theory appears to be optimum for predicting shear-wave velocities for shallow unconsolidated sediments in the Gulf of Mexico.

  4. Vortex Formation in a High Speed Dust Flow with Large Velocity Shear in RF Plasmas

    SciTech Connect

    Iizuka, Satoru; Gohda, Takuma

    2008-09-07

    We have investigated a rotation of a dust cloud disc with strong velocity shear in a radio frequency (RF) plasma. The flow pattern of the dusts was evaluated by the Navier Stokes Equation with shear viscosity due to the Coulomb interactions. We have clarified dynamic behaviors of the dusts and observed generation of micro-vortices around rotational center, when the velocity shear is enhanced.

  5. A special relation between Young's modulus, Rayleigh-wave velocity, and Poisson's ratio.

    PubMed

    Malischewsky, Peter G; Tuan, Tran Thanh

    2009-12-01

    Bayon et al. [(2005). J. Acoust. Soc. Am. 117, 3469-3477] described a method for the determination of Young's modulus by measuring the Rayleigh-wave velocity and the ellipticity of Rayleigh waves, and found a peculiar almost linear relation between a non-dimensional quantity connecting Young's modulus, Rayleigh-wave velocity and density, and Poisson's ratio. The analytical reason for this special behavior remained unclear. It is demonstrated here that this behavior is a simple consequence of the mathematical form of the Rayleigh-wave velocity as a function of Poisson's ratio. The consequences for auxetic materials (those materials for which Poisson's ratio is negative) are discussed, as well as the determination of the shear and bulk moduli.

  6. How required reserve ratio affects distribution and velocity of money

    NASA Astrophysics Data System (ADS)

    Xi, Ning; Ding, Ning; Wang, Yougui

    2005-11-01

    In this paper the dependence of wealth distribution and the velocity of money on the required reserve ratio is examined based on a random transfer model of money and computer simulations. A fractional reserve banking system is introduced to the model where money creation can be achieved by bank loans and the monetary aggregate is determined by the monetary base and the required reserve ratio. It is shown that monetary wealth follows asymmetric Laplace distribution and latency time of money follows exponential distribution. The expression of monetary wealth distribution and that of the velocity of money in terms of the required reserve ratio are presented in a good agreement with simulation results.

  7. Improved Shear Wave Group Velocity Estimation Method Based on Spatiotemporal Peak and Thresholding Motion Search.

    PubMed

    Amador Carrascal, Carolina; Chen, Shigao; Manduca, Armando; Greenleaf, James F; Urban, Matthew W

    2017-04-01

    Quantitative ultrasound elastography is increasingly being used in the assessment of chronic liver disease. Many studies have reported ranges of liver shear wave velocity values for healthy individuals and patients with different stages of liver fibrosis. Nonetheless, ongoing efforts exist to stabilize quantitative ultrasound elastography measurements by assessing factors that influence tissue shear wave velocity values, such as food intake, body mass index, ultrasound scanners, scanning protocols, and ultrasound image quality. Time-to-peak (TTP) methods have been routinely used to measure the shear wave velocity. However, there is still a need for methods that can provide robust shear wave velocity estimation in the presence of noisy motion data. The conventional TTP algorithm is limited to searching for the maximum motion in time profiles at different spatial locations. In this paper, two modified shear wave speed estimation algorithms are proposed. The first method searches for the maximum motion in both space and time [spatiotemporal peak (STP)]; the second method applies an amplitude filter [spatiotemporal thresholding (STTH)] to select points with motion amplitude higher than a threshold for shear wave group velocity estimation. The two proposed methods (STP and STTH) showed higher precision in shear wave velocity estimates compared with TTP in phantom. Moreover, in a cohort of 14 healthy subjects, STP and STTH methods improved both the shear wave velocity measurement precision and the success rate of the measurement compared with conventional TTP.

  8. Effects of ExB velocity shear and magnetic shear on turbulence and transport in magnetic confinement devices

    SciTech Connect

    Burrell, K.H.

    1996-11-01

    One of the scientific success stories of fusion research over the past decade is the development of the ExB shear stabilization model to explain the formation of transport barriers in magnetic confinement devices. This model was originally developed to explain the transport barrier formed at the plasma edge in tokamaks after the L (low) to H (high) transition. This concept has the universality needed to explain the edge transport barriers seen in limiter and divertor tokamaks, stellarators, and mirror machines. More recently, this model has been applied to explain the further confinement improvement from H (high)-mode to VH (very high)-mode seen in some tokamaks, where the edge transport barrier becomes wider. Most recently, this paradigm has been applied to the core transport barriers formed in plasmas with negative or low magnetic shear in the plasma core. These examples of confinement improvement are of considerable physical interest; it is not often that a system self-organizes to a higher energy state with reduced turbulence and transport when an additional source of free energy is applied to it. The transport decrease that is associated with ExB velocity shear effects also has significant practical consequences for fusion research. The fundamental physics involved in transport reduction is the effect of ExB shear on the growth, radial extent and phase correlation of turbulent eddies in the plasma. The same fundamental transport reduction process can be operational in various portions of the plasma because there are a number ways to change the radial electric field Er. An important theme in this area is the synergistic effect of ExB velocity shear and magnetic shear. Although the ExB velocity shear appears to have an effect on broader classes of microturbulence, magnetic shear can mitigate some potentially harmful effects of ExB velocity shear and facilitate turbulence stabilization.

  9. Shear viscosity to entropy density ratio in nuclear multifragmentation

    SciTech Connect

    Pal, Subrata

    2010-05-15

    Nuclear multifragmentation in intermediate-energy heavy-ion collisions has long been associated with liquid-gas phase transition. We calculate the shear viscosity to entropy density ratio eta/s for an equilibrated system of nucleons and fragments produced in multifragmentation within an extended statistical multifragmentation model. The temperature dependence of eta/s exhibits behavior surprisingly similar to that of H{sub 2}O. In the coexistence phase of fragments and light particles, the ratio eta/s reaches a minimum of depth comparable to that for water in the vicinity of the critical temperature for liquid-gas phase transition. The effects of freeze-out volume and surface symmetry energy on eta/s in multifragmentation are studied.

  10. Crustal shear-wave velocity structure beneath Sumatra from receiver function modeling

    NASA Astrophysics Data System (ADS)

    Bora, Dipok K.; Borah, Kajaljyoti; Goyal, Ayush

    2016-05-01

    We estimated the shear-wave velocity structure and Vp/Vs ratio of the crust beneath the Sumatra region by inverting stacked receiver functions from five three-component broadband seismic stations, located in diverse geologic setting, using a well known non-linear direct search approach, Neighborhood Algorithm (NA). Inversion results show significant variation of sediment layer thicknesses from 1 km beneath the backarc basin (station BKNI and PMBI) to 3-7 km beneath the coastal part of Sumatra region (station LHMI and MNAI) and Nias island (station GSI). Average sediment layer shear velocity (Vss) beneath all the stations is observed to be less (∼1.35 km/s) and their corresponding Vp/Vs ratio is very high (∼2.2-3.0). Crustal thickness beneath Sumatra region varies between 27 and 35 km, with exception of 19 km beneath Nias island, with average crustal Vs ∼3.1-3.4 km/s (Vp/Vs ∼1.8). It is well known that thick sediments with low Vs (and high Vp/Vs) amplify seismic waves even from a small-magnitude earthquake, which can cause huge damage in the zone. This study can provide the useful information of the crust for the Sumatra region. Since, Sumatra is an earthquake prone zone, which suffered the strong shaking of Great Andaman-Sumatra earthquake; this study can also be helpful for seismic hazard assessment.

  11. The Shear Viscosity to Entropy Ratio:. a Status Report

    NASA Astrophysics Data System (ADS)

    Cremonini, Sera

    This review highlights some of the lessons that the holographic gauge/gravity duality has taught us regarding the behavior of the shear viscosity to entropy density in strongly coupled field theories. The viscosity to entropy ratio has been shown to take on a very simple universal value in all gauge theories with an Einstein gravity dual. Here we describe the origin of this universal ratio, and focus on how it is modified by generic higher derivative corrections corresponding to curvature corrections on the gravity side of the duality. In particular, certain curvature corrections are known to push the viscosity to entropy ratio below its universal value. This disproves a longstanding conjecture that such a universal value represents a strict lower bound for any fluid in nature. We discuss the main developments that have led to insight into the violation of this bound, and consider whether the consistency of the theory is responsible for setting a fundamental lower bound on the viscosity to entropy ratio.

  12. Mantle transition zone shear velocity gradients beneath USArray

    NASA Astrophysics Data System (ADS)

    Schmandt, Brandon

    2012-11-01

    Broadband P-to-s scattering isolated by teleseismic receiver function analysis is used to investigate shear velocity (VS) gradients in the mantle transition zone beneath USArray. Receiver functions from 2244 stations were filtered in multiple frequency bands and migrated to depth through P and S tomography models. The depth-migrated receiver functions were stacked along their local 410 and 660 km discontinuity depths to reduce stack incoherence and more accurately recover the frequency-dependent amplitudes of P410s and P660s. The stacked waveforms were inverted for one-dimensional VS between 320 and 840 km depth. First, a gradient-based inversion was used to find a least-squares solution and a subsequent Monte Carlo search about that solution constrained the range of VS profiles that provide an acceptable fit to the receiver function stacks. Relative to standard references models, all the acceptable models have diminished VS gradients surrounding the 410, a local VS gradient maximum at 490-500 km depth, and an enhanced VS gradient above the 660. The total 410 VS increase of 6.3% is greater than in reference models, and it occurs over a thickness of 20 km. However, 60% of this VS increase occurs over only 6 km. The 20 km total thickness of the 410 and diminished VS gradients surrounding the 410 are potential indications of high water content in the regional transition zone. An enhanced VS gradient overlying the 660 likely results from remnants of subduction lingering at the base of the transition zone. Cool temperatures from slabs subducted since the late Cretaceous and longer-term accumulation of former ocean crust both may contribute to the high gradient above the 660. The shallow depth of the 520 km discontinuity, 490-500 km, implies that the regional mean temperature in the transition zone is 110-160 K cooler than the global mean. A concentrated Vs gradient maximum centered near 660 km depth and a low VS gradient below 675 km confirms that the ringwoodite to

  13. Orbital transfer vehicle engine technology high velocity ratio diffusing crossover

    NASA Astrophysics Data System (ADS)

    Lariviere, Brian W.

    1992-12-01

    High speed, high efficiency head rise multistage pumps require continuous passage diffusing crossovers to effectively convey the pumped fluid from the exit of one impeller to the inlet of the next impeller. On Rocketdyne's Orbital Transfer Vehicle (OTV), the MK49-F, a three stage high pressure liquid hydrogen turbopump, utilizes a 6.23 velocity ratio diffusing crossover. This velocity ratio approaches the diffusion limits for stable and efficient flow over the operating conditions required by the OTV system. The design of the high velocity ratio diffusing crossover was based on advanced analytical techniques anchored by previous tests of stationary two-dimensional diffusers with steady flow. To secure the design and the analytical techniques, tests were required with the unsteady whirling characteristics produced by an impeller. A tester was designed and fabricated using a 2.85 times scale model of the MK49-F turbopumps first stage, including the inducer, impeller, and the diffusing crossover. Water and air tests were completed to evaluate the large scale turbulence, non-uniform velocity, and non-steady velocity on the pump and crossover head and efficiency. Suction performance tests from 80 percent to 124 percent of design flow were completed in water to assess these pump characteristics. Pump and diffuser performance from the water and air tests were compared with the actual MK49-F test data in liquid hydrogen.

  14. Orbital Transfer Vehicle Engine Technology High Velocity Ratio Diffusing Crossover

    NASA Technical Reports Server (NTRS)

    Lariviere, Brian W.

    1992-01-01

    High speed, high efficiency head rise multistage pumps require continuous passage diffusing crossovers to effectively convey the pumped fluid from the exit of one impeller to the inlet of the next impeller. On Rocketdyne's Orbital Transfer Vehicle (OTV), the MK49-F, a three stage high pressure liquid hydrogen turbopump, utilizes a 6.23 velocity ratio diffusing crossover. This velocity ratio approaches the diffusion limits for stable and efficient flow over the operating conditions required by the OTV system. The design of the high velocity ratio diffusing crossover was based on advanced analytical techniques anchored by previous tests of stationary two-dimensional diffusers with steady flow. To secure the design and the analytical techniques, tests were required with the unsteady whirling characteristics produced by an impeller. A tester was designed and fabricated using a 2.85 times scale model of the MK49-F turbopumps first stage, including the inducer, impeller, and the diffusing crossover. Water and air tests were completed to evaluate the large scale turbulence, non-uniform velocity, and non-steady velocity on the pump and crossover head and efficiency. Suction performance tests from 80 percent to 124 percent of design flow were completed in water to assess these pump characteristics. Pump and diffuser performance from the water and air tests were compared with the actual MK49-F test data in liquid hydrogen.

  15. Near-Surface Shear-Wave Velocity Measurements in Unlithified Sediment

    NASA Astrophysics Data System (ADS)

    Rickards, Benjamin Thomas

    Shear-wave (S-wave) velocity can be directly correlated to material stiffness making it a valuable physical property that has found uses in construction, engineering, and environmental projects. This study compares three different methods, Multichannel Analysis of Surface Waves (MASW), S-wave tomography, and downhole seismic for measuring S-wave velocities, investigates and identifies the differences among the methods' results, and prioritizes the different methods for S-wave use at the U. S. Army's Yuma Proving Grounds (YPG) north of Yuma, AZ. A large signal-to-noise ratio and a layered depositional architecture at the study site gives the MASW method much potential, but higher-mode energy resulting from velocity discontinuities reduces the effectiveness of the method shallower than 20 ft. First arrival analysis provides evidence of a velocity discontinuity within the first 10 feet of unconsolidated sediment. S-wave first arrivals were picked using impulsive sledgehammer data which were then used for both tomographic inversion and refraction analysis. Three-component downhole seismic data were collected by using a locking geophone coupled with the borehole casing to estimate seismic velocities directly. This study helps to identify the strengths and weaknesses of each of these methods at sites similar to YPG. MASW results show a low-velocity layer at a depth of about 50 feet that is verified by downhole seismic data and is undetectable through traditional refraction tomography. However S-wave refraction tomography provides more convincing results at shallow depths where the MASW method fails. Using both methods in an integrated fashion provide the most accurate depiction of S-wave velocity characteristics in the shallow unconsolidated sediments at YPG.

  16. Shear wave velocity-based evaluation and design of stone column improved ground for liquefaction mitigation

    NASA Astrophysics Data System (ADS)

    Zhou, Yanguo; Sun, Zhengbo; Chen, Jie; Chen, Yunmin; Chen, Renpeng

    2017-04-01

    The evaluation and design of stone column improvement ground for liquefaction mitigation is a challenging issue for the state of practice. In this paper, a shear wave velocity-based approach is proposed based on the well-defined correlations of liquefaction resistance (CRR)-shear wave velocity ( V s)-void ratio ( e) of sandy soils, and the values of parameters in this approach are recommended for preliminary design purpose when site specific values are not available. The detailed procedures of pre- and post-improvement liquefaction evaluations and stone column design are given. According to this approach, the required level of ground improvement will be met once the target V s of soil is raised high enough (i.e., no less than the critical velocity) to resist the given earthquake loading according to the CRR- V s relationship, and then this requirement is transferred to the control of target void ratio (i.e., the critical e) according to the V s- e relationship. As this approach relies on the densification of the surrounding soil instead of the whole improved ground and is conservative by nature, specific considerations of the densification mechanism and effect are given, and the effects of drainage and reinforcement of stone columns are also discussed. A case study of a thermal power plant in Indonesia is introduced, where the effectiveness of stone column improved ground was evaluated by the proposed V s-based method and compared with the SPT-based evaluation. This improved ground performed well and experienced no liquefaction during subsequent strong earthquakes.

  17. Alignments of the galaxies in and around the Virgo cluster with the local velocity shear

    SciTech Connect

    Lee, Jounghun; Rey, Soo Chang; Kim, Suk

    2014-08-10

    Observational evidence is presented for the alignment between the cosmic sheet and the principal axis of the velocity shear field at the position of the Virgo cluster. The galaxies in and around the Virgo cluster from the Extended Virgo Cluster Catalog that was recently constructed by Kim et al. are used to determine the direction of the local sheet. The peculiar velocity field reconstructed from the Sloan Digital Sky Survey Data Release 7 is analyzed to estimate the local velocity shear tensor at the Virgo center. Showing first that the minor principal axis of the local velocity shear tensor is almost parallel to the direction of the line of sight, we detect a clear signal of alignment between the positions of the Virgo satellites and the intermediate principal axis of the local velocity shear projected onto the plane of the sky. Furthermore, the dwarf satellites are found to appear more strongly aligned than their normal counterparts, which is interpreted as an indication of the following. (1) The normal satellites and the dwarf satellites fall in the Virgo cluster preferentially along the local filament and the local sheet, respectively. (2) The local filament is aligned with the minor principal axis of the local velocity shear while the local sheet is parallel to the plane spanned by the minor and intermediate principal axes. Our result is consistent with the recent numerical claim that the velocity shear is a good tracer of the cosmic web.

  18. The lithospheric shear-wave velocity structure of Saudi Arabia: Young volcanism in an old shield

    NASA Astrophysics Data System (ADS)

    Tang, Zheng; Julià, Jordi; Zahran, Hani; Mai, P. Martin

    2016-06-01

    We investigate the lithospheric shear-wave velocity structure of Saudi Arabia by conducting H-κ stacking analysis and jointly inverting teleseismic P-receiver functions and fundamental-mode Rayleigh wave group velocities at 56 broadband stations deployed by the Saudi Geological Survey (SGS). The study region, the Arabian plate, is traditionally divided into the western Arabian shield and the eastern Arabian platform: The Arabian shield itself is a complicated mélange of crustal material, composed of several Proterozoic terrains separated by ophiolite-bearing suture zones and dotted by outcropping Cenozoic volcanic rocks (locally known as harrats). The Arabian platform is primarily covered by 8 to 10 km of Paleozoic, Mesozoic and Cenozoic sedimentary rocks. Our results reveal high Vp/Vs ratios in the region of Harrat Lunayyir, which are interpreted as solidified magma intrusions from old magmatic episodes in the shield. Our results also indicate slow velocities and large upper mantle lid temperatures below the southern and northern tips of the Arabian shield, when compared with the values obtained for the central shield. We argue that our inferred patterns of lid velocity and temperature are due to heating by thermal conduction from the Afar plume (and, possibly, the Jordan plume), and that volcanism in western Arabia may result from small-scale adiabatic ascent of magma diapirs.

  19. Low Velocity Difference Thermal Shear Layer Mixing Rate Measurements

    NASA Technical Reports Server (NTRS)

    Bush, Robert H.; Culver, Harry C. M.; Weissbein, Dave; Georgiadis, Nicholas J.

    2013-01-01

    Current CFD modeling techniques are known to do a poor job of predicting the mixing rate and persistence of slot film flow in co-annular flowing ducts with relatively small velocity differences but large thermal gradients. A co-annular test was devised to empirically determine the mixing rate of slot film flow in a constant area circular duct (D approx. 1ft, L approx. 10ft). The axial rate of wall heat-up is a sensitive measure of the mixing rate of the two flows. The inflow conditions were varied to simulate a variety of conditions characteristic of moderate by-pass ratio engines. A series of air temperature measurements near the duct wall provided a straightforward means to measure the axial temperature distribution and thus infer the mixing rate. This data provides a characterization of the slot film mixing rates encountered in typical jet engine environments. The experimental geometry and entrance conditions, along with the sensitivity of the results as the entrance conditions vary, make this a good test for turbulence models in a regime important to modern air-breathing propulsion research and development.

  20. Temporal changes in shear velocity from ambient noise at New Zealand geothermal fields

    NASA Astrophysics Data System (ADS)

    Civilini, F.; Savage, M. K.; Townend, J.

    2016-12-01

    We use ambient noise to compare shear velocity changes with geothermal production processes at the Ngatamariki and Rotokawa geothermal fields, located in the central North Island of New Zealand. We calculate shear velocity changes through an analysis of cross correlation functions of diffusive seismic wavefields between stations, which are proportional to Green's functions of the station path. Electricity production at Ngatamariki uses an 82 MW binary type power station manufactured by Ormat Technologies, which began operations in mid-2013 and is owned and operated by Mighty River Power. The "Nga Awa Purua" triple flash power plant at the Rotokawa geothermal field was established in 2010 with parnership between Mighty River Power and Tauhara North No. 2 trust and currently operates 174 MW of generation. The seismometers of both networks, deployed primarily to observe microseismicity within the field, were installed prior to well stimulation and the start of production. Although cultural noise dominates the energy spectrum, a strong natural ambient noise signal can be detected when filtering below 1 Hz. Despite similar noise settings, the signal-to-noise ratio of cross correlation stacks at Rotokawa was more than two times greater than at Ngatamariki. We use stacks of cross correlations between stations prior to the onset of production as references, and compare them with cross correlations of moving stacks in time periods of well stimulation and the onset of electricity production.

  1. The influence of the arrangements of multi-sensor probe arrays on the accuracy of simultaneously measured velocity and velocity gradient-based statistics in turbulent shear flows

    NASA Astrophysics Data System (ADS)

    Vukoslavčević, P. V.; Wallace, J. M.

    2013-06-01

    A highly resolved turbulent channel flow direct numerical simulation (DNS) with Re τ = 200 has been used to investigate the influence of the arrangements of the arrays (array configurations), within the sensing area of a multi-array hot-wire probe on the measurement accuracy of velocity and velocity gradient-based statistics. To eliminate all effects related to the sensor response and array characteristics (such as sensor dimensions, overheat ratio, thermal cross talk, number and orientations of the sensors and uniqueness range) so that this study could be focused solely on the effects of the array configurations (positions and separations), a concept of a perfect array was introduced, that is, one that can exactly and simultaneously measure all three velocity components at its center. The velocity component values, measured by these perfect arrays, are simply the DNS values computed at these points. Using these velocity components, the velocity and velocity gradient-based statistics were calculated assuming a linear velocity variation over the probes' sensing areas. The calculated values are compared to the DNS values for various array arrangements to study the influence of these arrangements on the measurement accuracy. Typical array configurations that previously have been used for physical probes were tested. It is demonstrated that the array arrangements strongly influence the accuracy of some of the velocity and velocity gradient-based statistics and that no single configuration exists, for a given spatial resolution, which gives the best accuracy for all of the statistics characterizing a turbulent shear flow.

  2. Phase-averaged wall shear stress, wall pressure, and near-wall velocity field measurements in a whirling annular seal

    SciTech Connect

    Morrison, G.L.; Winslow, R.B.; Thames, H.D. III

    1996-07-01

    The flow field inside a 50 percent eccentric whirling annular seal operating at a Reynolds number of 24,000 and a Taylor number of 6600 has been measured using a three-dimensional laser-Doppler anemometer system. Flush mount pressure and wall shear stress probes have been used to measure the stresses (normal and shear) along the length of the stator. The rotor was mounted eccentrically on the shaft so that the rotor orbit was circular and rotated at the same speed as the shaft (a whirl ratio of 1.0). This paper presents mean pressure, mean wall shear stress magnitude, and mean wall shear stress direction distributions along the length of the seal. Phase-averaged wall pressure and wall shear stress are presented along with phase-averaged mean velocity and turbulence kinetic energy distributions located 0.16c from the stator wall, where c is the seal clearance. The relationships between the velocity, turbulence, wall pressure, and wall shear stress are very complex and do not follow simple bulk flow predictions.

  3. The relationships between large-scale variations in shear velocity, density, and compressional velocity in the Earth's mantle

    NASA Astrophysics Data System (ADS)

    Moulik, P.; Ekström, G.

    2016-04-01

    A large data set of surface wave phase anomalies, body wave travel times, normal-mode splitting functions, and long-period waveforms is used to investigate the scaling between shear velocity, density, and compressional velocity in the Earth's mantle. We introduce a methodology that allows construction of joint models with various levels of scaling complexity (ϱ = dlnρ/dlnvS, ν = dlnvS/dlnvP), in order to detect seismological signatures of chemical heterogeneity. We demonstrate that the data sets considered cannot be fit concurrently with a uniform ν or a positive and uniform ϱ throughout the mantle. The variance reductions to P wave travel times and vP-sensitive modes are up to 40% higher with our preferred model of anisotropic shear and compressional velocity than the recent anisotropic shear velocity model S362ANI+M, which was constructed assuming a uniform ν throughout the mantle. Several features reported in earlier tomographic studies persist after the inclusion of new and larger data sets; anticorrelation between bulk sound and shear velocities in the lowermost mantle as well as an increase in ν with depth in the lower mantle are largely independent of the regularization scheme. When correlations between density and shear velocity variations are imposed in the lowermost mantle, variance reductions of several spheroidal and toroidal modes deteriorate by as much as 40%. Recent measurements of the splitting of 0S2, in particular, are largely incompatible with perfectly correlated shear velocity and density heterogeneity throughout the mantle. A way to significantly improve the fits to various data sets is by allowing independent density perturbations in the lowermost mantle. Our preferred joint model consists of denser-than-average anomalies (˜1% peak to peak) at the base of the mantle roughly coincident with the low-velocity superplumes. The relative variation of shear velocity, density, and compressional velocity in our study disfavors a purely thermal

  4. Measurement of shear-wave velocity by ultrasound critical-angle reflectometry (UCR)

    NASA Technical Reports Server (NTRS)

    Mehta, S.; Antich, P.; Blomqvist, C. G. (Principal Investigator)

    1997-01-01

    There exists a growing body of research that relates the measurement of pressure-wave velocity in bone to different physiological conditions and treatment modalities. The shear-wave velocity has been less studied, although it is necessary for a more complete understanding of the mechanical properties of bone. Ultrasound critical-angle reflectometry (UCR) is a noninvasive and nondestructive technique previously used to measure pressure-wave velocities both in vitro and in vivo. This note describes its application to the measurement of shear-wave velocity in bone, whether directly accessible or covered by soft tissue.

  5. Integrating shear velocity observations of the Hudson Bay

    NASA Astrophysics Data System (ADS)

    Porritt, R. W.; Miller, M. S.; Darbyshire, F. A.

    2013-12-01

    Hudson Bay is the core of the Laurentia craton of North America. This region contains some of the thickest lithosphere globally, reaching 250-300 km depth. Previous studies have shown that much of this region is composed of amalgamated proto-continents including the Western Churchill and Superior provinces and that much of the structure of these constituents has been retained since the Trans-Hudson Orogen at 1.8 Ga. Using the Hudson Bay Lithospheric Experiment (HuBLE) and other permanent and POLARIS broadband seismic data, we image the region with S to P receiver functions, joint inversion of P to S receiver functions with surface waves, and teleseismic S and P wave travel-times. The receiver function imaging reveals a persistent mid-lithospheric layer at ~80 km depth under all stations, but a variable lithospheric thickness. The teleseismic S delay times show a pattern of early arrivals around the center of the network, beneath Hudson Bay where the lithosphere is thickest, while the P delay times are early in the Superior province relative to the Western Churchill province. This suggests higher Vp/Vs ratios in the Superior province, which is evidence that stacked oceanic plates formed this province. The relatively flat Moho imaged by earlier receiver function studies and the lower mantle Vp/Vs of the Western Churchill province provides evidence of formation by plume head extraction. The joint inversion shows an LAB that is typically a broad discontinuity spanning ~20-30 km at ~220 km depth suggesting a primarily thermal boundary zone. The mid-lithospheric layer is composed of increasing velocity from the ~40 km depth Moho defined by H-k stacking of PRFs to a broad, constant velocity lithospheric lid spanning 80-200 km depth. We suggest this mid-lithospheric layer represents the mantle lithosphere of the proto-continents prior to collision and the lid formed due to post-collisional cooling. The integration of these seismic datasets furthers our understanding of

  6. Velocity and shear rate estimates of some non-Newtonian oscillatory flows in tubes

    NASA Astrophysics Data System (ADS)

    Kutev, N.; Tabakova, S.; Radev, S.

    2016-10-01

    The two-dimensional Newtonian and non-Newtonian (Carreau viscosity model used) oscillatory flows in straight tubes are studied theoretically and numerically. The corresponding analytical solution of the Newtonian flow and the numerical solution of the Carreau viscosity model flow show differences in velocity and shear rate. Some estimates for the velocity and shear rate differences are theoretically proved. As numerical examples the blood flow in different type of arteries and the polymer flow in pipes are considered.

  7. Numerical Investigation of Vasospasm Detection by Extracranial Blood Velocity Ratios.

    PubMed

    Ryu, Jaiyoung; Ko, Nerissa; Hu, Xiao; Shadden, Shawn C

    2017-01-01

    Early diagnosis of vasospasm following subarachnoid hemorrhage can prevent cerebral ischemia and improve neurological outcomes. This study numerically evaluates the relevance of extracranial blood velocity indices to detect vasospasm. A numerical model of cerebral blood flow was used to evaluate the hemodynamics associated with anterior and posterior vasospasm under normal and impaired cerebral autoregulation conditions. Extracranial blood velocities at the carotid and vertebral arteries and their ratios between ipsilateral and contralateral, anterior and posterior, and downstream and upstream arteries were monitored during vasospasm progression. For current clinical indices that track blood velocities at vasospastic arterial segments using transcranial Doppler (TCD), we observed that velocities increased initially and then decreased with vasospasm progression. This nonmonotonic behavior can lead to false-negative decisions in moderate to severe vasospasm. Alternatively, volumetric flow decreased monotonically at the affected arteries, leading to blood velocities upstream of the vasospastic artery also decreasing monotonically. Based on this principle, we demonstrate that velocity ratios between the carotid and vertebral arteries may better identify moderate to severe vasospasm and improve sensitivity and specificity of vasospasm detection. The velocity indices proposed in this study may enable new or improved noninvasive diagnosis of vasospasm using extracranial Doppler ultrasound. Compared to current clinical indices, the new indices may improve the handling of (1) scenarios of severe vasospasm or impaired cerebral autoregulation, (2) systemic changes in blood pressure and cardiac output, (3) vasospasm occurring in arteries distal to the cerebral circle region, and (4) cases with insufficient acoustic bone window for TCD. The results provide a concrete basis for future clinical evaluation of extracranial indices for vasospasm detection. © 2017 S. Karger AG

  8. Experimental Investigation of Adiabatic Shear Banding at Different Impact Velocities

    DTIC Science & Technology

    1993-01-01

    relation of the power form, J. .%Iech. Working Technology 1j (1987), 143. (341 T.W. Wright and J.W. Walter . On stress collapse in adiabatic shear bands, 1...Mccl. Phys. Solids ], 11987). 701. [35) T.W. W-ight and J.W. Walter . Adiabatic shear bands in one dimension, in: Mechanical Pro- perties of Materials...metals. in Constinifive Relations and Their Physical Basis. RisO Natl. Laboratory, Roskilde. Daremnark (1987). 387. (381 J.R. Klepaczko. A general

  9. The radial velocity, velocity dispersion, and mass-to-light ratio of the Sculptor dwarf galaxy

    NASA Technical Reports Server (NTRS)

    Armandroff, T. E.; Da Costa, G. S.

    1986-01-01

    The radial velocity, velocity dispersion, and mass-to-light ratio for 16 K giants in the Sculptor dwarf galaxy are calculated. Spectra at the Ca II triplet are analyzed using cross-correlation techniques in order to obtain the mean velocity of + 107.4 + or - 2.0 km/s. The dimensional velocity dispersion estimated as 6.3 (+1.1, -1.3) km/s is combined with the calculated core radius and observed central surface brightness to produce a mass-to-light ratio of 6.0 in solar units. It is noted that the data indicate that the Sculptor contains a large amount of mass not found in globular clusters, and the mass is either in the form of remnant stars or low-mass dwarfs.

  10. Spatial correlation of shear-wave velocity in the San Francisco Bay Area sediments

    USGS Publications Warehouse

    Thompson, E.M.; Baise, L.G.; Kayen, R.E.

    2007-01-01

    Ground motions recorded within sedimentary basins are variable over short distances. One important cause of the variability is that local soil properties are variable at all scales. Regional hazard maps developed for predicting site effects are generally derived from maps of surficial geology; however, recent studies have shown that mapped geologic units do not correlate well with the average shear-wave velocity of the upper 30 m, Vs(30). We model the horizontal variability of near-surface soil shear-wave velocity in the San Francisco Bay Area to estimate values in unsampled locations in order to account for site effects in a continuous manner. Previous geostatistical studies of soil properties have shown horizontal correlations at the scale of meters to tens of meters while the vertical correlations are on the order of centimeters. In this paper we analyze shear-wave velocity data over regional distances and find that surface shear-wave velocity is correlated at horizontal distances up to 4 km based on data from seismic cone penetration tests and the spectral analysis of surface waves. We propose a method to map site effects by using geostatistical methods based on the shear-wave velocity correlation structure within a sedimentary basin. If used in conjunction with densely spaced shear-wave velocity profiles in regions of high seismic risk, geostatistical methods can produce reliable continuous maps of site effects. ?? 2006 Elsevier Ltd. All rights reserved.

  11. Effect of rotation and velocity shear on tearing layer stability in tokamak plasmas

    NASA Astrophysics Data System (ADS)

    White, Ryan L.; Fitzpatrick, Richard

    2015-10-01

    Using a resistive generalization of the Frieman-Rotenberg formalism, the leading-order effects of velocity shear and rotation on linear tearing layer stability are studied for tokamak equilibria. The layer equations for resistive interchange modes are derived for arbitrary equilibrium rotation and velocity shear. The resulting layer equations do not conserve parity and are not simplified by Fourier transform. Thus, many standard numerical techniques cannot be implemented in a straightforward manner. Layer equations are also derived in the constant- Ψ limit. The constant- Ψ dispersion relation is obtained and is used to study the leading-order effects of rotation and velocity shear on the critical value of Δ' required for tearing instability. It is found that rotation and velocity shear can couple with the parallel current and the current gradient in the layer to reduce Δ'crit . If parallel currents are sufficiently weak to compete with second-order effects, velocity shear can be stabilizing, while rotation is found to have a destabilizing effect. Second-order coupling of velocity shear and rotation can have either sign, and thus can affect stability in either direction.

  12. Shear Wave Velocity Estimates through Combined Use of Passive Techniques in a Tectonically Active Area

    NASA Astrophysics Data System (ADS)

    Biswas, Rajib; Baruah, Saurabh

    2016-12-01

    We made an attempt to assess the shear wave velocity values VSand, to a lesser extent, the VP values from ambient noise recordings in an array configuration. Five array sites were situated in the close proximity to borehole sites. Shear wave velocity profiles were modeled at these five array sites with the aid of two computational techniques, viz. spatial autocorrelation (SPAC) and H/V ellipticity. Out of these five array sites, velocity estimates could be reliably inferred at three locations. The shear wave velocities estimated by these methods are found to be quite consistent with each other. The computed VS values up to 30 m depth are in the range from 275 to 375 m/s in most of the sites, which implies prevalence of a low velocity zone at some pocket areas. The results were corroborated by evidence of site geology as well as geotechnical information.

  13. Calculation of Near-Bank Velocity and Boundary Shear Stress

    USDA-ARS?s Scientific Manuscript database

    Detailed knowledge of the flow and boundary shear stress fields near the banks of natural channels is essential for making accurate calculations of rates of near-bank sediment transport and geomorphic adjustment. This paper presents a test of a relatively simple, fully predictive, numerical method f...

  14. Correlations Between Shear Wave Velocity and In-Situ Penetration Test Results for Korean Soil Deposits

    NASA Astrophysics Data System (ADS)

    Sun, Chang-Guk; Cho, Chang-Soo; Son, Minkyung; Shin, Jin Soo

    2013-03-01

    Shear wave velocity ( V S) can be obtained using seismic tests, and is viewed as a fundamental geotechnical characteristic for seismic design and seismic performance evaluation in the field of earthquake engineering. To apply conventional geotechnical site investigation techniques to geotechnical earthquake engineering, standard penetration tests (SPT) and piezocone penetration tests (CPTu) were undertaken together with a variety of borehole seismic tests for a range of sites in Korea. Statistical modeling of the in-situ testing data identified correlations between V S and geotechnical in-situ penetration data, such as blow counts ( N value) from SPT and CPTu data including tip resistance ( q t), sleeve friction ( f s), and pore pressure ratio ( B q). Despite the difference in strain levels between conventional geotechnical penetration tests and borehole seismic tests, it is shown that the suggested correlations in this study is applicable to the preliminary determination of V S for soil deposits.

  15. Animal models of surgically manipulated flow velocities to study shear stress-induced atherosclerosis.

    PubMed

    Winkel, Leah C; Hoogendoorn, Ayla; Xing, Ruoyu; Wentzel, Jolanda J; Van der Heiden, Kim

    2015-07-01

    Atherosclerosis is a chronic inflammatory disease of the arterial tree that develops at predisposed sites, coinciding with locations that are exposed to low or oscillating shear stress. Manipulating flow velocity, and concomitantly shear stress, has proven adequate to promote endothelial activation and subsequent plaque formation in animals. In this article, we will give an overview of the animal models that have been designed to study the causal relationship between shear stress and atherosclerosis by surgically manipulating blood flow velocity profiles. These surgically manipulated models include arteriovenous fistulas, vascular grafts, arterial ligation, and perivascular devices. We review these models of manipulated blood flow velocity from an engineering and biological perspective, focusing on the shear stress profiles they induce and the vascular pathology that is observed. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

  16. Agyrotropic pressure tensor induced by the plasma velocity shear

    NASA Astrophysics Data System (ADS)

    Pegoraro, Francesco; Del Sarto, Danele; Califano, Francesco

    2016-10-01

    We show that the spatial inhomogeneity of a shear flow in a fluid plasma is transferred to a pressure anisotropy that has both a gyrotropic and a non gyrotropic component. We investigate this process both analytically and numerically by including the full pressure tensor dynamics. We determine the time evolution of the pressure agyrotropy and in general of the pressure tensor anisotropization which arise from the action of both the magnetic eld and the flow strain tensor. This mechanism can affect the onset and development of shear-induced fluid instabilities in plasmas and is relevant to the understanding of the origin of some of the non-Maxwellian distribution functions evidenced both in Vlasov simulations and in space plasma measurements that exhibit pressure agyrotropy.

  17. Bathymetrically controlled velocity-shear front at a tidal river confluence

    NASA Astrophysics Data System (ADS)

    Blain, Cheryl Ann; Mied, Richard P.; McKay, Paul; Chen, Wei; Rhea, W. Joseph

    2015-08-01

    Nonbuoyant front formation at the confluence of Nanjemoy Creek and the main Potomac River (MD) channel is examined. Terra satellite ASTER imagery reveals a sediment color front emerging from Nanjemoy Creek when the Potomac is near maximum ebb. Nearly contemporaneous ASTER and Landsat ETM+ imagery are used to extract surface velocities, which suggest a velocity shear front is collocated with the color front. In situ velocities (measured by RiverRay traverses near the Nanjemoy Creek mouth) confirm the shear front's presence. A finite-element simulation (using ADCIRC) replicates the observed velocity-shear front and is applied to decipher its physics. Three results emerge: (1) the velocity-shear front forms, confined to a shoal downstream of the creek-river confluence for most of the tidal cycle, (2) a simulation with a flat bottom in Nanjemoy Creek and Potomac River (i.e., no bathymetry variation) indicates the velocity-shear front never forms, hence the front cannot exist without the bathymetry, and (3) an additional simulation with a blocked-off Creek entrance demonstrates that while the magnitude of the velocity shear is largely unchanged without the creek, shear front formation is delayed in time. Without the Creek, there is no advection of the M6 tidal constituent (generated by nonlinear interaction of the flow with bottom friction) onto the shoals, only a locally generated contribution. A tidal phase difference between Nanjemoy and Potomac causes the ebbing Nanjemoy Creek waters to intrude into the Potomac as far south as its deep channel, and draw from a similar location in the Potomac during Nanjemoy flood.

  18. A Simple Method to Predict Threshold Shear Velocity in the Field

    NASA Astrophysics Data System (ADS)

    Li, J.; Okin, G. S.; Herrick, J. E.; Miller, M. E.; Munson, S. M.; Belnap, J.

    2009-12-01

    A very important parameter in predicting wind erosion is the threshold shear velocity, which is the minimal shear velocity required to initiate deflation of soil particles. Modeling and wind tunnel are primary methods in predicting threshold shear velocity. However, most models have limited applications in the presence of roughness elements, and running a wind tunnel in the field is labor-intensive and time-consuming. Soil crust (both physical and biological) is known to be a crucial factor affecting soil stability and threshold shear velocity. In this report, a simple and portable field method was tested in multiple locations of Utah for the estimation of threshold shear velocity. This method includes measuring size of holes (length and width) induced by shooting a “bullet ball” or “BB” gun, applying a pocket penetrometer, and a torvane on soil surface in the field. In the first stage of the experiment, a conventional wind tunnel was run in combination with BB gun, penetrometer, and torvane in field conditions for a range of soil texture. Results from both the BB gun and penetrometer applied at 45 degree to the ground were significantly correlated with the threshold shear velocity obtained using the wind tunnel (R2=0.70, P<0.001). In the second stage, BB gun and penetrometer method was applied to a serial of sites which have BSNE wind erosion monitors and known horizontal sediment fluxes. Our results showed that a combination of BB gun and penetrometer is able to provide decent prediction of threshold shear velocity in the presence of vegetation under different soil physical and biological conditions.

  19. Shear banding in a lyotropic lamellar phase. I. Time-averaged velocity profiles

    NASA Astrophysics Data System (ADS)

    Salmon, Jean-Baptiste; Manneville, Sébastien; Colin, Annie

    2003-11-01

    Using velocity profile measurements based on dynamic light scattering and coupled to structural and rheological measurements in a Couette cell, we present evidences for a shear banding scenario in the shear flow of the onion texture of a lyotropic lamellar phase. Time-averaged measurements clearly show the presence of structural shear banding in the vicinity of a shear-induced transition, associated with the nucleation and growth of a highly sheared band in the flow. Our experiments also reveal the presence of slip at the walls of the Couette cell. Using a simple mechanical approach, we demonstrate that our data confirm the classical assumption of the shear banding picture, in which the interface between bands lies at a given stress σ*. We also outline the presence of large temporal fluctuations of the flow field, which are the subject of the second part of this paper [Salmon et al., Phys. Rev. E 68, 051504 (2003)].

  20. Compressional and shear wave velocities in granular materials to 2.5 kilobars

    NASA Technical Reports Server (NTRS)

    Talwani, P.; Nur, A.; Kovach, R. L.

    1973-01-01

    The velocities of seismic compressional waves and, for the first time, shear wave velocities in silica sand, volcanic ash, and basalt powder were determined under hydrostatic confining pressures to 2.5 kb. Simultaneously, the porosity of these materials was obtained as a function of confining pressure. The presented results have important implications for the self-compaction hypothesis that has been postulated to explain the lunar near-surface seismic velocity variation.

  1. Shear Wave Velocity Imaging Using Transient Electrode Perturbation: Phantom and ex vivo Validation

    PubMed Central

    Varghese, Tomy; Madsen, Ernest L.

    2011-01-01

    This paper presents a new shear wave velocity imaging technique to monitor radio-frequency and microwave ablation procedures, coined electrode vibration elastography. A piezoelectric actuator attached to an ablation needle is transiently vibrated to generate shear waves that are tracked at high frame rates. The time-to-peak algorithm is used to reconstruct the shear wave velocity and thereby the shear modulus variations. The feasibility of electrode vibration elastography is demonstrated using finite element models and ultrasound simulations, tissue-mimicking phantoms simulating fully (phantom 1) and partially ablated (phantom 2) regions, and an ex vivo bovine liver ablation experiment. In phantom experiments, good boundary delineation was observed. Shear wave velocity estimates were within 7% of mechanical measurements in phantom 1 and within 17% in phantom 2. Good boundary delineation was also demonstrated in the ex vivo experiment. The shear wave velocity estimates inside the ablated region were higher than mechanical testing estimates, but estimates in the untreated tissue were within 20% of mechanical measurements. A comparison of electrode vibration elastography and electrode displacement elastography showed the complementary information that they can provide. Electrode vibration elastography shows promise as an imaging modality that provides ablation boundary delineation and quantitative information during ablation procedures. PMID:21075719

  2. Shear-wave velocity of slope sediments near Hudson Canyon from analysis of ambient noise

    NASA Astrophysics Data System (ADS)

    Miller, N. C.; Ten Brink, U. S.; Collins, J. A.; McGuire, J. J.; Flores, C. H.

    2014-12-01

    We present new ambient noise data that help constrain the shear strength of marine sediments on the continental slope north of Hudson Canyon on the U.S. Atlantic margin. Sediment shear strength is a key parameter in models of potentially tsunamigenic, submarine slope failures, but shear strength is difficult to measure in situ and is expected to evolve in time with changes in pore pressure. The ambient noise data were recorded by 11 short-period, ocean-bottom seismometers and hydrophones deployed in a ~1 by 1.5 km array for ~6 months on the continental slope. These high frequency (~0.1 - 50 Hz), narrow-aperture data are expected to record noise propagating as interface waves and/or resonating in the upper ~500 m of sediment. Propagation of interface waves is controlled by the shear-wave velocity of the sediment, which we measure by calculating lag-times in cross-correlations of waveforms recorded by pairs of receivers. These measurements of shear-wave velocity will be used to constrain shear strength. The data also appear to record wind-generated noise resonating in layered sediment. We expect this resonance to also be sensitive to shear-wave velocity, and spectral analysis and modeling of harmonics may provide a second constraint on sediment shear strength. Both the correlogram- and spectral-based measurements can be made using hour- to day-long segments of data, enabling us to constrain temporal evolution of shear-wave velocity and potential forcing mechanisms (e.g., tidal and storm loading and submarine groundwater discharge) through the ~6 month deployment.

  3. Effect of particle size distribution on the correlation between liquefaction resistance and shear wave velocity of granular soils

    NASA Astrophysics Data System (ADS)

    Zhou, Changtao; Xu, Xiao Min; Cheng, Yi Pik

    2017-06-01

    Shear wave method has been increasingly popular in assessing the liquefaction potential of granular soils. Two particle-scale parameters, the inter-particle friction and the shear modulus of grains, play vital roles in correlation between Cyclic Resistance Ratio (CRR) and shear wave velocity corrected by overburden stress (Vs1). Series of drained one-dimensional compression tests were simulated on samples of different inter-particle friction angles assigned during preparation stage. Uniformity coefficients of these Particle Size Distribution (PSD) curves are 2 and 4 whose average particle size d50 are identical. The shearing results, as well as their assigned inter-particle friction angles form calibration curves for real sands. Dissimilar PSD curves result in different calibration outcomes. For Silica sand no.8, these curves give divergent inter-particle friction angles. This study calibrates particle shear modulus for Silica sand no.8 as well. Different PSD curves give divergent values of particle shear modulus. PSDs show impacts on calibrations of both vital parameters, which have converse effects on CRR-Vs1 curves. This study suggests that the CRR-Vs1 correlation should be independent of PSDs.

  4. Wall Shear Stress, Wall Pressure and Near Wall Velocity Field Relationships in a Whirling Annular Seal

    NASA Technical Reports Server (NTRS)

    Morrison, Gerald L.; Winslow, Robert B.; Thames, H. Davis, III

    1996-01-01

    The mean and phase averaged pressure and wall shear stress distributions were measured on the stator wall of a 50% eccentric annular seal which was whirling in a circular orbit at the same speed as the shaft rotation. The shear stresses were measured using flush mounted hot-film probes. Four different operating conditions were considered consisting of Reynolds numbers of 12,000 and 24,000 and Taylor numbers of 3,300 and 6,600. At each of the operating conditions the axial distribution (from Z/L = -0.2 to 1.2) of the mean pressure, shear stress magnitude, and shear stress direction on the stator wall were measured. Also measured were the phase averaged pressure and shear stress. These data were combined to calculate the force distributions along the seal length. Integration of the force distributions result in the net forces and moments generated by the pressure and shear stresses. The flow field inside the seal operating at a Reynolds number of 24,000 and a Taylor number of 6,600 has been measured using a 3-D laser Doppler anemometer system. Phase averaged wall pressure and wall shear stress are presented along with phase averaged mean velocity and turbulence kinetic energy distributions located 0.16c from the stator wall where c is the seal clearance. The relationships between the velocity, turbulence, wall pressure and wall shear stress are very complex and do not follow simple bulk flow predictions.

  5. Wall Shear Stress, Wall Pressure and Near Wall Velocity Field Relationships in a Whirling Annular Seal

    NASA Technical Reports Server (NTRS)

    Morrison, Gerald L.; Winslow, Robert B.; Thames, H. Davis, III

    1996-01-01

    The mean and phase averaged pressure and wall shear stress distributions were measured on the stator wall of a 50% eccentric annular seal which was whirling in a circular orbit at the same speed as the shaft rotation. The shear stresses were measured using flush mounted hot-film probes. Four different operating conditions were considered consisting of Reynolds numbers of 12,000 and 24,000 and Taylor numbers of 3,300 and 6,600. At each of the operating conditions the axial distribution (from Z/L = -0.2 to 1.2) of the mean pressure, shear stress magnitude, and shear stress direction on the stator wall were measured. Also measured were the phase averaged pressure and shear stress. These data were combined to calculate the force distributions along the seal length. Integration of the force distributions result in the net forces and moments generated by the pressure and shear stresses. The flow field inside the seal operating at a Reynolds number of 24,000 and a Taylor number of 6,600 has been measured using a 3-D laser Doppler anemometer system. Phase averaged wall pressure and wall shear stress are presented along with phase averaged mean velocity and turbulence kinetic energy distributions located 0.16c from the stator wall where c is the seal clearance. The relationships between the velocity, turbulence, wall pressure and wall shear stress are very complex and do not follow simple bulk flow predictions.

  6. Wavefield Analysis of Rayleigh Waves for Near-Surface Shear-Wave Velocity

    NASA Astrophysics Data System (ADS)

    Zeng, Chong

    2011-12-01

    Shear (S)-wave velocity is a key property of near-surface materials and is the fundamental parameter for many environmental and engineering geophysical studies. Directly acquiring accurate S-wave velocities from a seismic shot gather is usually difficult due to the poor signal-to-noise ratio. The relationship between Rayleigh-wave phase velocity and frequency has been widely utilized to estimate the S-wave velocities in shallow layers using the multichannel analysis of surface waves (MASW) technique. Hence, Rayleigh wave is a main focus of most near-surface seismic studies. Conventional dispersion analysis of Rayleigh waves assumes that the earth is laterally homogeneous and the free surface is horizontally flat, which limits the application of surface-wave methods to only 1D earth models or very smooth 2D models. In this study I extend the analysis of Rayleigh waves to a 2D domain by employing the 2D full elastic wave equation so as to address the lateral heterogeneity problem. I first discuss the accurate simulation of Rayleigh waves through finite-difference method and the boundary absorbing problems in the numerical modeling with a high Poisson's ratio (> 0.4), which is a unique near-surface problem. Then I develop an improved vacuum formulation to generate accurate synthetic seismograms focusing on Rayleigh waves in presence of surface topography and internal discontinuities. With these solutions to forward modeling of Rayleigh waves, I evaluate the influence of surface topography to conventional dispersion analysis in 2D and 3D domains by numerical investigations. At last I examine the feasibility of inverting waveforms of Rayleigh waves for shallow S-wave velocities using a genetic algorithm. Results of the study show that Rayleigh waves can be accurately simulated in near surface using the improved vacuum formulation. Spurious reflections during the numerical modeling can be efficiently suppressed by the simplified multiaxial perfectly matched layers. The

  7. Shear-wave velocity profiling according to three alternative approaches: A comparative case study

    NASA Astrophysics Data System (ADS)

    Dal Moro, G.; Keller, L.; Al-Arifi, N. S.; Moustafa, S. S. R.

    2016-11-01

    The paper intends to compare three different methodologies which can be used to analyze surface-wave propagation, thus eventually obtaining the vertical shear-wave velocity (VS) profile. The three presented methods (currently still quite unconventional) are characterized by different field procedures and data processing. The first methodology is a sort of evolution of the classical Multi-channel Analysis of Surface Waves (MASW) here accomplished by jointly considering Rayleigh and Love waves (analyzed according to the Full Velocity Spectrum approach) and the Horizontal-to-Vertical Spectral Ratio (HVSR). The second method is based on the joint analysis of the HVSR curve together with the Rayleigh-wave dispersion determined via Miniature Array Analysis of Microtremors (MAAM), a passive methodology that relies on a small number (4 to 6) of vertical geophones deployed along a small circle (for the common near-surface application the radius usually ranges from 0.6 to 5 m). Finally, the third considered approach is based on the active data acquired by a single 3-component geophone and relies on the joint inversion of the group-velocity spectra of the radial and vertical components of the Rayleigh waves, together with the Radial-to-Vertical Spectral Ratio (RVSR). The results of the analyses performed while considering these approaches (completely different both in terms of field procedures and data analysis) appear extremely consistent thus mutually validating their performances. Pros and cons of each approach are summarized both in terms of computational aspects as well as with respect to practical considerations regarding the specific character of the pertinent field procedures.

  8. The P-wave boundary of the Large-Low Shear Velocity Province beneath the Pacific

    NASA Astrophysics Data System (ADS)

    Frost, Daniel A.; Rost, Sebastian

    2014-10-01

    The Large Low Shear Velocity Provinces (LLSVPs) in the lower mantle represent volumetrically significant thermal or chemical or thermo-chemical heterogeneities. Their structure and boundaries have been widely studied, mainly using S-waves, but much less is known about their signature in the P-wavefield. We use an extensive dataset recorded at USArray to create, for the first time, a high-resolution map of the location, shape, sharpness, and extent of the boundary of the Pacific LLSVP using P (Pdiff)-waves. We find that the northern edge of the Pacific LLSVP is shallow dipping (26° relative to the horizontal) and diffuse (∼120 km wide transition zone) whereas the eastern edge is steeper dipping (70°) and apparently sharp (∼40 km wide). We trace the LLSVP boundary up to ∼500 km above the CMB in most areas, and 700 km between 120° and 90°W at the eastern extent of the boundary. Apparent P-wave velocity drops are ∼1-3% relative to PREM, indicating a strong influence of LLSVPs on P-wave velocity, at least in the high-frequency wavefield, in contrast to previous studies. A localised patch with a greater velocity drop of ∼15-25% is detected, defined by large magnitude gradients of the travel-time residuals. We identify this as a likely location of an Ultra-Low Velocity Zone (ULVZ), matching the location of a previously detected ULVZ in this area. The boundary of a separate low velocity anomaly, of a similar height to the LLSVP, is detected in the north-west Pacific, matching tomographic images. This outlier appears to be connected to the main LLSVP through a narrow channel close to the CMB and may be in the process of joining or splitting from the main LLSVP. We also see strong velocity increases in the lower mantle to the east of the LLSVP, likely detecting subducted material beneath central America. The LLSVP P-wave boundary is similar to that determined in high-resolution S-wave studies and follows the -0.4% ΔVS iso-velocity contour in the S40RTS

  9. Finite frequency tomography of D″ shear velocity heterogeneity beneath the Caribbean

    NASA Astrophysics Data System (ADS)

    Hung, Shu-Huei; Garnero, Edward J.; Chiao, Ling-Yun; Kuo, Ban-Yuan; Lay, Thorne

    2005-07-01

    The shear velocity structure in the lowermost 500 km of the mantle beneath the Caribbean and surrounding areas is determined by seismic tomography applied to a suite of Sd-SKS, ScS-S, (Scd + Sbc)-S, and ScS-(Scd + Sbc) differential times, where (Scd + Sbc) is a pair of overlapping triplication arrivals produced by shear wave interaction with an abrupt velocity increase at the top of the D″ region. The inclusion of the triplication arrivals in the inversion, a first for a deep mantle tomographic model, is possible because of the widespread presence of a D″ velocity discontinuity in the region. The improved ray path sampling provided by the triplication arrivals yields improved vertical resolution of velocity heterogeneity within and above the D″ region. The reference velocity model, taken from a prior study of waveforms in the region, has a 2.9% shear velocity discontinuity 250 km above the core-mantle boundary (CMB). Effects of aspherical structure in the mantle at shallower depths than the inversion volume are suppressed by applying corrections for several different long-wavelength shear velocity tomography models. Born-Fréchet kernels are used to characterize how the finite frequency data sample the structure for all of the differential arrival time combinations; inversions are performed with and without the kernels. The use of three-dimensional kernels stabilizes the tomographic inversion relative to a ray theory parameterization, and a final model with 60- and 50-km correlation lengths in the lateral and radial dimensions, respectively, is retrieved. The resolution of the model is higher than that of prior inversions, with 3-4% velocity fluctuations being resolved within what is commonly described as a circum-Pacific ring of high velocities. A broad zone of relatively high shear velocity material extends throughout the lower mantle volume beneath the Gulf of Mexico, with several percent lower shear velocities being found beneath northern South America

  10. Finite-Frequency Tomography of D'' Shear Velocity Heterogeneity beneath the Caribbean

    NASA Astrophysics Data System (ADS)

    Hung, S.; Garnero, E. J.; Chiao, L.; Kuo, B.; Lay, T.

    2004-12-01

    The shear velocity structure in the lowermost 500 km of the mantle beneath the Caribbean and surrounding areas is determined by seismic tomography applied to a suite of Sdiff-SKS, ScS-S, (Scd+Sbc)-S, and ScS-(Scd+Sbc) differential times, where (Scd+Sbc) is a pair of overlapping triplication arrivals produced by shear wave interaction with an abrupt velocity increase at the top of the D'' region. The inclusion of the triplication arrivals in the inversion, a first for a deep mantle tomographic model, is possible because of the widespread presence of a D'' velocity discontinuity in the region. The additional raypath sampling provided by the triplication arrivals yields improved vertical resolution of velocity heterogeneity within and above the D'' region. The reference velocity model, taken from a prior study of waveforms in the region, has a 2.9% shear velocity discontinuity 250 km above the CMB. Effects of aspherical structure in the mantle at shallower depths than the inversion volume are suppressed by applying corrections for several different long-wavelength shear velocity tomography models. Born-Fréchet kernels are used to characterize how the finite-frequency data sample the structure for all of the differential arrival time combinations; inversions are performed with and without the kernels. The use of 3-D kernels stabilizes the tomographic inversion relative to a ray theory parameterization, and a final model with 60 and 50 km correlation lengths in the the lateral and radial dimensions, respectively, is retrieved. The resolution of the model is higher than that of prior inversions, with 3 to 4% velocity fluctuations being resolved within what is commonly described as a circum-Pacific ring of high velocities. A broad zone of relatively high shear velocity material extends throughout the lower mantle volume beneath the Gulf of Mexico, with several percent lower shear velocities being found beneath northern South America. Concentrated low velocity regions

  11. Single Tracking Location Methods Suppress Speckle Noise in Shear Wave Velocity Estimation

    PubMed Central

    Elegbe, Etana C.; McAleavey, Stephen A.

    2014-01-01

    In ultrasound-based elastography methods, the estimation of shear wave velocity typically involves the tracking of speckle motion due to an applied force. The errors in the estimates of tissue displacement, and thus shear wave velocity, are generally attributed to electronic noise and decorrelation due to physical processes. We present our preliminary findings on another source of error, namely, speckle-induced bias in phase estimation. We find that methods that involve tracking in a single location, as opposed to multiple locations, are less sensitive to this source of error since the measurement is differential in nature and cancels out speckle-induced phase errors. PMID:23493611

  12. Single tracking location methods suppress speckle noise in shear wave velocity estimation.

    PubMed

    Elegbe, Etana C; McAleavey, Stephen A

    2013-04-01

    In ultrasound-based elastography methods, the estimation of shear wave velocity typically involves the tracking of speckle motion due to an applied force. The errors in the estimates of tissue displacement, and thus shear wave velocity, are generally attributed to electronic noise and decorrelation due to physical processes. We present our preliminary findings on another source of error, namely, speckle-induced bias in phase estimation. We find that methods that involve tracking in a single location, as opposed to multiple locations, are less sensitive to this source of error since the measurement is differential in nature and cancels out speckle-induced phase errors.

  13. Crustal and Uppermost Mantle Shear Velocity Structure across the Mariana Trench

    NASA Astrophysics Data System (ADS)

    Cai, C.; Wiens, D.; Lizarralde, D.

    2015-12-01

    We investigate the shear wave structure of the crust and uppermost mantle across the Northern and Central Mariana trench using data recorded by a temporary network deployed in 2012-2013, including 7 island stations and 20 ocean bottom seismographs (OBSs). The goal of this study is to constrain velocity variations resulting from possible serpentinization of the incoming plate and the forearc mantle, and thus better understand the water budget of subduction zones. We use an ambient noise analysis method to reveal surface wave phase velocities at short period (8-30 s). Vertical component cross correlations show distinct fundamental and 1st higher-mode Rayleigh wave signals, especially between station pairs in the incoming plate. The 1st higher-mode Rayleigh wave is of significant importance for resolving crustal and shallowest upper mantle structure in regions covered by deep water. A multichannel cross correlation method (Eikonal tomography) is applied to Rayleigh waves from teleseismic earthquakes to obtain phase velocity at 25-80 s period. Finally the combined phase velocity curve from noise and teleseismic earthquakes is inverted at each point to determine the shear velocity structure. Preliminary inversion results for the incoming plate indicate slightly thickened crust that may be caused by a large Cretaceous igneous event associated with nearby seamounts. A high velocity anomaly emerges at around 20 km depth in the same region. We will present the entire 3-D shear wave velocity model across the trench during the AGU fall meeting.

  14. Shear-wave velocity of surficial geologic sediments in Northern California: Statistical distributions and depth dependence

    USGS Publications Warehouse

    Holzer, T.L.; Bennett, M.J.; Noce, T.E.; Tinsley, J. C.

    2005-01-01

    Shear-wave velocities of shallow surficial geologic units were measured at 210 sites in a 140-km2 area in the greater Oakland, California, area near the margin of San Francisco Bay. Differences between average values of shear-wave velocity for each geologic unit computed by alternative approaches were in general smaller than the observed variability. Averages estimated by arithmetic mean, geometric mean, and slowness differed by 1 to 8%, while coefficients of variation ranged from 14 to 25%. With the exception of the younger Bay mud that underlies San Francisco Bay, velocities of the geologic units are approximately constant with depth. This suggests that shear-wave velocities measured at different depths in these surficial geologic units do not need to be normalized to account for overburden stress in order to compute average values. The depth dependence of the velocity of the younger Bay mud most likely is caused by consolidation. Velocities of each geologic unit are consistent with a normal statistical distribution. Average values increase with geologic age, as has been previously reported. Velocities below the water table are about 7% less than those above it. ?? 2005, Earthquake Engineering Research Institute.

  15. D″ shear velocity heterogeneity, anisotropy and discontinuity structure beneath the Caribbean and Central America

    NASA Astrophysics Data System (ADS)

    Garnero, Edward J.; Lay, Thorne

    2003-11-01

    The D″ region in the lowermost mantle beneath the Caribbean and Central America is investigated using shear waves from South American earthquakes recorded by seismic stations in North America. We present a large-scale, composite study of volumetric shear velocity heterogeneity, anisotropy, and the possible presence of a D″ discontinuity in the region. Our data set includes: 328 S( Sdiff)- SKS differential travel times, 300 ScS-S differential travel times, 125 S( Sdiff) and 120 ScS shear wave splitting measurements, and 297 seismograms inspected for Scd, the seismic phase refracted from a high-velocity D″ layer. Broadband digital data are augmented by high-quality digitized analog WWSSN data, providing extensive path coverage in our study area. In all, data from 61 events are utilized. In some cases, a given seismogram can be used for velocity heterogeneity, anisotropy, and discontinuity analyses. Significant mid-mantle structure, possibly associated with the ancient subducted Farallon slab, affects shear wave travel times and must be corrected for to prevent erroneous mapping of D″ shear velocity. All differential times are corrected for contributions from aspherical mantle structure above D″ using a high-resolution tomography model. Travel time analyses demonstrate the presence of pervasive high velocities in D″, with the highest velocities localized to a region beneath Central America, approximately 500-700 km in lateral dimension. Short wavelength variability overprints this general high-velocity background. Corrections are also made for lithospheric anisotropy beneath the receivers. Shear wave splitting analyses of the corrected waveforms reveal D″ anisotropy throughout the study area, with a general correlation with heterogeneity strength. Evidence for Scd arrivals is pervasive across the study area, consistent with earlier work, but there are a few localized regions (100-200 km) lacking clear Scd arrivals, which indicates heterogeneity in the

  16. Preliminary Shear Velocity Tomography of Mt St Helens, Washington from iMUSH Array

    NASA Astrophysics Data System (ADS)

    Crosbie, K.; Abers, G. A.; Creager, K. C.; Moran, S. C.; Denlinger, R. P.; Ulberg, C. W.

    2015-12-01

    The imaging Magma Under Mount St Helens (iMUSH) experiment will illuminate the crust beneath Mt St Helens volcano. The ambient noise tomography (ANT) component of this experiment measures shear velocity structure, which is more sensitive than P velocity to the presence of melt and other pore fluids. Seventy passive-source broadband seismometers for iMUSH were deployed in the summer of 2014 in a dense array of 100 Km diameter with a 10 km station spacing. We cross correlated ambient noise in 120 s windows and summed the result over many months for pairs of stations. Then frequency-domain methods on these cross correlations are employed to measure the phase velocities (Ekström et al. Geophys Rev Lett, 2009). Unlike velocities attained by group velocity methods, velocities for path lengths as small as one wavelength can be measured, enabling analysis of higher frequency signals and increasing spatial resolution. The minimum station spacing from which signals can be recovered ranges from 12 km at 0.18 Hz, a frequency that dominantly samples the upper crust to 20 km, to 37 km at 0.04 Hz, a frequency sensitive to structure through the crust and uppermost mantle, with lower spacing at higher frequencies. These phase velocities are tomographically inverted to obtain shear velocity maps for each frequency, assuming ray theory. Initial shear velocity maps for frequencies between 0.04-0.18 Hz reveal low-velocity sediments in the Puget Lowland west of Mount St Helens at 0.16-0.18 Hz, and a low velocity zone near 0.10 Hz between Mt Rainier and Mt Adams, east of Mount St Helens. The latter may reflect large-scale crustal plumbing of the arc between volcanic centers. In subsequent analyses these ANT results will be jointly inverted with receiver functions in order to further resolve crustal and upper mantle structure.

  17. 3D tomographic reconstruction of the internal velocity field of an immiscible drop in a shear flow

    NASA Astrophysics Data System (ADS)

    Kerdraon, Paul; Dalziel, Stuart B.; Goldstein, Raymond E.; Landel, Julien R.; Peaudecerf, Francois J.

    2015-11-01

    We study experimentally the internal flow of a drop attached to a flat substrate and immersed in an immiscible shear flow. Transport inside the drop can play a crucial role in cleaning applications. Internal advection can enhance the mass transfer across the drop surface, thus increasing the cleaning rate. We used microlitre water-glycerol drops on a hydrophobic substrate. The drops were spherical and did not deform significantly under the shear flow. An oil phase of relative viscosity 0.01 to 1 was flowed over the drop. Typical Reynolds numbers inside the drops were of the order of 0.1 to 10. Using confocal microscopy, we performed 3D tomographic reconstruction of the flow field in the drop. The in-plane velocity field was measured using micro-PIV, and the third velocity component was computed from incompressibility. To our knowledge, this study gives the first experimental measurement of the three-dimensional internal velocity field of a drop in a shear flow. Numerical simulations and theoretical models published in the past 30 years predict a toroidal internal recirculation flow, for which the entire surface flows streamwise. However, our measurements reveal a qualitatively different picture with a two-lobed recirculation, featuring two stagnation points at the surface and a reverse surface flow closer to the substrate. This finding appears to be independent of Reynolds number and viscosity ratio in the ranges studied; we conjecture that the observed flow is due to the effect of surfactants at the drop surface.

  18. Dissipation and velocity distribution at the shear-driven jamming transition

    NASA Astrophysics Data System (ADS)

    Olsson, Peter

    2016-04-01

    We investigate energy dissipation and the distribution of particle velocities at the jamming transition for overdamped shear-driven frictionless disks in two dimensions at zero temperature. We find that the dissipation is caused by the fastest particles and that the fraction of particles responsible for the dissipation decreases towards zero as jamming is approached. These particles belong to an algebraic tail of the velocity distribution that approaches ˜v-3 as jamming is approached. We further find that different measures of the velocity diverge differently, which means that concepts such as typical velocity may no longer be used, a finding that should have implications for analytical approaches to shear-driven jamming.

  19. Shockwave determination of the shear velocity at very high pressures. [for determining properties of planetary interiors

    NASA Technical Reports Server (NTRS)

    Anderson, O. L.

    1972-01-01

    A shock wave experiment is described for confirming changes in density, from seismic interpretation, for determining the properties of planet interiors. The experiment focuses on the problem of measurements in a pressure region, where the shear velocity tends to vanish, or become very small. Pressure-sensitive lattice stability, and the equations for an atomic model of the NaCl lattice are discussed along with the particle velocity shock technique.

  20. Shear velocity structure of the crust and upper mantle of Madagascar derived from surface wave tomography

    NASA Astrophysics Data System (ADS)

    Pratt, Martin J.; Wysession, Michael E.; Aleqabi, Ghassan; Wiens, Douglas A.; Nyblade, Andrew A.; Shore, Patrick; Rambolamanana, Gérard; Andriampenomanana, Fenitra; Rakotondraibe, Tsiriandrimanana; Tucker, Robert D.; Barruol, Guilhem; Rindraharisaona, Elisa

    2017-01-01

    The crust and upper mantle of the Madagascar continental fragment remained largely unexplored until a series of recent broadband seismic experiments. An island-wide deployment of broadband seismic instruments has allowed the first study of phase velocity variations, derived from surface waves, across the entire island. Late Cenozoic alkaline intraplate volcanism has occurred in three separate regions of Madagascar (north, central and southwest), with the north and central volcanism active until <1 Ma, but the sources of which remains uncertain. Combined analysis of three complementary surface wave methods (ambient noise, Rayleigh wave cross-correlations, and two-plane-wave) illuminate the upper mantle down to depths of 150 km. The phase-velocity measurements from the three methods for periods of 8-182 s are combined at each node and interpolated to generate the first 3-D shear-velocity model for sub-Madagascar velocity structure. Shallow (upper 10 km) low-shear-velocity regions correlate well with sedimentary basins along the west coast. Upper mantle low-shear-velocity zones that extend to at least 150 km deep underlie the north and central regions of recent alkali magmatism. These anomalies appear distinct at depths <100 km, suggesting that any connection between the zones lies at depths greater than the resolution of surface-wave tomography. An additional low-shear velocity anomaly is also identified at depths 50-150 km beneath the southwest region of intraplate volcanism. We interpret these three low-velocity regions as upwelling asthenosphere beneath the island, producing high-elevation topography and relatively low-volume magmatism.

  1. Shear Wave Velocity Structure of the Pampean Flat Slab Region from Ambient Noise Tomography

    NASA Astrophysics Data System (ADS)

    Porter, R. C.; Beck, S. L.; Zandt, G.; Warren, L. M.; Alvarado, P. M.; Gilbert, H. J.

    2010-12-01

    The South American Cordillera formed by the subduction of the Nazca plate beneath South America. While this is often considered a ‘typical’ compressive upper plate subduction zone, there are several along-strike variations in both the nature of subduction and the style of deformation. From 30° to 32° S the Nazca plate flattens out at 100 km depth for ~300 km before resuming a steeper angle of subduction. Flat slab subduction shutoff of arc magmatism and caused deformation to migrate inboard into the Sierras Pampeanas. While flat slab subduction has had a profound impact on the regions’s tectonics, the presence of preexisting features related to the rifting of Gondwanaland and the accretion of terranes have also had a large impact on deformation. We use ambient noise tomography (ANT) to calculate regional shear wave velocities to better understand the tectonic development of the Pampean flat slab region. ANT utilizes the cross correlation of seismic noise to approximate the Green’s function between two seismic stations. Using this technique, we measure Rayleigh wave phase velocities at periods between 8 and 30 seconds, allowing us to measure shear wave velocities down to 40 km depth. Initial tomography results show a strong correlation between phase velocity and basin structure. Fast phase velocities at the 10 second period correlate with the Sierra de Pie de Palo, Sierra de Valle Fertil in the west and the Sierras de Cordoba in the east, while slow velocities correlate with the Bermejo and Cuyo basins. At longer periods (beyond 20 seconds), there is a pattern of slow phase velocities in the west beneath the Precordillera and the high Andes while fast phase velocities are present in the east beneath the Sierras Pampeanas. These fast velocities most likely reflect faster mid- to lower crustal velocities and a shallower Moho. To further our interpretation we inverted phase velocities to calculate regional shear wave structure. At shallow depths (< 15 km) the

  2. Liquefaction assessment based on combined use of CPT and shear wave velocity measurements

    NASA Astrophysics Data System (ADS)

    Bán, Zoltán; Mahler, András; Győri, Erzsébet

    2017-04-01

    resistance (qc1Ncs), the overburden corrected shear wave velocity (V S1), and the magnitude and effective stress corrected cyclic stress ratio (CSRM=7.5,σv'=1atm) were considered as input variables. In this case the graphical representation of the cyclic resistance ratio curve for a given probability has been replaced by a surface that separates the liquefaction and non-liquefaction cases.

  3. Estimation of near-surface shear-wave velocity by inversion of Rayleigh waves

    USGS Publications Warehouse

    Xia, J.; Miller, R.D.; Park, C.B.

    1999-01-01

    The shear-wave (S-wave) velocity of near-surface materials (soil, rocks, pavement) and its effect on seismic-wave propagation are of fundamental interest in many groundwater, engineering, and environmental studies. Rayleigh-wave phase velocity of a layered-earth model is a function of frequency and four groups of earth properties: P-wave velocity, S-wave velocity, density, and thickness of layers. Analysis of the Jacobian matrix provides a measure of dispersion-curve sensitivity to earth properties. S-wave velocities are the dominant influence on a dispersion curve in a high-frequency range (>5 Hz) followed by layer thickness. An iterative solution technique to the weighted equation proved very effective in the high-frequency range when using the Levenberg-Marquardt and singular-value decomposition techniques. Convergence of the weighted solution is guaranteed through selection of the damping factor using the Levenberg-Marquardt method. Synthetic examples demonstrated calculation efficiency and stability of inverse procedures. We verify our method using borehole S-wave velocity measurements.Iterative solutions to the weighted equation by the Levenberg-Marquardt and singular-value decomposition techniques are derived to estimate near-surface shear-wave velocity. Synthetic and real examples demonstrate the calculation efficiency and stability of the inverse procedure. The inverse results of the real example are verified by borehole S-wave velocity measurements.

  4. Finite Larmor radius assisted velocity shear stabilization of the interchange instability in magnetized plasmas

    SciTech Connect

    Ng Sheungwah; Hassam, A.B.

    2005-06-15

    Finite Larmor radius (FLR) effects, originally shown to stabilize magnetized plasma interchange modes at short wavelength, are shown to assist velocity shear stabilization of long wavelength interchanges. It is shown that the FLR effects result in stabilization with roughly the same efficacy as the stabilization from dissipative (resistive and viscous) effects found earlier.

  5. Generation of large-scale vorticity in a homogeneous turbulence with a mean velocity shear.

    PubMed

    Elperin, Tov; Kleeorin, Nathan; Rogachevskii, Igor

    2003-07-01

    An effect of a mean velocity shear on a turbulence and on the effective force which is determined by the gradient of the Reynolds stresses is studied. Generation of a mean vorticity in a homogeneous incompressible nonhelical turbulent flow with an imposed mean velocity shear due to an excitation of a large-scale instability is found. The instability is caused by a combined effect of the large-scale shear motions ("skew-induced" deflection of equilibrium mean vorticity) and "Reynolds stress-induced" generation of perturbations of mean vorticity. Spatial characteristics of the instability, such as the minimum size of the growing perturbations and the size of perturbations with the maximum growth rate, are determined. This instability and the dynamics of the mean vorticity are associated with Prandtl's turbulent secondary flows.

  6. Parallel-velocity-shear-modified drift wave in negative ion plasmas

    NASA Astrophysics Data System (ADS)

    Ichiki, R.; Kaneko, T.; Hayashi, K.; Tamura, S.; Hatakeyama, R.

    2009-03-01

    A systematic investigation of the effects of a parallel velocity shear and negative ions on the collisionless drift wave instability has for the first time been realized by simultaneously using a segmented tungsten hot plate of a Q-machine and sulfur hexafluoride (SF6) gas in a magnetized potassium plasma. The parallel velocity shear of the positive ion flow tends to decrease the fluctuation level of the drift wave. The introduction of negative ions first increases the fluctuation level and then starts to decrease it at the negative ion exchange fraction of around 10%, while keeping the above-mentioned shear effect qualitatively. In addition, a simple dispersion relation based on the local model has been calculated to show that it can predict wave characteristics similar to the experimental results. Our findings provide a potential for gaining a more profound insight into the physics of space/circumterrestrial plasmas.

  7. Influence of velocity shear on the Rayleigh-Taylor instability. Memorandum report

    SciTech Connect

    Guzdar, P.N.; Satyanarayana, P.; Huba, J.D.; Ossakow, S.L.

    1981-12-16

    The influence of a transverse velocity shear on the Rayleigh-Taylor instability is investigated. It is found that a sheared velocity flow can substantially reduce the growth rate of the Rayleigh-Taylor instability in the short wavelength regime (i.e., kL > 1 where L is the scale length of the density inhomogeneity), and causes the growth rate to maximize at kL < 1.0. Applications of this result to ionospheric phenomena (equatorial spread F (ESF) and ionospheric plasma clouds) are discussed. In particular, the effect of shear could account for, at times, the 100's of km modulation observed on the bottomside of the ESF ionosphere and the km scale size wavelengths observed in barium cloud prompt striation phenomena.

  8. Novel Rotating Hairy Black Hole in (2+1)-Dimensions and Shear Viscosity to Entropy Ratio

    NASA Astrophysics Data System (ADS)

    Naji, J.; Heshmatian, S.

    2014-08-01

    The novel rotating hairy black hole metric in (2 + 1) dimensions, which is an exact solution to the field equations of the Einstein-scalar AdS theory with a non-minimal coupling, considered in this paper and some hydrodynamics quantities such as diffusion constant and shear viscosity investigated. By using thermodynamics quantities such as temperature and entropy we can use diffusion constant to obtain shear viscosity and then calculate shear viscosity to entropy ratio.

  9. Fiber angle and aspect ratio influence the shear mechanics of oriented electrospun nanofibrous scaffolds.

    PubMed

    Driscoll, Tristan P; Nerurkar, Nandan L; Jacobs, Nathan T; Elliott, Dawn M; Mauck, Robert L

    2011-11-01

    Fibrocartilages, including the knee meniscus and the annulus fibrosus (AF) of the intervertebral disc, play critical mechanical roles in load transmission across joints and their function is dependent upon well-defined structural hierarchies, organization, and composition. All, however, are compromised in the pathologic transformations associated with tissue degeneration. Tissue engineering strategies that address these key features, for example, aligned nanofibrous scaffolds seeded with mesenchymal stem cells (MSCs), represent a promising approach for the regeneration of these fibrous structures. While such engineered constructs can replicate native tissue structure and uniaxial tensile properties, the multidirectional loading encountered by these tissues in vivo necessitates that they function adequately in other loading modalities as well, including shear. As previous findings have shown that native tissue tensile and shear properties are dependent on fiber angle and sample aspect ratio, respectively, the objective of the present study was to evaluate the effects of a changing fiber angle and sample aspect ratio on the shear properties of aligned electrospun poly(ε-caprolactone) (PCL) scaffolds, and to determine how extracellular matrix deposition by resident MSCs modulates the measured shear response. Results show that fiber orientation and sample aspect ratio significantly influence the response of scaffolds in shear, and that measured shear strains can be predicted by finite element models. Furthermore, acellular PCL scaffolds possessed a relatively high shear modulus, 2-4 fold greater than native tissue, independent of fiber angle and aspect ratio. It was further noted that under testing conditions that engendered significant fiber stretch, the aggregate resistance to shear was higher, indicating a role for fiber stretch in the overall shear response. Finally, with time in culture, the shear modulus of MSC laden constructs increased, suggesting that

  10. On the Origin of High Shear Wave Velocities in the Deep Roots of Cratons

    NASA Astrophysics Data System (ADS)

    Zeng, L.; Duncan, M. S.; Garber, J. M.; Hernandez, J. A.; Maurya, S.; Zhang, H.; Faul, U.; McCammon, C. A.; Montagner, J. P.; Moresi, L. N.; Romanowicz, B. A.; Rudnick, R. L.; Stixrude, L. P.

    2016-12-01

    Some seismic models derived from tomographic studies indicate very high shear wave velocities around 150 km depth, which cannot be explained by standard cratonic peridotite compositions derived from kimberlites, even under the assumption of very cold geotherms (i.e. 28mW/m3 surface heat flux). We present the results of a multi-disciplinary study conducted at the CIDER Summer 2016 program in Santa Barbara (CA), in which we have reviewed various geophysical and petrological constraints on the nature of cratonic roots (seismic velocities, electrical conductivity, gravity, lithologies) and explored a range of possible solutions. We find that matching the high shear wave velocities requires a large proportion of eclogite that is not matched by observed eclogite proportions in kimberlite samples. The high shear velocity of diamond makes it a viable candidate to account for such high velocities, in a proportion that is compatible with the global carbon budget. Our most recent results will be presented as well as suggestions for possible mechanisms for diamond formation and emplacement.

  11. Shear-wave velocity compilation for Northridge strong-motion recording sites

    USGS Publications Warehouse

    Borcherdt, Roger D.; Fumal, Thomas E.

    2002-01-01

    Borehole and other geotechnical information collected at the strong-motion recording sites of the Northridge earthquake of January 17, 1994 provide an important new basis for the characterization of local site conditions. These geotechnical data, when combined with analysis of strong-motion recordings, provide an empirical basis to evaluate site coefficients used in current versions of US building codes. Shear-wave-velocity estimates to a depth of 30 meters are derived for 176 strong-motion recording sites. The estimates are based on borehole shear-velocity logs, physical property logs, correlations with physical properties and digital geologic maps. Surface-wave velocity measurements and standard penetration data are compiled as additional constraints. These data as compiled from a variety of databases are presented via GIS maps and corresponding tables to facilitate use by other investigators.

  12. Statistics of particle pair relative velocity in the homogeneous shear flow

    NASA Astrophysics Data System (ADS)

    Gualtieri, P.; Picano, F.; Sardina, G.; Casciola, C. M.

    2012-02-01

    Small scale clustering of inertial particles and relative velocity of particle pairs have been fully characterized for statistically steady homogeneous isotropic flows. Depending on the particle Stokes relaxation time, the spatial distribution of the disperse phase results in a multi-scale manifold characterized by local particle concentration and voids and, because of finite inertia, the two nearby particles have high probability to exhibit large relative velocities. Both effects might explain the speed-up of particle collision rate in turbulent flows. Recently it has been shown that the large scale geometry of the flow plays a crucial role in organizing small scale particle clusters. For instance, a mean shear preferentially orients particle patterns. In this case, depending on the Stokes time, anisotropic clustering may occur even in the inertial range of scales where the turbulent fluctuations which drive the particles have already recovered isotropy. Here we consider the statistics of particle pair relative velocity in the homogeneous shear flow, the prototypical flow which manifests anisotropic clustering at small scales. We show that the mean shear, by imprinting anisotropy on the large scale velocity fluctuations, dramatically affects the particle relative velocity distribution even in the range of small scales where the anisotropic mechanisms of turbulent kinetic energy production are sub-dominant with respect to the inertial energy transfer which drives the carrier fluid velocity towards isotropy. We find that the particles’ populations which manifest strong anisotropy in their relative velocities are the same which exhibit small scale clustering. In contrast to any Kolmogorov-like picture of turbulent transport these phenomena may persist even below the smallest dissipative scales where the residual level of anisotropy may eventually blow-up. The observed anisotropy of particle relative velocity and spatial configuration is suggested to influence the

  13. Frictional strength of wet- and dry- talc gouge in high-velocity shear experiments

    NASA Astrophysics Data System (ADS)

    Chen, X.; Reches, Z.; Elwood Madden, A. S.

    2015-12-01

    The strength of the creeping segment of the San Andres fault may be controlled by the distinct weakness and stability of talc (Moore & Rymer, 2007). We analyze talc frictional strength at high slip-velocity of 0.002 - 0.66 m/s, long slip-distances of 0.01 m to 33 m, and normal stresses up to 4.1 MPa. This analysis bridges the gap between nucleation stage of low velocity/distance, and the frictional behavior during large earthquakes. We tested wet and dry samples of pure talc gouge in a confined rotary cell, and continuously monitored the slip-velocity, stresses, dilation and temperature. We run 29 experiments of single and stepped velocities to obtain 243 values of quasi-static frictional coefficients. Dry talc gouge showed distinct slip-strengthening: friction coefficient of µ ~0.4 at short slip-distances of D < 0.1 m, and it increased systematically to µ ~0.8 at slip-distances of D = 0.1- 1 m; at D > 1 m, the frictional strength saturated at µ= 0.8 - 1 level. Wet talc gouge (16-20% water) displayed low frictional strength of µ= 0.1-0.3, in agreement with published triaxial tests. The stepped-velocity runs revealed a consistent velocity-strengthening trend. For a velocity jump from V1 to V2, we used VD = (µ2 -µ1)/ln (V2/V1), and found that on average VD = 0.06 and 0.03 for dry and wet talc, respectively, and for slip distances shorter than 1 m. Microstructural analysis of post-shearing wet talc gouge revealed extreme slip localization to a principal-slip-zone of a few microns, and significant shear compaction of 10-30%. In contrast, dry talc gouge exhibited distributed shear in a wide zone and systematic shear dilation (10-50%). We propose slip along weak interlayer talc plates and thermal-pressurization as the possible weakening mechanisms for wet talc. The development of distributed secondary fault network along with substantial grain crushing is responsible for slip-strengthening in dry condition. Fig. 1. Friction maps of talc gouge as function of slip

  14. Mantle shear-wave velocity structure beneath the Hawaiian hot spot.

    PubMed

    Wolfe, Cecily J; Solomon, Sean C; Laske, Gabi; Collins, John A; Detrick, Robert S; Orcutt, John A; Bercovici, David; Hauri, Erik H

    2009-12-04

    Defining the mantle structure that lies beneath hot spots is important for revealing their depth of origin. Three-dimensional images of shear-wave velocity beneath the Hawaiian Islands, obtained from a network of sea-floor and land seismometers, show an upper-mantle low-velocity anomaly that is elongated in the direction of the island chain and surrounded by a parabola-shaped high-velocity anomaly. Low velocities continue downward to the mantle transition zone between 410 and 660 kilometers depth, a result that is in agreement with prior observations of transition-zone thinning. The inclusion of SKS observations extends the resolution downward to a depth of 1500 kilometers and reveals a several-hundred-kilometer-wide region of low velocities beneath and southeast of Hawaii. These images suggest that the Hawaiian hot spot is the result of an upwelling high-temperature plume from the lower mantle.

  15. Linear and nonlinear studies of velocity shear driven three dimensional electron-magnetohydrodynamics instability

    SciTech Connect

    Gaur, Gurudatt; Das, Amita

    2012-07-15

    The study of electron velocity shear driven instability in electron magnetohydrodynamics (EMHD) regime in three dimensions has been carried out. It is well known that the instability is non-local in the plane defined by the flow direction and that of the shear, which is the usual Kelvin-Helmholtz mode, often termed as the sausage mode in the context of EMHD. On the other hand, a local instability with perturbations in the plane defined by the shear and the magnetic field direction exists which is termed as kink mode. The interplay of these two modes for simple sheared flow case as well as that when an external magnetic field exists has been studied extensively in the present manuscript in both linear and nonlinear regimes. Finally, these instability processes have been investigated for the exact 2D dipole solutions of EMHD equations [M. B. Isichenko and A. N. Marnachev, Sov. Phys. JETP 66, 702 (1987)] for which the electron flow velocity is sheared. It has been shown that dipoles are very robust and stable against the sausage mode as the unstable wavelengths are typically longer than the dipole size. However, we observe that they do get destabilized by the local kink mode.

  16. Effect of low-velocity or ballistic impact damage on the strength of thin composite and aluminum shear panels

    NASA Technical Reports Server (NTRS)

    Farley, G. L.

    1985-01-01

    Impact tests were conducted on shear panels fabricated from 6061-T6 aluminum and from woven fabric prepreg of Du Pont Kevlara fiber/epoxy resin and graphite fiber/epoxy resin. The shear panels consisted of three different composite laminates and one aluminum material configuration. Three panel aspect ratios were evaluated for each material configuration. Composite panels were impacted with a 1.27-cm (0.05-in) diameter aluminum sphere at low velocities of 46 m/sec (150 ft/sec) and 67 m/sec (220 ft/sec). Ballistic impact conditions consisted of a tumbled 0.50-caliber projectile impacting loaded composite and aluminum shear panels. The results of these tests indicate that ballistic threshold load (the lowest load which will result in immediate failure upon penetration by the projectile) varied between 0.44 and 0.61 of the average failure load of undamaged panels. The residual strengths of the panels after ballistic impact varied between 0.55 and 0.75 of the average failure strength of the undamaged panels. The low velocity impacts at 67 m/sec (220 ft/sec) caused a 15 to 20 percent reduction in strength, whereas the impacts at 46 m/sec (150 ft/sec) resulted in negligible strength loss. Good agreement was obtained between the experimental failure strengths and the predicted strength with the point stress failure criterion.

  17. 3-D shear velocity model of the Eastern and Southern Alps from ambient noise tomography

    NASA Astrophysics Data System (ADS)

    Qorbani, Ehsan; Zigone, Dimitri; Bokelmann, Götz; AlpArray-EASI Working Group

    2017-04-01

    The eastern and southern part of the Alpine chain is considered to be an area of complex tectonics, both in the crust and the lithosphere. Having a relatively dense network of seismic stations in this region provides an opportunity to study crustal velocity structure with ambient-noise tomography. In this study, we show results from ambient noise correlations. We used two year of continuous data recorded at 59 permanent stations and 19 stations of the AlpArray-EASI profile during 2014 and 2015. Cross correlations of ambient noise are computed in order to estimate the Green's functions of surface waves propagating between the station pairs. Dispersion curves of Rayleigh and Love waves are constructed between 2 and 40 seconds and are then inverted to obtain group velocity maps at different frequency. The Rayleigh and Love wave group velocity measurements are inverted for shear-wave velocities. We present here a 3-D shear-wave velocity model for the Eastern and Southern Alps. Our results show that velocity variations at short periods (up to 10 km depth) correlate well with the surface geology, e.g. tectonic features and faults. The results clearly show low velocity zones associated with the Po-Plain and the Molasse Basin. Under the Molasse basin the low velocity anomaly extends down to 10 km depth. We also observe a high-velocity anomaly surrounded by Northern Calcareous Alps and Dolomites (Southern Limestone Alps), where its southern edge is well-marked by the Periadriatic and Giudicarie lines. Sharp-high velocity zones at shallower depth are also observed which seem to be associated with the highly metamorphic basement, e.g. the Campo and Ötztal nappes.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    The Anatolian Plate consists of various lithospheric terranes amalgamated during the closure of the Tethys Ocean, and is currently extruding to the west in response to a combination of the collision of the Arabian plate in the east and the roll back of the Aegean subduction zone in the west. We used Ambient Noise Tomography (ANT) at periods <= 40s to investigate the crust and uppermost mantle structure of the Anatolian Plate. We computed a total of 13,779 unique cross-correlations using one sample-per-second vertical component broadband seismic data from 215 stations from 8 different networks over a period of 7 years to compute fundamental-mode Rayleigh wave dispersion curves following the method of Benson et al. (2007). We then inverted the dispersion data to calculate phase velocity maps for 11 periods from 8 s - 40 s throughout Anatolia and the Aegean regions (Barmin et al. 2001). Using smoothed Moho values derived from Vanacore et al. (2013) in our starting models, we inverted our dispersion curves using a linear least-squares iterative inversion scheme (Herrmann & Ammon 2004) to produce a 3-D shear-wave velocity model of the crust and uppermost mantle throughout Anatolia and the Aegean. We find a good correlation between our seismic shear wave velocities and paleostructures (suture zones) and modern deformation (basin formation and fault deformation). The most prominent crustal velocity contrasts occur across intercontinental sutures zones, resulting from the juxtaposition of the compositionally different basements of the amalgamated terranes. At shallow depths, seismic velocity contrasts correspond closely with surficial features. The Thrace, Cankiri and Tuz Golu basins, and accretionary complexes related to the closure of the Neotethys are characterized by slow shear wave velocities, while the Menderes and Kirsehir Massifs, Pontides, and Istanbul Zone are characterized by fast velocities. We find that the East Anatolia Plateau has slow shear-wave velocities

  19. Mixing properties of coaxial jets with large velocity ratios and large inverse density ratios

    NASA Astrophysics Data System (ADS)

    Alexander Schumaker, S.; Driscoll, James F.

    2012-05-01

    An experimental study was conducted to better understand the mixing properties of coaxial jets as several parameters were systematically varied, including the velocity ratio, density ratio, and the Reynolds number. Diameters of the inner and outer jet were also varied. Coaxial jets are commonly used to mix fluids due to the simplicity of their geometry and the rapid mixing that they provide. A measure of the overall mixing efficiency is the stoichiometric mixing length (Ls), which is the distance along the jet centerline where the two fluids have mixed to some desired concentration, which was selected to be the stoichiometric concentration for H2/O2 and CH4/O2 in this case. For 56 cases, the profiles of mean mixture fraction, rms mixture fraction fluctuations (unmixedness), and Ls were measured using acetone planar laser induced fluorescence diagnostics. Results were compared to three mixing models. The entrainment model of Villermaux and Rehab showed good agreement with the data, indicating that the proper non-dimensional scaling parameter is the momentum flux ratio M. The work extends the existing database of coaxial jet scalar mixing properties because it considers the specific regime of large values of both the velocity ratio and the inverse density ratio, which is the regime in which rocket injectors operate. Also the work focuses on the mixing up to Ls where previous work focused on the mixing up to the end of the inner core. The Reynolds numbers achieved for a number of cases were considerably larger than previous gas mixing studies, which insures that the jet exit boundary conditions are fully turbulent.

  20. Shear velocity structure of the Tyrrhenian region in relation to volcanism and tectonics

    NASA Astrophysics Data System (ADS)

    Paulssen, H.; Greve, S.

    2012-12-01

    We present a detailed 3D shear velocity model of the Tyrrhenian Sea and surrounding onshore areas down to about 160 km depth. The high resolution of the model is achieved through the measurement of interstation Rayleigh wave dispersion curves in a small regional setting with dense station coverage. The most noticeable structure is a pronounced, nearly ringshaped low velocity region at about 80 km depth surrounding the Tyrrhenian Sea: from Corsica to the western part of the Italian mainland, continuing to the western part of Sicily and Sardinia. The thickness of this low velocity region is constrained to a maximum of 40 km, and it is independent of the chosen inversion parameters or the background model. The low values of the shear velocity suggest the presence of fluids or melt. The lateral extent of the low velocity region beneath the Italian mainland is well correlated with the locations of subduction-related volcanism, but there is also a striking continuation of the anomalous low-velocity region along the Northern Tyrrhenian Sea towards (and beneath) the island of Corsica. The recent (<5 Ma) magmatism along the Italian peninsula and the older (5-9 Ma) magmatism of the Northern Tyrrhenian Sea are associated with the subduction of the Adriatic slab beneath the Apennines, indicating mantle contamination with continental crustal material. Slab rollback, the eastward migration of the Adriatic subduction zone during the last 15 My, has been invoked to explain the eastward decrease in the age of the volcanism along the Northern Tyrrhenian Sea. Our seismic results now suggest that the anomalous mantle is still present beneath Corsica and the Northern Tyrrhenian Sea, although it does not produce any active volcanism anymore. The picture for the Southern Tyrrhenian Sea is different. Intriguingly, the sublithospheric low velocity anomaly does not continue to southeasternmost part of the Tyrrhenian Sea where the volcanism of the Aeolian arc is related to subduction of the

  1. Simultaneous Concentration and Velocity Maps in Particle Suspensions under Shear from Rheo-Ultrasonic Imaging

    NASA Astrophysics Data System (ADS)

    Saint-Michel, Brice; Bodiguel, Hugues; Meeker, Steven; Manneville, Sébastien

    2017-07-01

    We extend a previously developed ultrafast ultrasonic technique [T. Gallot et al., Rev. Sci. Instrum. 84, 045107 (2013), 10.1063/1.4801462] to concentration-field measurements in non-Brownian particle suspensions under shear. The technique provides access to time-resolved concentration maps within the gap of a Taylor-Couette cell simultaneously to local velocity measurements and standard rheological characterization. Benchmark experiments in homogeneous particle suspensions are used to calibrate the system. We then image heterogeneous concentration fields that result from centrifugation effects, from the classical Taylor-Couette instability, and from sedimentation or shear-induced resuspension.

  2. Improving the shear wave velocity structure beneath Bucharest (Romania) using ambient vibrations

    NASA Astrophysics Data System (ADS)

    Manea, Elena Florinela; Michel, Clotaire; Poggi, Valerio; Fäh, Donat; Radulian, Mircea; Balan, Florin Stefan

    2016-11-01

    Large earthquakes from the intermediate-depth Vrancea seismic zone are known to produce in Bucharest ground motion characterized by predominant long periods. This phenomenon has been interpreted as the combined effect of both seismic source properties and site response of the large sedimentary basin. The thickness of the unconsolidated Quaternary deposits beneath the city is more than 200 m, the total depth of sediments is more than 1000 m. Complex basin geometry and the low seismic wave velocities of the sediments are primarily responsible for the large amplification and long duration experienced during earthquakes. For a better understanding of the geological structure under Bucharest, a number of investigations using non-invasive methods have been carried out. With the goal to analyse and extract the polarization and dispersion characteristics of the surface waves, ambient vibrations and low-magnitude earthquakes have been investigated using single station and array techniques. Love and Rayleigh dispersion curves (including higher modes), Rayleigh waves ellipticity and SH-wave fundamental frequency of resonance (f0SH) have been inverted simultaneously to estimate the shear wave velocity structure under Bucharest down to a depth of about 8 km. Information from existing borehole logs was used as prior to reduce the non-uniqueness of the inversion and to constrain the shallow part of the velocity model (<300 m). In this study, we use data from a 35-km diameter array (the URS experiment) installed by the National Institute for Earth Physics and by the Karlsruhe Institute of Technology during 10 months in the period 2003-2004. The array consisted of 32 three-component seismological stations, deployed in the urban area of Bucharest and adjacent zones. The large size of the array and the broad-band nature of the available sensors gave us the possibility to characterize the surface wave dispersion at very low frequencies (0.05-1 Hz) using frequency-wavenumber techniques

  3. Ratio of surface roughness to flow scale as additional parameter for shear-induced hemolysis.

    PubMed

    Watanabe, Nobuo; Ueda, Sunao; Nagashima, Kentaro; Oguri, Taku; Mita, Toshihiro

    2016-06-15

    In addition to the conventional knowledge that shear stress and its exposure time should have a large impact on hemolysis, it became obvious through Dr. Maruyama's study that surface roughness would be the additional factor for high shear-induced hemolysis. Concerning this new information, we hypothesized that the ratio of surface roughness to the flow scale should play a role as the additional factor for shear-induced hemolysis. The purpose of this study was to develop a constant shear generator as the method to provide a controlled shear flow field with the combination between the controlled surface roughness and the flow scale to the blood cells. Its preliminary application was to validate our hypothesis. We prototyped the constant shear stress generator with the cylindrical cone-cup structure made from the acrylic material. This chamber had 3 flow scales of 1.00, 1.25, and 1.5 mm according to the change of the inner stationary cone, at which the surface roughness was distributed into the several levels between 0.14 and 0.92 micrometers in arithmetic average roughness. Using this shear chamber, we examined what effect the flow scale and the surface roughness had on hemolysis. Our experimental data showed the tendency of a positive correlation between the ratio of surface roughness to the flow scale and the induced hemolysis levels, validating our hypothesis. The ratio of the surface roughness to the flow scale should be the additional parameter for shear-induced hemolysis.

  4. Kinetic Reconnection Simulations for CME Initiation Driven by Velocity-Shear

    NASA Astrophysics Data System (ADS)

    Black, C.; Antiochos, S. K.; Karpen, J.; DeVore, C. R.; Germaschewski, K.

    2012-12-01

    In the standard model for coronal mass ejections (CME) and/or solar flares, the free energy for the event resides in the strongly sheared magnetic field of a filament channel. The pre-eruption force balance consists of an upward force due to the magnetic pressure of the sheared field balanced by a downward tension due to overlying unsheared field. Magnetic reconnection is widely believed to be the mechanism that disrupts this force balance, leading to explosive eruption. For understanding CME/flare initiation, therefore, it is critical to model the onset or reconnection that is driven by the buildup of magnetic shear. In MHD simulations, the application of a magnetic field shear is a trivial matter. However, kinetic effects are important in the diffusion region and thus, it is important to examine this process with PIC simulations as well. The implementation of such a driver in PIC methods is nontrivial. The field must be sheared self-consistently/ indirectly to prevent the generation of waves that destroy the desired system. In the work presented here, we discuss methods for applying a velocity shear perpendicular to the plane of reconnection for a nonperiodic system. We also discuss the implementation of boundary conditions that are open to electric currents that flow through the system boundary. C.B. is supported through an appointment to the NASA Postdoctoral Program at GSFC, administered by Oak Ridge Associated Universities through a contract with NASA.

  5. 3D Shear Wave Velocity Structure and Seismic Anisotropy beneath Northern Tibet

    NASA Astrophysics Data System (ADS)

    Ceylan, S.; Ni, J. F.; Chen, Y. J.; Tilmann, F.; Yang, Y.; Ritzwoller, M. H.; Sandvol, E. A.

    2010-12-01

    Recent studies have revealed that uplift of the Tibetan plateau may be related to removal of lithospheric mantle and resulting emplacement of hotter, less dense asthenospheric material. In addition to these modes of deformation, other studies have proposed that plateau uplift and crustal thickening have occurred through a process of lateral crustal flow. In order to study the evolution and continental dynamics of the Tibetan plateau, we deployed 74 broadband seismic stations throughout northern Tibet. We have measured the fundamental mode Rayleigh wave phase velocities using the two plane wave approach for periods between 20-143 seconds and verified our results utilizing a two station method. Similar to the fast directions obtained from teleseismic shear wave splitting, our measurements indicate significant (>2%) azimuthal anisotropy throughout the upper mantle down to depths exceeding 250 km, with a dominantly east-west fast direction. Although we observe some variations in fast directions with depth, they are generally consistent (i.e., within 15 degrees). Furthermore, we observe a correlation between fast directions and strikes of major fault zones that may be indicative of vertically coherent deformation within the mantle. Our 3D tomographic models show an uppermost mantle low velocity zone north of Bangong-Nujiang Suture (BNS) in northern Tibet, and a high velocity anomaly extending ~200 km centered on BNS. We suspect that the low velocity zone is due to warmer and thinner lithosphere in the northern Qiangtang and Songpan-Gonzi terranes. At depth, we observe high velocity bodies to the south both in our phase velocity and shear wave velocity maps, possibly indicative of underthrusting Indian lithosphere. Further, high velocity bodies weaken with decreasing depth, which could be alternatively interpreted as delaminating Asian lithosphere. Shear-wave velocities and dispersion curves for northern Tibet are lower than those of Southern Tibet at depths ~80-190 km

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

    NASA Astrophysics Data System (ADS)

    James, Esther Kezia Candace

    Oceanic lithosphere constitutes the upper boundary layer of the Earth's convecting mantle. Its structure and evolution provide a vital window on the dynamics of the mantle and important clues to how the motions of Earth's surface plates are coupled to convection in the mantle below. The three-dimensional shear-velocity structure of the upper mantle beneath the Atlantic Ocean is investigated to gain insight into processes that drive formation of oceanic lithosphere. Travel times are measured for approximately 10,000 fundamental-mode Rayleigh waves, in the period range 30-130 seconds, traversing the Atlantic basin. Paths with >30% of their length through continental upper mantle are excluded to maximize sensitivity to the oceanic upper mantle. The lateral distribution of Rayleigh wave phase velocity in the Atlantic upper mantle is explored with two approaches. One, phase velocity is allowed to vary only as a function of seafloor age. Two, a general two-dimensional parameterization is utilized in order to capture perturbations to age-dependent structure. Phase velocity shows a strong dependence on seafloor age, and removing age-dependent velocity from the 2-D maps highlights areas of anomalously low velocity, almost all of which are proximal to locations of hotspot volcanism. Depth-dependent variations in vertically-polarized shear velocity (Vsv) are determined with two sets of 3-D models: a layered model that requires constant VSV in each depth layer, and a splined model that allows VSV to vary continuously with depth. At shallow depths (˜75 km) the seismic structure shows the expected dependence on seafloor age. At greater depths (˜200 km) high-velocity lithosphere is found only beneath the oldest seafloor; velocity variations beneath younger seafloor may result from temperature or compositional variations within the asthenosphere. The age-dependent phase velocities are used to constrain temperature in the mantle and show that, in contrast to previous results for

  7. Shear Velocity Structure of the Mount St. Helens Region from the iMUSH array

    NASA Astrophysics Data System (ADS)

    Crosbie, K.; Abers, G. A.; Creager, K. C.; Denlinger, R. P.; Moran, S. C.; Foster, A. E.; Ulberg, C. W.; Kiser, E.

    2016-12-01

    The imaging Magma Under Mount St. Helens (iMUSH) experiment was designed to illuminate the deep magmatic plumbing system of this arc volcano. The 70-element iMUSH broadband array was deployed for 2 years with 10 km station spacing and a 100 km aperture. We image shear velocity structure using ambient noise tomography (ANT). Rayleigh wave phase velocities at 0.05 to 0.18 Hz are calculated from cross correlations of ambient noise on vertical channels for seismic station pairs. The minimum resolvable wavelength ranges from 33 km at 0.18 Hz to 60 km at 0.05 Hz, with sensitivity throughout the crust and uppermost mantle. Phase velocity maps show a high velocity zone beneath and west of Mount St Helens (MSH) and a low velocity zone beneath Mount Adams, 50 km east, at all frequencies. Beamforming of background noise in subarrays confirms the absolute phase velocities determined by ANT and overall E-W trends, within 0.15 km/s. The ANT phase velocity maps are inverted for shear velocities (Vs) at each 0.1 by 0.1 degree map pixel. At 0-5 km depth a low velocity feature is imaged several tens of km NW of MSH. It lies adjacent to the northwestern portion of the St. Helens seismic zone, and to sediments just west of the ancestral Cascades. Crust at 10-30 km depth has high Vs (> 3.8 km/s) west of MSH and lower Vs (< 3.5 km/s) to the east with the boundary directly beneath MSH and the lowest Vs beneath Mount Adams. At mantle depths this pattern reverses, and Vs is around 4.2 km/s beneath and west of MSH compared to >4.6 km/s to the east. The crustal velocity pattern resembles that expected of crustal temperature variations between the cold forearc and hot volcanic crust. Furthermore, the faster velocities west of MSH may delineate the mafic Siletzia terrane, whose eastern extent is unclear. Lower velocities NE of MSH correlate with the southern Washington Cascades electromagnetic conductor, suggesting a common origin. In the upper mantle, lower velocities west of MSH are

  8. Phase velocities and attentuations of shear, Lamb, and Rayleigh waves in plate-like tissues submerged in a fluid (L)

    PubMed Central

    Nenadic, Ivan Z.; Urban, Matthew W.; Bernal, Miguel; Greenleaf, James F.

    2011-01-01

    In the past several decades, the fields of ultrasound and magnetic resonance elastography have shown promising results in noninvasive estimates of mechanical properties of soft tissues. These techniques often rely on measuring shear wave velocity due to an external or internal source of force and relating the velocity to viscoelasticity of the tissue. The mathematical relationship between the measured velocity and material properties of the myocardial wall, arteries, and other organs with non-negligible boundary conditions is often complicated and computationally expensive. A simple relationship between the Lamb–Rayleigh dispersion and the shear wave dispersion is derived for both the velocity and attenuation. The relationship shows that the shear wave velocity is around 20% higher than the Lamb–Rayleigh velocity and that the shear wave attenuation is about 20% lower than the Lamb–Rayleigh attenuation. Results of numerical simulations in the frequency range 0–500 Hz are presented. PMID:22225009

  9. Phase velocities and attenuations of shear, Lamb, and Rayleigh waves in plate-like tissues submerged in a fluid (L).

    PubMed

    Nenadic, Ivan Z; Urban, Matthew W; Bernal, Miguel; Greenleaf, James F

    2011-12-01

    In the past several decades, the fields of ultrasound and magnetic resonance elastography have shown promising results in noninvasive estimates of mechanical properties of soft tissues. These techniques often rely on measuring shear wave velocity due to an external or internal source of force and relating the velocity to viscoelasticity of the tissue. The mathematical relationship between the measured velocity and material properties of the myocardial wall, arteries, and other organs with non-negligible boundary conditions is often complicated and computationally expensive. A simple relationship between the Lamb-Rayleigh dispersion and the shear wave dispersion is derived for both the velocity and attenuation. The relationship shows that the shear wave velocity is around 20% higher than the Lamb-Rayleigh velocity and that the shear wave attenuation is about 20% lower than the Lamb-Rayleigh attenuation. Results of numerical simulations in the frequency range 0-500 Hz are presented.

  10. Shear wave velocity structure of the Anatolian Plate: anomalously slow crust in southwestern Turkey

    NASA Astrophysics Data System (ADS)

    Delph, Jonathan R.; Biryol, C. Berk; Beck, Susan L.; Zandt, George; Ward, Kevin M.

    2015-07-01

    The Anatolian Plate is composed of different lithospheric blocks and ribbon continents amalgamated during the closure of the Paleotethys Ocean and Neotethys Ocean along a subduction margin. Using ambient noise tomography, we investigate the crustal and uppermost mantle shear wave velocity structure of the Anatolian Plate. A total of 215 broad-band seismic stations were used spanning 7 yr of recording to compute 13 778 cross-correlations and obtain Rayleigh wave dispersion measurements for periods between 8 and 40 s. We then perform a shear wave inversion to calculate the seismic velocity structure of the crust and uppermost mantle. Our results show that the overall crustal shear wave velocities of the Anatolian crust are low (˜3.4 km s-1), indicative of a felsic overall composition. We find that prominent lateral seismic velocity gradients correlate with Tethyan suture zones, supporting the idea that the neotectonic structures of Turkey are exploiting the lithospheric weaknesses associated with the amalgamation of Anatolia. Anomalously slow shear wave velocities (˜3.15 km s-1 at 25 km) are located in the western limb of the Isparta Angle in southwestern Turkey. In the upper crust, we find that these low shear wave velocities correlate well with the projected location of a carbonate platform unit (Bey Dağlari) beneath the Lycian Nappe complex. In the lower crust and upper mantle of this region, we propose that the anomalously slow velocities are due to the introduction of aqueous fluids related to the underplating of accretionary material from the underthrusting of a buoyant, attenuated continental fragment similar to the Eratosthenes seamount. We suggest that this fragment controlled the location of the formation of the Subduction-Transform Edge Propagator fault in the eastern Aegean Sea during rapid slab rollback of the Aegean Arc in early Miocene times. Lastly, we observe that the uppermost mantle beneath continental Anatolia is generally slow (˜4.2 km s-1

  11. Interchange and Flow Velocity Shear Instabilities in the Presence of Finite Larmor Radius Effects

    NASA Astrophysics Data System (ADS)

    Sotnikov, V.; Kim, T.; Mishin, E.; Genoni, T.; Rose, D.; Mehlhorn, T.

    2014-09-01

    Ionospheric irregularities cause scintillations of electromagnetic signals that can severely affect navigation and transionospheric communication, in particular during Equatorial Plasma Bubbles (EPBs) events. However, the existing ionospheric models do not describe density irregularities with typical scales of several ion Larmor radii that affect UHF and L bands. These irregularities can be produced in the process of nonlinear evolution of interchange or flow velocity shear instabilities. The model of nonlinear development of these instabilities based on two-fluid hydrodynamic description with inclusion of finite Larmor radius effects will be presented. The derived nonlinear equations will be numerically solved by using the code Flute, which was originally developed for High Energy Density applications and modified to describe interchange and flow velocity shear instabilities in the ionosphere. The high-resolution simulations will be driven by the ambient conditions corresponding to the AFRL C/NOFS satellite low-resolution data during EPBs.

  12. Correlation Analysis between Spin, Velocity Shear, and Vorticity of Baryonic and Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Liu, L. L.

    2016-05-01

    Using cosmological hydrodynamic simulations, we investigate the alignments between velocity shear, vorticity, and the spin of dark matter halos, and study the correlation between baryonic and dark matter. We find that (1) mis-alignment between vorticity of baryonic and dark matter would develop on scales < 0.2h-1 Mpc; (2) the vorticity of baryonic matter exhibits stronger alignment/anti-alignment with the eigenvectors of velocity shear than that of dark matter; (3) small/massive halos spinning parallel/perpendicular to the host filaments are sensitive to the identification of cosmic web, simulation box size, and resolution. These factors might complicate the connection between the spins of dark matter halos and galaxies, and affect the correlation signal of the alignments of galaxy spin with nearby large-scale structures.

  13. Near-surface characterization of a geotechnical site in north-east Missouri using shear-wave velocity measurements

    USGS Publications Warehouse

    Ismail, A.; Anderson, N.

    2007-01-01

    Shear-wave velocity (Vs) as a function of soil stiffness is an essential parameter in geotechnical characterization of the subsurface. In this study, multichannel analysis of surface wave (MASW) and downhole methods were used to map the shear-wave velocity-structure and depth to the bed-rock surface at a 125m ?? 125m geotechnical site in Missouri. The main objective was to assess the suitability of the site for constructing a large, heavy building. The acquired multichannel surface wave data were inverted to provide 1D shear-wave velocity profile corresponding to each shot gather. These 1D velocity profiles were interpolated and contoured to generate a suite of 2D shear-wave velocity sections. Integrating the shear-wave velocity data from the MASW method with the downhole velocity data and the available borehole lithologic information enabled us to map shear-wave velocity-structure to a depth on the order of 20m. The bedrock surface, which is dissected by a significant cut-and-fill valley, was imaged. The results suggest that the study site will require special consideration prior to construction. The results also demonstrate the successful use of MASW methods, when integrated with downhole velocity measurements and borehole lithologic information, in the characterization of the near surface at the geotechnical sites. ?? 2007 European Association of Geoscientists & Engineers.

  14. Combined Resistivity and Shear Wave Velocity Soil-type Estimation Beneath a Coastal Protection Levee.

    NASA Astrophysics Data System (ADS)

    Lorenzo, J. M.; Goff, D.; Hayashi, K.

    2015-12-01

    Unconsolidated Holocene deltaic sediments comprise levee foundation soils in New Orleans, USA. Whereas geotechnical tests at point locations are indispensable for evaluating soil stability, the highly variable sedimentary facies of the Mississippi delta create difficulties to predict soil conditions between test locations. Combined electrical resistivity and seismic shear wave studies, calibrated to geotechnical data, may provide an efficient methodology to predict soil types between geotechnical sites at shallow depths (0- 10 m). The London Avenue Canal levee flank of New Orleans, which failed in the aftermath of Hurricane Katrina, 2005, presents a suitable site in which to pioneer these geophysical relationships. Preliminary cross-plots show electrically resistive, high-shear-wave velocity areas interpreted as low-permeability, resistive silt. In brackish coastal environments, low-resistivity and low-shear-wave-velocity areas may indicate both saturated, unconsolidated sands and low-rigidity clays. Via a polynomial approximation, soil sub-types of sand, silt and clay can be estimated by a cross-plot of S-wave velocity and resistivity. We confirm that existent boring log data fit reasonably well with the polynomial approximation where 2/3 of soil samples fall within their respective bounds—this approach represents a new classification system that could be used for other mid-latitude, fine-grained deltas.

  15. Windblown sand saltation: A statistical approach to fluid threshold shear velocity

    NASA Astrophysics Data System (ADS)

    Raffaele, Lorenzo; Bruno, Luca; Pellerey, Franco; Preziosi, Luigi

    2016-12-01

    The reliable prediction in probabilistic terms of the consequences of aeolian events related to sand transport phenomena is a key element for human activities in arid regions. Threshold shear velocity generating sand lifting is a key component of such a prediction. It suffers from the effect of uncertainties of different origin, such as those related to the physical phenomena, measurement procedures, and modelling. Semi empirical models are often fitted to a small amount of data, while recent probabilistic models needs the probability distribution of several random variables. Triggered by this motivation, this paper proposes a purely statistical approach to fluid threshold shear velocity for sand saltation, treated as a single comprehensive random variable. A data set is derived from previously published studies. Estimates of conditional probability distributions of threshold shear velocity for given grain diameters are given. The obtained statistical moments are critically compared to some deterministic semi empirical models refitted to the same collected data. The proposed statistical approach allows to obtain high order statistics useful for practical purposes.

  16. Shear-velocity structure, radial anisotropy and dynamics of the Tibetan crust

    NASA Astrophysics Data System (ADS)

    Agius, Matthew R.; Lebedev, Sergei

    2014-12-01

    Geophysical and geological data suggest that Tibetan middle crust is a partially molten, mechanically weak layer, but it is debated whether this low-viscosity layer is present beneath the entire plateau, what its properties are, how it deforms, and what role it has played in the plateau's evolution. Broad-band seismic surface waves yield resolution in the entire depth range of the Tibetan crust and can be used to constrain its shear-wave velocity structure (indicative of crustal composition, temperature and partial melting) and radial anisotropy (indicative of the patterns of deformation). We measured Love- and Rayleigh-wave phase-velocity curves in broad period ranges (up to 7-200 s) for a few tens of pairs and groups of stations across Tibet, combining, in each case, hundreds of interstation measurements, made with cross-correlation and waveform-inversion methods. Shear-velocity profiles were then determined by extensive series of non-linear inversions of the data, designed to constrain the depth-dependent ranges of isotropic-average shear speeds and radial anisotropy. Shear wave speeds within the Tibetan middle crust are anomalously low and, also, show strong lateral variations across the plateau. The lowest mid-crustal shear speeds are found in the north and west of the plateau (˜3.1-3.2 km s-1), within a pronounced low-velocity zone. In southeastern Tibet, crustal shear wave speeds increase gradually towards southeast, whereas in the north, the change across the Kunlun Fault is relatively sharp. The lateral variations of shear speeds within the crust are indicative of those in temperature. A mid-crustal temperature of 800 °C, reported previously, can account for the low shear velocities across Lhasa. In the north, the temperature is higher and exceeds the solidus, resulting in partial melting that we estimate at 3-6 per cent. Strong radial anisotropy is required by the data in western-central Tibet (>5 per cent) but not in northeastern Tibet. The amplitude

  17. Modeling Compressional and Shear Wave Velocities of Unconsolidated Sediments in the Vadose Zone

    NASA Astrophysics Data System (ADS)

    Berge, P. A.

    2001-12-01

    Recent advances in seismic surveys have provided ways to image shallow structure in highly attenuating soils and near-surface rock. Applications include using surface wave methods to find tunnels; mapping landfills with seismic refraction methods; finding faults, the water table, or other strong heterogeneities using seismic reflection surveys. Recent improvements in laboratory ultrasonic measurement techniques have provided reliable data on compressional and shear wave velocities in soils at low pressures analogous to the top few meters to tens of meters of the subsurface. The availability of these data points the way for development of interpretation methods that may allow seismologists to obtain more information from their data in the future. For environmental applications, improvements to interpretation methods could lead to reliable detection of second-order features such as changes in soil saturation, presence of dense non-aqueous phase liquids, or changes in clay content. Traditional modeling techniques developed in the oil industry are optimized for consolidated materials at pressures and depths greater than those typical for environmental applications. The shallow subsurface velocities are highly nonlinear and the soils are highly attenuating, and these characteristics must be considered when modeling velocities (and also when processing seismic data). Various factors, including grain contact roughness, location of clay with respect to sand grains, location of fluid in the partially-saturated case, loose vs. dense packing, all affect the compressional and shear wave velocities and attenuation and their pressure (depth) dependence. Care must be taken when applying effective medium theories or grain-contact theories to model shallow soil velocity behavior. Unconsolidated materials at low pressures show much greater variation in compressional vs. shear wave properties than consolidated materials and high-pressure applications would show. Despite the modeling

  18. The frictional strength of talc gouge in high-velocity shear experiments

    NASA Astrophysics Data System (ADS)

    Chen, Xiaofeng; Elwood Madden, Andrew S.; Reches, Ze'ev

    2017-05-01

    Talc is present in several large-scale fault zones worldwide and is mineralogically stable at temperature of the upper crust. It is therefore necessary to gain a better understanding of the frictional behavior of talc under a wide range of slip velocity conditions occurring during the seismic cycle. We analyzed the frictional and structural characteristics of room-dry and water-saturated talc gouge by shear experiments on a confined gouge layer at slip velocity range of 0.002-0.66 m/s and normal stress up to 4.1 MPa. Room-dry talc showed a distinct slip-strengthening with the initial friction coefficient of μ 0.4 increased systematically to μ 1 at slip distance D > 1 m. Room-dry talc also displayed velocity-strengthening at slip distances shorter than 1 m. The water-saturated talc gouge displayed systematic low frictional strength of μ = 0.1-0.3 for the entire experimental range, with clear velocity-strengthening behavior with positive (a-b) values (rate dependence parameter of rate and state friction) of 0.01-0.04. The microstructural analyses revealed distributed shear and systematic dilation (up to 50%) for the room-dry talc, in contrast to the extreme slip localization and strong shear compaction for water-saturated talc. We propose that talc frictional strength is controlled by lubrication along cleavage surfaces that is facilitated by adsorbed water (room-dry) and surplus water (water-saturated). This mechanism can explain our experimental observations of slip-strengthening and velocity-strengthening for both types of talc gouge, as well as other clay minerals. It is thus expected that talc presence in fault zones would enhance creep and inhibit unstable slip.

  19. Anisotropic Shear-wave Velocity Structure of East Asian Upper Mantle from Waveform Tomography

    NASA Astrophysics Data System (ADS)

    Chong, J.; Yuan, H.; French, S. W.; Romanowicz, B. A.; Ni, S.

    2012-12-01

    East Asia is a seismically active region featuring active tectonic belts, such as the Himalaya collision zone, western Pacific subduction zones and the Tianshan- Baikal tectonic belt. In this study, we applied full waveform time domain tomography to image 3D isotropic, radially and azimuthally anisotropic upper mantle shear velocity structure of East Asia. High quality teleseismic waveforms were collected for both permanent and temporary stations in the target and its adjacent regions, providing good ray path coverage of the study region. Fundamental and overtone wave packets, filtered down to 60 sec, were inverted for isotropic and radially anisotropic shear wave structure using normal mode asymptotic coupling theory (NACT: Li and Romanowicz, 1995). Joint inversion of SKS measurements and seismic waveforms was then carried out following the methodology described in (Marone and Romanowicz, 2007). The 3D velocity model shows strong lateral heterogeneities in the target region, which correlate well with the surface geology in East Asia. Our model shows that Indian lithosphere has subducted beneath Tibet with a different northern reach from western to eastern Tibet,. We also find variations of the slab geometry in Western Pacific subduction zones. Old and stable regions, such as, Indian shield, Siberia platform, Tarim and Yangtze blocks are found to have higher shear wave velocity in the upper mantle. Lower velocity anomalies are found in regions like Baikal rift, Tienshan, Indochina block, and the regions along Japan island-Ryukyu Trench and Izu-bonin Trench. The dominant fast and slow velocity boundaries in the study region are well correlated with tectonic belts, such as the central Asian orogenic belt and Alty/Qilian-Qinling/Dabie orogenic belt. Our radially anisotropic model shows Vsh> Vsv in oceanic regions and at larger depths(>300km), and Vsv > Vsh in some orogenic zones.. We'll show preliminary results of azimuthally anisotropic joint inversion of SKS

  20. Shallow Shear Velocity and Seismic Microzonation of the Las Vegas Urban Basin

    NASA Astrophysics Data System (ADS)

    Rasmussen, T.; Smith, S. B.; Clark, M.; Lopez, C.; Loughner, C.; Park, H.; Scott, J. B.; Thelen, W.; Greschke, B.; Louie, J. N.

    2003-12-01

    In July 2003 we performed a seismic microzonation study of the Las Vegas basin along a 15 kilometer transect. Using 120 Reftek RT-125 "Texans" on loan from PASSCAL, we completed this transect in two days. 4.5-Hz geophones collected Rayleigh-wave data for dispersion analysis and velocity-profile modeling. Only passive urban seismic noise sources are needed for this refraction microtremor analysis; freeway and commuter traffic are used in this case. Using a geophone spacing of 20 meters, fifty 260-m array sections were analyzed to create a transect of 30-m shear velocity measurements 15 km long. The transect runs approximately parallel to Interstate 15 from Cheyenne Avenue at the north to Tropicana Avenue at the south, passing most of The Strip and downtown Las Vegas. We added a few refraction lines, with a sledgehammer source, to augment the microtremor dispersion data with P velocities. The lowest shear velocities observed in Las Vegas are in the NEHRP class D range, at 230 m/s, well above the NEHRP class E range. These lower velocities are found near Interstate 15 and Lake Mead Blvd. Velocities then rise smoothly southward to the middle of the NEHRP-C range (450-600 m/s) near Sahara Blvd. to the south. There appears to be a slight decline further south to Tropicana Blvd. Our results from only 3 km out of the 15-km-long transect have velocities near or below the NEHRP-C/D boundary at 350 m/s. This survey suggests a medium-scale study with a limited budget can be completed in a short time. The study is a crucial new step in the characterization of the effects of ground shaking due to a seismic source in the surrounding region. Similar studies have been completed in the Reno area basin and in the Los Angeles Basin. All of these studies suggest that shallow shear velocity does not correlate well with geologic map units. The range of velocities within one map unit is greater than the average difference between units.

  1. Mixing layer and coherent structures in compound channel flows: Effects of transverse flow, velocity ratio, and vertical confinement

    NASA Astrophysics Data System (ADS)

    Proust, S.; Fernandes, J. N.; Leal, J. B.; Rivière, N.; Peltier, Y.

    2017-04-01

    Turbulent mixing layers associated with streamwise uniform and nonuniform flows in compound channels (main channel with adjacent floodplains) are experimentally investigated. The experiments start with uniform flow conditions. The streamwise nonuniformity is then generated by imposing an imbalance in the upstream discharge distribution between main channel (MC) and floodplains (FPs), keeping the total discharge constant, which results in a transverse depth-averaged mean flow. This study first aims at assessing the effect of a transverse flow on the mixing layer and coherent structures that form at the MC/FP interfaces. A wide range of initial velocity ratio or dimensionless shear between MC and FP is tested. The study second aims at assessing the effect of this velocity ratio on the mixing layer, for a fixed vertical confinement of flow. The total discharge was then varied to quantify the confinement effect. The results show that, far from the inlet section, Reynolds-stresses increase with local velocity ratio for a fixed confinement and decrease with confinement for a fixed velocity ratio. It is also shown that, irrespective of confinement, the existence of quasi-two-dimensional coherent structures is driven by velocity ratio and the direction and magnitude of transverse flow. These structures cannot develop if velocity ratio is lower than 0.3 and if a strong transverse flow toward the MC occurs. In the latter case, the transverse flow is the predominant contribution to momentum exchange (compared with turbulent mixing and secondary currents), convex mean velocity profiles are observed, preventing the formation of quasi-two-dimensional structures.

  2. Group velocity dispersion characteristics and one-dimensional regional shear velocity structure of the eastern Indian craton

    NASA Astrophysics Data System (ADS)

    Mandal, Prantik

    2017-02-01

    In the past three years, a semi-permanent network of fifteen 3-component broadband seismographs has become operational in the eastern Indian shield region occupying the Archean (∼2.5-3.6 Ga) Singhbhum-Odisha craton (SOC) and the Proterozoic (∼1.0-2.5 Ga) Chotanagpur Granitic Gneissic terrane (CGGT). The reliable and accurate broadband data for the recent 2015 Nepal earthquake sequence from 10 broadband stations of this network enabled us to estimate the group velocity dispersion characteristics and one-dimensional regional shear velocity structure of the region. First, we measure fundamental mode Rayleigh- and Love-wave group velocity dispersion curves in the period range of 7-70 s and then invert these curves to estimate the crustal and upper mantle structure below the eastern Indian craton (EIC). We observe that group velocities of Rayleigh and Love waves in SOC are relatively high in comparison to those of CGGT. This could be attributed to a relatively mafic-rich crust-mantle structure in SOC resulting from two episodes of magmatism associated with the 1.6 Ga Dalma and ∼117 Ma Rajmahal volcanisms. The best model for the EIC from the present study is found to be a two-layered crust, with a 14-km thick upper-crust (UC) of average shear velocity (Vs) of 3.0 km/s and a 26-km thick lower-crust (LC) of average Vs of 3.6 km/s. The present study detects a sharp drop in Vs (∼-2 to 3%) at 120-260 km depths, underlying the EIC, representing the probable seismic lithosphere-asthenosphere boundary (LAB) at 120 km depth. Such sharp fall in Vs below the LAB indicates a partially molten layer. Further, a geothermal gradient extrapolated from the surface heat flow shows that such a gradient would intercept the wet basalt solidus at 88-103 km depths, suggesting a 88-103 km thick thermal lithosphere below the EIC. This could also signal the presence of small amounts of partial melts. Thus, this 2-3% drop in Vs could be attributed to the presence of partial melts in the

  3. Ultra Low Velocity Zone existence in the high shear velocity region beneath Cocos Plate, Central America, and the Caribbean

    NASA Astrophysics Data System (ADS)

    Yu, S.; Garnero, E.; Shim, S. H. D.; Zhao, C.

    2014-12-01

    The lowermost mantle beneath subduction is typically characterized by higher than average shear wave speeds, often with the presence of one or more D" discontinuities. These regions are considered the cooler parts of the convective cycle, in contrast to warmer zones of convective return flow, namely, the vicinity of large low shear velocity provinces (LLSVPs). Ultra-low velocity zones (ULVZs) have been long characterized as related to elevated temperature (and/or chemistry) of LLSVP regions. However, some past work has suggested evidence for ULVZ in the presumed cooler regions. In this study we investigate the region beneath the Cocos Plate, Central America, and the Carribbean for ULVZ using high quality broadband Transportable Array data from EarthScope's USArray for the presence of ULVZs. We utilize an ScS-stripping technique that combines a precursor and postcursor to ScS that arise from ULVZ structure, if present. The precursor is a reflection off the top of the ULVZ, while the postcursor is a core-reflection with an added reverberation between the ULVZ top and the core-mantle boundary (CMB). We collected data from deep South American earthquakes recorded in North America and stack data in geographic bins. We find clear evidence for a ULVZ beneath the Gulf of Mexico, but the rest of the study area appears to lack any significant structure. The structure we find is of the order of 100 km wide. The ULVZ properties will be constrained by comparison to predictions from synthetic seismograms. We explore hypotheses for the origin of a ULVZ in a high shear velocity region. These include mineralogical heterogeneities that convective currents have collected; notable possibilities are accumulated melts from subducted materials, such as ocean crust basalts and banded-iron formation. If water can be transported by subducted slabs to the deep mantle, it can significantly decrease the melting temperature of mantle materials and cause such anomalies. A ULVZ a relatively cold

  4. Evidence for a change in the global shear velocity pattern ˜ 1,000 km depth

    NASA Astrophysics Data System (ADS)

    Durand, Stephanie; Debayle, Eric; Ricard, Yanick; Zaroli, Christophe; Lambotte, Sophie

    2017-04-01

    In this study, we show evidence for a change in the shear velocity spectrum around 1,000 km depth based on a new shear velocity tomographic model of the Earth's mantle, SEISGLOB2. SEISGLOB2 is based on Rayleigh surface wave phase velocities, self- and cross-coupling structure coefficients of spheroidal normal modes and body wave travel times which are, for the first time, combined in a tomographic inversion. SEISGLOB2 is developed up to spherical harmonic degree 40 and in 21 spline functions. The spectrum of SEISGLOB2 shows it is the flattest around 1,000 km depth and this flattening occurs between 800 and 1,500 km depth. The presence of such a transition in the spectrum suggests an accumulation of shorter scale heterogeneities at around 1,000 km depth. This change in the spectrum is also observed when looking at the model, where some behaviour changes of slabs, hotspots and LLSVPs occur around 1,000 km depth. The existence of such a velocity change in the mid-mantle can have great impacts on our understanding of the mantle dynamics and should thus be taken into account in future modeling.

  5. Simultaneous inversion for mantle shear velocity and the topography of transition zone discontinuities

    NASA Astrophysics Data System (ADS)

    Gu, Y. J.; Dziewonski, A. M.

    2001-05-01

    A method is presented for the simultaneous inversions of shear velocity in the mantle and the topography of transition zone discontinuities. Each travel time residual, corrected for crust and free surface topography, is modeled as resulting from contributions from three-dimensional shear velocity perturbations to a spherical Earth model and boundary undulations to the 410 and 660 km discontinuities. This approach minimizes tradeoffs between velocity and topography. We expand the lateral variations in velocity and the topography of each discontinuity using 362 spherical B-splines; we expand the radial variations using 14 cubic B-splines. To increase the reliability of the measurements, particularly in the undersampled southern hemisphere, we re-examine the topography of the 410- and 660 km discontinuities from more than 21,000 SH-component records. This new data set is significantly larger than those used earlier studies of SS precursors. The long-wavelength features of our new topography maps of the 410- and 660-km discontinuities are compatible with results of earlier studies: the large-scale patterns are dominated by low degree spherical harmonics, particularly at degrees 1 and 2. We also include an independent measurement of the global transition zone thickness for additional constraints on the structure in the transition zone. The best-fit model from the joint inversion reduces the variance of the absolute and differential travel times of S, SS and ScS by 40 to 70 %, and the differential travel times of SS precursors by up to 90%.

  6. Noninvasive measurement of steady and pulsating velocity profiles and shear rates in arteries using echo PIV: in vitro validation studies.

    PubMed

    Kim, Hyoung-Bum; Hertzberg, Jean; Lanning, Craig; Shandas, Robin

    2004-08-01

    Although accurate measurement of velocity profiles, multiple velocity vectors, and shear stress in arteries is important, there is still no easy method to obtain such information in vivo. We report on the utility of combining ultrasound contrast imaging with particle image velocimetry (PIV) for noninvasive measurement of velocity vectors. This method (echo PIV) takes advantage of the strong backscatter characteristics of small gas-filled microbubbles (contrast) seeded into the flow. The method was tested in vitro. The steady flow analytical solution and optical PIV measurements (for pulsatile flow) were used for comparison. When compared to the analytical solution, both echo PIV and optical PIV resolved the steady velocity profile well. Error in shear rate as measured by echo PIV (8%) was comparable to the error of optical PIV (6.5%). In pulsatile flow, echo PIV velocity profiles agreed well with optical PIV profiles. Echo PIV followed the general profile of pulsatile shear stress across the artery but underestimated wall shear at certain time points. However, error in shear from echo PIV was an order of magnitude less than error from current shear measurement methods. These studies indicate that echo PIV is a promising technique for noninvasive measurement of velocity profiles and shear stress.

  7. Continuous monitoring of shear wave velocity at the Montevecchio earthflow (Forlì-Cesena Province, Northern Apennines)

    NASA Astrophysics Data System (ADS)

    Bertello, Lara; Berti, Matteo; Castellaro, Silvia

    2016-04-01

    of June are not significant because the geophones were buried and moved downslope of about 50 meters. On the 1st of June the monitoring system was retrieved e reinstalled in its original position. From the first week of June to the 25th of July, the landslide slowed down and reached a velocity of 1 cm/d and accordingly, the Vs shows an increasing trend, except for the drop on the 22th-23th of June. Observing the video, the landslide did not accelerate; maybe the drop in shear wave velocity is a direct consequence of a rainfall event that occurred on the 22th, but we are still working on this aspect. A preliminary interpretation of the observed relationship between the displacement rate of the landslide and the shear wave velocity of the moving mass relies on the changes in the consistence of the material. During the phase of fast moving, the soil probably increases the void ratio and loses its stiffness, so Vs are low. At the contrary, during the phase of slow moving, the void ratio is relatively low and Vs are higher.

  8. On the role of spectral resolution in velocity shear layer measurements by Doppler reflectometry

    SciTech Connect

    Happel, T.; Blanco, E.; Estrada, T.

    2010-10-15

    The signal quality of a Doppler reflectometer depends strongly on its spectral resolution, which is influenced by the microwave beam properties and the radius of curvature of the cutoff layer in the plasma. If measured close to a strong perpendicular velocity shear layer, the spectrum of the backscattered signal is influenced by different velocities. This can give rise to two Doppler shifted peaks in the spectrum as observed in TJ-II H-mode plasmas. It is shown by two-dimensional full wave simulations that the two peaks are separable provided the spectral resolution of the system is sufficient. However, if the spectral resolution is poor, the two peaks blend into one and yield an intermediate and incorrect velocity.

  9. The surface shape and structure of the high magnetic and velocity shear magnetopause: CLUSTER observations

    NASA Astrophysics Data System (ADS)

    Budnik, E.; Fedorov, A.; Louarn, P.; Reme, H.; Dunlop, M.

    2003-04-01

    In case when 4 Cluster satellites spend relatively long time in the vicinity of the magnetopause, the relative motion of the satellites and the magnetopause current layer allows to reconstruct the shape of the magnetopause surface. The properties of ion distribution and magnetic field across the magnetopause show that high magnetic and velocity shear magnetopause is a wide layer of open field lines dragged tailward with different velocities. Rapidly moving flux tubes pass in the external layer while slowly convecting ones are located deeper in the boundary layer. We show that such a behavior can be explained in terms of spatial distribution of the entered magnetosheath plasma along reconnected field lines and successive bending of magnetospheric parts of reconnected lines. This "distributed line bending" causes the observed distribution of plasma velocity in the BL.

  10. Shear wave velocity variation across the Taupo Volcanic Zone, New Zealand, from receiver function inversion

    USGS Publications Warehouse

    Bannister, S.; Bryan, C.J.; Bibby, H.M.

    2004-01-01

    The Taupo Volcanic Zone (TVZ), New Zealand is a region characterized by very high magma eruption rates and extremely high heat flow, which is manifest in high-temperature geothermal waters. The shear wave velocity structure across the region is inferred using non-linear inversion of receiver functions, which were derived from teleseismic earthquake data. Results from the non-linear inversion, and from forward synthetic modelling, indicate low S velocities at ???6- 16 km depth near the Rotorua and Reporoa calderas. We infer these low-velocity layers to represent the presence of high-level bodies of partial melt associated with the volcanism. Receiver functions at other stations are complicated by reverberations associated with near-surface sedimentary layers. The receiver function data also indicate that the Moho lies between 25 and 30 km, deeper than the 15 ?? 2 km depth previously inferred for the crust-mantle boundary beneath the TVZ. ?? 2004 RAS.

  11. Crustal shear velocity structure in the Southern Lau Basin constrained by seafloor compliance

    NASA Astrophysics Data System (ADS)

    Zha, Yang; Webb, Spahr C.

    2016-05-01

    Seafloor morphology and crustal structure vary significantly in the Lau back-arc basin, which contains regions of island arc formation, rifting, and seafloor spreading. We analyze seafloor compliance: deformation under long period ocean wave forcing, at 30 ocean bottom seismometers to constrain crustal shear wave velocity structure along and across the Eastern Lau Spreading Center (ELSC). Velocity models obtained through Monte Carlo inversion of compliance data show systematic variation of crustal structure in the basin. Sediment thicknesses range from zero thickness at the ridge axis to 1400 m near the volcanic arc. Sediment thickness increases faster to the east than to the west of the ELSC, suggesting a more abundant source of sediment near the active arc volcanoes. Along the ELSC, upper crustal velocities increase from the south to the north where the ridge has migrated farther away from the volcanic arc front. Along the axial ELSC, compliance analysis did not detect a crustal low-velocity body, indicating less melt in the ELSC crustal accretion zone compared to the fast spreading East Pacific Rise. Average upper crust shear velocities for the older ELSC crust produced when the ridge was near the volcanic arc are 0.5-0.8 km/s slower than crust produced at the present-day northern ELSC, consistent with a more porous extrusive layer. Crust in the western Lau Basin, which although thought to have been produced through extension and rifting of old arc crust, is found to have upper crustal velocities similar to older oceanic crust produced at the ELSC.

  12. Lithospheric shear velocity structure of South Island, New Zealand, from amphibious Rayleigh wave tomography

    NASA Astrophysics Data System (ADS)

    Ball, Justin S.; Sheehan, Anne F.; Stachnik, Joshua C.; Lin, Fan-Chi; Yeck, William L.; Collins, John A.

    2016-05-01

    We present a crust and mantle 3-D shear velocity model extending well offshore of New Zealand's South Island, imaging the lithosphere beneath the South Island as well as the Campbell and Challenger Plateaus. Our model is constructed via linearized inversion of both teleseismic (18-70 s period) and ambient noise-based (8-25 s period) Rayleigh wave dispersion measurements. We augment an array of 4 land-based and 29 ocean bottom instruments deployed off the South Island's east and west coasts in 2009-2010 by the Marine Observations of Anisotropy Near Aotearoa experiment with 28 land-based seismometers from New Zealand's permanent GeoNet array. Major features of our shear wave velocity (Vs) model include a low-velocity (Vs < 4.4 km/s) body extending from near surface to greater than 75 km depth beneath the Banks and Otago Peninsulas and high-velocity (Vs~4.7 km/s) mantle anomalies underlying the Southern Alps and off the northwest coast of the South Island. Using the 4.5 km/s contour as a proxy for the lithosphere-asthenosphere boundary, our model suggests that the lithospheric thickness of Challenger Plateau and central South Island is substantially greater than that of the inner Campbell Plateau. The high-velocity anomaly we resolve at subcrustal depths (>50 km) beneath the central South Island exhibits strong spatial correlation with upper mantle earthquake hypocenters beneath the Alpine Fault. The ~400 km long low-velocity zone we image beneath eastern South Island and the inner Bounty Trough underlies Cenozoic volcanics and the locations of mantle-derived helium measurements, consistent with asthenospheric upwelling in the region.

  13. Anisotropic shear-wave velocity structure of the Earth's mantle: A global model

    NASA Astrophysics Data System (ADS)

    Kustowski, B.; EkströM, G.; DziewońSki, A. M.

    2008-06-01

    We combine a new, large data set of surface wave phase anomalies, long-period waveforms, and body wave travel times to construct a three-dimensional model of the anisotropic shear wave velocity in the Earth's mantle. Our modeling approach is improved and more comprehensive compared to our earlier studies and involves the development and implementation of a new spherically symmetric reference model, simultaneous inversion for velocity and anisotropy, as well as discontinuity topographies, and implementation of nonlinear crustal corrections for waveforms. A comparison of our new three-dimensional model, S362ANI, with two other models derived from comparable data sets but using different techniques reveals persistent features: (1) strong, ˜200-km-thick, high-velocity anomalies beneath cratons, likely representing the continental lithosphere, underlain by weaker, fast anomalies extending below 250 km, which may represent continental roots, (2) weak velocity heterogeneity between 250 and 400 km depths, (3) fast anomalies extending horizontally up to 2000-3000 km in the mantle transition zone beneath subduction zones, (4) lack of strong long-wavelength heterogeneity below 650 km suggesting inhibiting character of the upper mantle-lower mantle boundary, and (5) slow-velocity superplumes beneath the Pacific and Africa. The shear wave radial anisotropy is strongest at 120 km depth, in particular beneath the central Pacific. Lateral anisotropic variations appreciably improve the fit to data that are predominantly sensitive to the uppermost and lowermost mantle but not to the waveforms that control the transition zone and midmantle depths. Tradeoffs between lateral variations in velocity and anisotropy are negligible in the uppermost mantle but noticeable at the bottom of the mantle.

  14. Approximation of wave action flux velocity in strongly sheared mean flows

    NASA Astrophysics Data System (ADS)

    Banihashemi, Saeideh; Kirby, James T.; Dong, Zhifei

    2017-08-01

    Spectral wave models based on the wave action equation typically use a theoretical framework based on depth uniform current to account for current effects on waves. In the real world, however, currents often have variations over depth. Several recent studies have made use of a depth-weighted current U˜ due to [Skop, R. A., 1987. Approximate dispersion relation for wave-current interactions. J. Waterway, Port, Coastal, and Ocean Eng. 113, 187-195.] or [Kirby, J. T., Chen, T., 1989. Surface waves on vertically sheared flows: approximate dispersion relations. J. Geophys. Res. 94, 1013-1027.] in order to account for the effect of vertical current shear. Use of the depth-weighted velocity, which is a function of wavenumber (or frequency and direction) has been further simplified in recent applications by only utilizing a weighted current based on the spectral peak wavenumber. These applications do not typically take into account the dependence of U˜ on wave number k, as well as erroneously identifying U˜ as the proper choice for current velocity in the wave action equation. Here, we derive a corrected expression for the current component of the group velocity. We demonstrate its consistency using analytic results for a current with constant vorticity, and numerical results for a measured, strongly-sheared current profile obtained in the Columbia River. The effect of choosing a single value for current velocity based on the peak wave frequency is examined, and we suggest an alternate strategy, involving a Taylor series expansion about the peak frequency, which should significantly extend the range of accuracy of current estimates available to the wave model with minimal additional programming and data transfer.

  15. PICASSO: Shear velocities in the Western Mediterranean from Rayleigh Wave tomography

    NASA Astrophysics Data System (ADS)

    Palomeras, I.; Thurner, S.; Levander, A.

    2012-12-01

    The Western Mediterranean has been affected by complex subduction and slab rollback, simultaneously with compression due to African-European convergence. The deformed region occupies a wide area from the intra-continental Atlas mountain belt in Morocco to the southern Iberian Massif in Spain. Evolutionary models of the Western Mediterranean invoke extensive slab rollback and compression in the Cenozoic, as well as likely upper mantle delamination scenarios during formation of the Alboran domain, the Betics, Rif, and Atlas Mountains. PICASSO (Program to Investigate Convective Alboran Sea System Overturn) is a multidisciplinary, international investigation of the Alboran System and surrounding areas. In this study we have analyzed data from the 95 PICASSO broadband stations with data from the Spanish IberArray and Siberia Array in Spain and Morocco, the University of Muenster array in the Atlas Mountains and the permanent Spanish and Portuguese networks. We present Rayleigh wave tomography results made from 168 teleseimic events recorded by 237 stations from April 2009 to April 2011. We measured Rayleigh phase velocities using the two-plane-wave method to remove complications due to multi-pathing, and finite-frequency kernels to improve lateral resolution. Phase velocities were then inverted for shear velocity structure on a grid of 0.5 by 0.5 degree to form a well-resolved 3D shear velocity model to 230 km depth. Our results show low S-velocities (2.9 km/s) in the crust beneath the Gibraltar Strait. Low upper mantle S-velocities are mapped beneath the Middle and High Atlas at ~60 km depth suggesting an elevated asthenosphere beneath these young mountain belts, in agreement with receiver functions analysis (Thurner et al, this session). Beneath the Western Alboran Sea, upper-mantle velocities change laterally from high velocities (>4.5 km/s) in the east to lower velocities to the west (~4.3 km/s). The Rayleigh wave tomography is consistent with P-tomography that

  16. Site response, shallow shear-wave velocity, and damage in Los Gatos, California, from the 1989 Loma Prieta earthquake

    USGS Publications Warehouse

    Hartzell, S.; Carver, D.; Williams, R.A.

    2001-01-01

    Aftershock records of the 1989 Loma Prieta earthquake are used to calculate site response in the frequency band of 0.5-10 Hz at 24 locations in Los Gatos, California, on the edge of the Santa Clara Valley. Two different methods are used: spectral ratios relative to a reference site on rock and a source/site spectral inversion method. These two methods complement each other and give consistent results. Site amplification factors are compared with surficial geology, thickness of alluvium, shallow shear-wave velocity measurements, and ground deformation and structural damage resulting from the Loma Prieta earthquake. Higher values of site amplification are seen on Quaternary alluvium compared with older Miocene and Cretaceous units of Monterey and Franciscan Formation. However, other more detailed correlations with surficial geology are not evident. A complex pattern of alluvial sediment thickness, caused by crosscutting thrust faults, is interpreted as contributing to the variability in site response and the presence of spectral resonance peaks between 2 and 7 Hz at some sites. Within the range of our field measurements, there is a correlation between lower average shear-wave velocity of the top 30 m and 50% higher values of site amplification. An area of residential homes thrown from their foundations correlates with high site response. This damage may also have been aggravated by local ground deformation. Severe damage to commercial buildings in the business district, however, is attributed to poor masonry construction.

  17. Comparing shear-wave velocity profiles inverted from multichannel surface wave with borehole measurements

    USGS Publications Warehouse

    Xia, J.; Miller, R.D.; Park, C.B.; Hunter, J.A.; Harris, J.B.; Ivanov, J.

    2002-01-01

    Recent field tests illustrate the accuracy and consistency of calculating near-surface shear (S)-wave velocities using multichannel analysis of surface waves (MASW). S-wave velocity profiles (S-wave velocity vs. depth) derived from MASW compared favorably to direct borehole measurements at sites in Kansas, British Columbia, and Wyoming. Effects of changing the total number of recording channels, sampling interval, source offset, and receiver spacing on the inverted S-wave velocity were studied at a test site in Lawrence, Kansas. On the average, the difference between MASW calculated Vs and borehole measured Vs in eight wells along the Fraser River in Vancouver, Canada was less than 15%. One of the eight wells was a blind test well with the calculated overall difference between MASW and borehole measurements less than 9%. No systematic differences were observed in derived Vs values from any of the eight test sites. Surface wave analysis performed on surface data from Wyoming provided S-wave velocities in near-surface materials. Velocity profiles from MASW were confirmed by measurements based on suspension log analysis. ?? 2002 Elsevier Science Ltd. All rights reserved.

  18. Shear wave velocity versus quality factor: results from seismic noise recordings

    NASA Astrophysics Data System (ADS)

    Boxberger, Tobias; Pilz, Marco; Parolai, Stefano

    2017-08-01

    The assessment of the shear wave velocity (vs) and shear wave quality factor (Qs) for the shallow structure below a site is necessary to characterize its site response. In the past, methods based on the analysis of seismic noise have been shown to be very efficient for providing a sufficiently accurate estimation of the vs versus depth at reasonable costs for engineering seismology purposes. In addition, a slight modification of the same method has proved to be able to provide realistic Qs versus depth estimates. In this study, data sets of seismic noise recorded by microarrays of seismic stations in different geological environments of Europe and Central Asia are used to calculate both vs and Qs versus depth profiles. Analogous to the generally adopted approach in seismic hazard assessment for mapping the average shear wave velocity in the uppermost 30 m (vs30) as a proxy of the site response, this approach was also applied to the quality factor within the uppermost 30 m (Qs30). A slightly inverse correlation between both parameters is found based on a methodological consistent determination for different sites. Consequently, a combined assessment of vs and Qs by seismic noise analysis has the potential to provide a more comprehensive description of the geological structure below a site.

  19. Direct ambient noise tomography for 3-D near surface shear velocity structure: methodology and applications

    NASA Astrophysics Data System (ADS)

    Yao, H.; Fang, H.; Li, C.; Liu, Y.; Zhang, H.; van der Hilst, R. D.; Huang, Y. C.

    2014-12-01

    Ambient noise tomography has provided essential constraints on crustal and uppermost mantle shear velocity structure in global seismology. Recent studies demonstrate that high frequency (e.g., ~ 1 Hz) surface waves between receivers at short distances can be successfully retrieved from ambient noise cross-correlation and then be used for imaging near surface or shallow crustal shear velocity structures. This approach provides important information for strong ground motion prediction in seismically active area and overburden structure characterization in oil and gas fields. Here we propose a new tomographic method to invert all surface wave dispersion data for 3-D variations of shear wavespeed without the intermediate step of phase or group velocity maps.The method uses frequency-dependent propagation paths and a wavelet-based sparsity-constrained tomographic inversion. A fast marching method is used to compute, at each period, surface wave traveltimes and ray paths between sources and receivers. This avoids the assumption of great-circle propagation that is used in most surface wave tomographic studies, but which is not appropriate in complex media. The wavelet coefficients of the velocity model are estimated with an iteratively reweighted least squares (IRLS) algorithm, and upon iterations the surface wave ray paths and the data sensitivity matrix are updated from the newly obtained velocity model. We apply this new method to determine the 3-D near surface wavespeed variations in the Taipei basin of Taiwan, Hefei urban area and a shale and gas production field in China using the high-frequency interstation Rayleigh wave dispersion data extracted from ambient noisecross-correlation. The results reveal strong effects of off-great-circle propagation of high-frequency surface waves in these regions with above 30% shear wavespeed variations. The proposed approach is more efficient and robust than the traditional two-step surface wave tomography for imaging complex

  20. A global shear velocity model of the mantle from normal modes and surface waves

    NASA Astrophysics Data System (ADS)

    durand, S.; Debayle, E.; Ricard, Y. R.; Lambotte, S.

    2013-12-01

    We present a new global shear wave velocity model of the mantle based on the inversion of all published normal mode splitting functions and the large surface wave dataset measured by Debayle & Ricard (2012). Normal mode splitting functions and surface wave phase velocity maps are sensitive to lateral heterogeneities of elastic parameters (Vs, Vp, xi, phi, eta) and density. We first only consider spheroidal modes and Rayleigh waves and restrict the inversion to Vs, Vp and the density. Although it is well known that Vs is the best resolved parameter, we also investigate whether our dataset allows to extract additional information on density and/or Vp. We check whether the determination of the shear wave velocity is affected by the a priori choice of the crustal model (CRUST2.0 or 3SMAC) or by neglecting/coupling poorly resolved parameters. We include the major discontinuities, at 400 and 670 km. Vertical smoothing is imposed through an a priori gaussian covariance matrix on the model and we discuss the effect of coupling/decoupling the inverted structure above and below the discontinuities. We finally discuss the large scale structure of our model and its geodynamical implications regarding the amount of mass exchange between the upper and lower mantle.

  1. Studying the instantaneous velocity field in gas-sheared liquid films in a horizontal duct

    NASA Astrophysics Data System (ADS)

    Vasques, Joao; Tokarev, Mikhail; Cherdantsev, Andrey; Hann, David; Hewakandamby, Buddhika; Azzopardi, Barry

    2016-11-01

    In annular flow, the experimental validation of the basic assumptions on the liquid velocity profile is vital for developing theoretical models of the flow. However, the study of local velocity of liquid in gas-sheared films has proven to be a challenging task due to the highly curved and disturbed moving interface of the phases, small scale of the area of interrogation, high velocity gradients and irregular character of the flow. This study reports on different optical configurations and interface-tracking methods employed in a horizontal duct in order to obtain high-resolution particle image velocimetry (PIV) data in such types of complex flows. The experimental envelope includes successful measurements in 2D and 3D waves regimes, up to the disturbance wave regime. Preliminary data show the presence of complex structures in the liquid phase, which includes re-circulation areas below the liquid interface due to the gas-shearing action, together with non-uniform transverse movements of the liquid phase close to the wall due to the presence of 3D waves at the interface. With the aid of the moving interface-tracking, PIV, time-resolved particle-tracking velocimetry and vorticity measurements were performed.

  2. Effect of mean velocity shear on the dissipation rate of turbulent kinetic energy

    NASA Technical Reports Server (NTRS)

    Yoshizawa, Akira; Liou, Meng-Sing

    1992-01-01

    The dissipation rate of turbulent kinetic energy in incompressible turbulence is investigated using a two-scale DIA. The dissipation rate is shown to consist of two parts; one corresponds to the dissipation rate used in the current turbulence models of eddy-viscosity type, and another comes from the viscous effect that is closely connected with mean velocity shear. This result can elucidate the physical meaning of the dissipation rate used in the current turbulence models and explain part of the discrepancy in the near-wall dissipation rates between the current turbulence models and direct numerical simulation of the Navier-Stokes equation.

  3. Effects of a sheared ion velocity on the linear stability of ITG modes

    SciTech Connect

    Lontano, M.; Lazzaro, E.; Varischetti, M. C.

    2006-11-30

    The linear dispersion of the ion temperature gradient (ITG) modes, in the presence of a non uniform background ion velocity U(parallel sign) U(parallel sign)(x) ez, in the direction of the sheared equilibrium magnetic field B0 = B0(x) ez, has been studied in the frame of the two-fluid guiding center approximation, in slab geometry. Generally speaking, the presence of an ion flow destabilizes the oscillations. The role of the excited K-H instability is discussed.

  4. Using pressure and seismological broadband ocean data to model shear wave velocities in the north Atlantic.

    NASA Astrophysics Data System (ADS)

    Rios, Celia; Dahm, Torsten; Jegen, Marion

    2010-05-01

    Seafloor compliance is the transfer function between pressure and vertical displacement at the seafloor Infragravity waves in the oceanic layer have long periods in the range of 30 - 500 s and obey a simple frequency-wavenumber relation. Seafloor compliance from infragravity waves can be analyzed with single station recordings to determinate sub-seafloor shear wave velocities. Previous studies in the Pacific Ocean have demonstrated that reliable near-surface shear wave profiles can be derived from infragravity wave compliance. However, these studies indicate that, beside the water depth the compliance measurements are limited by instrument sensitivity, calibration uncertainties and possibly other effects. In this work seafloor compliance and infragravity waves are observed at two different locations in the Atlantic Ocean: the Logatchev hydrothermal field at the Mid Atlantic Ridge and the Azores (Sao Miguel Island). The data was acquired with the broadband ocean compliance station developed at the University of Hamburg as well as ocean station from the German instrument pool for amphibian seismology (DEPAS) equipped with broadband seismometers and pressure sensors. Vertical velocity and pressure data were used to calculate power spectral densities and normalized compliance along two profiles (one in each location). Power spectral densities show a dominant peak at low frequencies (0.01-0.035Hz) limited by the expected cut-off frequency, which is dependent on the water depth at each station. The peak has been interpreted as a strong infragravity wave with values between 10-14 and 10-11 (m/s2)2/Hz and 104 and 106 (Pa2)2/Hz for acceleration and pressure respectively. The results show compliance values between 10-10 and 10-8 1/Pa and its estimations take into account the coherence between seismic and pressure signals in order to confirm that the seismic signals in the infragravity waves are caused by pressure sources. Shear wave velocity models, with depth resolution

  5. Velocity profile and wall shear stress of saccular aneurysms at the anterior communicating artery.

    PubMed

    Yamaguchi, Ryuhei; Ujiie, Hiroshi; Haida, Sayaka; Nakazawa, Nobuhiko; Hori, Tomokatsu

    2008-01-01

    It has recently been shown that the aspect ratio (dome/neck) of an aneurysm correlates well with intraaneurysmal blood flow. Aneurysms with an aspect ratio larger than 1.6 carry a higher risk of rupture. We examined the effect of aspect ratio (AR) on intra-aneurysmal flow using experimental models. Flow visualization with particle imaging velocimetry and measurement of wall shear stress using laser Doppler anemometry were performed on three different aneurysm models: AR 0.5, 1.0, and 2.0. Intraaneurysmal flow consists of inflow, circulation, and outflow. Rapid inflow impinged on the distal neck creating a stagnant point. Rapid flow and maximum wall shear stress were observed in the vicinity of the stagnant point. By changing the Reynold's number, the stagnant point moved. By increasing the AR of the aneurysm, vortices inside the aneurysm sac closed and very slow flow was observed, resulting in very low shear stress markedly at a Reynold's number of 250, compatible with the diastolic phase. In the aneurysm model AR 2.0, both rapid flow at the neck and vortices inside the aneurysm are sufficient to activate platelets, making a thrombus that may anchor on the dome where very slow flow takes place. Hemodynamics in aneurysms larger than AR 2.0 definitely contribute to thrombus formation.

  6. Stratified shear flow in an inclined duct: near-instantaneous 3D velocity and density measurements

    NASA Astrophysics Data System (ADS)

    Partridge, Jamie; Lefauve, Adrien; Dalziel, Stuart; Linden, Paul

    2016-11-01

    We present results from a new experimental setup to study the exchange flow in an inclined square duct between two reservoirs containing fluids of different densities. This system can exhibit stratified shear wave motions, and has a distinct parameter threshold above which turbulence is triggered and progressively fills a larger fraction of the duct. To probe these intrinsically 3D flows, we introduce a new setup in which a traversing laser sheet allows us to obtain near-instantaneous 3D velocity and density fields. Three components of velocity are measured on successive 2D planes using stereo particle image velocimetry (PIV) with density information obtained simultaneously using laser induced fluorescence (LIF). Supported by EPSRC Programme Grant EP/K034529/1 entitled "Mathematical Underpinnings of Stratified Turbulence".

  7. Earthquake Energy Dissipation in Light of High-Velocity, Slip-Pulse Shear Experiments

    NASA Astrophysics Data System (ADS)

    Reches, Z.; Liao, Z.; Chang, J. C.

    2014-12-01

    We investigated the energy dissipation during earthquakes by analysis of high-velocity shear experiments conducted on room-dry, solid samples of granite, tonalite, and dolomite sheared at slip-velocity of 0.0006-1m/s, and normal stress of 1-11.5MPa. The experimental fault were loaded in one of three modes: (1) Slip-pulse of abrupt, intense acceleration followed by moderate deceleration; (2) Impact by a spinning, heavy flywheel (225 kg); and (3) Constant velocity loading. We refer to energy dissipation in terms of power-density (PD=shear stress*slip-velocity; units of MW/m^2), and Coulomb-energy-density (CED= mechanical energy/normal stress; units of m). We present two aspects: Relative energy dissipation of the above loading modes, and relative energy dissipation between impact experiments and moderate earthquakes. For the first aspect, we used: (i) the lowest friction coefficient of the dynamic weakening; (ii) the work dissipated before reaching the lowest friction; and (iii) the cumulative mechanical work during the complete run. The results show that the slip-pulse/impact modes are energy efficient relatively to the constant-velocity mode as manifested by faster, more intense weakening and 50-90% lower energy dissipation. Thus, for a finite amount of pre-seismic crustal energy, the efficiency of slip-pulse would amplify earthquake instability. For the second aspect, we compare the experimental CED of the impact experiments to the reported breakdown energy (EG) of moderate earthquakes, Mw = 5.6 to 7.2 (Chang et al., 2012). In is commonly assumed that the seismic EG is a small fraction of the total earthquake energy, and as expected in 9 out of 11 examined earthquakes, EG was 0.005 to 0.07 of the experimental CED. We thus speculate that the experimental relation of Coulomb-energy-density to total slip distance, D, CED = 0.605 × D^0.933, is a reasonable estimate of total earthquake energy, a quantity that cannot be determined from seismic data.

  8. Jet length/velocity ratio: a new index for echocardiographic evaluation of chronic aortic regurgitation.

    PubMed

    Güvenç, Tolga Sinan; Karaçimen, Denizhan; Erer, Hatice Betül; İlhan, Erkan; Sayar, Nurten; Karakuş, Gültekin; Çekirdekçi, Elif; Eren, Mehmet

    2015-01-01

    Management of aortic regurgitation depends on the assessment for severity. Echocardiography remains as the most widely available tool for evaluation of aortic regurgitation. In this manuscript, we describe a novel parameter, jet length/velocity ratio, for the diagnosis of severe aortic regurgitation. A total of 30 patients with aortic regurgitation were included to this study. Severity of aortic regurgitation was assessed with an aortic regurgitation index incorporating five echocardiographic parameters. Jet length/velocity ratio is calculated as the ratio of maximum jet penetrance to mean velocity of regurgitant flow. Jet length/velocity ratio was significantly higher in patients with severe aortic regurgitation (2.03 ± 0.53) compared to patients with less than severe aortic regurgitation (1.24 ± 0.32, P < 0.001). Correlation of jet length/velocity ratio with aortic regurgitation index was very good (r(2) = 0.86) and correlation coefficient was higher for jet length/velocity ratio compared to vena contracta, jet width/LVOT ratio and pressure half time. For a cutoff value of 1.61, jet length/velocity ratio had a sensitivity of 92% and specificity of 88%, with an AUC value of 0.955. Jet length/velocity ratio is a novel parameter that can be used to assess severity of chronic aortic regurgitation. Main limitation for usage of this novel parameter is jet impringement to left ventricular wall. © 2014, Wiley Periodicals, Inc.

  9. Three Urban Transects of Shallow Shear-Velocity Using the Refraction Microtremor Method

    NASA Astrophysics Data System (ADS)

    Scott, J. B.; Clark, M.; Lopez, C. T.; Pancha, A.; Rasmussen, T.; Smith, S. B.; Thelen, W. A.; Louie, J. N.

    2004-12-01

    Surveys of shallow shear velocity in the Reno, Los Angeles and Las Vegas urban areas give us information assisting in the mitigation of earthquake hazards, and in response to a damaging earthquake. The three transects (16, 60, and 15 km long respectively) were completed quickly and economically using the refraction microtremor method, providing characterizations of over 300 separate sites. Shear-wave velocity averaged over 30 m depth (Vs30) is unexpectedly smooth along all three transects, exhibiting realistic fractal dimensions of 1.5 to 1.8. For the Reno transect, which follows the Truckee River, most of the urban area shows NEHRP class C velocities. Very little of the profile shows velocities in the NEHRP class D range. Neither geological nor agricultural soil map units can serve to predict NEHRP hazard class or shallow velocities in the Reno area, aside from distinguishing between volcanic rock and sediments. Measured along the San Gabriel River, Vs30 values through Azusa and the Santa Fe Dam area are significantly higher than the NEHRP C/D range (270-555 m/s) expected from existing hazard mapping. Vs30 values in the southern 30 km of the Los Angeles transect were well within the previously expected NEHRP class D range (180-360 m/s). Measurements at Alamitos Bay were slightly above the expected NEHRP D/E range (90-270 m/s). In Las Vegas, the lowest velocities in the transect, at the NEHRP C/D boundary, are near intra-basin faults found near I-15 and Lake Mead Blvd. Velocities then rise smoothly to the middle of the NEHRP-C range near Sahara Blvd. to the south. Caliche cementation of alluvium in parts of Las Vegas elevates Vs30 values to 500-600 m/s. Vs100 values for the three transects, averaging to the 100 m depth to which most of our measurements are valid, show trends mimicking the Vs30 trends. Across all three cities our measurements correlate poorly against available USDA soil maps, geologic mapping, and hazard mapping. Surface maps do not predict the

  10. SIP Shear Walls: Cyclic Performance of High-Aspect-Ratio Segments and Perforated Walls

    Treesearch

    Vladimir Kochkin; Douglas R. Rammer; Kevin Kauffman; Thomas Wiliamson; Robert J. Ross

    2015-01-01

    Increasing stringency of energy codes and the growing market demand for more energy efficient buildings gives structural insulated panel (SIP) construction an opportunity to increase its use in commercial and residential buildings. However, shear wall aspect ratio limitations and lack of knowledge on how to design SIPs with window and door openings are barriers to the...

  11. Spatial-temporal spectra of velocity fluctuations in turbulent shear flows

    NASA Astrophysics Data System (ADS)

    He, Guowei; Wu, Ting; Zhao, Xin

    2015-11-01

    Space-time correlation or its Fourier form, spatial-temporal spectrum, is a minimal quantity to statistically characterize the temporal evolutions of spatial structures in turbulent flows. The Kraichnan-Tennekes random-sweeping model is well-known for spatial-temporal spectra in isotropic and homogeneous turbulence. Recently, Wilczek, Stevens and Meneveau (J. Fluid Mech. 2015 vol. 769, R1) have developed a simple model for spatial-temporal spectra in the Logarithmic layer of wall turbulence. In this study, we propose a model equation for turbulent shear flows. This model equation includes both sweeping and stretching effects and its solution gives an analytical expression for spatial-temporal spectra of stream-wise velocities. The results obtained are compared with the data from direct numerical simulation (DNS) of turbulent channel flows. It is found that this model is reasonably consistent with the DNS results for either small or large shear rates. This model is also discussed in comparison with the EA (elliptic approximation) model for space-time correlations in turbulent shear flows (Phys. Rev. E 79 046316 2009).

  12. Shear-wave velocity structure beneath the Ngauruhoe Volcano, New Zealand using receiver function inversion with the genetic algorithm

    NASA Astrophysics Data System (ADS)

    Park, I.; Kim, K. Y.; Jolly, A. D.

    2014-12-01

    The Ngauruhoe Volcano is an andesitic volcano of 2,291 m height in the North Island, New Zealand. One-dimensional shear-wave velocity (Vs) structure beneath the OTVZ seismic station near the volcano was inferred by the genetic algorithm (GA) inversion of radial receiver functions (RFs). Radial RFs were derived from 337 teleseismic events (Mw ≥ 5.5 and epicentral distances between 30° and 90°) recorded by a broad-band seismometer at the seismic station during the period from November 11, 2011 to September 11, 2013. Among the derived RFs, only 87 RFs with higher signal to noise ratios were used for the GA inversion method. Three hundred velocity models for 100 generations were derived using velocity models comprising 32 layers with a maximum depth of 60 km. The inverted models were averaged to obtain the final Vs model, which indicates a clear discontinuity at a depth of 18±1 km where Vs abruptly increases from 3.1 to 4.0 km/s. Above the sharp Vs discontinuity indicating the Moho, an average Vs is 2.8 km/s. Low-velocity layers (LVLs) are identified at depths of 10-16 km in the lower crust (Vs < 3.0 km/s) and 28-40 km in the upper mantle (Vs < 4.4 km/s). Corresponding average Vs are 2.8 and 4.2 km/s, respectively. The thin crust with relatively low velocities and existence of LVLs in the lower crust and upper mantle allude to the presence of magma associated with the subducting Pacific Plate. The limited number of teleseismic events recorded at the OTVZ station prevents from further investigation into the effect of RFs of dipping boundaries and anisotropy.

  13. Three-dimensional Shear Wave Velocity Structure of The Upper Mantle Below Antarctica

    NASA Astrophysics Data System (ADS)

    Danesi, S.; Morelli, A.

    We measure fundamental-mode Rayleigh and Love surface wave group dispersion curves from seismograms recorded by stations in the Antarctic continent and neigh- boring lands at latitude below -30. Our growing regional dataset is merged with the global dataset of phase velocity measurements by Ekström et al. (1997, JGR 102, 8137-8157). Our inversion procedure is divided in two steps. The first is a linear to- mographic inversion of the dispersion measurements to model laterally heterogeneous group velocity at different periods. Wave slowness is parameterized by spline interpo- lation on a geographical grid, with knots equally spaced by 250 km in an orthographic projection. For each point in these maps we then compute the vertical profile of shear wave velocity vs. depth by iterative nonlinear inversion. Crustal properties are as- sumed to be known and follow the CRUST2.0 model (Bassin et al., 2000, EOS Trans AGU, 81 F897). The resulting vS model shows intense negative anomalies under oceanic ridges, at least down to 150 km. The strongest values are related to young oceanic crust near rapidly opening ridges. Shallow low velocity anomalies characterize volcanic provinces and hot-spots in Marie Byrd Land, Ross Sea, Kerguelen, Balleny and South Sandwich archipelagoes. Only few slow anomalies reach depths below 150km (West Antarctica, Ross Sea and the triple junction among Southeast Pacific-South Pacific- Indian Ridges). The East Antarctica archean craton has deep, fast (cold) continental roots reaching at least 200km in depth.

  14. One-dimensional seismic response of two-layer soil deposits with shear wave velocity inversion

    SciTech Connect

    Ding Yuqin; Pagliaroli, Alessandro; Lanzo, Giuseppe

    2008-07-08

    The paper presents the results of a parametric study with the purpose of investigating the 1D linear and equivalent linear seismic response of a 30 meters two-layer soil deposits characterized by a stiff layer overlying a soft layer. The thickness of the soft layer was assumed equal to 0.25, 0.5 and 0.75 H, being H the total thickness of the deposit. The shear wave velocity of the soft layer was assumed equal to V{sub s} = 90 and 180 m/s while for the stiff layer V{sub s} = 360, 500 and 700 m/s were considered. Six accelerograms extracted by an Italian database characterized by different predominant periods ranging from 0.1 to 0.7 s were used as input outcropping motion. For the equivalent liner analyses, the accelerograms were scaled at three different values of peak ground acceleration (PGA), namely 0.1, 0.3 and 0.5 g. The numerical results show that the two-layer ground motion is generally deamplified in terms of PGA with respect to the outcrop PGA. This reduction is mainly controlled by the shear wave velocity of the soft layer, being larger for lower V{sub s} values, by the amount of nonlinearity experienced by the soft soil during the seismic shaking and, to a minor extent, by the thickness of the soft soil layer.

  15. Microstreaming velocity field and shear stress created by an oscillating encapsulated microbubble near a cell membrane

    NASA Astrophysics Data System (ADS)

    Wang, Li; Tu, Juan; Guo, Xia-Sheng; Xu, Di; Zhang, Dong

    2014-12-01

    Sonoporation mediated by microbubbles is being extensively studied as a promising technology to facilitate gene/drug delivery to cells. However, the theoretical study regarding the mechanisms involved in sonoporation is still in its infancy. Microstreaming generated by pulsating microbubble near the cell membrane is regarded as one of the most important mechanisms in the sonoporation process. Here, based on an encapsulated microbubble dynamic model with considering nonlinear rheological effects of both shell elasticity and viscosity, the microstreaming velocity field and shear stress generated by an oscillating microbubble near the cell membrane are theoretically simulated. Some factors that might affect the behaviors of microstreaming are thoroughly investigated, including the distance between the bubble center and cell membrane (d), shell elasticity (χ), and shell viscosity (κ). The results show that (i) the presence of cell membrane can result in asymmetric microstreaming velocity field, while the constrained effect of the membrane wall decays with increasing the bubble-cell distance; (ii) the bubble resonance frequency increases with the increase in d and χ, and the decrease in κ, although it is more dominated by the variation of shell elasticity; and (iii) the maximal microstreaming shear stress on the cell membrane increases rapidly with reducing the d, χ, and κ. The results suggest that microbubbles with softer and less viscous shell materials might be preferred to achieve more efficient sonoporation outcomes, and it is better to have bubbles located in the immediate vicinity of the cell membrane.

  16. Shear-wave velocity-based probabilistic and deterministic assessment of seismic soil liquefaction potential

    USGS Publications Warehouse

    Kayen, R.; Moss, R.E.S.; Thompson, E.M.; Seed, R.B.; Cetin, K.O.; Der Kiureghian, A.; Tanaka, Y.; Tokimatsu, K.

    2013-01-01

    Shear-wave velocity (Vs) offers a means to determine the seismic resistance of soil to liquefaction by a fundamental soil property. This paper presents the results of an 11-year international project to gather new Vs site data and develop probabilistic correlations for seismic soil liquefaction occurrence. Toward that objective, shear-wave velocity test sites were identified, and measurements made for 301 new liquefaction field case histories in China, Japan, Taiwan, Greece, and the United States over a decade. The majority of these new case histories reoccupy those previously investigated by penetration testing. These new data are combined with previously published case histories to build a global catalog of 422 case histories of Vs liquefaction performance. Bayesian regression and structural reliability methods facilitate a probabilistic treatment of the Vs catalog for performance-based engineering applications. Where possible, uncertainties of the variables comprising both the seismic demand and the soil capacity were estimated and included in the analysis, resulting in greatly reduced overall model uncertainty relative to previous studies. The presented data set and probabilistic analysis also help resolve the ancillary issues of adjustment for soil fines content and magnitude scaling factors.

  17. Correlation Analysis between Spin, Velocity Shear, and Vorticity of Baryonic and Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Li-li, Liu

    2017-04-01

    Based on the cosmological hydrodynamic simulations, we investigate the correlations between the spin, velocity shear and vorticity in dark matter halos, as well as the relationship between the baryonic matter and the dark matter. We find that (1) the difference between the vorticity of baryonic matter and that of dark matter is evident on the scales of < 0.2 h-1 Mpc; (2) the vorticity of baryonic matter exhibits a stronger correlation with the tensor of velocity shear than the vorticity of dark matter does; and (3) the spinning direction of small-mass dark matter halos tends to be parallel to the direction of their host filaments, while the spinning direction of massive dark matter halos tends to be perpendicular to the direction of their host filaments, and the intensity of this kind correlation depends on the size of simulation box, and the simulation accuracy. These factors may cause the relationship between the the spins of dark matter halos and those of galaxies to be complicated, and affect the correlation between the galaxy spins and the nearby large-scale structures.

  18. Shear velocity estimates on the inner shelf off Grays Harbor, Washington, USA

    USGS Publications Warehouse

    Sherwood, C.R.; Lacy, J.R.; Voulgaris, G.

    2006-01-01

    Shear velocity was estimated from current measurements near the bottom off Grays Harbor, Washington between May 4 and June 6, 2001 under mostly wave-dominated conditions. A downward-looking pulse-coherent acoustic Doppler profiler (PCADP) and two acoustic-Doppler velocimeters (field version; ADVFs) were deployed on a tripod at 9-m water depth. Measurements from these instruments were used to estimate shear velocity with (1) a modified eddy-correlation (EC) technique, (2) the log-profile (LP) method, and (3) a dissipation-rate method. Although values produced by the three methods agreed reasonably well (within their broad ranges of uncertainty), there were important systematic differences. Estimates from the EC method were generally lowest, followed by those from the inertial-dissipation method. The LP method produced the highest values and the greatest scatter. We show that these results are consistent with boundary-layer theory when sediment-induced stratification is present. The EC method provides the most fundamental estimate of kinematic stress near the bottom, and stratification causes the LP method to overestimate bottom stress. These results remind us that the methods are not equivalent and that comparison among sites and with models should be made carefully. ?? 2006 Elsevier Ltd. All rights reserved.

  19. Effects of neutral interactions on velocity-shear-driven plasma waves

    SciTech Connect

    Enloe, C. L.; Tejero, E. M.; Amatucci, W. E.; Crabtree, C.; Ganguli, G.; Sotnikov, V.

    2014-06-15

    In a laboratory experiment, we demonstrate the substantial effects that collisions between charged and neutral particles have on low-frequency (Ω{sub i} ≪ ω ≪ Ω{sub e}) shear-driven electrostatic lower hybrid waves in a plasma. We establish a strong (up to 2.5 kV/m) highly localized electric field with a length scale shorter than the ion gyroradius, so that the ions in the plasma, unlike the electrons, do not develop the full E × B drift velocity. The resulting shear in the particle velocities initiates the electron-ion hybrid (EIH) instability, and we observe the formation of strong waves in the vicinity of the shear with variations in plasma densities of 10% or greater. Our experimental configuration allows us to vary the neutral background density by more than a factor of two while holding the charged particle density effectively constant. Not surprisingly, increasing the neutral density decreases the growth rate/saturation amplitude of the waves and increases the threshold electric field necessary for wave formation, but the presence of neutrals affects the dominant wave frequency as well. We show that a 50% increase in the neutral density decreases the wave frequency by 20% while also suppressing the electric field dependence of the frequency that is observed when fewer neutrals are present. The majority of these effects, as well as the values of the frequencies we observe, closely match the predictions of previously developed linear EIH instability theory, for which we present the results of a numerical solution.

  20. Shear wave velocity of the healthy thyroid gland in children with acoustic radiation force impulse elastography.

    PubMed

    Ceyhan Bilgici, Meltem; Sağlam, Dilek; Delibalta, Semra; Yücel, Serap; Tomak, Leman; Elmalı, Muzaffer

    2017-04-19

    Acoustic radiation force impulse imaging is a kind of shear wave elastography that can be used in children for differentiating thyroid pathologies. Possible changes in the healthy thyroid gland in children may create difficulties in the use of shear wave velocities (SWV) in thyroid pathologies. The aim of this study was to define the normal values of SWV for the healthy thyroid gland in children, elucidate the correlation of the SWV values with potential influencing factors, and evaluate intra-operator reproducibility of the SWV. Between January 2015 and December 2015, a total of 145 healthy children (81 girls, 64 boys; mean age, 10.5 ± 3.14 years; range 6-17 years) were enrolled in the study. The SWV and volume of the thyroid gland were determined. The mean shear wave velocity of the thyroid gland was 1.22 ± 0.20 m/s. There was no correlation between age and the mean SWV of the thyroid gland (Spearman Rho = 0.049, p = 0.556). There was also no correlation between the thyroid gland volume or BSA and the mean SWV. The only correlation detected was between BSA and total thyroid gland volume (p < 0.001). In the present study, the SWV of the healthy thyroid gland in children was determined. There was no correlation between the SWV of the thyroid gland and age, BSA, or thyroid gland volume.

  1. High-flow-velocity and shear-rate imaging by use of color Doppler optical coherence tomography.

    PubMed

    van Leeuwen, T G; Kulkarni, M D; Yazdanfar, S; Rollins, A M; Izatt, J A

    1999-11-15

    Color Doppler optical coherence tomography (CDOCT) is capable of precise velocity mapping in turbid media. Previous CDOCT systems based on the short-time Fourier transform have been limited to maximum flow velocities of the order of tens of millimeters per second. We describe a technique, based on interference signal demodulation at multiple frequencies, to extend the physiological relevance of CDOCT by increasing the dynamic range of measurable velocities to hundreds of millimeters per second. The physiologically important parameter of shear rate is also derived from CDOCT measurements. The measured flow-velocity profiles and shear-rate distributions correlate very well with theoretical predictions. The multiple demodulation technique, therefore, may be useful to monitor blood flow in vivo and to identify regions with high and low shear rates.

  2. Vector magnetic field evolution, energy storage, and associated photospheric velocity shear within a flare-productive active region

    NASA Technical Reports Server (NTRS)

    Krall, K. R.; Smith, J. B., Jr.; Hagyard, M. J.; West, E. A.; Cummings, N. P.

    1982-01-01

    Sheared photospheric velocity fields inferred from spot motions for April 5-7, 1980, are compared with both transverse magnetic field orientation changes and with the region's flare history. Rapid spot motions and high inferred velocity shear coincide with increased field alignment along the longitudinal neutral line and with increased flare activity, while a later decrease in velocity shear precedes a more relaxed magnetic configuration and decrease in flare activity. It is estimated that magnetic reconfiguration produced by the relative velocities of the spots could cause storage of about 10 to the 32nd erg/day, while flares occurring during this time expended no more than about 10 to the 31st erg/day.

  3. Isotropic and anisotropic shear velocity model of the NA upper mantle using EarthScope data

    NASA Astrophysics Data System (ADS)

    Leiva, J.; Clouzet, P.; French, S. W.; Yuan, H.; Romanowicz, B. A.

    2013-12-01

    The EarthScope TA deployment has provided dense array coverage across the continental US and with it, the opportunity for high resolution 3D seismic velocity imaging of both lithosphere and asthenosphere in the continent. Building upon our previous work, we present a new 3D isotropic, radially and azimuthally anisotropic shear wave model of the North American (NA) lithospheric mantle, using full waveform tomography and shorter-period (40 s) waveform data. Our isotropic velocity model exhibits pronounced spatial correlation between major tectonic localities of the eastern NA continent, as evidenced in the geology, and seismic anomalies, suggesting recurring episodes of tectonic events not only are well exposed at the surface, but also leave persistent scars in the continental lithosphere mantle, marked by isotropic and radially anisotropic velocity anomalies that reach as deep as 100-150 km. In eastern North America, our Vs images distinguish the fast velocity cratonic NA from the deep rooted large volume high velocity blocks which are east of the continent rift margin and extend 200-300 km offshore into Atlantic. In between is a prominent narrow band of low velocities that roughly follows the south and eastern Laurentia rift margin and extends into New England. The lithosphere associated with this low velocity band is thinned likely due to combined effects of repeated rifting processes along the rift margin and northward extension of the Bermuda low-velocity channel across the New England region. Deep rooted high velocity blocks east of the Laurentia margin are proposed to represent the Proterozoic Gondwanian terranes of pan-African affinity, which were captured during the Rodinia formation but left behind during the opening of the Atlantic Ocean. The anisotropy model takes advantage of the up-to-date SKS compilation in the continent and new splitting results from Greenland. The new joint waveform and SKS splitting data inversion is carried out with a 2

  4. Analysis shear wave velocity structure obtained from surface wave methods in Bornova, Izmir

    SciTech Connect

    Pamuk, Eren Akgün, Mustafa; Özdağ, Özkan Cevdet

    2016-04-18

    Properties of the soil from the bedrock is necessary to describe accurately and reliably for the reduction of earthquake damage. Because seismic waves change their amplitude and frequency content owing to acoustic impedance difference between soil and bedrock. Firstly, shear wave velocity and depth information of layers on bedrock is needed to detect this changing. Shear wave velocity can be obtained using inversion of Rayleigh wave dispersion curves obtained from surface wave methods (MASW- the Multichannel Analysis of Surface Waves, ReMi-Refraction Microtremor, SPAC-Spatial Autocorrelation). While research depth is limeted in active source study, a passive source methods are utilized for deep depth which is not reached using active source methods. ReMi method is used to determine layer thickness and velocity up to 100 m using seismic refraction measurement systems.The research carried out up to desired depth depending on radius using SPAC which is utilized easily in conditions that district using of seismic studies in the city. Vs profiles which are required to calculate deformations in under static and dynamic loads can be obtained with high resolution using combining rayleigh wave dispersion curve obtained from active and passive source methods. In the this study, Surface waves data were collected using the measurements of MASW, ReMi and SPAC at the İzmir Bornova region. Dispersion curves obtained from surface wave methods were combined in wide frequency band and Vs-depth profiles were obtained using inversion. Reliability of the resulting soil profiles were provided by comparison with theoretical transfer function obtained from soil paremeters and observed soil transfer function from Nakamura technique and by examination of fitting between these functions. Vs values are changed between 200-830 m/s and engineering bedrock (Vs>760 m/s) depth is approximately 150 m.

  5. Velocity shear driven instability and its effect on magnetic reconnection: MMS observations compared with PIC simulation results

    NASA Astrophysics Data System (ADS)

    Hwang, K. J.; Choi, E.; Sibeck, D. G.; Giles, B. L.; Goldstein, M.; Pollock, C.; Ergun, R.; Gershman, D. J.; Dorelli, J.; Avanov, L. A.; Paterson, W. R.; Burch, J. L.; Russell, C.; Strangeway, R. J.; Torbert, R. B.

    2016-12-01

    Both observations and simulations indicate the frequent occurrence, often simultaneously, of current-driven magnetic reconnection and velocity shear driven flow vortices on the Earth's dayside magnetopause. MMS spacecraft observations not only enable the quantitative testing of micro and meso-scale reconnection physics but also permit the calculation of flow vorticities. Here we inspect MMS observations including an event on 19 September 2015 to determine how the current-driven and shear-driven instabilities interact to determine microscopic (magnetic topology) to macroscopic (merging rate) aspects of dayside reconnection. In particular, we examine the effects of flow vorticity on dayside dynamics in terms of R, the ratio between the plasma vorticity parallel to the magnetic field and the cyclotron frequency for each relevant species. We consider two cases: (1) the dusk magnetopause where the flow vorticity is parallel to the magnetic field and ions gyrate opposite the vortex and (2) the dawn magnetopause where the flow vorticity is antiparallel to the magnetic field and ions gyrate with the vortex. Our synthesized MMS observations and PIC simulation results show that flow vorticity, a fluid quantity, when it is sufficiently large (i.e., greater than the relevant gyro-frequencies), becomes an important parameter indicating coupling to the kinetic regime.

  6. Measurement of viscosity and shear wave velocity of a liquid or slurry for on-line process control.

    PubMed

    Greenwood, Margaret Stautberg; Bamberger, Judith Ann

    2002-08-01

    An on-line sensor to measure the density of a liquid or slurry, based on longitudinal wave reflection at the solid-fluid interface, has been developed by the staff at Pacific Northwest National Laboratory. The objective of this research is to employ shear wave reflection at the solid-fluid interface to provide an on-line measurement of viscosity as well. Both measurements are of great interest for process control in many industries. Shear wave reflection measurements were conducted for a variety of liquids. By analyzing multiple reflections within the solid (only 0.63 cm thick-similar to pipe wall thickness) we increased the sensitivity of the measurement. At the sixth echo, sensitivity was increased sufficiently and this echo was used for fluid interrogation. Shear wave propagation of ultrasound in liquids is dependent upon the viscosity and the shear modulus. The data are analyzed using the theory for light liquids (such as water and sugar water solutions) and also using the theory for highly viscous liquids (such as silicone oils). The results show that, for light liquids, the shear wave reflection measurements interrogate the viscosity. However, for highly viscous liquids, it is the shear wave modulus that dominates the shear wave reflection. Since the density is known, the shear wave velocity in the liquid can be determined from the shear wave modulus. The results show that shear wave velocities in silicone oils are very small and range from 315 to 2389 cm/s. Shear wave reflection measurements are perhaps the only way that shear wave velocity in liquids can be determined, because the shear waves in liquids are highly attenuated. These results show that, depending on the fluid characteristics, either the viscosity or the shear wave velocity can be used for process control. There are several novel features of this sensor: (1) The sensor can be mounted as part of the wall of a pipeline or tank or submerged in a tank. (2) The sensor is very compact and can be

  7. Focussing effects at the edge of the Large Low Shear Velocity Provinces

    NASA Astrophysics Data System (ADS)

    Rost, S.; Nowacki, A.

    2015-12-01

    Tomographic images of the Earth's lowermost mantle are dominated by two equatorial and nearly antipodal regions of large-scale reductions in seismic S-wave velocities beneath the central Pacific and Africa. These Large Low Shear Velocity Provinces (LLSVPs) are much less constrained in tomographic P-wave models. This discrepancy, together with other geophysical data, led to the interpretation of LLSVPs as thermo-chemical piles, but models of purely thermal LLSVPs might also be able to explain the geophysical data. Data from seismic arrays and high-resolution processing techniques are able to precisely determine the slowness vector of incoming seismic energy and therefore to extract velocity and directivity information from the seismic data directly. Here we use records of P and Pdiff from the medium aperture, short-period, vertical component Yellowknife array (YKA) located in northern Canada and S/Sdiff from stations of the Canadian POLARIS network. Using seismicity from the western Pacific rim allows good sampling of the lowermost mantle in the region of the Pacific LLSVP and the northern Pacific. The slowness information extracted from the array data using the high-resolution F-statistic allows detailed mapping of the LLSVP boundary and indicates a sharp boundary and velocity reductions of several percent. The data also indicate a second region of strongly reduced seismic velocities to the north of the Pacific LLSVP beneath the Sea of Okhotsk that does not seem to be connected to the main LLSVP, and which is not consistently resolved in S-wave tomography models. We observe very strong focussing and defocussing effects along the LLSVP boundary that indicate strong and small-scale heterogeneities in the vicinity of the LLSVP boundary beyond what can be explained by LLSVP material. This detection allows further insight into the structure and dynamics of the LLSVP. Using seismic wave propagation simulations we are aiming to resolve both structure and shape of these

  8. Shear wave velocity structure beneath southern California: Mantle at crustal depths beneath the Borderlands

    NASA Astrophysics Data System (ADS)

    Rau, C. J.; Forsyth, D. W.; Wang, Y.

    2009-12-01

    We use Rayleigh waves to invert for the shear velocity structure beneath the Borderlands of southern California. Fundamental mode Rayleigh waves from 101 teleseismic events at a complete range of azimuths were recorded by a maximum of 102 stations, including stations belonging to the USArray. This ray coverage gives us an unprecedentedly well-resolved view of the lower crust and upper mantle structure beneath the Borderlands. We observe a high velocity anomaly beneath the Gulf of Santa Catalina and the northern end of the San Diego Trough that dips slightly to the west toward the southern portion of the Santa Catalina Basin. This anomaly is on the order of 15-20% faster than typical mid-crustal velocities in the southern California region. The magnitude of this fast anomaly requires that it be derived from a mantle source. Southern California has undergone a complex tectonic history, closely associated with the subduction of the Farallon plate system, the rotation of the Western Transverse Ranges, and the subsequent extension that lead to the formation of the basins of the Borderlands. Taking the magnitude of the velocity anomaly and the tectonic history of the region into account, we interpret this fast anomaly to represent mantle material that has risen to crustal levels associated with the formation of a metamorphic core complex in the Borderlands. Previous studies reference the extension that occurred in response to the rotation of the Western Transverse Ranges and the subsequent emplacement of the Catalina Schist as mechanisms for the formation of a metamorphic core complex in the Borderlands region. However, we see no sign of low velocities in the deeper mantle that characterize other areas in the region that are thought to have experienced upwelling.

  9. Probing Near Surface Shear Velocity Structure from Ambient Noise in Hefei Urban Area

    NASA Astrophysics Data System (ADS)

    Li, C.; Yao, H.; Fang, H.

    2014-12-01

    Ambient noise tomography has widely been used to achieve high resolution 3-D crustal velocity structure. Recently, various studies also indicate that high-frequency surface wave signals can be extracted from cross correlation of ambient noise. So it makes ambient noise tomography capable to investigate near surface velocity structure. This is important for studies related to strong motion estimation due to earthquakes and characterization of structure in oil and gas exploration fields. Here we investigate near surface 3-D velocity structure using high-frequency (0.5 - 2 Hz) ambient noise tomography in the urban area of Hefei city, Anhui province in eastern China. We collected continuous ambient noise data of two weeks from 17 stations in the center of city with a lateral scale about 5 km by 7 km. The S-transform technique is used to stack vertical-component cross-correlation functions from hourly data, which yields much higher SNR of the high frequency surface waves than traditional linear stack. We developed a ray-tracing based iterative surface wave tomography method with spatial smoothing constraints (model regularization) based on ray path density.This method is used to construct frequency-dependent phase velocity maps in the study area, which can account for the effect of ray bending in the tomographic inversion. We also developed a new direct surface wave inversion method to iteratively invert surface wave dispersion data of all paths for 3-D variations of shear wave velocity in the study area without the intermediate step of phase or group velocity maps.The method uses frequency dependent propagation paths and a wavelet-based sparsity-constrained tomography inversion. Hefei city is located in a basin and its southern suburb close to the Chao Lake, the fifth largest lake in China. The inversion results show that the north part has much higher velocity(~2.5 km/s) in the top several hundred meters than the south part(~0.8 km/s), basically consistent with the

  10. Comparison of ultrasound B-mode, strain imaging, acoustic radiation force impulse displacement and shear wave velocity imaging using real time clinical breast images

    NASA Astrophysics Data System (ADS)

    Manickam, Kavitha; Machireddy, Ramasubba Reddy; Raghavan, Bagyam

    2016-04-01

    It has been observed that many pathological process increase the elastic modulus of soft tissue compared to normal. In order to image tissue stiffness using ultrasound, a mechanical compression is applied to tissues of interest and local tissue deformation is measured. Based on the mechanical excitation, ultrasound stiffness imaging methods are classified as compression or strain imaging which is based on external compression and Acoustic Radiation Force Impulse (ARFI) imaging which is based on force generated by focused ultrasound. When ultrasound is focused on tissue, shear wave is generated in lateral direction and shear wave velocity is proportional to stiffness of tissues. The work presented in this paper investigates strain elastography and ARFI imaging in clinical cancer diagnostics using real time patient data. Ultrasound B-mode imaging, strain imaging, ARFI displacement and ARFI shear wave velocity imaging were conducted on 50 patients (31 Benign and 23 malignant categories) using Siemens S2000 machine. True modulus contrast values were calculated from the measured shear wave velocities. For ultrasound B-mode, ARFI displacement imaging and strain imaging, observed image contrast and Contrast to Noise Ratio were calculated for benign and malignant cancers. Observed contrast values were compared based on the true modulus contrast values calculated from shear wave velocity imaging. In addition to that, student unpaired t-test was conducted for all the four techniques and box plots are presented. Results show that, strain imaging is better for malignant cancers whereas ARFI imaging is superior than strain imaging and B-mode for benign lesions representations.

  11. DETECTION OF THE VELOCITY SHEAR EFFECT ON THE SPATIAL DISTRIBUTIONS OF THE GALACTIC SATELLITES IN ISOLATED SYSTEMS

    SciTech Connect

    Lee, Jounghun; Choi, Yun-Young E-mail: yy.choi@khu.ac.kr

    2015-02-01

    We report a detection of the effect of the large-scale velocity shear on the spatial distributions of the galactic satellites around the isolated hosts. Identifying the isolated galactic systems, each of which consists of a single host galaxy and its satellites, from the Seventh Data Release of the Sloan Digital Sky Survey and reconstructing linearly the velocity shear field in the local universe, we measure the alignments between the relative positions of the satellites from their isolated hosts and the principal axes of the local velocity shear tensors projected onto the plane of sky. We find a clear signal that the galactic satellites in isolated systems are located preferentially along the directions of the minor principal axes of the large-scale velocity shear field. Those galactic satellites that are spirals, are brighter, are located at distances larger than the projected virial radii of the hosts, and belong to the spiral hosts yield stronger alignment signals, which implies that the alignment strength depends on the formation and accretion epochs of the galactic satellites. It is also shown that the alignment strength is quite insensitive to the cosmic web environment, as well as the size and luminosity of the isolated hosts. Although this result is consistent with the numerical finding of Libeskind et al. based on an N-body experiment, owing to the very low significance of the observed signals, it remains inconclusive whether or not the velocity shear effect on the satellite distribution is truly universal.

  12. First seismic shear wave velocity profile of the lunar crust as extracted from the Apollo 17 active seismic data by wavefield gradient analysis

    NASA Astrophysics Data System (ADS)

    Sollberger, David; Schmelzbach, Cedric; Robertsson, Johan O. A.; Greenhalgh, Stewart A.; Nakamura, Yosio; Khan, Amir

    2016-04-01

    We present a new seismic velocity model of the shallow lunar crust, including, for the first time, shear wave velocity information. So far, the shear wave velocity structure of the lunar near-surface was effectively unconstrained due to the complexity of lunar seismograms. Intense scattering and low attenuation in the lunar crust lead to characteristic long-duration reverberations on the seismograms. The reverberations obscure later arriving shear waves and mode conversions, rendering them impossible to identify and analyze. Additionally, only vertical component data were recorded during the Apollo active seismic experiments, which further compromises the identification of shear waves. We applied a novel processing and analysis technique to the data of the Apollo 17 lunar seismic profiling experiment (LSPE), which involved recording seismic energy generated by several explosive packages on a small areal array of four vertical component geophones. Our approach is based on the analysis of the spatial gradients of the seismic wavefield and yields key parameters such as apparent phase velocity and rotational ground motion as a function of time (depth), which cannot be obtained through conventional seismic data analysis. These new observables significantly enhance the data for interpretation of the recorded seismic wavefield and allow, for example, for the identification of S wave arrivals based on their lower apparent phase velocities and distinct higher amount of generated rotational motion relative to compressional (P-) waves. Using our methodology, we successfully identified pure-mode and mode-converted refracted shear wave arrivals in the complex LSPE data and derived a P- and S-wave velocity model of the shallow lunar crust at the Apollo 17 landing site. The extracted elastic-parameter model supports the current understanding of the lunar near-surface structure, suggesting a thin layer of low-velocity lunar regolith overlying a heavily fractured crust of basaltic

  13. The African Large Low Shear Velocity Province: Boundary Positions and Anisotropy Measurements

    NASA Astrophysics Data System (ADS)

    Smith, R.; Rost, S.; Nowacki, A.

    2016-12-01

    Tomographic images of Earth's lowermost mantle are dominated by two, large, nearly antipodal regions of reduced seismic velocities. These areas, known as the Large Low Shear Velocity Provinces (LLSVPs), are located beneath Africa and the Pacific. This study is focussed on the African LLSVP and seeks to map its northern & north-western boundaries using P- and S-waves. While the LLSVPs are often picked as a certain percentage velocity drop in the varying tomographical models, no consensus exists how to choose the boundaries. Using detailed information from probes sensitive to the structure across the LLSVP boundary allows us to both define the boundary and to characterise LLSVP structure. Here we present data from large, deep earthquakes in South America, India, Asia and the South Sandwich Islands (magnitude > 5.5 & depth > 100km) recorded at broadband receivers across Africa, Europe, North and South America to provide extensive coverage of the African LLSVP. The data present excellent coverage of the north-western boundary of the African LLSVP with both Pdiff and Sdiff. Using traveltime and anisotropy information we develop a model of the northern and north-western boundaries of the LLSVP. Contrasting the P- and S-waves allows better insight into the origin of the LLSVPs. The dataset also contains several previously undetected smaller scale features. The anisotropy structure indicates weaker anisotropy within the LLSVP in agreement with an absence of post-perovskite in the LLSVP or change in dynamics of the mantle material inside or outside of the LLSVP.

  14. Compressional and shear-wave velocity versus depth relations for common rock types in northern California

    USGS Publications Warehouse

    Brocher, T.M.

    2008-01-01

    This article presents new empirical compressional and shear-wave velocity (Vp and Vs) versus depth relationships for the most common rock types in northern California. Vp versus depth relations were developed from borehole, laboratory, seismic refraction and tomography, and density measurements, and were converted to Vs versus depth relations using new empirical relations between Vp and Vs. The relations proposed here account for increasing overburden pressure but not for variations in other factors that can influence velocity over short distance scales, such as lithology, consolidation, induration, porosity, and stratigraphic age. Standard deviations of the misfits predicted by these relations thus provide a measure of the importance of the variability in Vp and Vs caused by these other factors. Because gabbros, greenstones, basalts, and other mafic rocks have a different Vp and Vs relationship than sedimentary and granitic rocks, the differences in Vs between these rock types at depths below 6 or 7 km are generally small. The new relations were used to derive the 2005 U.S. Geological Survey seismic velocity model for northern California employed in the broadband strong motion simulations of the 1989 Loma Prieta and 1906 San Francisco earthquakes; initial tests of the model indicate that the Vp model generally compares favorably to regional seismic tomography models but that the Vp and Vs values proposed for the Franciscan Complex may be about 5% too high.

  15. Sheared velocity flows as a source of pressure anisotropy in low collisionality plasmas

    NASA Astrophysics Data System (ADS)

    Del Sarto, Daniele; Pegoraro, Francesco; Cerri, Silvio Sergio; Califano, Francesco; Tenerani, Anna

    2015-04-01

    Non-Maxwellian metaequilibrium states may exist in low-collisionality plasmas as evidenced by direct (particle distributions) and indirect (e.g., instabilities driven by pressure anisotropy) satellite and laboratory measurements. These are directly observed in the solar wind (e.g. [1]), in magnetospheric reconnection events [2], in magnetically confined plasmas [3] or in simulations of Vlasov turbulence [4]. By including the full pressure tensor dynamics in a fluid plasma model, we show that a sheared velocity field can provide an effective mechanism that makes an initial isotropic state anisotropic. We discuss how the propagation of "magneto-elastic" waves can affect the pressure tensor anisotropization and the small scale formation that arise from the interplay between the gyrotropic terms due to the magnetic field and flow vorticity, and the non-gyropropic effect of the flow strain tensor. We support this analysis by a numerical integration of the nonlinear equations describing the pressure tensor evolution. This anisotropization mechanism might provide a good candidate for the understanding of the observed correlation between the presence of a sheared velocity flow and the signature of pressure anisotropies which are not yet explained within the standard models based e.g. on the CGL paradigm (see also [5]). Examples of these signatures are provided by the threshold lowering of ion-Weibel instabilities in the geomagnetic tail, observed in concomitance to the presence of a velocity shear in the near-earth plasma profile [6], or by the relatively stronger anisotropization measured for core protons in the fast solar wind [4,7] or in "space simulation" laboratory plasma experiments [3]. 1] E. Marsch et al., Journ. Geophys. Res. 109, A04120 (2004); Yu. V. Khotyainstev at el., Phys. Rev. Lett. 106, 165001 (2011). [2] N. Aunai et al., Ann. Geophys. 29, 1571 (2011); N. Aunai et al., Journ. Geophys. Res. 116, A09232 (2011). [3] E.E. Scime et al., Phys. Plasmas 7, 2157

  16. Sheared velocity flows as a source of pressure anisotropy in low collisionality plasmas

    NASA Astrophysics Data System (ADS)

    Del Sarto, D.; Pegoraro, F.; Califano, F.

    2014-12-01

    Non-Maxwellian metaequilibrium states may exist in low-collisionality plasmas as evidenced by direct (particle distributions) and indirect (e.g., instabilities driven by pressure anisotropy) satellite and laboratory measurements. These are directly observed in the solar wind (e.g. [1]), in magnetospheric reconnection events [2], in magnetically confined plasmas [3] or in simulations of Vlasov turbulence [4]. By including the full pressure tensor dynamics in a fluid plasma model, we show that a sheared velocity field can provide an effective mechanism that makes an initial isotropic state anisotropic. We discuss how the propagation of magneto-elastic waves can affect the pressure tensor anisotropization and the small scale formation that arise from the interplay between the gyrotropic terms due to the magnetic field and the flow vorticity and the non-gyropropic effect of the flow strain tensor. We support this analysis by a numerical integration of the nonlinear equations describing the pressure tensor evolution. This anisotropization mechanism might provide a good candidate for the understanding of the observed correlation between the presence of a sheared velocity flow and the signature of pressure anisotropies which are not yet explained within the standard models based e.g. on the CGL paradigm. Examples of these signatures are provided e.g. by the threshold lowering of ion-Weibel instabilities in the geomagnetic tail, observed in concomitance to the presence of a velocity shear in the near-earth plasma profile [5], or by the relatively stronger anisotropization measured for core protons in the fast solar wind [4,6] or in "space simulation" laboratory plasma experiments [3]. [1] E. Marsch et al., Journ. Geophys. Res. 109, A04120 (2004); Yu. V. Khotyainstev at el., Phys. Rev. Lett. 106, 165001 (2011). [2] N. Aunai et al., Ann. Geophys. 29, 1571 (2011); N. Aunai et al., Journ. Geophys. Res. 116, A09232 (2011). [3] E.E. Scime et al., Phys. Plasmas 7, 2157 (2000). [4

  17. Experimental measurement of settling velocity of spherical particles in unconfined and confined surfactant-based shear thinning viscoelastic fluids.

    PubMed

    Malhotra, Sahil; Sharma, Mukul M

    2014-01-03

    An experimental study is performed to measure the terminal settling velocities of spherical particles in surfactant based shear thinning viscoelastic (VES) fluids. The measurements are made for particles settling in unbounded fluids and fluids between parallel walls. VES fluids over a wide range of rheological properties are prepared and rheologically characterized. The rheological characterization involves steady shear-viscosity and dynamic oscillatory-shear measurements to quantify the viscous and elastic properties respectively. The settling velocities under unbounded conditions are measured in beakers having diameters at least 25x the diameter of particles. For measuring settling velocities between parallel walls, two experimental cells with different wall spacing are constructed. Spherical particles of varying sizes are gently dropped in the fluids and allowed to settle. The process is recorded with a high resolution video camera and the trajectory of the particle is recorded using image analysis software. Terminal settling velocities are calculated from the data. The impact of elasticity on settling velocity in unbounded fluids is quantified by comparing the experimental settling velocity to the settling velocity calculated by the inelastic drag predictions of Renaud et al.(1) Results show that elasticity of fluids can increase or decrease the settling velocity. The magnitude of reduction/increase is a function of the rheological properties of the fluids and properties of particles. Confining walls are observed to cause a retardation effect on settling and the retardation is measured in terms of wall factors.

  18. Experimental Measurement of Settling Velocity of Spherical Particles in Unconfined and Confined Surfactant-based Shear Thinning Viscoelastic Fluids

    PubMed Central

    Malhotra, Sahil; Sharma, Mukul M.

    2014-01-01

    An experimental study is performed to measure the terminal settling velocities of spherical particles in surfactant based shear thinning viscoelastic (VES) fluids. The measurements are made for particles settling in unbounded fluids and fluids between parallel walls. VES fluids over a wide range of rheological properties are prepared and rheologically characterized. The rheological characterization involves steady shear-viscosity and dynamic oscillatory-shear measurements to quantify the viscous and elastic properties respectively. The settling velocities under unbounded conditions are measured in beakers having diameters at least 25x the diameter of particles. For measuring settling velocities between parallel walls, two experimental cells with different wall spacing are constructed. Spherical particles of varying sizes are gently dropped in the fluids and allowed to settle. The process is recorded with a high resolution video camera and the trajectory of the particle is recorded using image analysis software. Terminal settling velocities are calculated from the data. The impact of elasticity on settling velocity in unbounded fluids is quantified by comparing the experimental settling velocity to the settling velocity calculated by the inelastic drag predictions of Renaud et al.1 Results show that elasticity of fluids can increase or decrease the settling velocity. The magnitude of reduction/increase is a function of the rheological properties of the fluids and properties of particles. Confining walls are observed to cause a retardation effect on settling and the retardation is measured in terms of wall factors. PMID:24430257

  19. Large-scale shear velocity structure of the upper mantle beneath Europe and surrounding regions

    NASA Astrophysics Data System (ADS)

    Legendre, C. P.; Meier, T. M.; Lebedev, S.; Friederich, W.

    2009-12-01

    The automated multimode waveform inversion technique developed by Lebedev et al. (2005) was applied to available data of broadband stations in Europe and surrounding regions. It performs a fitting of the complete waveform starting from the S-wave onset to the surface wave. Assuming the location and focal mechanism of a considered earthquake as known, the first basic step is to consider each available seismogram separately and to find the 1D-model that can explain the filtered seismogram best. In a second step, each 1D-model serves as a linear constraint in an inversion for a 3D S-wave velocity model of the upper mantle. We collected data for the years from 1990 to 2006 from all permanent stations for which data were available via the data centers of ORFEUS, GEOFON amd IRIS, and from others that build the Virtual European Seismological Network (VEBSN). In addition, we incorporated data from temporary experiments like SVEKALAPKO, TOR and the Eifel plume project as well as permanent stations in France. Just recently we were also able to add the data recorded by the temporary broadband EGELADOS network in the southern Aegean. In this way, a huge data set of about 500000 seismograms came about from which about 60000 1D-models could be constructed. The resulting models exhibit an overwhelming structural detail in relation to the size of the region considered in the inversion. They are to our knowledge the most detailed models of shear wave velocity currently available for the European upper mantle and surroundings. Most prominent features are an extremely sharp demarcation of the East European platform from Western Europe. Narrow high velocity regions follow the Hellenic arc and the Ionian trench toward the north. Whereas high velocities are found beneath the western Alps between about 100 km to 200 km depth, the eastern Alps show a low velocity anomaly at these depths. Low velocity zones are found at depths around 150 km in the Pannonian basin, the back-arc of the

  20. Wingtip Vortices and Free Shear Layer Interaction in the Vicinity of Maximum Lift to Drag Ratio Lift Condition

    NASA Astrophysics Data System (ADS)

    Memon, Muhammad Omar

    between the lift induced drag (wingtip vortices) and parasite drag (free shear layer) can have a significant impact. Particle Image Velocimetry (PIV) experiments were performed at a) a water tunnel at ILR Aachen, Germany, and b) at the University of Dayton Low Speed Wind Tunnel in the near wake of an AR 6 wing with a Clark-Y airfoil to investigate the characteristics of the wingtip vortex and free shear layer at angles of attack in the vicinity of maximum aerodynamic efficiency for the wing. The data was taken 1.5 and 3 chord lengths downstream of the wing at varying free-stream velocities. A unique exergy-based technique was introduced to quantify distinct changes in the wingtip vortex axial core flow. The existence of wingtip vortex axial core flow transformation from wake-like (velocity less-than the freestream) to jet-like (velocity greater-than the freestream) behavior in the vicinity of the maximum (L/D) angles was observed. The exergy-based technique was able to identify the change in the out of plane profile and corresponding changes in the L/D performance. The resulting velocity components in and around the free shear layer in the wing wake showed counter flow in the cross-flow plane presumably corresponding to behavior associated with the flow over the upper and lower surfaces of the wing. Even though the velocity magnitudes in the free shear layer in cross-flow plane are a small fraction of the freestream velocity ( 10%), significant directional flow was observed. An indication of the possibility of the transfer of momentum (from inboard to outboard of the wing) was identified through spanwise flow corresponding to the upper and lower surfaces through the free shear layer in the wake. A transition from minimal cross flow in the free shear layer to a well-established shear flow in the spanwise direction occurs in the vicinity of maximum lift-to-drag ratio (max L/D) angle of attack. A distinctive balance between the lift induced drag and parasite drag was

  1. Integration of SH seismic reflection and Love-wave dispersion data for shear wave velocity determination over quick clays

    NASA Astrophysics Data System (ADS)

    Comina, Cesare; Krawczyk, Charlotte M.; Polom, Ulrich; Socco, Laura Valentina

    2017-09-01

    Quick clay is a water-saturated formation originally formed through flocculation and deposition in a marine to brackish environment. It is subsequently leached to low salinity by freshwater flow. If its strength decreases, then the flocculated structure collapses leading to landslides of varying destructiveness. Leaching can result in a reduction of the undisturbed shear strength of these clays and suggestions exist that a reduction in shear wave velocities is also possible. Integration of SH seismic reflection and Love-wave dispersion data was undertaken, in an area near the Göta River in southwest Sweden, to evaluate the potential of shear wave velocity imaging for detecting quick clays. Seismic reflection processing evidenced several geologically interesting interfaces related to the probable presence of quick clays (locally confirmed by boreholes) and sand-gravelly layers strongly contributing to water circulation within them. Dispersion data were extracted with a Gaussian windowing approach and inverted with a laterally constrained inversion using a priori information from the seismic reflection imaging. The inversion of dispersion curves has evidenced the presence of a low velocity layer (lvl, with a velocity reduction of ca. 30 per cent) probably associable to quick clays. This velocity reduction is enough to produce detectable phase-velocity differences in the field data and to achieve a better velocity resolution if compared to reflection seismic velocity analyses. The proposed approach has the potential of a comprehensive determination of the shear wave velocity distribution in the shallow subsurface. A sensitivity analysis of Love-wave dispersion data is also presented underlining that, despite limited dispersion of the data set and the velocity-reducing effect of quick-clay leaching, the proposed interpretation procedure arises as a valuable approach in quick clay and other lvl identification.

  2. Record of massive upwellings from the Pacific large low shear velocity province

    NASA Astrophysics Data System (ADS)

    Madrigal, Pilar; Gazel, Esteban; Flores, Kennet E.; Bizimis, Michael; Jicha, Brian

    2016-11-01

    Large igneous provinces, as the surface expression of deep mantle processes, play a key role in the evolution of the planet. Here we analyse the geochemical record and timing of the Pacific Ocean Large Igneous Provinces and preserved accreted terranes to reconstruct the history of pulses of mantle plume upwellings and their relation with a deep-rooted source like the Pacific large low-shear velocity Province during the Mid-Jurassic to Upper Cretaceous. Petrological modelling and geochemical data suggest the need of interaction between these deep-rooted upwellings and mid-ocean ridges in pulses separated by ~10-20 Ma, to generate the massive volumes of melt preserved today as oceanic plateaus. These pulses impacted the marine biota resulting in episodes of anoxia and mass extinctions shortly after their eruption.

  3. Record of massive upwellings from the Pacific large low shear velocity province.

    PubMed

    Madrigal, Pilar; Gazel, Esteban; Flores, Kennet E; Bizimis, Michael; Jicha, Brian

    2016-11-08

    Large igneous provinces, as the surface expression of deep mantle processes, play a key role in the evolution of the planet. Here we analyse the geochemical record and timing of the Pacific Ocean Large Igneous Provinces and preserved accreted terranes to reconstruct the history of pulses of mantle plume upwellings and their relation with a deep-rooted source like the Pacific large low-shear velocity Province during the Mid-Jurassic to Upper Cretaceous. Petrological modelling and geochemical data suggest the need of interaction between these deep-rooted upwellings and mid-ocean ridges in pulses separated by ∼10-20 Ma, to generate the massive volumes of melt preserved today as oceanic plateaus. These pulses impacted the marine biota resulting in episodes of anoxia and mass extinctions shortly after their eruption.

  4. Record of massive upwellings from the Pacific large low shear velocity province

    PubMed Central

    Madrigal, Pilar; Gazel, Esteban; Flores, Kennet E.; Bizimis, Michael; Jicha, Brian

    2016-01-01

    Large igneous provinces, as the surface expression of deep mantle processes, play a key role in the evolution of the planet. Here we analyse the geochemical record and timing of the Pacific Ocean Large Igneous Provinces and preserved accreted terranes to reconstruct the history of pulses of mantle plume upwellings and their relation with a deep-rooted source like the Pacific large low-shear velocity Province during the Mid-Jurassic to Upper Cretaceous. Petrological modelling and geochemical data suggest the need of interaction between these deep-rooted upwellings and mid-ocean ridges in pulses separated by ∼10–20 Ma, to generate the massive volumes of melt preserved today as oceanic plateaus. These pulses impacted the marine biota resulting in episodes of anoxia and mass extinctions shortly after their eruption. PMID:27824054

  5. A global shear velocity model of the mantle from normal modes, surface waves and body waves

    NASA Astrophysics Data System (ADS)

    Durand, S.; Debayle, E.; Ricard, Y. R.; Lambotte, S.; Zaroli, C.

    2014-12-01

    We present SEISGLOB2, a new global shear-wave velocity model of the mantle. SEISGLOB 2 results from the inversion of all published spheroidal mode splitting and coupling coefficients, completed with new measurements made in Strasbourg, of a large Rayleigh wave dataset measured by Debayle & Ricard (2012) and extended to long periods by Durand et al. (2014), and of a global dataset of S, SS and ScS travel times measured at ≈30 s period by Zaroli et al. (2010). These seismic data are sensitive to 3D heterogeneities of elastic parameters (Vs, Vp, ζ, φ, η in a transversly isotropic medium) and density. We discuss the depth and lateral resolution of our model and compare our results with other global tomographies. Although it is well known that Vs is the best resolved parameter, we also investigate whether our dataset allows to extract additional information on density and/or Vp.

  6. Development of a Flow Velocity Shear Instability in the Presence of Finite Larmor Radius Effects

    NASA Astrophysics Data System (ADS)

    Sotnikov, V. I.; Kim, T. C.; Mishin, E. V.; Genoni, T. C.; Rose, D. V.; Paraschiv, I.

    2014-12-01

    Ionospheric irregularities cause scintillations of electromagnetic signals that can severely affect navigation and transionospheric communication, in particular during Equatorial Plasma Bubbles (EPBs) events. However, the existing ionospheric models do not describe density irregularities with typical scales of several ion Larmor radii that affect UHF and L bands. These irregularities can be produced in the process of nonlinear evolution of interchange or flow velocity shear instabilities. We present the results of numerical simulations of excitation and nonlinear saturation of Kelvin-Helmholtz instability by means of two-fluid hydrodynamic model which includes finite Larmor radius effects. The high-resolution simulations are driven by the ambient conditions corresponding to the AFRL C/NOFS satellite low-resolution data during EPBs.

  7. Shear-wave velocity of marine sediments offshore Taiwan using ambient seismic noise

    NASA Astrophysics Data System (ADS)

    Lin, Yu-Tse; Lin, Jing-Yi; Kuo-Chen, Hao; Yeh, Yi-Chin; Cheng, Win-Bin

    2017-04-01

    Seismic ambient noise technology has many advantages over the traditional two-station method. The most important one is that noise is happening all the time and it can be widely and evenly distributed. Thus, the Green's Function of any station pair can be obtained through the data cross-correlation process. Many related studies have been performed to estimate the velocity structures based on the inland area. Only a few studies were reported for the marine area due to the relatively shorter recording time of ocean bottom seismometers (OBS) deployment and the high cost of the marine experiment. However, the understanding about the shear-wave velocity (Vs) of the marine sediments is very crucial for the hazard assessment related to submarine landslides, particularly with the growing of submarine resources exploration. In this study, we applied the ambient noise technique to four OBS seismic networks located offshore Taiwan in the aim of getting more information about the noise sources and having the preliminary estimation for the Vs of the marine sediments. Two of the seismic networks were deployed in the NE part of Taiwan, near the Ryukyu subduction system, whereas the others were in the SW area, on the continental margin rich in gas hydrate. Generally, ambient seismic noise could be associated with wind, ocean waves, rock fracturing and anthropogenic activity. In the southwestern Taiwan, the cross-correlation function obtained from two seismic networks indicate similar direction, suggestion that the source from the south part of the network could be the origin of the noise. However, the two networks in the northeastern Taiwan show various source direction, which could be caused by the abrupt change of bathymetry or the volcanic degassing effect frequently observed by the marine geophysical method in the area. The Vs determined from the dispersion curve shows a relatively higher value for the networks in the Okinawa Trough (OT) off NE Taiwan than that in the

  8. 3D Shear Velocity Structure of Crust and Upper Mantle in China From Ambient Noise Tomography

    NASA Astrophysics Data System (ADS)

    Sun, X.; Song, X.; Zheng, S.; Yang, Y.; Ritzwoller, M.

    2008-12-01

    We perform ambient noise tomography of China using the data from the China National Seismic Network and global and PASSCAL stations in the region. We obtain Rayleigh wave group and phase velocity dispersion maps at 1 by 1 degree grids for periods from 8 to 60 s. The results are combined with longer-period dispersion maps from global earthquake-based measurements. We then obtain the 3D shear velocity structure of the crust and upper mantle in China by inverting the dispersion curves at each grid. The inversion results show remarkable features for continental China and in particular the Tibetan Plateau (TP), including slow sedimentary layers of all the major basins at the shallow depth, striking east-west contrasts in Moho depth variation and lithosphere thickness, fast (strong) mid-lower crust and mantle lithosphere in major basins surrounding the TP (Tarim, Ordos, and Sichuan) (in contrast, Qaidam Basin does not have such a "deep root"). These strong blocks thus seem to play an important role in confining the deformation of the TP to be a triangular shape. The Moho changes from plateau to Tarim and Sichuan Basins are quite sharp. The India lithosphere seems to terminate around the Bangong Nujiang Suture as indicated by the fast-slow velocity contrast in the mantle lithosphere, but it seems to extend further north under E. Tibet. In northwest TP, slow anomalies extend from crust to great depth (200 km). A widespread, prominent low-velocity zone is observed in midcrust in the TP, which are generally connected and seem to reach to the surface near the margins of the TP, consistent with the notion of the growth of the TP by crustal channel flow and the extrusion of channel flow materials at the topographic fronts.

  9. LITHOSTRATIGRAPHY AND SHEAR-WAVE VELOCITY IN THE CRYSTALLIZED TOPOPAH SPRING TUFF, YUCCA MOUNTAIN, NEVADA

    SciTech Connect

    D. BUESCH; K.H. STOKOE; M. SCHUHEN

    2006-03-20

    Evaluation of the seismic response of the proposed spent nuclear fuel and high-level radioactive waste repository at Yucca Mountain, Nevada, is in part based on the seismic properties of the host rock, the 12.8-million-year-old Topopah Spring Tuff. Because of the processes that formed the tuff, the densely welded and crystallized part has three lithophysal and three nonlithophysal zones, and each zone has characteristic variations in lithostratigraphic features and structures of the rocks. Lithostratigraphic features include lithophysal cavities, rims on lithophysae and some fractures, spots (which are similar to rims but without an associated cavity or aperture), amounts of porosity resulting from welding, crystallization, and vapor-phase corrosion and mineralization, and fractures. Seismic properties, including shear-wave velocity (V{sub s}), have been measured on 38 pieces of core, and there is a good ''first order'' correlation with the lithostratigraphic zones; for example, samples from nonlithophysal zones have larger V{sub s} values compared to samples from lithophysal zones. Some samples have V{sub s} values that are beyond the typical range for the lithostratigraphic zone; however, these samples typically have one or more fractures, ''large'' lithophysal cavities, or ''missing pieces'' relative to the sample size. Shear-wave velocity data measured in the tunnels have similar relations to lithophysal and nonlithophysal rocks; however, tunnel-based values are typically smaller than those measured in core resulting from increased lithophysae and fracturing effects. Variations in seismic properties such as V{sub s} data from small-scale samples (typical and ''flawed'' core) to larger scale traverses in the tunnels provide a basis for merging our understanding of the distributions of lithostratigraphic features (and zones) with a method to scale seismic properties.

  10. Compositional layering within the large low shear-wave velocity provinces in the lower mantle

    NASA Astrophysics Data System (ADS)

    Ballmer, Maxim D.; Schumacher, Lina; Lekic, Vedran; Thomas, Christine; Ito, Garrett

    2016-12-01

    The large low shear-wave velocity provinces (LLSVP) are thermochemical anomalies in the deep Earth's mantle, thousands of km wide and ˜1800 km high. This study explores the hypothesis that the LLSVPs are compositionally subdivided into two domains: a primordial bottom domain near the core-mantle boundary and a basaltic shallow domain that extends from 1100 to 2300 km depth. This hypothesis reconciles published observations in that it predicts that the two domains have different physical properties (bulk-sound versus shear-wave speed versus density anomalies), the transition in seismic velocities separating them is abrupt, and both domains remain seismically distinct from the ambient mantle. We here report underside reflections from the top of the LLSVP shallow domain, supporting a compositional origin. By exploring a suite of two-dimensional geodynamic models, we constrain the conditions under which well-separated "double-layered" piles with realistic geometry can persist for billions of years. Results show that long-term separation requires density differences of ˜100 kg/m3 between LLSVP materials, providing a constraint for origin and composition. The models further predict short-lived "secondary" plumelets to rise from LLSVP roofs and to entrain basaltic material that has evolved in the lower mantle. Long-lived, vigorous "primary" plumes instead rise from LLSVP margins and entrain a mix of materials, including small fractions of primordial material. These predictions are consistent with the locations of hot spots relative to LLSVPs, and address the geochemical and geochronological record of (oceanic) hot spot volcanism. The study of large-scale heterogeneity within LLSVPs has important implications for our understanding of the evolution and composition of the mantle.

  11. Lithostratigraphy and shear-wave velocity in the crystallized Topopah Spring Tuff, Yucca Mountain, Nevada

    USGS Publications Warehouse

    Buesch, D.C.; Stokoe, K.H.; Won, K.C.; Seong, Y.J.; Jung, J.L.; Schuhen, M.D.

    2006-01-01

    Evaluation of the potential future response to seismic events of the proposed spent nuclear fuel and high-level radioactive waste repository at Yucca Mountain, Nevada, is in part based on the seismic properties of the host rock, the 12.8-million-year-old Topopah Spring Tuff. Because of the processes that formed the tuff, the densely welded and crystallized part has three lithophysal and three nonlithophysal zones, and each zone has characteristic variations in lithostratigraphic features and structures of the rocks. Lithostratigraphic features include lithophysal cavities; rims on lithophysae and some fractures; spots (which are similar to rims but without an associated cavity or aperture); amounts of porosity resulting from welding, crystallization, and vapor-phase corrosion and mineralization; and fractures. Seismic properties, including shear-wave velocity (Vs), have been measured on 38 pieces of core, and there is a good "first order" correlation with the lithostratigraphic zones; for example, samples from nonlithophysal zones have larger Vs values compared to samples from lithophysal zones. Some samples have Vs values that are outside the typical range for the lithostratigraphic zone; however, these samples typically have one or more fractures, "large" lithophysal cavities, or "missing pieces" relative to the sample size. Shear-wave velocity data measured in the tunnels have similar relations to lithophysal and nonlithophysal rocks; however, tunnel-based values are typically smaller than those measured in core resulting from increased lithophysae and fracturing effects. Variations in seismic properties such as Vs data from small-scale samples (typical and "flawed" core) to larger scale transects in the tunnels provide a basis for merging our understanding of the distributions of lithostratigraphic features (and zones) with a method to scale seismic properties.

  12. Effect of velocity ratio on plane mixing layer development - Influence of the splitter plate wake

    NASA Technical Reports Server (NTRS)

    Mehta, R. D.

    1991-01-01

    The effect of the velocity ratio on the approach of a plane mixing layer to self-similarity was investigated experimentally. In the experiment, plane mixing layers with velocity ratios 0.5, 0.6, 0.7, 0.8, and 0.9 were generated in a mixing-layer wind tunnel consisting of two individually driven legs, in which the two streams were allowed to merge at the sharp edge of a tappered splitter plate. The leg driven by the bigger blower was operated at a free-stream velocity in the test section of 21 m/s, while the flow speed in the other leg was varied to change the velocity ratio. For each velocity ratio, the mean flow- and turbulence measurements were carried out at eight streamwise locations. Results showed that, for velocity ratios between 0.5 and 0.7, self-similarity of the mixing layer was achieved, with the asymptotic states comparable; mixing layers with higher velocity ratios failed to achieve a self-similar state within the measurement domain.

  13. Micromechanical processes of frictional aging and the affect of shear stress on fault healing: insights from material characterization and ultrasonic velocity measurements

    NASA Astrophysics Data System (ADS)

    Ryan, K. L.; Marone, C.

    2015-12-01

    During the seismic cycle, faults repeatedly fail and regain strength. The gradual strength recovery is often referred to as frictional healing, and existing works suggest that healing can play an important role in determining the mode of fault slip ranging from dynamic rupture to slow earthquakes. Laboratory studies can play an important role in identifying the processes of frictional healing and their evolution with shear strain during the seismic cycle. These studies also provide data for laboratory-derived friction constitutive laws, which can improve dynamic earthquake models. Previous work shows that frictional healing varies with shear stress on a fault during the interseismic period. Unfortunately, the micromechanical processes that cause shear stress dependent frictional healing are not well understood and cannot be incorporated into current earthquake models. In fault gouge, frictional healing involves compaction and particle rearrangement within sheared granular layers. Therefore, to address these issues, we investigate the role grain size reduction plays in frictional re-strengthening processes at different levels of shear stress. Sample material was preserved from biaxial deformation experiments on granular Westerly granite. The normal stress was held constant at 25 MPa and we performed several 100 second slide-hold-slide tests in each experiment. We conducted a series of 5 experiments each with a different value of normalized shear stress (ranging from 0 to 1), defined as the ratio of the pre-hold shear stress to the shear stress during the hold. The particle size distribution for each sample was analyzed. In addition, acoustic measurements were recorded throughout our experiments to investigate variations in ultrasonic velocity and signal amplitude that reflect changes in the elastic moduli of the layer. Acoustic monitoring provides information about healing mechanisms and can provide a link between laboratory studies and tectonic fault zones.

  14. Coupling of microprocesses and macroprocesses due to velocity shear: An application to the low-altitude ionosphere

    NASA Technical Reports Server (NTRS)

    Ganguli, G.; Keskinen, M. J.; Romero, H.; Heelis, R.; Moore, T.; Pollock, C.

    1994-01-01

    Recent observations indicate that low-altitude (below 1500 km) ion energization and thermal ion upwelling are colocated in the convective flow reversal region. In this region the convective velocity V(sub perpendicular) is generally small but spatial gradients in V(sub perpendicular) can be large. As a result, Joule heating is small. The observed high level of ion heating (few electron volts or more) cannot be explained by classical Joule heating alone but requires additional heating sources such as plasma waves. At these lower altitudes, sources of free energy are not obvious and hence the nature of ion energization remains ill understood. The high degree of correlation of ion heating with shear in the convective velocity (Tsunoda et al., 1989) is suggestive of an important role of velocity shear in this phenomenon. We provide more recent evidence for this correlation and show that even a small amount of velocity shear in the transverse flow is sufficient to excite a large-scale Kelvin-Helmholtz mode, which can nonlinearly steepen and give rise to highly stressed regions of strongly sheared flows. Futhermore, these stressed regions of strongly sheared flows may seed plasma waves in the range of ion cyclotron to lower hybrid frequencies, which are potential sources for ion heating. This novle two-step mechanism for ion energization is applied to typical observations of low-altitude thermal ion upwelling events.

  15. Partially obstructed channel: Contraction ratio effect on the flow hydrodynamic structure and prediction of the transversal mean velocity profile

    NASA Astrophysics Data System (ADS)

    Ben Meftah, M.; Mossa, M.

    2016-11-01

    In this manuscript, we focus on the study of flow structures in a channel partially obstructed by arrays of vertical, rigid, emergent, vegetation/cylinders. Special attention is given to understand the effect of the contraction ratio, defined as the ratio of the obstructed area width to the width of the unobstructed area, on the flow hydrodynamic structures and to analyze the transversal flow velocity profile at the obstructed-unobstructed interface. A large data set of transversal mean flow velocity profiles and turbulence characteristics is reported from experiments carried out in a laboratory flume. The flow velocities and turbulence intensities have been measured with a 3D Acoustic Doppler Velocimeter (ADV)-Vectrino manufactured by Nortek. It was observed that the arrays of emergent vegetation/cylinders strongly affect the flow structures, forming a shear layer immediately next to the obstructed-unobstructed interface, followed by an adjacent free-stream region of full velocity flow. The experimental results show that the contraction ratio significantly affects the flow hydrodynamic structure. Adaptation of the Prandtl's log-law modified by Nikuradse led to the determination of a characteristic hydrodynamic roughness height to define the array resistance to the flow. Moreover, an improved modified log-law predicting the representative transversal profile of the mean flow velocity, at the obstructed-unobstructed interface, is proposed. The benefit of this modified log-law is its easier practical applicability, i.e., it avoids the measurements of some sensitive turbulence parameters, in addition, the flow hydrodynamic variables forming it are predictable, using the initial hydraulic conditions.

  16. OCT-based quantification of flow velocity, shear force, and power generated by a biological ciliated surface (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Huang, Brendan K.; Khokha, Mustafa K.; Loewenberg, Michael; Choma, Michael A.

    2016-03-01

    In cilia-driven fluid flow physiology, quantification of flow velocity, shearing force, and power dissipation is important in defining abnormal ciliary function. The capacity to generate flow can be robustly described in terms of shearing force. Dissipated power can be related to net ATP consumption by ciliary molecular motors. To date, however, only flow velocity can be routinely quantified in a non-invasive, non-contact manner. Additionally, traditional power-based metrics rely on metabolic consumption that reflects energy consumption not just from cilia but also from all active cellular processes. Here, we demonstrate the estimation of all three of these quantities (flow velocity, shear force, and power dissipation) using only optical coherence tomography (OCT). Specifically, we develop a framework that can extract force and power information from vectorial flow velocity fields obtained using OCT-based methods. We do so by (a) estimating the viscous stress tensor from flow velocity fields to estimate shearing force and (b) using the viscous stress tensor to estimate the power dissipation function to infer total mechanical power. These estimates have the advantage of (a) requiring only a single modality, (b) being non-invasive in nature, and (c) being reflective of only the net power work generated by a ciliated surface. We demonstrate our all-optical approach to the estimation of these parameters in the Xenopus animal model system under normal and increased viscous loading. Our preliminary data support the hypothesis that the Xenopus ciliated surface can increase force output under loading conditions.

  17. Collisionless microtearing modes in large aspect ratio Tokamaks with weak reversed shear configurations

    NASA Astrophysics Data System (ADS)

    Krishna Swamy, Aditya; Ganesh, Rajaraman; Brunner, Stephan; Vaclavik, Jan; Villard, Laurent

    2015-11-01

    Gyrokinetic simulations have found Collisionless Microtearing Modes (MTM) to be linearly unstable in sharp temperature gradient regions of tokamaks, typically with high magnetic shear. The collisionless MTM is driven by the magnetic drift resonance of passing electrons, aided by the closeness of Mode Rational Surfaces (MRS) arising due to the high shear. Here, the role of global safety factor profile variation on the MTM instability and global mode structure is studied, in particular in weak reverse shear (WRS) configurations in large aspect ratio tokamaks. At lower shear profiles, multiple MTM branches are found with tearing parity as well as mixed parity. The linear growth rates of MTM is found to be weakened and linearly unstable modes are found whose global mode structures of φ~ and Ã∥ exhibit Mixed Parity. For the same equilibrium profiles and parameters, AITG instability is also studied and global mode structures are compared with MTM. The growth rate spectrum is found to extend to shorter/mesoscale wavelengths in WRS. Several other characteristics of MTMs and AITG are recovered in the WRS configuration, such as the dependency on free energy source and on plasma β.

  18. Fault rupture as a series of nano-seismic events during high-velocity shear experiments

    NASA Astrophysics Data System (ADS)

    Zu, X.; Reches, Z.; Chen, X.; Chang, J. C.; Carpenter, B. M.

    2015-12-01

    The rupture process of experimental faults is investigated here by monitoring nano-seismic events (NSE) during slip in a rotary shear apparatus. Our experimental faults are made of two rock blocks with one to four miniature 3D accelerometers that are glued to the stationary block at distance of ~ 2 cm from the fault surface. Accelerations in the frequency range of 1 Hz to 200 kHz are recorded in slip-parallel (x), slip-transverse (y), and slip-vertical (z) directions. We conducted a series of 45 experiments on diorite and dolomite samples in two loading styles: classical velocity controlled loading, and power-density loading, in which the power-density (shear stress times slip velocity) is selected, and stick-slip events develop spontaneously according to the experimental fault response. The 3D accelerometer data were recorded at 106 samples/s, with acceleration resolution of 10 mV/g in recoding range of +/- 5 V. The experiments were conducted at slip-velocity of 0.001-0.8 m/s and slip distance up to 1.38 m. The accelerometer observations revealed tens to hundreds of NSEs per slip in both loading styles; peak acceleration ranged from 1g to over 500g. A typical stick-slip with tens of NSEs in Fig. 1, shows: (1) An initial NSE at ~59.72 s (green) that coincides with a small stress drop (~10%, red); (2) Simultaneous macroscopic slip initiation (blue); (3) A swarm of NSEs occur as the fault slips, each NSE lasts 1-2 milliseconds; and (4) Details of the initial NSE are shown in Fig. 2. Based on waveform cross-correlation between frequency band from 20 kHz to 70kHz, we identify several groups of NSE clusters, and apply empirical Green's function method to analyze event source spectra based on Brune-type source model. These NSEs are indicators of rupture propagation during the experimental fault slip.

  19. Physical modelling of the effect of fractures on compressional and shear wave velocities

    NASA Astrophysics Data System (ADS)

    Gurevich, Boris; Lebedev, Maxim; Glubokovskikh, Stanislav; Dyskin, Arcady; Pasternak, Elena; Vialle, Stephanie

    2016-04-01

    Ultrasonic measurements were performed on a sample of polyester resin permeated by multiple fractures. The samples were prepared by mixing high doses of catalyst, about 7-10 % with the liquid resin base. The mix was then heated in an oven at 60° C for a period of 1 hour. This operation produced many shrinkage cracks varying in size from 8 mm to 20 mm (Sahouryeh et al., 2002). The produced samples were parallelepiped 50 mm x 50 mm in cross-section with height of 100 mm. Micro-CT scanning of the sample reveals many open fractures with apertures 0.2 - 0.4 mm. Elastic properties of the fractured samples were derived from ultrasonic measurements using piezo-electric transducers. These measurements give compressional (Vp) and shear (Vs) wave velocities of 2450 and 1190 m/s, respectively, giving Vp/Vs = 2.04. At the same time the velocities in the intact resin are Vp=2460 and Vs=1504 m/s, respectively, with Vp/Vs = 1.63. Thus we see that the fractures have a negligible effect on the Vp (within the measurement error) but a dramatic effect on Vs (about 20%). This contradicts the common understanding that the effects of dry fractures on Vp and Vs are similar in magnitude. Indeed, assuming very roughly that the distribution of fractures is isotropic, we can estimate the cumulative normal fracture compliance from the difference between shear moduli of the intact and fractured resin to be 0.30 GPa-1 and fracture density of 0.41. This value can be used to estimate the effective bulk modulus of the fractured material. The corresponding p-wave velocity, Vp = 1860 m/s, is significantly lower that the observed value. The results suggest that an equivalent medium approximation is not applicable in this case, probably due to the fact that the long-wave approximation is inadequate. Indeed the fractures are larger than the wavelength that corresponds to the peak frequencies of the power spectrum of the signal. This suggests a strong influence of diffraction. Furthermore, the

  20. Dissipative structures of diffuse molecular gas. III. Small-scale intermittency of intense velocity-shears

    NASA Astrophysics Data System (ADS)

    Hily-Blant, P.; Falgarone, E.; Pety, J.

    2008-04-01

    Aims: We further characterize the structures tentatively identified on thermal and chemical grounds as the sites of dissipation of turbulence in molecular clouds (Papers I and II). Methods: Our study is based on two-point statistics of line centroid velocities (CV), computed from three large 12CO maps of two fields. We build the probability density functions (PDF) of the CO line centroid velocity increments (CVI) over lags varying by an order of magnitude. Structure functions of the line CV are computed up to the 6th order. We compare these statistical properties in two translucent parsec-scale fields embedded in different large-scale environments, one far from virial balance and the other virialized. We also address their scale dependence in the former, more turbulent, field. Results: The statistical properties of the line CV bear the three signatures of intermittency in a turbulent velocity field: (1) the non-Gaussian tails in the CVI PDF grow as the lag decreases, (2) the departure from Kolmogorov scaling of the high-order structure functions is more pronounced in the more turbulent field, (3) the positions contributing to the CVI PDF tails delineate narrow filamentary structures (thickness ~0.02 pc), uncorrelated to dense gas structures and spatially coherent with thicker ones (~0.18 pc) observed on larger scales. We show that the largest CVI trace sharp variations of the extreme CO linewings and that they actually capture properties of the underlying velocity field, uncontaminated by density fluctuations. The confrontation with theoretical predictions leads us to identify these small-scale filamentary structures with extrema of velocity-shears. We estimate that viscous dissipation at the 0.02 pc-scale in these structures is up to 10 times higher than average, consistent with their being associated with gas warmer than the bulk. Last, their average direction is parallel (or close) to that of the local magnetic field projection. Conclusions: Turbulence in these

  1. Hamstrings to quadriceps peak torque ratios diverge between sexes with increasing isokinetic angular velocity.

    PubMed

    Hewett, Timothy E; Myer, Gregory D; Zazulak, Bohdanna T

    2008-09-01

    Our purpose was to determine if females demonstrate decreased hamstrings to quadriceps peak torque (H/Q) ratios compared to males and if H/Q ratios increase with increased isokinetic velocity in both sexes. Maturation disproportionately increases hamstrings peak torque at high velocity in males, but not females. Therefore, we hypothesised that mature females would demonstrate decreased H/Q ratios compared to males and the difference in H/Q ratio between sexes would increase as isokinetic velocity increased. Studies that analysed the H/Q ratio with gravity corrected isokinetic strength testing reported between 1967 and 2004 were included in our review and analysis. Keywords were hamstrings/quadriceps, isokinetics, peak torque and gravity corrected. Medline and Smart databases were searched combined with cross-checked bibliographic reference lists of the publications to determine studies to be included. Twenty-two studies were included with a total of 1568 subjects (1145 male, 423 female). Males demonstrated a significant correlation between H/Q ratio and isokinetic velocity (R=0.634, p<0.0001), and a significant difference in the isokinetic H/Q ratio at the lowest angular velocity (47.8+/-2.2% at 30 degrees /s) compared to the highest velocity (81.4+/-1.1% at 360 degrees /s, p<0.001). In contrast, females did not demonstrate a significant relationship between H/Q ratio and isokinetic velocity (R=0.065, p=0.77) or a change in relative hamstrings strength as the speed increased (49.5+/-8.8% at 30 degrees /s; 51.0+/-5.7% at 360 degrees /s, p=0.84). Gender differences in isokinetic H/Q ratios were not observed at slower angular velocities. However, at high knee flexion/extension angular velocities, approaching those that occur during sports activities, significant gender differences were observed in the H/Q ratio. Females, unlike males, do not increase hamstrings to quadriceps torque ratios at velocities that approach those of functional activities.

  2. Inversion of surface wave data for subsurface shear wave velocity profiles characterized by a thick buried low-velocity layer

    NASA Astrophysics Data System (ADS)

    Farrugia, Daniela; Paolucci, Enrico; D'Amico, Sebastiano; Galea, Pauline

    2016-08-01

    The islands composing the Maltese archipelago (Central Mediterranean) are characterized by a four-layer sequence of limestones and clays. A common feature found in the western half of the archipelago is Upper Coralline Limestone (UCL) plateaus and hillcaps covering a soft Blue Clay (BC) layer which can be up to 75 m thick. The BC layer introduces a velocity inversion in the stratigraphy, implying that the VS30 (traveltime average sear wave velocity (VS) in the upper 30 m) parameter is not always suitable for seismic microzonation purposes. Such a layer may produce amplification effects, however might not be included in the VS30 calculations. In this investigation, VS profiles at seven sites characterized by such a lithological sequence are obtained by a joint inversion of the single-station Horizontal-to-Vertical Spectral Ratios (H/V or HVSR) and effective dispersion curves from array measurements analysed using the Extended Spatial Auto-Correlation technique. The lithological sequence gives rise to a ubiquitous H/V peak between 1 and 2 Hz. All the effective dispersion curves obtained exhibit a `normal' dispersive trend at low frequencies, followed by an inverse dispersive trend at higher frequencies. This shape is tentatively explained in terms of the presence of higher mode Rayleigh waves, which are commonly present in such scenarios. Comparisons made with the results obtained at the only site in Malta where the BC is missing below the UCL suggest that the characteristics observed at the other seven sites are due to the presence of the soft layer. The final profiles reveal a variation in the VS of the clay layer with respect to the depth of burial and some regional variations in the UCL layer. This study presents a step towards a holistic seismic risk assessment that includes the implications on the site effects induced by the buried clay layer. Such assessments have not yet been done for Malta.

  3. Near-surface shear-wave velocity measurements in unlithified sediment

    USGS Publications Warehouse

    Richards, B.T.; Steeples, D.; Miller, R.; Ivanov, J.; Peterie, S.; Sloan, S.D.; McKenna, J.R.

    2011-01-01

    S-wave velocity can be directly correlated to material stiffness and lithology making it a valuable physical property that has found uses in construction, engineering, and environmental projects. This study compares different methods for measuring S-wave velocities, investigating and identifying the differences among the methods' results, and prioritizing the different methods for optimal S-wave use at the U. S. Army's Yuma Proving Grounds YPG. Multichannel Analysis of Surface Waves MASW and S-wave tomography were used to generate S-wave velocity profiles. Each method has advantages and disadvantages. A strong signal-to-noise ratio at the study site gives the MASW method promising resolution. S-wave first arrivals are picked on impulsive sledgehammer data which were then used for the tomography process. Three-component downhole seismic data were collected in-line with a locking geophone, providing ground truth to compare the data and to draw conclusions about the validity of each data set. Results from these S-wave measurement techniques are compared with borehole seismic data and with lithology data from continuous samples to help ascertain the accuracy, and therefore applicability, of each method. This study helps to select the best methods for obtaining S-wave velocities for media much like those found in unconsolidated sediments at YPG. ?? 2011 Society of Exploration Geophysicists.

  4. Shear Induced Alignment of Low Aspect Ratio Gold Nanorods in Newtonian Fluids.

    PubMed

    Xie, Donglin; Lista, Marco; Qiao, Greg G; Dunstan, Dave E

    2015-10-01

    The flow-induced alignment of small gold nanorods ranging in aspect ratio from 2.4 to 4.2 in aqueous sucrose solutions is reported. Optical absorption spectra have been measured over a range of shear rates using polarized incident light in an optically transparent quartz Couette cell. The measured spectral changes are directly attributed to the shear-induced anisotropy in the suspension due to particle alignment that saturates at Péclet number of around 200. The measured optical changes are reversible, indicating that the nanorods do not undergo aggregation during measurement. Numerical simulations show that the spectral shifts are consistent with the rods flipping between extreme orientations of the Jeffery's orbits and that the effect of the Brownian motion on the gold nanorods cannot be ignored even at large Péclet number.

  5. Explicit use of the Biot coefficient in predicting shear-wave velocity of water-saturated sediments

    USGS Publications Warehouse

    Lee, M.W.

    2006-01-01

    Predicting the shear-wave (S-wave) velocity is important in seismic modelling, amplitude analysis with offset, and other exploration and engineering applications. Under the low-frequency approximation, the classical Biot-Gassmann theory relates the Biot coefficient to the bulk modulus of water-saturated sediments. If the Biot coefficient under in situ conditions can be estimated, the shear modulus or the S-wave velocity can be calculated. The Biot coefficient derived from the compressional-wave (P-wave) velocity of water-saturated sediments often differs from and is less than that estimated from the S-wave velocity, owing to the interactions between the pore fluid and the grain contacts. By correcting the Biot coefficients derived from P-wave velocities of water-saturated sediments measured at various differential pressures, an accurate method of predicting S-wave velocities is proposed. Numerical results indicate that the predicted S-wave velocities for consolidated and unconsolidated sediments agreewell with measured velocities. ?? 2006 European Association of Geoscientists & Engineers.

  6. Slip-localization within confined gouge powder sheared at moderate to high slip-velocity

    NASA Astrophysics Data System (ADS)

    Reches, Zeev; Chen, Xiaofeng; Morgan, Chance; Madden, Andrew

    2015-04-01

    Slip along faults in the upper crust is always associated with comminution and formation of non-cohesive gouge powder that can be lithified to cataclasite. Typically, the fine-grained powders (grain-size < 1 micron) build a 1-10 cm thick inner-core of a fault-zone. The ubiquitous occurrence of gouge powder implies that gouge properties may control the dynamic weakening of faults. Testing these properties is the present objective. We built a Confined ROtary Cell, CROC, with a ring-shape, ~3 mm thick gouge chamber, with 62.5 and 81.2 mm of inner and outer diameters. The sheared powder is sealed by two sets of seals pressurized by nitrogen. In CROC, we can control the pore-pressure and to inject fluids, and to monitor CO2 and H2O concentration; in addition, we monitor the standard mechanical parameters (slip velocity, stresses, dilation, and temperature). We tested six types of granular materials (starting grain-size in microns): Talc (<250), Kasota dolomite (125-250), ooides grains (125-250), San Andreas fault zone powder (< 840), montmorillonite powder (1-2), kaolinite powder and gypsum. The experimental slip-velocity ranged 0.001-1 m/s, slip distances from a few tens of cm to tens of m, effective normal stress up to 6.1 MPa. The central ultra-microscopic (SEM) observation is that almost invariably the slip was localized along principal-slip-zone (PSZ) within the granular layer. Even though the starting material was loose, coarse granular material, the developed PSZ was cohesive, hard, smooth and shining. The PSZ is about 1 micron thick, and built of agglomerated, ultra-fine grains (20-50 nm) that were pulverized from the original granular material. We noted that PSZs of the different tested compositions display similar characteristics in terms of structure, grain size, and roughness. Further, we found striking similarities between PSZ in the granular samples and the PZS that developed along experimental faults made of solid rock that were sheared at similar

  7. 3-D shear wave radially and azimuthally anisotropic velocity model of the North American upper mantle

    NASA Astrophysics Data System (ADS)

    Yuan, Huaiyu; Romanowicz, Barbara; Fischer, Karen M.; Abt, David

    2011-03-01

    Using a combination of long period seismic waveforms and SKS splitting measurements, we have developed a 3-D upper-mantle model (SAWum_NA2) of North America that includes isotropic shear velocity, with a lateral resolution of ˜250 km, as well as radial and azimuthal anisotropy, with a lateral resolution of ˜500 km. Combining these results, we infer several key features of lithosphere and asthenosphere structure. A rapid change from thin (˜70-80 km) lithosphere in the western United States (WUS) to thick lithosphere (˜200 km) in the central, cratonic part of the continent closely follows the Rocky Mountain Front (RMF). Changes with depth of the fast axis direction of azimuthal anisotropy reveal the presence of two layers in the cratonic lithosphere, corresponding to the fast-to-slow discontinuity found in receiver functions. Below the lithosphere, azimuthal anisotropy manifests a maximum, stronger in the WUS than under the craton, and the fast axis of anisotropy aligns with the absolute plate motion, as described in the hotspot reference frame (HS3-NUVEL 1A). In the WUS, this zone is confined between 70 and 150 km, decreasing in strength with depth from the top, from the RMF to the San Andreas Fault system and the Juan de Fuca/Gorda ridges. This result suggests that shear associated with lithosphere-asthenosphere coupling dominates mantle deformation down to this depth in the western part of the continent. The depth extent of the zone of increased azimuthal anisotropy below the cratonic lithosphere is not well resolved in our study, although it is peaked around 270 km, a robust result. Radial anisotropy is such that, predominantly, ξ > 1, where ξ= (Vsh/Vsv)2, under the continent and its borders down to ˜200 km, with stronger ξ in the bordering oceanic regions. Across the continent and below 200 km, alternating zones of weaker and stronger radial anisotropy, with predominantly ξ < 1, correlate with zones of small lateral changes in the fast axis direction of

  8. The uppermost mantle shear wave velocity structure of eastern Africa from Rayleigh wave tomography: constraints on rift evolution

    NASA Astrophysics Data System (ADS)

    O'Donnell, J. P.; Adams, A.; Nyblade, A. A.; Mulibo, G. D.; Tugume, F.

    2013-08-01

    An expanded model of the 3-D shear wave velocity structure of the uppermost mantle beneath eastern Africa has been developed using earthquakes recorded by the AfricaArray East African Seismic Experiment in conjunction with data from permanent stations and previously deployed temporary stations. The combined data set comprises 331 earthquakes recorded on a total of 95 seismic stations spanning Kenya, Uganda, Tanzania, Zambia and Malawi. In this study, data from 149 earthquakes were used to determine fundamental-mode Rayleigh wave phase velocities at periods ranging from 20 to 182 s using the two-plane wave method, and then combined with the similarly processed published measurements and inverted for a 3-D shear wave velocity model of the uppermost mantle. New features in the model include (1) a low-velocity region in western Zambia, (2) a high-velocity region in eastern Zambia, (3) a low-velocity region in eastern Tanzania and (4) low-velocity regions beneath the Lake Malawi rift. When considered in conjunction with mapped seismicity, these results support a secondary western rift branch striking southwestwards from Lake Tanganyika, likely exploiting the relatively weak lithosphere of the southern Kibaran Belt between the Bangweulu Block and the Congo Craton. We estimate a lithospheric thickness of ˜150-200 km for the substantial fast shear wave anomaly imaged in eastern Zambia, which may be a southward subsurface extension of the Bangweulu Block. The low-velocity region in eastern Tanzania suggests that the eastern rift branch trends southeastwards offshore eastern Tanzania coincident with the purported location of the northern margin of the proposed Ruvuma microplate. Pronounced velocity lows along the Lake Malawi rift are found beneath the northern and southern ends of the lake, but not beneath the central portion of the lake.

  9. Slip Stability and Strength Evolution of quartz-calcite-clay Gouge during High-Velocity Shear Experiments

    NASA Astrophysics Data System (ADS)

    Morgan, C.; Carpenter, B. M.; Reches, Z.

    2016-12-01

    Faults exhibit a spectrum of slip modes, from unstable, seismic slip to stable, aseismic creep. These modes are controlled by fault-zone composition, fault structure, and the environmental/mechanical loading conditions. Our study focuses on the influence of the mineralogical composition of fault gouge on the dynamic behavior and slip-stability of the host fault. The analysis includes high-velocity shear experiments a ring-shaped gouge chamber inside a confined rotary cell. The experiments were conducted with quartz-calcite-clay (montmorillonite) mixtures as general representation of gouge compositions. Initial sample grain size was 150-420 µm and was either room-dry or water-saturated. We monitored CO2 and H2O emissions, shear and normal stresses, slip velocity, dilation and temperature. We conducted 119 shear experiments over a large slip-velocity range (0.001 to 1.5 m/s) and slip-distance range (10 cm to >15m) with both velocity-stepping and constant-velocity loading. The main preliminary results are the following: (1) Dynamic strength is strongly affected by composition: increase of clay content above 15% leads to progressive strengthening whereas increase of calcite content leads to progressive intense weakening; (2) The dynamic friction coefficient ranges widely from very low ( 0.1) to very high (>1) with a dependence on the main mineralogical groups (calcite, quartz, clay); (3) Within each sample, the velocity-dependence of the friction coefficient showed complex trends, with velocity-weakening with low clay content, velocity-strengthening with high clay content, and no velocity dependence; (4) Pressure-injection of water reduced the shear stress due to reduction of effective normal stress; and (5) Emissions of CO2 and H2O increased drastically during high-velocity shear of samples that are calcite-rich and clay-rich, respectively. Future work will include systematic quantification of the above relations directed to application of the experimental results to

  10. Effect of consolidation ratios on maximum dynamic shear modulus of sands

    NASA Astrophysics Data System (ADS)

    Xiaoming, Yuan; Jing, Sun; Rui, Sun

    2005-06-01

    The dynamic shear modulus (DSM) is the most basic soil parameter in earthquake or other dynamic loading conditions and can be obtained through testing in the field or in the laboratory. The effect of consolidation ratios of the maximum DSM for two types of sand is investigated by using resonant column tests. And, an increment formula to obtain the maximum DSM for cases of consolidation ratio k c>1 is presented. The results indicate that the maximum DSM rises rapidly when k c is near 1 and then slows down, which means that the power function of the consolidation ratio increment k c-1 can be used to describe the variation of the maximum DSM due to k c>1. The results also indicate that the increase in the maximum DSM due to k c>1 is significantly larger than that predicted by Hardin and Black's formula.

  11. Time evolving bed shear stress due the passage of gravity currents estimated with ADVP velocity measurements

    NASA Astrophysics Data System (ADS)

    Zordan, Jessica; Schleiss, Anton J.; Franca, Mário J.

    2016-04-01

    Density or gravity currents are geophysical flows driven by density gradients between two contacting fluids. The physical trigger mechanism of these phenomena lays in the density differences which may be caused by differences in the temperature, dissolved substances or concentration of suspended sediments. Saline density currents are capable to entrain bed sediments inducing signatures in the bottom of sedimentary basins. Herein, saline density currents are reproduced in laboratory over a movable bed. The experimental channel is of the lock-exchange type, it is 7.5 m long and 0.3 m wide, divided into two sections of comparable volumes by a sliding gate. An upstream reach serves as a head tank for the dense mixture; the current propagates through a downstream reach where the main measurements are made. Downstream of the channel a tank exist to absorb the reflection of the current and thus artifacts due to the limited length of the channel. High performance thermoplastic polyurethane simulating fine sediments forms the movable bed. Measures of 3D instantaneous velocities will be made with the use of the non-intrusive technique of the ADV (Acoustic Doppler Current Profiler). With the velocity measurements, the evolution in time of the channel-bed shear stress due the passage of gravity currents is estimated. This is in turn related to the observed erosion and to such parameters determinant for the dynamics of the current as initial density difference, lock length and channel slope. This work was funded by the ITN-Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme FP7-PEOPLE-2013-ITN under REA grant agreement n_607394-SEDITRANS.

  12. Flow patterns and distributions of fluid velocity and wall shear stress in the human internal carotid and middle cerebral arteries.

    PubMed

    Takeuchi, Shigekazu; Karino, Takeshi

    2010-03-01

    The aim of this study is to elucidate the relationship between the flow patterns and the preferred sites of the development of atherosclerotic lesions and cerebral aneurysms in the human ICA and MCA. Five isolated transparent arterial trees containing the ICA and MCA with a sufficient length of the carotid siphon were prepared from humans postmortem, and flow patterns and distributions of fluid velocity and wall shear stress in these vessels were studied in detail using flow visualization and high-speed cinemicrographic techniques. In the carotid siphon that contained several acute bends, due to the impingement and deflection of the flow at the bends, a strong and complex helicoidal flow formed. As a result, the approaching velocity profile was flattened at the terminal bifurcation of the ICA, but it was sharpened at the first bifurcation of the MCA. Thus, at this latter bifurcation, fluid elements impinged on the vessel wall around the flow divider with much larger velocity than that at the preceding terminal bifurcation of the ICA. Throughout the entire arterial tree, atherosclerotic lesions were found almost exclusively in regions of low wall shear stress. The carotid siphon provided a flattened approaching velocity profile at the terminal bifurcation of the ICA, making the hemodynamic stresses (pressure, tension, and shear stress) exerted on the vessel wall much lower than that at the bifurcation of the MCA where the approaching velocity profile was sharpened. This may account for the relatively low incidence of aneurysm formation at this site. Copyright © 2010 Elsevier Inc. All rights reserved.

  13. Shear Stress-Normal Stress (Pressure) Ratio Decides Forming Callus in Patients with Diabetic Neuropathy

    PubMed Central

    Noguchi, Hiroshi; Takehara, Kimie; Ohashi, Yumiko; Suzuki, Ryo; Yamauchi, Toshimasa; Kadowaki, Takashi; Sanada, Hiromi

    2016-01-01

    Aim. Callus is a risk factor, leading to severe diabetic foot ulcer; thus, prevention of callus formation is important. However, normal stress (pressure) and shear stress associated with callus have not been clarified. Additionally, as new valuables, a shear stress-normal stress (pressure) ratio (SPR) was examined. The purpose was to clarify the external force associated with callus formation in patients with diabetic neuropathy. Methods. The external force of the 1st, 2nd, and 5th metatarsal head (MTH) as callus predilection regions was measured. The SPR was calculated by dividing shear stress by normal stress (pressure), concretely, peak values (SPR-p) and time integral values (SPR-i). The optimal cut-off point was determined. Results. Callus formation region of the 1st and 2nd MTH had high SPR-i rather than noncallus formation region. The cut-off value of the 1st MTH was 0.60 and the 2nd MTH was 0.50. For the 5th MTH, variables pertaining to the external forces could not be determined to be indicators of callus formation because of low accuracy. Conclusions. The callus formation cut-off values of the 1st and 2nd MTH were clarified. In the future, it will be necessary to confirm the effect of using appropriate footwear and gait training on lowering SPR-i. PMID:28050567

  14. Shear Stress-Normal Stress (Pressure) Ratio Decides Forming Callus in Patients with Diabetic Neuropathy.

    PubMed

    Amemiya, Ayumi; Noguchi, Hiroshi; Oe, Makoto; Takehara, Kimie; Ohashi, Yumiko; Suzuki, Ryo; Yamauchi, Toshimasa; Kadowaki, Takashi; Sanada, Hiromi; Mori, Taketoshi

    2016-01-01

    Aim. Callus is a risk factor, leading to severe diabetic foot ulcer; thus, prevention of callus formation is important. However, normal stress (pressure) and shear stress associated with callus have not been clarified. Additionally, as new valuables, a shear stress-normal stress (pressure) ratio (SPR) was examined. The purpose was to clarify the external force associated with callus formation in patients with diabetic neuropathy. Methods. The external force of the 1st, 2nd, and 5th metatarsal head (MTH) as callus predilection regions was measured. The SPR was calculated by dividing shear stress by normal stress (pressure), concretely, peak values (SPR-p) and time integral values (SPR-i). The optimal cut-off point was determined. Results. Callus formation region of the 1st and 2nd MTH had high SPR-i rather than noncallus formation region. The cut-off value of the 1st MTH was 0.60 and the 2nd MTH was 0.50. For the 5th MTH, variables pertaining to the external forces could not be determined to be indicators of callus formation because of low accuracy. Conclusions. The callus formation cut-off values of the 1st and 2nd MTH were clarified. In the future, it will be necessary to confirm the effect of using appropriate footwear and gait training on lowering SPR-i.

  15. Comparison of phase velocities from array measurements of Rayleigh waves associated with microtremor and results calculated from borehole shear-wave velocity profiles

    USGS Publications Warehouse

    Liu, Hsi-Ping; Boore, David M.; Joyner, William B.; Oppenheimer, David H.; Warrick, Richard E.; Zhang, Wenbo; Hamilton, John C.; Brown, Leo T.

    2000-01-01

    Shear-wave velocities (VS) are widely used for earthquake ground-motion site characterization. VS data are now largely obtained using borehole methods. Drilling holes, however, is expensive. Nonintrusive surface methods are inexpensive for obtaining VS information, but not many comparisons with direct borehole measurements have been published. Because different assumptions are used in data interpretation of each surface method and public safety is involved in site characterization for engineering structures, it is important to validate the surface methods by additional comparisons with borehole measurements. We compare results obtained from a particular surface method (array measurement of surface waves associated with microtremor) with results obtained from borehole methods. Using a 10-element nested-triangular array of 100-m aperture, we measured surface-wave phase velocities at two California sites, Garner Valley near Hemet and Hollister Municipal Airport. The Garner Valley site is located at an ancient lake bed where water-saturated sediment overlies decomposed granite on top of granite bedrock. Our array was deployed at a location where seismic velocities had been determined to a depth of 500 m by borehole methods. At Hollister, where the near-surface sediment consists of clay, sand, and gravel, we determined phase velocities using an array located close to a 60-m deep borehole where downhole velocity logs already exist. Because we want to assess the measurements uncomplicated by uncertainties introduced by the inversion process, we compare our phase-velocity results with the borehole VS depth profile by calculating fundamental-mode Rayleigh-wave phase velocities from an earth model constructed from the borehole data. For wavelengths less than ~2 times of the array aperture at Garner Valley, phase-velocity results from array measurements agree with the calculated Rayleigh-wave velocities to better than 11%. Measurement errors become larger for wavelengths 2

  16. Accuracy of velocity and shear rate measurements using pulsed Doppler ultrasound: a comparison of signal analysis techniques.

    PubMed

    Markou, C P; Ku, D N

    1991-01-01

    An experimental investigation was instituted to evaluate the performance of Doppler ultrasound signal processing techniques for measuring fluid velocity under well-defined flow conditions using a 10-MHz multigated pulsed ultrasound instrument. Conditions of fully developed flow in a rigid, circular tube were varied over a Reynolds number range between 500 and 8000. The velocity across the tube was determined using analog and digital zero crossing detectors and three digital spectrum estimators. Determination of the Doppler frequency from analog or digital zero crossing detectors gave accurate velocity values for laminar and moderately turbulent flow away from the wall (0.969 less than or equal to r less than or equal to 0.986). Three digital spectrum estimators, Fast Fourier Transform, Burg autoregressive method, and minimum variance method, were slightly more accurate than the zero crossing detector (0.984 less than or equal to r less than or equal to 0.994), especially at points close to the walls and with higher levels of turbulence. Steep velocity gradients and transit-time-effects from high velocities produced significantly larger errors in velocity measurement. Wall shear rate estimates were most precise when calculated using the position of the wall and two velocity points. The calculated wall shears were within 20%-30% of theoretically predicted values.

  17. Frictional Properties and Microstructure of Calcite-Rich Fault Gouges Sheared at Sub-Seismic Sliding Velocities

    NASA Astrophysics Data System (ADS)

    Verberne, B. A.; Spiers, C. J.; Niemeijer, A. R.; De Bresser, J. H. P.; De Winter, D. A. M.; Plümper, O.

    2014-10-01

    We report an experimental and microstructural study of the frictional properties of simulated fault gouges prepared from natural limestone (96 % CaCO3) and pure calcite. Our experiments consisted of direct shear tests performed, under dry and wet conditions, at an effective normal stress of 50 MPa, at 18-150 °C and sliding velocities of 0.1-10 μm/s. Wet experiments used a pore water pressure of 10 MPa. Wet gouges typically showed a lower steady-state frictional strength ( μ = 0.6) than dry gouges ( μ = 0.7-0.8), particularly in the case of the pure calcite samples. All runs showed a transition from stable velocity strengthening to (potentially) unstable velocity weakening slip above 80-100 °C. All recovered samples showed patchy, mirror-like surfaces marking boundary shear planes. Optical study of sections cut normal to the shear plane and parallel to the shear direction showed both boundary and inclined shear bands, characterized by extreme grain comminution and a crystallographic preferred orientation. Cross-sections of boundary shears, cut normal to the shear direction using focused ion beam—SEM, from pure calcite gouges sheared at 18 and 150 °C, revealed dense arrays of rounded, ~0.3 μm-sized particles in the shear band core. Transmission electron microscopy showed that these particles consist of 5-20 nm sized calcite nanocrystals. All samples showed evidence for cataclasis and crystal plasticity. Comparing our results with previous models for gouge friction, we suggest that frictional behaviour was controlled by competition between crystal plastic and granular flow processes active in the shear bands, with water facilitating pressure solution, subcritical cracking and intergranular lubrication. Our data have important implications for the depth of the seismogenic zone in tectonically active limestone terrains. Contrary to recent claims, our data also demonstrate that nanocrystalline mirror-like slip surfaces in calcite(-rich) faults are not

  18. A comparison of four geophysical methods for determining the shear wave velocity of soils

    USGS Publications Warehouse

    Anderson, N.; Thitimakorn, T.; Ismail, A.; Hoffman, D.

    2007-01-01

    The Missouri Department of Transportation (MoDOT) routinely acquires seismic cone penetrometer (SCPT) shear wave velocity control as part of the routine investigation of soils within the Mississippi Embayment. In an effort to ensure their geotechnical investigations are as effective and efficient as possible, the SCPT tool and several available alternatives (crosshole [CH]; multichannel analysis of surface waves [MASW]; and refraction microtremor [ReMi]) were evaluated and compared on the basis of field data acquired at two test sites in southeast Missouri. These four methods were ranked in terms of accuracy, functionality, cost, other considerations, and overall utility. It is concluded that MASW data are generally more reliable than SCPT data, comparable to quality ReMi data, and only slightly less accurate than CH data. However, the other advantages of MASW generally make it a superior choice over the CH, SCPT, and ReMi methods for general soil classification purposes to depths of 30 m. MASW data are less expensive than CH data and SCPT data and can normally be acquired in areas inaccessible to drill and SCPT rigs. In contrast to the MASW tool, quality ReMi data can be acquired only in areas where there are interpretable levels of "passive" acoustic energy and only when the geophone array is aligned with the source(s) of such energy.

  19. Measurements of Wall Shear Stress and Aortic Pulse Wave Velocity in Swine with Familial Hypercholesterolemia

    PubMed Central

    Wentland, Andrew L.; Wieben, Oliver; Shanmuganayagam, Dhanansayan; Krueger, Christian G.; Meudt, Jennifer J.; Consigny, Daniel; Rivera, Leonardo; McBride, Patrick E.; Reed, Jess D.; Grist, Thomas M.

    2014-01-01

    PURPOSE To assess measurements of pulse wave velocity (PWV) and wall shear stress (WSS) in a swine model of atherosclerosis. MATERIALS AND METHODS Nine familial hypercholesterolemic (FH) swine with angioplasty balloon catheter-induced atherosclerotic lesions to the abdominal aorta (injured group) and ten uninjured FH swine were evaluated with a 4D phase contrast (PC) MRI acquisition, as well as with radial and Cartesian 2D PC acquisitions, on a 3T MR scanner. PWV values were computed from the 2D and 4D PC techniques, compared between the injured and uninjured swine, and were validated against reference standard pressure probe-based PWV measurements. WSS values were also computed from the 4D PC MRI technique and compared between injured and uninjured groups. RESULTS PWV values were significantly greater in the injured than in the uninjured groups with the 4D PC MRI technique (p=0.03) and pressure probes (p=0.02). No significant differences were found in PWV between groups using the 2D PC techniques (p=0.75–0.83). No significant differences were found for WSS values between the injured and uninjured groups. CONCLUSION The 4D PC MRI technique provides a promising means of evaluating PWV and WSS in a swine model of atherosclerosis, providing a potential platform for developing the technique for the early detection of atherosclerosis. PMID:24964097

  20. Predominant Periods and Shear Wave Velocity an indicator for Sediment Thickness, Caracas, Venezuela

    NASA Astrophysics Data System (ADS)

    Rocabado, V.; Schmitz, M.

    2013-05-01

    Within the Caracas seismic microzoning project, carried out by Venezuelan Foundation for Seismological Research (FUNVISIS), more than 1500 single measurements of ambient noise have been done since mid-90's in order to determinate fundamental periods of soil. In this work we show the result of these single stations applying H/V analysis, with period values between 0.2s and 2.4s, we propose a new relationship to estimate sediment thickness from period values, including the effect of the surface sediment layers, considering the values of shear-wave velocities for the first 30 m (Vs30) and the Vs value of the sedimentary layer, just above bedrock. The results indicate that this relationship generates more accurate estimates of sediment thickness comparing with depth values from other geophysical methods; this relationship was calibrated with information from 4 depth boreholes in Caracas, obtaining accurate depth values. The main objective of this new relationship is consider local information of soils in other cities, for local relationships between periods and sediment thickness, to generate accurate sediment thickness estimates from environmental noise measurements within seismic microzoning projects in Venezuela's most important cities.

  1. Uncertainty Estimation of Shear-wave Velocity Structure from Bayesian Inversion of Microtremor Array Dispersion Data

    NASA Astrophysics Data System (ADS)

    Dosso, S. E.; Molnar, S.; Cassidy, J.

    2010-12-01

    Bayesian inversion of microtremor array dispersion data is applied, with evaluation of data errors and model parameterization, to produce the most-probable shear-wave velocity (VS) profile together with quantitative uncertainty estimates. Generally, the most important property characterizing earthquake site response is the subsurface VS structure. The microtremor array method determines phase velocity dispersion of Rayleigh surface waves from multi-instrument recordings of urban noise. Inversion of dispersion curves for VS structure is a non-unique and nonlinear problem such that meaningful evaluation of confidence intervals is required. Quantitative uncertainty estimation requires not only a nonlinear inversion approach that samples models proportional to their probability, but also rigorous estimation of the data error statistics and an appropriate model parameterization. A Bayesian formulation represents the solution of the inverse problem in terms of the posterior probability density (PPD) of the geophysical model parameters. Markov-chain Monte Carlo methods are used with an efficient implementation of Metropolis-Hastings sampling to provide an unbiased sample from the PPD to compute parameter uncertainties and inter-relationships. Nonparametric estimation of a data error covariance matrix from residual analysis is applied with rigorous a posteriori statistical tests to validate the covariance estimate and the assumption of a Gaussian error distribution. The most appropriate model parameterization is determined using the Bayesian information criterion (BIC), which provides the simplest model consistent with the resolving power of the data. Parameter uncertainties are found to be under-estimated when data error correlations are neglected and when compressional-wave velocity and/or density (nuisance) parameters are fixed in the inversion. Bayesian inversion of microtremor array data is applied at two sites in British Columbia, the area of highest seismic risk in

  2. Two-component laser Doppler anemometer for measurement of velocity and turbulent shear stress near prosthetic heart valves.

    PubMed

    Woo, Y R; Yoganathan, A P

    1985-01-01

    The velocity and turbulent shear stress measured in the immediate vicinity of prosthetic heart valves play a vital role in the design and evaluation of these devices. In the past hot wire/film and one-component laser Doppler anemometer (LDA) systems were used extensively to obtain these measurements. Hot wire/film anemometers, however, have some serious disadvantages, including the inability to measure the direction of the flow, the disturbance of the flow field caused by the probe, and the need for frequent calibration. One-component LDA systems do not have these problems, but they cannot measure turbulent shear stresses directly. Since these measurements are essential and are not available in the open literature, a two-component LDA system for measuring velocity and turbulent shear stress fields under pulsatile flow conditions was assembled under an FDA contract. The experimental methods used to create an in vitro data base of velocity and turbulent shear stress fields in the immediate vicinity of prosthetic heart valves of various designs in current clinical use are also discussed.

  3. Predicting the liquefaction phenomena from shear velocity profiling: Empirical approach to 6.3 Mw, May 2006 Yogyakarta earthquake

    SciTech Connect

    Hartantyo, Eddy; Brotopuspito, Kirbani S.; Sismanto; Waluyo

    2015-04-24

    The liquefactions phenomena have been reported after a shocking 6.5Mw earthquake hit Yogyakarta province in the morning at 27 May 2006. Several researchers have reported the damage, casualties, and soil failure due to the quake, including the mapping and analyzing the liquefaction phenomena. Most of them based on SPT test. The study try to draw the liquefaction susceptibility by means the shear velocity profiling using modified Multichannel Analysis of Surface Waves (MASW). This paper is a preliminary report by using only several measured MASW points. The study built 8-channel seismic data logger with 4.5 Hz geophones for this purpose. Several different offsets used to record the high and low frequencies of surface waves. The phase-velocity diagrams were stacked in the frequency domain rather than in time domain, for a clearer and easier dispersion curve picking. All codes are implementing in Matlab. From these procedures, shear velocity profiling was collected beneath each geophone’s spread. By mapping the minimum depth of shallow water table, calculating PGA with soil classification, using empirical formula for saturated soil weight from shear velocity profile, and calculating CRR and CSR at every depth, the liquefaction characteristic can be identify in every layer. From several acquired data, a liquefiable potential at some depth below water table was obtained.

  4. Predicting the liquefaction phenomena from shear velocity profiling: Empirical approach to 6.3 Mw, May 2006 Yogyakarta earthquake

    NASA Astrophysics Data System (ADS)

    Hartantyo, Eddy; Brotopuspito, Kirbani S.; Sismanto, Waluyo

    2015-04-01

    The liquefactions phenomena have been reported after a shocking 6.5Mw earthquake hit Yogyakarta province in the morning at 27 May 2006. Several researchers have reported the damage, casualties, and soil failure due to the quake, including the mapping and analyzing the liquefaction phenomena. Most of them based on SPT test. The study try to draw the liquefaction susceptibility by means the shear velocity profiling using modified Multichannel Analysis of Surface Waves (MASW). This paper is a preliminary report by using only several measured MASW points. The study built 8-channel seismic data logger with 4.5 Hz geophones for this purpose. Several different offsets used to record the high and low frequencies of surface waves. The phase-velocity diagrams were stacked in the frequency domain rather than in time domain, for a clearer and easier dispersion curve picking. All codes are implementing in Matlab. From these procedures, shear velocity profiling was collected beneath each geophone's spread. By mapping the minimum depth of shallow water table, calculating PGA with soil classification, using empirical formula for saturated soil weight from shear velocity profile, and calculating CRR and CSR at every depth, the liquefaction characteristic can be identify in every layer. From several acquired data, a liquefiable potential at some depth below water table was obtained.

  5. Effect of rotor meridional velocity ratio on response to inlet radial and circumferential distortion

    NASA Technical Reports Server (NTRS)

    Sanger, N. L.

    1979-01-01

    Three single transonic fan stages, each having a different meridional velocity ratio across its rotor, were tested with two magnitudes of tip radial distortion and with a 90 deg circumferential distortion imposed on the inlet flow. The rotor with the lowest meridional velocity ratio (less than 0.9 at the tip) demonstrated the least degradation of performance due to these distortions. Loss and deviation angle data (as needed for performance prediction with radial distortion) calculated along actual streamlines for radially distorted flow and correlated against diffusion factor, showed consistent agreement with data calculated along design streamlines for undistorted flow.

  6. Rayleigh-wave phase-velocity maps and three-dimensional shear velocity structure of the western US from local non-plane surface wave tomography

    USGS Publications Warehouse

    Pollitz, F.F.; Snoke, J. Arthur

    2010-01-01

    We utilize two-and-three-quarter years of vertical-component recordings made by the Transportable Array (TA) component of Earthscope to constrain three-dimensional (3-D) seismic shear wave velocity structure in the upper 200 km of the western United States. Single-taper spectral estimation is used to compile measurements of complex spectral amplitudes from 44 317 seismograms generated by 123 teleseismic events. In the first step employed to determine the Rayleigh-wave phase-velocity structure, we implement a new tomographic method, which is simpler and more robust than scattering-based methods (e.g. multi-plane surface wave tomography). The TA is effectively implemented as a large number of local arrays by defining a horizontal Gaussian smoothing distance that weights observations near a given target point. The complex spectral-amplitude measurements are interpreted with the spherical Helmholtz equation using local observations about a succession of target points, resulting in Rayleigh-wave phase-velocity maps at periods over the range of 18–125 s. The derived maps depend on the form of local fits to the Helmholtz equation, which generally involve the nonplane-wave solutions of Friederich et al. In a second step, the phase-velocity maps are used to derive 3-D shear velocity structure. The 3-D velocity images confirm details witnessed in prior body-wave and surface-wave studies and reveal new structures, including a deep (>100 km deep) high-velocity lineament, of width ∼200 km, stretching from the southern Great Valley to northern Utah that may be a relic of plate subduction or, alternatively, either a remnant of the Mojave Precambrian Province or a mantle downwelling. Mantle seismic velocity is highly correlated with heat flow, Holocene volcanism, elastic plate thickness and seismicity. This suggests that shallow mantle structure provides the heat source for associated magmatism, as well as thinning of the thermal lithosphere, leading to relatively high

  7. Near Surface Shear Wave Velocity Model of the Sacramento-San Joaquin Delta

    NASA Astrophysics Data System (ADS)

    Shuler, S.; Craig, M. S.; Hayashi, K.; Galvin, J. L.; Deqiang, C.; Jones, M. G.

    2015-12-01

    Multichannel analysis of surface wave measurements (MASW) and microtremor array measurements (MAM) were performed at twelve sites across the Sacramento-San Joaquin Delta to obtain high resolution shear wave velocity (VS) models. Deeper surveys were performed at four of the sites using the two station spatial autocorrelation (SPAC) method. For the MASW and MAM surveys, a 48-channel seismic system with 4.5 Hz geophones was used with a 10-lb sledgehammer and a metal plate as a source. Surveys were conducted at various locations on the crest of levees, the toe of the levees, and off of the levees. For MASW surveys, we used a record length of 2.048 s, a sample interval of 1 ms, and 1 m geophone spacing. For MAM, ambient noise was recorded for 65.536 s with a sampling interval of 4 ms and 1 m geophone spacing. VS was determined to depths of ~ 20 m using the MASW method and ~ 40 m using the MAM method. Maximum separation between stations in the two-station SPAC surveys was typically 1600 m to 1800 m, providing coherent signal with wavelengths in excess of 5 km and depth penetration of as much as 2000 m. Measured values of VS30 in the study area ranged from 97 m/s to 257 m/s, corresponding to NEHRP site classifications D and E. Comparison of our measured velocity profiles with available geotechnical logs, including soil type, SPT, and CPT, reveals the existence of a small number of characteristic horizons within the upper 40m in the Delta: levee fill material, peat, transitional silty sand, and eolian sand at depth. Sites with a peat layer at the surface exhibited extremely low values of VS. Based on soil borings, the thickness of peat layers were approximately 0 m to 8 m. The VS for the peat layers ranged from 42 m/s to 150 m/s while the eolian sand layer exhibited VS ranging from of 220 m/s to 370 m/s. Soft near surface soils present in the region pose an increased earthquake hazard risk due to the potential for high ground accelerations.

  8. Velocity measurement on Taylor Couette flow of a magnetic fluid with small aspect ratio

    NASA Astrophysics Data System (ADS)

    Kikura, Hiroshige; Aritomi, Masanori; Takeda, Yasushi

    2005-03-01

    In this paper, the application of ultrasonic velocity profile (UVP) method to investigate magnetic-fluids flow is described. The objective of the research is to measure the internal flow of a magnetic fluid on Taylor-Couette flow with small aspect ratio using the UVP method and to analyze the influence of the applied magnetic field. The flow structure of a magnetic fluid in a concentric annular geometry with a small aspect ratio of 3 and a radius ratio of 0.6 for an inner-cylinder rotation was investigated. Axial velocity distributions were measured using the UVP measurement technique. A non-uniform magnetic field was applied to the flow field using a permanent magnet, located outside of the cylinders. The results demonstrated that the UVP method was capable to provide the information on the structure of Taylor-Couette flow with small aspect ratio, in a magnetic fluid.

  9. Lateral heterogeneity scales in regional and global upper mantle shear velocity models

    NASA Astrophysics Data System (ADS)

    Meschede, Matthias; Romanowicz, Barbara

    2015-02-01

    We analyse the lateral heterogeneity scales of recent upper mantle tomographic shear velocity (Vs) global and regional models. Our goal is to constrain the spherical harmonics power spectrum over the largest possible range of scales to get an estimate of the strength and statistical distribution of both long and small-scale structure. We use a spherical multitaper method to obtain high quality power spectral estimates from the regional models. After deconvolution of the employed taper functions, we combine global and regional spectral estimates from scales of 20 000 to around 200 km (degree 100). In contrast to previous studies that focus on linear power spectral densities, we interpret the logarithmic power per harmonic degree l as heterogeneity strength at a particular depth and horizontal scale. Throughout the mantle, we observe in recent global models, that their low degree spectrum is anisotropic with respect to Earth's rotation axis. We then constrain the uppermost mantle spectrum from global and regional models. Their power spectra transfer smoothly into each other in overlapping spectral bands, and model correlation is in general best in the uppermost 250 km (i.e. the `heterosphere'). In Europe, we see good correlation from the largest scales down to features of about 500 km. Detailed analysis and interpretation of spectral shape in this depth range shows that the heterosphere has several characteristic length scales and varying spectral decay rates. We interpret these as expressions of different physical processes. At larger depths, the correlation between different models drops, and the power spectrum exhibits strong small scale structure whose location and strength is not as well resolved at present. The spectrum also has bands with elevated power that likely correspond to length scales that are enhanced due to the inversion process.

  10. Record of Cyclical Massive Upwellings from the Pacific Large Low Shear Velocity Province in the Mesozoic

    NASA Astrophysics Data System (ADS)

    Gazel, E.; Madrigal, P.; Flores, K. E.; Bizimis, M.; Jicha, B. R.

    2016-12-01

    Global tomography and numerical models suggest that mantle plume occurrences are closely linked to the margins of the large low shear velocity provinces (LLSVPs). In these locations the ascent of material from the core-mantle boundary connects the deep Earth with surface processes through mantle plume activity, forming large igneous provinces (LIPs) and some of the modern hotspot volcanoes. Petrological and geodynamic evidence suggest a link between the formation of oceanic plateaus and the interactions of mantle plumes and mid-ocean ridges (MOR). Therefore, it is possible to trace the potential interactions between MORs and deep mantle plume upwellings by referencing the tectonic and magmatic evolution of the Pacific Plate in time to the current location of the LLSVP, considering the long-lived ( 500 Ma) existence of these thermochemical anomalies. We identified episodic upwellings of the Pacific LLSVP during the Mesozoic separated by 10 to 20 Ma, by reconstructing the kinematic evolution of the Pacific Plate in the last 170 Ma. The fact that the bulk emplacement of LIPs ( 120-80 Ma) in the Pacific coincides with the timing of the Cretaceous Normal Superchron, that can be related to fluctuations of mantle-core heat fluxes further supports the hypothesis of deep mantle origin for LIPs. The potential cyclicity of LIP emplacement could be tied to core heat fluctuations interacting with the lower mantle, the rheology contrast of material crossing the transition zone (either upwelling hot material or downgoing dense slabs as mantle avalanches), the rate of entrainment of recycled materials, or a combination of the processes mentioned. Recognizing patterns and possible cycles is crucial to the link between deep processes and life as these pulses impacted the marine biota resulting in episodes of anoxia and mass extinctions shortly after their eruption.

  11. Shear wave velocity mapping of Hat Yai district, southern Thailand: implication for seismic site classification

    NASA Astrophysics Data System (ADS)

    Yordkayhun, Sawasdee; Sujitapan, Chedtaporn; Chalermyanont, Tanit

    2015-02-01

    Soil characteristics play an important role in the degree of ground shaking due to local site amplification during an earthquake. The objectives of this work are to study shear wave velocity (Vs) distribution in the near surface, and to develop a seismic site classification map for soil effect characterization and seismic hazard assessment in Hat Yai district, southern Thailand. The Vs determination based on the multichannel analysis of surface waves technique, has been carried out and analyzed at 70 measuring sites throughout the district. On the basis of the weighted-average Vs in the upper 30 m depth (Vs30), a seismic site classification map, based on the National Earthquake Hazards Reduction Program (NEHRP) standard has been developed. It is found that the NEHRP site class in Hat Yai can be classified into four groups in accordance with the value of Vs30 within the range of about 150 to 1160 m s-1. Most parts of the study area are typically classified as site class C and D. Site class C is mostly found within the colluvial and terrace deposits in the western and eastern part of the area, whereas site class D is concentrated in the alluvial sediment of the middle and northern flood plain areas. A small portion of site class B is observed in the western mountain ranges, where there is a thin overburden on the firm rock. There is a remarkably low Vs30 value at only one site, located near the main stream in the northern part of the study area. The results imply that the soil characteristics in the central and northern Hat Yai district pose a medium to high amplification rate with respect to the other regions. Although Vs data alone are insufficient to verify the potential of the amplification of ground shaking, this study provides an initial attempt to understand seismic hazards in the study area.

  12. Low shear velocities in the sub-lithospheric mantle beneath the Indian shield?

    NASA Astrophysics Data System (ADS)

    Kumar, M. Ravi; Saikia, Dipankar; Singh, Arun; Srinagesh, D.; Baidya, P. R.; Dattatrayam, R. S.

    2013-03-01

    Ever since its breakup from the Gondwanaland ~140 Myr ago, the Indian plate was ravaged by four hot spots. Although the surface manifestations of such deep processes are evident in terms of large igneous provinces like the Deccan and the fast drift of the Indian plate, the modifications to the deep structure remain to be grasped. In this study, we investigate the mantle transition zone (TZ) structure beneath the Indian shield region using ~14,000 teleseismic receiver functions from 77 broadband stations sited on diverse geologic terrains. The arrival times of the P-to-s (Ps) conversions from the 410 km discontinuity at most cratonic stations appear to be delayed by ~2 s in comparison with the times observed for other Precambrian shield regions like Africa, Australia, and Canada. Such delays in the conversions from the 410 km discontinuity below the Indian shield suggest low shear wave speeds in the lithospheric and sub-lithospheric mantles due to higher temperatures, together with a thinner high velocity lid that contrasts with a thicker one found beneath most Archean cratons. A thin transition zone beneath most of the cratonic stations lends support to the enhanced temperatures within the TZ itself. Also, a further delay of the TZ discontinuities is observed for stations on the southern granulite terrain, which was under the influence of the Marion plume that is responsible for the separation of Madagascar from India. Although the data do not conclusively show evidence for a 520 km discontinuity, an LVL atop the 410 cannot be ruled out beneath certain geological provinces of the Indian shield.

  13. Is cerebroplacental ratio a marker of impaired fetal growth velocity and adverse pregnancy outcome?

    PubMed

    Khalil, Asma; Morales-Rosello, José; Khan, Naila; Nath, Mintu; Agarwal, Priya; Bhide, Amar; Papageorghiou, Aris; Thilaganathan, Basky

    2017-06-01

    The cerebroplacental ratio has been proposed as a marker of failure to reach growth potential near term. Low cerebroplacental ratio, regardless of the fetal size, is independently associated with the need for operative delivery for presumed fetal compromise and with neonatal unit admission at term. The main aim of this study was to evaluate whether the cerebroplacental ratio at term is a marker of reduced fetal growth rate. The secondary aim was to investigate the relationship between a low cerebroplacental ratio at term, reduced fetal growth velocity, and adverse pregnancy outcome. This was a retrospective cohort study of singleton pregnancies in a tertiary referral center. The abdominal circumference was measured at 20-24 weeks' gestation and both abdominal circumference and fetal Dopplers recorded at or beyond 35 weeks, within 2 weeks of delivery. Abdominal circumference and birthweight values were converted into Z scores and centiles, respectively, and fetal Doppler parameters into multiples of median, adjusting for gestational age. Abdominal circumference growth velocity was quantified using the difference in the abdominal circumference Z score, comparing the scan at or beyond 35 weeks with the scan at 20-24 weeks. Both univariable and multivariable logistic regression analyses were performed to investigate the association between low cerebroplacental ratio and the low abdominal circumference growth velocity (in the lowest decile) and to identify and adjust for potential confounders. As a sensitivity analysis, we refitted the model excluding the data on pregnancies with small-for-gestational-age neonates. The study included 7944 pregnancies. Low cerebroplacental ratio multiples of median was significantly associated with both low abdominal circumference growth velocity (adjusted odds ratio, 2.10; 95% confidence interval, 1.71-2.57, P <0.001) and small for gestational age (adjusted odds ratio, 3.60; 95% confidence interval, 3.04-4.25, P < .001). After the

  14. Deep ReMi Imaging - Mapping Shear-Wave Velocities to 1 km Depth and Greater Using Refraction Microtremor

    NASA Astrophysics Data System (ADS)

    Louie, J. N.; Pancha, A.; Munger, D.; Law, C.; Adams, D.; Mick, T. M.; Pullammanappallil, S. K.

    2016-12-01

    The Refraction Microtremor (ReMi) surface-wave technique, in use since 2002, has become a standard tool for assessing urban shear-wave velocities for engineering applications. ReMi is effective for site-class studies as well as assessing ground conditions, including 1D and 2D velocity-depth profiling to shallow depths of approximately 100 m. Over the last few years, we have successfully extended the application of the method to depths greater than 1 km. The use of deep ReMi, which relies primarily on ambient noise, for estimation of shear-wave velocities to kilometer depths, allows for mapping the thickness and velocity of deep urban basins. Accurate 3D modeling and calibration of recorded earthquake ground motions in urban areas is one use of deep ReMi results. Such models have the potential to be an essential part of seismic hazard evaluation. We present results from several deep ReMi studies conducted in the Reno-area and Tahoe basins of Nevada and California. Wireless instruments coupled with low-frequency geophones deployed in 3-km-long arrays across the densely populated urban environment acquired data in 2012, 2014, and 2015. In addition to mapping basement as deep as 900 m, the lateral velocity variations reveal deep-seated fault structure in the initial studies. A study of the Reno-area basin in 2016 employed arrays of 90 IRIS-PASSCAL Texans, 15 and 22 km long. This data set appears to constrain a sub-basin interface between Tertiary volcanics and Mesozoic basement at 1-2 km depth. Characterization of shear velocity at greater than 100 m depth, to basement, along with previously unknown faults, is vital towards quantifying earthquake ground motion and seismic hazard potential in geologically complex urban basins. Our measurements will allow Nevada communities to become more resilient against natural hazards.

  15. Heat transfer, velocity-temperature correlation, and turbulent shear stress from Navier-Stokes computations of shock wave/turbulent boundary layer interaction flows

    NASA Technical Reports Server (NTRS)

    Wang, C. R.; Hingst, W. R.; Porro, A. R.

    1991-01-01

    The properties of 2-D shock wave/turbulent boundary layer interaction flows were calculated by using a compressible turbulent Navier-Stokes numerical computational code. Interaction flows caused by oblique shock wave impingement on the turbulent boundary layer flow were considered. The oblique shock waves were induced with shock generators at angles of attack less than 10 degs in supersonic flows. The surface temperatures were kept at near-adiabatic (ratio of wall static temperature to free stream total temperature) and cold wall (ratio of wall static temperature to free stream total temperature) conditions. The computational results were studied for the surface heat transfer, velocity temperature correlation, and turbulent shear stress in the interaction flow fields. Comparisons of the computational results with existing measurements indicated that (1) the surface heat transfer rates and surface pressures could be correlated with Holden's relationship, (2) the mean flow streamwise velocity components and static temperatures could be correlated with Crocco's relationship if flow separation did not occur, and (3) the Baldwin-Lomax turbulence model should be modified for turbulent shear stress computations in the interaction flows.

  16. Developments in the Use of Proximity and Ratio Cues in Velocity Judgments.

    ERIC Educational Resources Information Center

    Shire, Beatrice; Durkin, Kevin

    Young children's responses to a velocity inference task based on static pictorial stimuli giving cues of proximity and ratio were examined. Subjects (N=65) in preschool through second grade viewed pictures of snails moving horizontally or spiders suspended vertically and were asked to estimate which competitor would reach its destination first.…

  17. Developments in the Use of Proximity and Ratio Cues in Velocity Judgments.

    ERIC Educational Resources Information Center

    Shire, Beatrice; Durkin, Kevin

    Young children's responses to a velocity inference task based on static pictorial stimuli giving cues of proximity and ratio were examined. Subjects (N=65) in preschool through second grade viewed pictures of snails moving horizontally or spiders suspended vertically and were asked to estimate which competitor would reach its destination first.…

  18. Reynolds shear stress near its maxima, turbulent bursting process and associated velocity profle in a turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Afzal, Noor

    2014-11-01

    The Reynolds shear stress around maxima, turbulent bursting process and associate velocity profile in ZGP turbulent boundary layer is considered in the intermediate layer/mesolayer proposed by Afzal (1982 Ing. Arch. 53, 355-277), in addition to inner and outer layers. The intermediate length scale δm = δRτ- 1 / 2 having velocity Um = mUe with 1 / 2 <= m <= 2 / 3 where Ue is velocity at boundary layer edge. Long & Chen (1981 JFM) intermediate layer/ mesolayer scale δm = δRτ- 1 / 2 with velocity Um the friction velocity uτ, is untenable assumption (Afzal 1984 AIAA J). For channel/pipe flow, Sreenivasan et al. (1981989, 1997, 2006a,b) proposed critical layer / mesolayer, cited/adopted work Long and Chen and McKeon, B.J. & Sharma, A. 2010 JFM 658, page 370 stated ``retaining the assumption that the critical layer occurs when U (y) = (2 / 3) UCL (i.e. that the critical layer scales with y+ ~Rτ+ 2 / 3),'' both untenable assumptions, but ignored citation of papers Afzal 1982 onwards on pipe flow. The present turbulent boundary layer work shows that Reynolds shear maxima, shape factor and turbulent bursting time scale with mesolayer variables and Taylor length/time scale. Residence, Embassy Hotel Rasal Gang Aligarh 202001 UP India.

  19. Shear wave velocity and attenuation in the upper layer of ocean bottoms from long-range acoustic field measurements.

    PubMed

    Zhou, Ji-Xun; Zhang, Xue-Zhen

    2012-12-01

    Several physics-based seabed geoacoustic models (including the Biot theory) predict that compressional wave attenuation α(2) in sandy marine sediments approximately follows quadratic frequency dependence at low frequencies, i.e., α(2)≈kf(n) (dB/m), n=2. A recent paper on broadband geoacoustic inversions from low frequency (LF) field measurements, made at 20 locations around the world, has indicated that the frequency exponent of the effective sound attenuation n≈1.80 in a frequency band of 50-1000 Hz [Zhou et al., J. Acoust. Soc. Am. 125, 2847-2866 (2009)]. Carey and Pierce hypothesize that the discrepancy is due to the inversion models' neglect of shear wave effects [J. Acoust. Soc. Am. 124, EL271-EL277 (2008)]. The broadband geoacoustic inversions assume that the seabottom is an equivalent fluid and sound waves interact with the bottom at small grazing angles. The shear wave velocity and attenuation in the upper layer of ocean bottoms are estimated from the LF field-inverted effective bottom attenuations using a near-grazing bottom reflection expression for the equivalent fluid model, derived by Zhang and Tindle [J. Acoust. Soc. Am. 98, 3391-3396 (1995)]. The resultant shear wave velocity and attenuation are consistent with the SAX99 measurement at 25 Hz and 1000 Hz. The results are helpful for the analysis of shear wave effects on long-range sound propagation in shallow water.

  20. Studies of Shear Band Velocity Using Spatially and Temporally Resolved Measurements of Strain During Quasistatic Compression of Bulk Metallic Glass

    SciTech Connect

    Wright, W J; Samale, M; Hufnagel, T; LeBlanc, M; Florando, J

    2009-06-15

    We have made measurements of the temporal and spatial features of the evolution of strain during the serrated flow of Pd{sub 40}Ni{sub 40}P{sub 20} bulk metallic glass tested under quasistatic, room temperature, uniaxial compression. Strain and load data were acquired at rates of up to 400 kHz using strain gages affixed to all four sides of the specimen and a piezoelectric load cell located near the specimen. Calculation of the displacement rate requires an assumption about the nature of the shear displacement. If one assumes that the entire shear plane displaces simultaneously, the displacement rate is approximately 0.002 m/s. If instead one assumes that the displacement occurs as a localized propagating front, the velocity of the front is approximately 2.8 m/s. In either case, the velocity is orders of magnitude less than the shear wave speed ({approx}2000 m/s). The significance of these measurements for estimates of heating in shear bands is discussed.

  1. Shear velocity structure beneath the central United States: implications for the origin of the Illinois Basin and intraplate seismicity

    NASA Astrophysics Data System (ADS)

    Chen, Chen; Gilbert, Hersh; Andronicos, Christopher; Hamburger, Michael W.; Larson, Timothy; Marshak, Stephen; Pavlis, Gary L.; Yang, Xiaotao

    2016-03-01

    We present new estimates of lithospheric shear velocities for the intraplate seismic zones and the Illinois Basin in the U.S. midcontinent by analyzing teleseismic Rayleigh waves. We find that relatively high crustal shear velocities (VS) characterize the southern Illinois Basin, while relatively low crustal velocities characterize the middle and lower crust of the central and northern Illinois Basin. The observed high crustal velocities may correspond to high-density mafic intrusions emplaced into the crust during the development of the Reelfoot Rift, which may have contributed to the subsidence of the Illinois Basin. The low crustal VS beneath the central and northern basin follow the La Salle deformation belt. We also observe relatively low velocities in the mantle beneath the New Madrid seismic zone where VS decreases by about 7% compared to those outside of the rift. The low VS in the upper mantle also extends beneath the Wabash Valley and Ste. Genevieve seismic zones. Testing expected VS reductions based on plausible thermal heterogeneities for the midcontinent indicates that the 7% velocity reduction would not result from elevated temperatures alone. Instead this scale of anomaly requires a contribution from some combination of increased iron and water content. Both rifting and interaction with a mantle plume could introduce these compositional heterogeneities. Similar orientations for the NE-SW low-velocity zone and the Reelfoot Rift suggest a rift origin to the reduced velocities. The low VS upper mantle represents a weak region and the intraplate seismic zones would correspond to concentrated crustal deformation above weak mantle.

  2. Shear velocity structure of crust and uppermost mantle in China from surface wave tomography using ambient noise and earthquake data

    NASA Astrophysics Data System (ADS)

    Xu, Zhen J.; Song, Xiaodong; Zheng, Sihua

    2013-10-01

    We present a 3D model of shear velocity of crust and upper mantle in China and surrounding regions from surface wave tomography. We combine dispersion measurements from ambient noise correlation and traditional earthquake data. The stations include the China National Seismic Network, global networks, and all the available PASSCAL stations in the region over the years. The combined data sets provide excellent data coverage of the region for surface wave measurements from 8 to 120 s, which are used to invert for 3D shear wave velocity structure of the crust and upper mantle down to about 150 km. We also derive new models of the study region for crustal thickness and averaged S velocities for upper, mid, and lower crust and the uppermost mantle. The models provide a fundamental data set for understanding continental dynamics and evolution. The tomography results reveal significant features of crust and upper mantle structure, including major basins, Moho depth variation, mantle velocity contrast between eastern and western North China Craton, widespread low-velocity zone in mid-crust in much of the Tibetan Plateau, and clear velocity contrasts of the mantle lithosphere between north and southern Tibet with significant E- W variations. The low velocity structure in the upper mantle under north and eastern TP correlates with surface geological boundaries. A patch of high velocity anomaly is found under the eastern part of the TP, which may indicate intact mantle lithosphere. Mantle lithosphere shows striking systematic change from the western to eastern North China Craton. The Tanlu Fault appears to be a major lithosphere boundary.

  3. Lithospheric Shear Velocity Structure of South Island, New Zealand from Rayleigh Wave Tomography of Amphibious Array Data

    NASA Astrophysics Data System (ADS)

    Ball, J. S.; Sheehan, A. F.; Stachnik, J. C.; Lin, F. C.; Collins, J. A.

    2015-12-01

    We present the first 3D shear velocity model extending well offshore of New Zealand's South Island, imaging the lithosphere beneath Campbell and Challenger plateaus. Our model is constructed via linearized inversion of both teleseismic (18 -70 s period) and ambient noise-based (8 - 25 s period) Rayleigh wave dispersion measurements. We augment an array of 29 ocean-bottom instruments deployed off the South Island's east and west coasts in 2009-2010 with 28 New Zealand land-based seismometers. The ocean-bottom seismometers and 4 of the land seismometers were part of the Marine Observations of Anisotropy Near Aotearoa (MOANA) experiment, and the remaining land seismometers are from New Zealand's permanent GeoNet array. Major features of our shear wave velocity (Vs) model include a low-velocity (Vs<4.3km/s) body extending to at least 75km depth beneath the Banks and Otago peninsulas, a high-velocity (Vs~4.7km/s) upper mantle anomaly underlying the Southern Alps to a depth of 100km, and discontinuous lithospheric velocity structure between eastern and western Challenger Plateau. Using the 4.5km/s contour as a proxy for the lithosphere-asthenosphere boundary, our model suggests that the lithospheric thickness of Challenger Plateau is substantially greater than that of Campbell Plateau. The high-velocity anomaly we resolve beneath the central South Island exhibits strong spatial correlation with subcrustal earthquake hypocenters along the Alpine Fault (Boese et al., 2013). The ~400km-long low velocity zone we image beneath eastern South Island underlies Cenozoic volcanics and mantle-derived helium observations (Hoke et al., 2000) on the surface. The NE-trending low-velocity zone dividing Challenger Plateau in our model underlies a prominent magnetic discontinuity (Sutherland et al., 1999). The latter feature has been interpreted to represent a pre-Cretaceous crustal boundary, which our results suggest may involve the entire mantle lithosphere.

  4. Ultrasonic shear wave velocity in CLF/CMT graphite from room temperature to 2000/sup 0/F

    SciTech Connect

    Gieske, J.H.

    1980-11-01

    The temperature dependence of the ultrasonic shear velocity in CLF/CMT graphite was determined from room temperature to 2000/sup 0/F using a pulse-echo technique. Data are presented for five 0.75-inch-diameter specimens all machined from the same CLF/CMT billet. Plots of ultrasonic pulse-echo radial and axial scans of the billet which characterize the material property uniformity of the billet are also given.

  5. Shallow velocity structure and Poisson's ratio at the Tarzana, California, strong-motion accelerometer site

    USGS Publications Warehouse

    Catchings, R.D.; Lee, W.H.K.

    1996-01-01

    The 17 January 1994, Northridge, California, earthquake produced strong ground shaking at the Cedar Hills Nursery (referred to here as the Tarzana site) within the city of Tarzana, California, approximately 6 km from the epicenter of the mainshock. Although the Tarzana site is on a hill and is a rock site, accelerations of approximately 1.78 g horizontally and 1.2 g vertically at the Tarzana site are among the highest ever instrumentally recorded for an earthquake. To investigate possible site effects at the Tarzana site, we used explosive-source seismic refraction data to determine the shallow (<70 m) P- and S-wave velocity structure. Our seismic velocity models for the Tarzana site indicate that the local velocity structure may have contributed significantly to the observed shaking. P-wave velocities range from 0.9 to 1.65 km/sec, and S-wave velocities range from 0.20 and 0.6 km/sec for the upper 70 m. We also found evidence for a local S-wave low-velocity zone (LVZ) beneath the top of the hill. The LVZ underlies a CDMG strong-motion recording site at depths between 25 and 60 m below ground surface (BGS). Our velocity model is consistent with the near-surface (<30 m) P- and S-wave velocities and Poisson's ratios measured in a nearby (<30 m) borehole. High Poisson's ratios (0.477 to 0.494) and S-wave attenuation within the LVZ suggest that the LVZ may be composed of highly saturated shales of the Modelo Formation. Because the lateral dimensions of the LVZ approximately correspond to the areas of strongest shaking, we suggest that the highly saturated zone may have contributed to localized strong shaking. Rock sites are generally considered to be ideal locations for site response in urban areas; however, localized, highly saturated rock sites may be a hazard in urban areas that requires further investigation.

  6. Sediment and Crustal Shear Velocity Structure offshore New Zealand from Seafloor Compliance, Receiver Functions and Rayleigh Wave Dispersion

    NASA Astrophysics Data System (ADS)

    Ball, J. S.; Sheehan, A. F.; Stachnik, J. C.; Lin, F.; Collins, J. A.

    2013-12-01

    We have developed a joint Monte Carlo inversion of teleseismic receiver functions, seafloor compliance, and Rayleigh wave dispersion and apply it here to ocean bottom seismic (OBS) data from offshore New Zealand. With this method we estimate sediment and crustal thickness and shear velocity structure beneath the Bounty Trough and the Tasman Sea flanking the South Island of New Zealand. Teleseismic receiver functions and surface wave dispersion measurements provide complementary constraints on shear velocity structure and interface depths beneath seismic stations. At ocean bottom seismic (OBS) stations the interpretation of these measurements is complicated by strong sediment reverberations that obscure deeper impedance contrasts such as the Moho. In principle, the seafloor's response to ocean loading from infragravity waves (seafloor compliance) can be used to determine shallow shear velocity information. This velocity information can subsequently be used to better model the receiver function reverberations, allowing deeper interfaces of tectonic interest to be resolved. Data for this study were acquired in 2009-2010 by the Marine Observations of Anisotropy Near Aotearoa (MOANA) experiment, which deployed 30 broadband OBS and differential pressure gauges (DPGs) off the South Island of New Zealand. High-frequency (5Hz) receiver functions were estimated using multitaper cross-correlation for events in a 30-90 degree epicentral distance range. Coherence-weighted stacks binned by epicentral distance were produced in the frequency domain to suppress noise. Seafloor compliance was measured using multitaper pressure and acceleration spectra averaged from 120 days of continuous data without large transient events. Seafloor compliance measurements on the order of 10-9 Pa-1 are sensitive to shear velocity structure in the uppermost 5km of the crust and sediments. Rayleigh dispersion measurements were obtained at periods of 6-27s from ambient noise cross correlation. Sediment

  7. Shear wave velocity, seismic attenuation, and thermal structure of the continental upper mantle

    USGS Publications Warehouse

    Artemieva, I.M.; Billien, M.; Leveque, J.-J.; Mooney, W.D.

    2004-01-01

    Seismic velocity and attenuation anomalies in the mantle are commonly interpreted in terms of temperature variations on the basis of laboratory studies of elastic and anelastic properties of rocks. In order to evaluate the relative contributions of thermal and non-thermal effects on anomalies of attenuation of seismic shear waves, QS-1, and seismic velocity, VS, we compare global maps of the thermal structure of the continental upper mantle with global QS-1 and Vs maps as determined from Rayleigh waves at periods between 40 and 150 S. We limit the comparison to three continental mantle depths (50, 100 and 150 km), where model resolution is relatively high. The available data set does not indicate that, at a global scale, seismic anomalies in the upper mantle are controlled solely by temperature variations. Continental maps have correlation coefficients of <0.56 between VS and T and of <0.47 between QS and T at any depth. Such low correlation coefficients can partially be attributed to modelling arrefacts; however, they also suggest that not all of the VS and QS anomalies in the continental upper mantle can be explained by T variations. Global maps show that, by the sign of the anomaly, VS and QS usually inversely correlate with lithospheric temperatures: most cratonic regions show high VS and QS and low T, while most active regions have seismic and thermal anomalies of the opposite sign. The strongest inverse correlation is found at a depth of 100 km, where the attenuation model is best resolved. Significantly, at this depth, the contours of near-zero QS anomalies approximately correspond to the 1000 ??C isotherm, in agreement with laboratory measurements that show a pronounced increase in seismic attenuation in upper mantle rocks at 1000-1100 ??C. East-west profiles of VS, QS and T where continental data coverage is best (50??N latitude for North America and 60??N latitude for Eurasia) further demonstrate that temperature plays a dominant, but non-unique, role in

  8. Investigation of Ultrasound-Measured Flow Velocity, Flow Rate and Wall Shear Rate in Radial and Ulnar Arteries Using Simulation.

    PubMed

    Zhou, Xiaowei; Xia, Chunming; Stephen, Gandy; Khan, Faisel; Corner, George A; Hoskins, Peter R; Huang, Zhihong

    2017-05-01

    Parameters of blood flow measured by ultrasound in radial and ulnar arteries, such as flow velocity, flow rate and wall shear rate, are widely used in clinical practice and clinical research. Investigation of these measurements is useful for evaluating accuracy and providing knowledge of error sources. A method for simulating the spectral Doppler ultrasound measurement process was developed with computational fluid dynamics providing flow-field data. Specific scanning factors were adjusted to investigate their influence on estimation of the maximum velocity waveform, and flow rate and wall shear rate were derived using the Womersley equation. The overestimation in maximum velocity increases greatly (peak systolic from about 10% to 30%, time-averaged from about 30% to 50%) when the beam-vessel angle is changed from 30° to 70°. The Womersley equation was able to estimate flow rate in both arteries with less than 3% error, but performed better in the radial artery (2.3% overestimation) than the ulnar artery (15.4% underestimation) in estimating wall shear rate. It is concluded that measurements of flow parameters in the radial and ulnar arteries with clinical ultrasound scanners are prone to clinically significant errors. Copyright © 2017. Published by Elsevier Inc.

  9. Propagation of Scholte Waves in deep water in a seafloor with power-law shear velocity depth dependence.

    NASA Astrophysics Data System (ADS)

    Dorman, L. M.

    2015-12-01

    The seafloor plays an important role in the propagation ofseafloor noise because its low shear velocity forms a strongwaveguide and the high shear velocity gradient facilitatesconversion processes.In 2001 (JASA), O. A. Godin and D. M.F. Chapman studiedpropagation of interface (Scholte) waves in models with ashear speed profile with a power-law depth dependence.They analyzed of four datasets from shallow-watersites, which they fit well with two-parameter models.Furthermore, they show that for the exponent value of1/2, the mode wavefunctions are self-similar.Data from the deep seafloor from seafloor sources observedby Ocean-Bottom Seismographs frequently exhibit afundamental mode ending in an Airy phase with a frequencyof a few Hertz. This is, of course,, incompatiblewith self-similarity. Adjusting the power-law shear velocityprofile near the water interface, however, improvesthe fit of this simple model with a parsimoniousparameterization to data from the the deep seafloor.Approximation of a power-law model using thin layers ofuniform velocity is eased by using an editor with aninteractive graphical user interface.

  10. Measurements of velocity and wall shear stress inside a PTFE vascular graft model under steady flow conditions.

    PubMed

    Loth, F; Jones, S A; Giddens, D P; Bassiouny, H S; Glagov, S; Zarins, C K

    1997-05-01

    The flow field inside a model of a polytetrafluorethylene (PTFE) canine artery end-to-side bypass graft was studied under steady flow conditions using laser-Doppler anemometry. The anatomically realistic in vitro model was constructed to incorporate the major geometric features of the in vivo canine anastomosis geometry, most notably a larger graft than host artery diameter. The velocity measurements at Reynolds number 208, based on the host artery diameter, show the flow field to be three dimensional in nature. The wall shear stress distribution, computed from the near-wall velocity gradients, reveals a relatively low wall shear stress region on the wall opposite to the graft near the stagnation point approximately one artery diameter in axial length at the midplane. This low wall shear stress region extends to the sidewalls, suture lines, and along the PTFE graft where its axial length at the midplane is more than two artery diameters. The velocity distribution inside the graft model presented here provides a data set well suited for validation of numerical solutions on a model of this type.

  11. Variation of Crustal Shear Velocity Structure Along the Eastern Lau Back-Arc Spreading Center Constrained By Seafloor Compliance

    NASA Astrophysics Data System (ADS)

    Zha, Y.; Webb, S. C.; Dunn, R. A.

    2014-12-01

    Measurements of seafloor compliance, the deformation under long period (typically 30-300 s) ocean wave forcing, are primarily sensitive to crustal shear velocity structure. We analyze seafloor compliance from data collected from a subset of 50 broadband Ocean Bottom Seismographs (OBS) deployed at the Eastern Lau spreading center (ELSC) from 2009 to 2010. The ELSC is a 400-km-long back-arc spreading center lying closely to the Tonga subduction trench in the southwestern Pacific. Seafloor morphology, crustal seismic structure and lava composition data show rapid variations along the ridge as the ridge migrates away from the volcanic arc front to the north, indicating a decreasing influence of the subducting slab. We calculate seafloor compliance functions by taking the spectral transfer function between the vertical displacement and pressure signal recorded by the 4-component OBSs, which are equipped with differential pressure gauges (DPGs). In the ridge perpendicular direction, compliance amplitude vary by more than an order of magnitude from the ridge crest to older seafloor covered by sediment. Along the spreading ridge, compliance measured from on-axis sites increases southwards, indicative of a decrease in the upper crustal shear velocity possibly due to increasing porosity and a thickening extrusive layer [Jacobs et al., 2007; Dunn et al., 2013]. We apply a Markov Chain Monte Carlo method to invert the compliance functions for crustal shear velocities at various locations along the ELSC.

  12. Performance of a transonic fan stage designed for a low meridional velocity ratio

    NASA Technical Reports Server (NTRS)

    Moore, R. D.; Lewis, G. W., Jr.; Osborn, W. M.

    1978-01-01

    The aerodynamic performance and design parameters of a transonic fan stage are presented. The fan stage was designed for a meridional velocity ratio of 0.8 across the tip of the stage, a pressure ratio of 1.57, a flow of 29.5 kilograms per second, and a tip speed of 426 meters per second. Radial surveys were obtained over the stable operating range from 50 to 100 percent of design speed. The measured, peak efficiency (0.81) of the stage occurred at a pressure ratio of 1.58 and a flow of 28.7 kilograms per second.

  13. Poisson's ratio from polarization of acoustic zero-group velocity Lamb mode.

    PubMed

    Baggens, Oskar; Ryden, Nils

    2015-07-01

    Poisson's ratio of an isotropic and free elastic plate is estimated from the polarization of the first symmetric acoustic zero-group velocity Lamb mode. This polarization is interpreted as the ratio of the absolute amplitudes of the surface normal and surface in-plane components of the acoustic mode. Results from the evaluation of simulated datasets indicate that the presented relation, which links the polarization and Poisson's ratio, can be extended to incorporate plates with material damping. Furthermore, the proposed application of the polarization is demonstrated in a practical field case, where an increased accuracy of estimated nominal thickness is obtained.

  14. On the Derivation of a High-Velocity Tail from the Boltzmann-Fokker-Planck Equation for Shear Flow

    NASA Astrophysics Data System (ADS)

    Acedo, L.; Santos, A.; Bobylev, A. V.

    2002-12-01

    Uniform shear flow is a paradigmatic example of a nonequilibrium fluid state exhibiting non-Newtonian behavior. It is characterized by uniform density and temperature and a linear velocity profile U x ( y)= ay, where a is the constant shear rate. In the case of a rarefied gas, all the relevant physical information is represented by the one-particle velocity distribution function f( r, v)= f( V), with V≡ v- U( r), which satisfies the standard nonlinear integro-differential Boltzmann equation. We have studied this state for a two-dimensional gas of Maxwell molecules with a collision rate K( θ)∝lim ∈→0 ∈ -2 δ( θ- ∈), where θ is the scattering angle, in which case the nonlinear Boltzmann collision operator reduces to a Fokker-Planck operator. We have found analytically that for shear rates larger than a certain threshold value a th≃0.3520 ν (where ν is an average collision frequency and a th/ ν is the real root of the cubic equation 64 x 3+16 x 2+12 x-9=0) the velocity distribution function exhibits an algebraic high-velocity tail of the form f( V; a)˜| V|-4- σ( a) Φ( ϕ; a), where ϕ≡tan V y / V x and the angular distribution function Φ( ϕ; a) is the solution of a modified Mathieu equation. The enforcement of the periodicity condition Φ( ϕ; a)= Φ( ϕ+ π; a) allows one to obtain the exponent σ( a) as a function of the shear rate. It diverges when a→ a th and tends to a minimum value σ min≃1.252 in the limit a→∞. As a consequence of this power-law decay for a> a th, all the velocity moments of a degree equal to or larger than 2+ σ( a) are divergent. In the high-velocity domain the velocity distribution is highly anisotropic, with the angular distribution sharply concentrated around a preferred orientation angle ~ϕ( a), which rotates from ~ϕ=- π/4,3 π/4 when a→ a th to ~ϕ=0, π in the limit a→∞.

  15. On the modal damping ratios of shear-type structures equipped with Rayleigh damping systems

    NASA Astrophysics Data System (ADS)

    Trombetti, T.; Silvestri, S.

    2006-04-01

    The effects of added manufactured viscous dampers upon shear-type structures are analytically investigated here for the class of Rayleigh damping systems. The definitions of mass proportional damping (MPD) and stiffness proportional damping (SPD) systems are briefly recalled and their physical counterpart is derived. From basic physics, a detailed mathematical demonstration that the first modal damping ratio of a structure equipped with the MPD system is always larger than the first modal damping ratio of a structure equipped with the SPD system is provided here. All results are derived for the class of structures characterised by constant values of lateral stiffness and storey mass, under the equal "total size" constraint. The paper also provides closed form demonstrations of other properties of modal damping ratios which further indicate that the MPD and the SPD systems are respectively characterised by the largest and the smallest damping efficiency among Rayleigh damping systems subjected to base excitation. A numerical application with realistic data corresponding to an actual seven-storey building structure is presented to illustrate and verify the theoretical findings.

  16. Ratio of shear viscosity to entropy density in generalized theories of gravity

    SciTech Connect

    Brustein, Ram; Medved, A. J. M.

    2009-01-15

    Near the horizon of a black brane solution in anti-de Sitter space, the long-wavelength fluctuations of the metric exhibit hydrodynamic behavior. For Einstein's theory, the ratio of the shear viscosity of near-horizon metric fluctuations {eta} to the entropy per unit of transverse volume s is {eta}/s=1/4{pi}. We propose that, in generalized theories of gravity, this ratio is given by the ratio of two effective gravitational couplings and can be different than 1/4{pi}. Our proposal confirms that {eta}/s is equal to 1/4{pi} for any theory that can be transformed into Einstein's theory, such as F(R) gravity. Our proposal also implies that matter interactions--except those including explicit or implicit factors of the Riemann tensor--will not modify {eta}/s. The proposed formula reproduces, in a very simple manner, some recently found results for Gauss-Bonnet gravity. We also make a prediction for {eta}/s in Lovelock theories of any order or dimensionality.

  17. Shear Wave Velocity Structure of Southern African Crust: Evidence for Compositional Heterogeneity within Archaean and Proterozoic Terrains

    SciTech Connect

    Kgaswane, E M; Nyblade, A A; Julia, J; Dirks, P H H M; Durrheim, R J; Pasyanos, M E

    2008-11-11

    Crustal structure in southern Africa has been investigated by jointly inverting receiver functions and Rayleigh wave group velocities for 89 broadband seismic stations spanning much of the Precambrian shield of southern Africa. 1-D shear wave velocity profiles obtained from the inversion yield Moho depths that are similar to those reported in previous studies and show considerable variability in the shear wave velocity structure of the lower part of the crust between some terrains. For many of the Archaean and Proterozoic terrains in the shield, S velocities reach 4.0 km/s or higher over a substantial part of the lower crust. However, for most of the Kimberley terrain and adjacent parts of the Kheis Province and Witwatersrand terrain, as well as for the western part of the Tokwe terrain, mean shear wave velocities of {le} 3.9 km/s characterize the lower part of the crust along with slightly ({approx}5 km) thinner crust. These findings indicate that the lower crust across much of the shield has a predominantly mafic composition, except for the southwest portion of the Kaapvaal Craton and western portion of the Zimbabwe Craton, where the lower crust is intermediate-to-felsic in composition. The parts of the Kaapvaal Craton underlain by intermediate-to-felsic lower crust coincide with regions where Ventersdorp rocks have been preserved, and thus we suggest that the intermediate-to-felsic composition of the lower crust and the shallower Moho may have resulted from crustal melting during the Ventersdorp tectonomagmatic event at c. 2.7 Ga and concomitant crustal thinning caused by rifting.

  18. Determination of the full elastic moduli of single crystals using shear-wave velocities by Brillouin spectroscopy

    NASA Astrophysics Data System (ADS)

    Fan, D.; Mao, Z.; Lin, J.; Yang, J.

    2013-12-01

    Brillouin light scattering (BLS) is the inelastic scattering of monochromatic laser light by phonons in the GHz frequency range [1]. BLS spectroscopy can be used to measure sound velocities traveling along certain directions of a single crystal through the frequency shifts of the scattered light from the acoustic phonons [1]. Over the past few decades, BLS spectroscopy has been widely used to measure the velocities of acoustic waves for a wide range of Earth's materials, in which the full elastic constants were derived from the measured compressional (VP) and shear wave (VS) velocities. However, the VP velocities of minerals normally overlap with the shear-wave velocities of diamonds in Brillouin measurements approximately above 25 GPa [2-5] such that only VS of minerals can be measured experimentally. Theoretical models have showed that the shear-wave velocities of minerals also carry necessary information to invert the full elastic tensors [2], although previous studies at high pressures have focused on measuring velocities within the principle planes of the crystals. This leads to a strong trade-off among individual Cij, preventing the derivation of the full elastic tensors from the VS velocities alone [3-5]. In this study, we have come up with an elastic model to overcome this problem by finding a suitable crystallographic plane that has optimized VS-VP interactions in the elastic tensors. Using MgO, spinel and zoisite as test samples, we have used measured VP/VS or VS velocities of these crystals using BLS spectroscopy to derive their full elastic tensors. This new approach sheds lights on future high-pressure elasticity studies relevant to materials the Earth's deep interior. 1. Sinogeikin, S.V., Bass, J.D., Phys. Earth Planet. Inter., 120, 43 (2000). 2. Every, A. G., Phys. Rev. B., 22, 1746, (1980) 3. Marquardt, H., Speziale, S., Reichmann, H.J., Frost, D.J., and Schilling, F.R., Earth Planet. Sci. Lett., 287, 345 (2009). 4. Marquardt, H., Speziale, S

  19. Shear-wave velocity structure of the Tongariro Volcanic Centre, New Zealand: Fast Rayleigh and slow Love waves indicate strong shallow anisotropy

    NASA Astrophysics Data System (ADS)

    Godfrey, Holly J.; Fry, Bill; Savage, Martha K.

    2017-04-01

    Models of the velocity structure of volcanoes can help define possible magma pathways and contribute to calculating more accurate earthquake locations, which can help with monitoring volcanic activity. However, shear-wave velocity of volcanoes is difficult to determine from traditional seismic techniques, such as local earthquake tomography (LET) or refraction/reflection surveys. Here we use the recently developed technique of noise cross correlation of continuous seismic data to investigate the subsurface shear-wave velocity structure of the Tongariro Volcanic Centre (TgVC) of New Zealand, focusing on the active Ruapehu and Tongariro Volcanoes. We observe both the fundamental and first higher-order modes of Rayleigh and Love waves within our noise dataset, made from stacks of 15 min cross-correlation functions. We manually pick group velocity dispersion curves from over 1900 correlation functions, of which we consider 1373 to be high quality. We subsequently invert a subset of the fundamental mode Rayleigh- and Love-wave dispersion curves both independently and jointly for one dimensional shear-wave velocity (Vs) profiles at Ruapehu and Tongariro Volcanoes. Vs increases very slowly at a rate of approximately 0.2 km/s per km depth beneath Ruapehu, suggesting that progressive hydrothermal alteration mitigates the effects of compaction driven velocity increases. At Tongariro, we observe larger Vs increases with depth, which we interpret as different layers within Tongariro's volcanic system above altered basement greywacke. Slow Vs, on the order of 1-2 km/s, are compatible with P-wave velocities (using a Vp/Vs ratio of 1.7) from existing velocity profiles of areas within the TgVC, and the observations of worldwide studies of shallow volcanic systems that used ambient noise cross-correlation methods. Most of the measured group velocities of fundamental mode Love-waves across the TgVC are 0.1-0.4 km/s slower than those of fundamental mode Rayleigh-waves in the

  20. Shear velocity model for the westernmost Mediterranean from ambient noise and ballistic finite-frequency Rayleigh wave tomography

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    The westernmost Mediterranean comprises the Iberian Peninsula and Morocco, separated by the Alboran Sea and the Algerian Basin. From north to south this region consists of the Pyrenees, resulting from Iberia-Eurasia collision; the Iberian Massif, which has been undeformed since the end of the Paleozoic; the Central System and Iberian Chain, regions with intracontinental Oligocene-Miocene deformation; the Gibraltar Arc (Betics, Rif and Alboran terranes), resulting from post-Oligocene subduction roll-back; and the Atlas Mountains. We analyzed data from recent broad-band array deployments and permanent stations in the area (IberArray and Siberia arrays, the PICASSO array, the University of Munster array, and the Spanish, Portuguese and Moroccan National Networks) to characterize its lithospheric structure. The combined array of 350 stations has an average interstation spacing of ~60 km. We calculated the Rayleigh waves phase velocities from ambient noise (periods 4 to 40 s) and teleseismic events (periods 20 to 167 s). We inverted the phase velocities to obtain a shear velocity model for the lithosphere to ~200 km depth. Our results correlate well with the surface expression of the main structural units with higher crustal velocity for the Iberian Massif than for the Alpine Iberia and Atlas Mountains. The Gibraltar Arc has lower crustal shear velocities than the regional average at all crustal depths. It also shows an arc shaped anomaly with high upper mantle velocities (>4.6 km/s) at shallow depths (<65 km) interpreted as the subducting Alboran slab. The hanging slab is depressing the crust of the Gibraltar arc to ~55 km depth, as seen in receiver function data and active source seismic profiles. Low upper mantle velocities (<4.2 km/s) are observed beneath the Atlas, the northeastern end of the Betic Mountains and the Late Cenozoic volcanic fields in Iberia and Morocco, indicative of high temperatures at relatively shallow depths, and suggesting that the lithosphere

  1. A 3-D shear velocity model of the southern North American and Caribbean plates from ambient noise and earthquake tomography

    NASA Astrophysics Data System (ADS)

    Gaite, B.; Villaseñor, A.; Iglesias, A.; Herraiz, M.; Jiménez-Munt, I.

    2015-02-01

    We use group velocities from earthquake tomography together with group and phase velocities from ambient noise tomography (ANT) of Rayleigh waves to invert for the 3-D shear-wave velocity structure (5-70 km) of the Caribbean (CAR) and southern North American (NAM) plates. The lithospheric model proposed offers a complete image of the crust and uppermost-mantle with imprints of the tectonic evolution. One of the most striking features inferred is the main role of the Ouachita-Marathon-Sonora orogeny front on the crustal seismic structure of the NAM plate. A new imaged feature is the low crustal velocities along the USA-Mexico border. The model also shows a break of the east-west mantle velocity dichotomy of the NAM and CAR plates beneath the Isthmus of the Tehuantepec and the Yucatan Block. High upper-mantle velocities along the Mesoamerican Subduction Zone coincide with inactive volcanic areas while the lowest velocities correspond to active volcanic arcs and thin lithospheric mantle regions.

  2. Compositional layering within the large low shear-wave velocity provinces (LLSVPs) in the lower mantle

    NASA Astrophysics Data System (ADS)

    Ballmer, Maxim; Lekic, Vedran; Schumacher, Lina; Ito, Garrett; Thomas, Christine

    2016-04-01

    Seismic tomography reveals two antipodal LLSVPs in the Earth's mantle, each extending from the core-mantle boundary (CMB) up to ~1000 km depth. The LLSVPs are thought to host primordial mantle materials that bear witness of early-Earth processes, and/or subducted basalt that has accumulated in the mantle over billions of years. A compositional distinction between the LLSVPs and the ambient mantle is supported by anti-correlation of bulk-sound and shear-wave velocity (Vs) anomalies as well as abrupt lateral gradients in Vs along LLSVP margins. Both of these observations, however, are mainly restricted to the LLSVP bottom domains (2300~2900 km depth), or hereinafter referred to as "deep distinct domains" (DDD). Seismic sensitivity calculations suggest that DDDs are more likely to be composed of primordial mantle material than of basaltic material. On the other hand, the seismic signature of LLSVP shallow domains (1000~2300 km depth) is consistent with a basaltic composition, though a purely thermal origin cannot be ruled out. Here, we explore the dynamical, seismological, and geochemical implications of the hypothesis that the LLSVPs are compositionally layered with a primordial bottom domain (or DDD) and a basaltic shallow domain. We test this hypothesis using 2D thermochemical mantle-convection models. Depending on the density difference between primordial and basaltic materials, the materials either mix or remain separate as they join to form thermochemical piles in the deep mantle. Separation of both materials within these piles provides an explanation for LLSVP seismic properties, including substantial internal vertical gradients in Vs observed at 400-700 km height above the CMB, as well as out-of-plane reflections on LLSVP sides over a range of depths. Predicted geometry of thermochemical piles is compared to LLSVP and DDD shapes as constrained by seismic cluster analysis. Geodynamic models predict short-lived "secondary" plumelets to rise from LLSVP roofs and

  3. Frictional Behavior of Amphibolite at Seismic Slip Rates from High-velocity Rotary Shear Experiments

    NASA Astrophysics Data System (ADS)

    Jung, S.; Ree, J.; Hirose, T.; Lee, S.

    2012-12-01

    Gabbroic rocks of oceanic crust transform into amphibolite with depth at subduction zone, and thus frictional property of amphibolite may be important for a better understanding of subduction zone earthquakes. We report preliminary results of high-velocity rotary shear experiments on amphibolite at a seismic slip rate (~1.05 m/s) and normal stresses of 2-15 MPa. Amphibolite from the Imjingang belt of South Korea is composed of hornblende (0.5-1.5 mm) and plagioclase (0.25-0.5 mm) with rare occurrence of quartz. The frictional behavior of the amphibolite is characterized by two phases of unstable slip weakening separated by strengthening, followed by a final weakening with a very low steady-state friction coefficient of 0.07. The average coefficient of the first, second and final peak frictions is 0.48, 0.36 and 0.22, respectively. The fault zone consists of a principal slip zone (PSZ, 200-300 μm thick) with molten material mantled by damage zone (1-3 mm thick). In the damage zone, the color of hornblende grains becomes darker toward the PSZ and thin, black stripes occur along cleavage planes of hornblende in plane-polarized light. Also fracture density of hornblende and plagioclase increases relative to those of wall rock. The PSZ comprises molten material and mineral clasts (25-50 μm) and the clasts tend to concentrate along the center of the PSZ. The surface temperature of the fault zones measured by a radiation thermography during experiments is about 1060°C and the internal temperature of the fault zones could be higher than the measured temperature in view of the melting of hornblende and plagioclase. The frictional behavior of amphibolite is much different from that of gabbro where the overall friction is much higher with the final peak friction of 0.84-1.09 and steady-state friction of ~0.6 (Hirose and Shimamoto, 2005 in Journal of Geophysical Research). This difference may be due to dehydration of hornblende by frictional heating and lower viscosity of

  4. Compositional layering within the large low shear-wave velocity provinces (LLSVPs) in the lower mantle

    NASA Astrophysics Data System (ADS)

    Ballmer, M. D.; Lekic, V.; Thomas, C.; Schumacher, L.; Ito, G.

    2015-12-01

    Seismic tomography reveals two antipodal LLSVPs in the Earth's mantle, each extending from the core-mantle boundary (CMB) up to ~1000 km depth. The LLSVPs are thought to host primitive mantle materials that bear witness of early-Earth processes, and/or subducted basalt that has cumulated in the mantle over billions of years. A compositional distinction between the LLSVPs and the ambient mantle is supported by anti-correlation of bulk-sound and shear-wave velocity (Vs) anomalies as well as abrupt lateralgradients in Vs along LLSVP margins. Both of these observations, however, are mainly restricted to the LLSVP bottom domains (2300~2900 km depth). Comparison of seismic observations with mineral-physics data suggests that these bottom domains are more likely to be composed of primitive mantle than of basaltic material. On the other hand, the seismic signature of the LLSVP shallow domains (1000~2300 km depth) is consistent with a basaltic composition, though a purely thermal origin cannot be ruled out. Here, we explore the dynamical, seismological, and geochemical implications of the hypothesis that the LLSVPs are compositionally layered with a primitive bottom domain and a basaltic shallow domain (see Fig.). We test this hypothesis using 2D thermochemical mantle-convection models. Depending on the density difference between primitive and basaltic materials, the materials either mix or remain separate as they join to form thermochemical piles in the deep mantle. Separation of both materials within the piles provides an explanation for LLSVP seismic properties, including substantial internal vertical gradients in Vs observed at 400-700 km height above the CMB. Geodynamic models predict short-lived "secondary" plumelets to rise from the roofs of these compositionally layered piles while entraining basaltic material that has evolved in the lower mantle. Long-lived "primary" plumes rise from LLSVP margins and entrain a mix of materials, including small fractions of

  5. Shear wave velocity structure of the lower crust in southern Africa: Evidence for compositional heterogeneity within Archaean and Proterozoic terrains

    NASA Astrophysics Data System (ADS)

    Kgaswane, Eldridge M.; Nyblade, Andrew A.; Juliã, Jordi; Dirks, Paul H. G. M.; Durrheim, Raymond J.; Pasyanos, Michael E.

    2009-12-01

    The nature of the lower crust across the southern African shield has been investigated by jointly inverting receiver functions and Rayleigh wave group velocities for 89 broadband seismic stations located in Botswana, South Africa and Zimbabwe. For large parts of both Archaean and Proterozoic terrains, the velocity models obtained from the inversions show shear wave velocities ≥4.0 km/s below ˜20-30 km depth, indicating a predominantly mafic lower crust. However, for much of the Kimberley terrain and adjacent parts of the Kheis Province and Witwatersrand terrain in South Africa, as well as for the western part of the Tokwe terrain in Zimbabwe, shear wave velocities of ≤3.9 km/s are found below ˜20-30 km depth, indicating an intermediate-to-felsic lower crust. The areas of intermediate-to-felsic lower crust in South Africa coincide with regions where Ventersdorp rocks have been preserved, suggesting that the more evolved composition of the lower crust may have resulted from crustal reworking and extension during the Ventersdorp tectonomagmatic event at c. 2.7 Ga.

  6. Shear-wave Velocity Model from Rayleigh Wave Group Velocities Centered on the Sacramento/San Joaquin Delta

    NASA Astrophysics Data System (ADS)

    Fletcher, Jon B.; Erdem, Jemile

    2017-06-01

    Rayleigh wave group velocities obtained from ambient noise tomography are inverted for an upper crustal model of the Central Valley, California, centered on the Sacramento/San Joaquin Delta. Two methods were tried; the first uses SURF96, a least squares routine. It provides a good fit to the data, but convergence is dependent on the starting model. The second uses a genetic algorithm, whose starting model is random. This method was tried at several nodes in the model and compared to the output from SURF96. The genetic code is run five times and the variance of the output of all five models can be used to obtain an estimate of error. SURF96 produces a more regular solution mostly because it is typically run with a smoothing constraint. Models from the genetic code are generally consistent with the SURF96 code sometimes producing lower velocities at depth. The full model, calculated using SURF96, employed a 2-pass strategy, which used a variable damping scheme in the first pass. The resulting model shows low velocities near the surface in the Central Valley with a broad asymmetrical sedimentary basin located close to the western edge of the Central Valley near 122°W longitude. At shallow depths, the Rio Vista Basin is found nestled between the Pittsburgh/Kirby Hills and Midland faults, but a significant basin also seems to exist to the west of the Kirby Hills fault. There are other possible correlations between fast and slow velocities in the Central Valley and geologic features such as the Stockton Arch, oil or gas producing regions and the fault-controlled western boundary of the Central Valley.

  7. Inversion of Seismic Velocities to obtain the Crack and Pore Aspect Ratio Distribution

    NASA Astrophysics Data System (ADS)

    Zimmerman, R. W.; David, E. C.

    2010-12-01

    During a hydrostatic experiment, in the elastic regime, P and S elastic wave velocities measured on rock samples generally increase with pressure and reach asymptotic values at high pressures. This increase of seismic velocities with confining pressure is known to be caused by the closure of compliant pores, such as flat “cracks”, and therefore the high-pressure values of the velocities must reflect only the influence of stiff, “equant” pores. If the pores are assumed to be spheroids, the use of an effective medium theory, combined with a crack closure model, gives a model to relate the elastic properties to the microstructure at each pressure. Therefore, the pressure dependence of elastic velocities can be inverted to obtain the pore aspect ratio distribution. This is done more easily using data obtained in dry experiments, since pore fluids have a strong effect on velocities and to some extent mask the effect of the pore geometry. However, thus far most models have used restrictive assumptions, such as assuming that the stiff pores are spherical, or the interactions between inclusions can be neglected (such as Morlier’s method), which is unfortunately not realistic in most cases. Others methods, such as the one developed by Cheng and Toksoz (1979), assume that the rock contains a discrete distribution of crack aspect ratios, and are complicated to implement numerically. Moreover, in most work only the dry data have been inverted, or jointly the dry and wet data, but it seems that few works have tried to look in detail at a consistent pore model, that remains simple and is able to predict the dependence of Vp and Vs under saturated conditions, based on data collected on dry rocks. We assume that the rock contains a distribution of cracks with different aspect ratios, and two families of stiff pores, each with their own finite aspect ratio. We use this model to invert the wavespeeds to obtain aspect ratio distributions of some isotropic sandstones (Berea

  8. FULLY CONVECTIVE MAGNETO-ROTATIONAL TURBULENCE IN LARGE ASPECT-RATIO SHEARING BOXES

    SciTech Connect

    Bodo, G.; Rossi, P.; Cattaneo, F.; Mignone, A.

    2015-01-20

    We present a numerical study of turbulence and dynamo action in stratified shearing boxes with both finite and zero net magnetic flux. We assume that the fluid obeys the perfect gas law and has finite thermal diffusivity. The latter is chosen to be small enough so that vigorous convective states develop. The properties of these convective solutions are analyzed as the aspect ratio of the computational domain is varied and as the value of the mean field is increased. For the cases with zero net flux, we find that a well-defined converged state is obtained for large enough aspect ratios. In the converged state, the dynamo can be extremely efficient and can generate substantial toroidal flux. We identify solutions in which the toroidal field is mostly symmetric about the mid-plane and solutions in which it is mostly anti-symmetric. The symmetric solutions are found to be more efficient at transporting angular momentum and can give rise to a luminosity that is up to an order of magnitude larger than the corresponding value for the anti-symmetric states. In the cases with a finite net flux, the system appears to spend most of the time in the symmetric states.

  9. Aeolian Shear Stress Ratio Measurements within Mesquite-Dominated Landscapes of the Chihuahuan Desert, New Mexico, USA

    NASA Technical Reports Server (NTRS)

    King, James; Nickling, W. G.; Gilliles, J. A.

    2006-01-01

    A field study was conducted to ascertain the amount of protection that mesquite-dominated communities provide to the surface from wind erosion. The dynamics of the locally accelerated evolution of a mesquite/coppice dune landscape and the undetermined spatial dependence of potential erosion by wind from a shear stress partition model were investigated. Sediment transport and dust emission processes are governed by the amount of protection that can be provided by roughness elements. Although shear stress partition models exist that can describe this, their accuracy has only been tested against a limited dataset because instrumentation has previously been unable to provide the necessary measurements. This study combines the use of meteorological towers and surface shear stress measurements with Irwin sensors to measure the partition of shear stress in situ. The surface shear stress within preferentially aligned vegetation (within coppice dune development) exhibited highly skewed distributions, while a more homogenous surface stress was recorded at a site with less developed coppice dunes. Above the vegetation, the logarithmic velocity profile deduced roughness length (based on 10-min averages) exhibited a distinct correlation with compass direction for the site with vegetation preferentially aligned, while the site with more homogenously distributed vegetation showed very little variation in the roughness length. This distribution in roughness length within an area, defines a distribution of a resolved shear stress partitioning model based on these measurements, ultimately providing potential closure to a previously uncorrelated model parameter.

  10. Aeolian Shear Stress Ratio Measurements within Mesquite-Dominated Landscapes of the Chihuahuan Desert, New Mexico, USA

    NASA Technical Reports Server (NTRS)

    King, James; Nickling, W. G.; Gilliles, J. A.

    2006-01-01

    A field study was conducted to ascertain the amount of protection that mesquite-dominated communities provide to the surface from wind erosion. The dynamics of the locally accelerated evolution of a mesquite/coppice dune landscape and the undetermined spatial dependence of potential erosion by wind from a shear stress partition model were investigated. Sediment transport and dust emission processes are governed by the amount of protection that can be provided by roughness elements. Although shear stress partition models exist that can describe this, their accuracy has only been tested against a limited dataset because instrumentation has previously been unable to provide the necessary measurements. This study combines the use of meteorological towers and surface shear stress measurements with Irwin sensors to measure the partition of shear stress in situ. The surface shear stress within preferentially aligned vegetation (within coppice dune development) exhibited highly skewed distributions, while a more homogenous surface stress was recorded at a site with less developed coppice dunes. Above the vegetation, the logarithmic velocity profile deduced roughness length (based on 10-min averages) exhibited a distinct correlation with compass direction for the site with vegetation preferentially aligned, while the site with more homogenously distributed vegetation showed very little variation in the roughness length. This distribution in roughness length within an area, defines a distribution of a resolved shear stress partitioning model based on these measurements, ultimately providing potential closure to a previously uncorrelated model parameter.

  11. First principles study of the C/Si ratio effect on the ideal shear strength of β-SiC

    NASA Astrophysics Data System (ADS)

    Su, Wen; Li, Yingying; Nie, Chu; Xiao, Wei; Yan, Liqin

    2016-07-01

    The effect of the C/Si atomic ratio on the ideal shear strength of β-SiC is investigated with first principles calculations. β -SiC samples with different C/Si ratios are generated by Monte Carlo (MC) simulations with empirical inter-atomic SiC potential. Each SiC sample is sheared along the < 100> direction and the stress-strain curve is calculated from first principles. The results show that the ideal shear strength of SiC decreases with the increase of C/Si ratio. For a non-stoichiometric SiC sample, a C-C bond inside a large carbon cluster breaks first under shear strain condition due to the internal strain around the carbon clusters. Because the band gap is narrowed under shear strain conditions, a local maximum stress appears in the elastic region of the stress-strain curve for each SiC sample at certain strain condition. The yield strength may increase with the increase of C/Si ratio.

  12. Wall shear stress fluctuations: Mixed scaling and their effects on velocity fluctuations in a turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Diaz-Daniel, Carlos; Laizet, Sylvain; Vassilicos, J. Christos

    2017-05-01

    The present work investigates numerically the statistics of the wall shear stress fluctuations in a turbulent boundary layer (TBL) and their relation to the velocity fluctuations outside of the near-wall region. The flow data are obtained from a Direct Numerical Simulation (DNS) of a zero pressure-gradient TBL using the high-order flow solver Incompact3D [S. Laizet and E. Lamballais, "High-order compact schemes for incompressible flows: A simple and efficient method with quasi-spectral accuracy," J. Comput. Phys. 228(16), 5989 (2009)]. The maximum Reynolds number of the simulation is R e𝜃≈2000 , based on the free-stream velocity and the momentum thickness of the boundary layer. The simulation data suggest that the root-mean-squared fluctuations of the streamwise and spanwise wall shear-stress components τx and τz follow a logarithmic dependence on the Reynolds number, consistent with the empirical correlation of Örlü and Schlatter [R. Örlü and P. Schlatter, "On the fluctuating wall-shear stress in zero pressure-gradient turbulent boundary layer flows," Phys. Fluids 23, 021704 (2011)]. These functional dependencies can be used to estimate the Reynolds number dependence of the wall turbulence dissipation rate in good agreement with reference DNS data. Our results suggest that the rare negative events of τx can be associated with the extreme values of τz and are related to the presence of coherent structures in the buffer layer, mainly quasi-streamwise vortices. We also develop a theoretical model, based on a generalisation of the Townsend-Perry hypothesis of wall-attached eddies, to link the statistical moments of the filtered wall shear stress fluctuations and the second order structure function of fluctuating velocities at a distance y from the wall. This model suggests that the wall shear stress fluctuations may induce a higher slope in the turbulence energy spectra of streamwise velocities than the one predicted by the Townsend-Perry attached

  13. GAS EXCITATION IN ULIRGs: MAPS OF DIAGNOSTIC EMISSION-LINE RATIOS IN SPACE AND VELOCITY

    SciTech Connect

    Soto, Kurt T.; Martin, Crystal L.

    2012-11-15

    Emission-line spectra extracted at multiple locations across 39 ultraluminous infrared galaxies have been compiled into a spectrophotometric atlas. Line profiles of H{alpha}, [N II], [S II], [O I], H{beta}, and [O III] are resolved and fit jointly with common velocity components. Diagnostic ratios of these line fluxes are presented in a series of plots, showing how the Doppler shift, line width, gas excitation, and surface brightness change with velocity at fixed position and also with distance from the nucleus. One general characteristic of these spectra is the presence of shocked gas extending many kiloparsecs from the nucleus. In some systems, the rotation curves of the emitting gas indicate motions that suggest gas disks, which are most frequent at early merger stages. At these early merger stages, the emission line ratios indicate the presence of shocked gas, which may be triggered by the merger event. We also report the general characteristics of the integrated spectra.

  14. 3D isotropic shear wave velocity structure of the lithosphere-asthenosphere system underneath the Alpine-Mediterranean Mobile belt

    NASA Astrophysics Data System (ADS)

    El-Sharkawy, Amr; Weidle, Christian; Christiano, Luigia; Lebedev, Sergei; Meier, Thomas

    2017-04-01

    The Alpine-Mediterranean mobile belt is, tectonically, one of the most complicated and active regions in the world. Since the Mesozoic, collisions between Gondwana-derived continental blocks and Eurasia, due to the closure of a number of rather small ocean basins, have shaped the Mediterranean geology. During the late Mesozoic, it was dominated by subduction zones (e.g., in Anatolia, the Dinarides, the Carpathians, the Alps, the Apennines, and the Betics), which inverted the extensional regime, consuming the previously formed oceanic lithosphere, the adjacent passive continental margins and presumably partly also continental lithosphere. The location, distribution, and evolution of these subduction zones were mainly controlled by the continental or oceanic nature, density, and thickness of the lithosphere inherited from the Mesozoic rift after the European Variscan Orogeny. Despite the numerous studies that have attempted to characterize the lithosphere-asthenosphere structure in that area, details of the lithospheric structure and dynamics, as well as flow in the asthenosphere are, however, poorly known. A 3D shear-wave velocity structure of the lithosphere-asthenosphere system in the Mediterranean is investigated using new tomographic images obtained from surface wave tomography. An automated algorithm for inter-station phase velocity measurements is applied here to obtain both Rayleigh and Love fundamental mode phase velocities. We utilize a database consisting of more than 4000 seismic events recorded by more than 2000 broadband seismic stations within the area, provided by the European Integrated Data Archive (WebDc/EIDA) and IRIS. Moreover, for the first time, data from the Egyptian National Seismological Network (ENSN), recorded by up to 25 broad band seismic stations, are also included in the analysis. For each station pair, approximately located on the same great circle path, the recorded waveforms are cross correlated and the dispersion curves of

  15. Signal-to-noise ratio, contrast-to-noise ratio and their trade-offs with resolution in axial-shear strain elastography

    NASA Astrophysics Data System (ADS)

    Thitaikumar, Arun; Krouskop, Thomas A.; Ophir, Jonathan

    2007-01-01

    In axial-shear strain elastography, the local axial-shear strain resulting from the application of quasi-static axial compression to an inhomogeneous material is imaged. In this paper, we investigated the image quality of the axial-shear strain estimates in terms of the signal-to-noise ratio (SNRasse) and contrast-to-noise ratio (CNRasse) using simulations and experiments. Specifically, we investigated the influence of the system parameters (beamwidth, transducer element pitch and bandwidth), signal processing parameters (correlation window length and axial window shift) and mechanical parameters (Young's modulus contrast, applied axial strain) on the SNRasse and CNRasse. The results of the study show that the CNRasse (SNRasse) is maximum for axial-shear strain values in the range of 0.005-0.03. For the inclusion/background modulus contrast range considered in this study (<10), the CNRasse (SNRasse) is maximum for applied axial compressive strain values in the range of 0.005%-0.03%. This suggests that the RF data acquired during axial elastography can be used to obtain axial-shear strain elastograms, since this range is typically used in axial elastography as well. The CNRasse (SNRasse) remains almost constant with an increase in the beamwidth while it increases as the pitch increases. As expected, the axial shift had only a weak influence on the CNRasse (SNRasse) of the axial-shear strain estimates. We observed that the differential estimates of the axial-shear strain involve a trade-off between the CNRasse (SNRasse) and the spatial resolution only with respect to pitch and not with respect to signal processing parameters. Simulation studies were performed to confirm such an observation. The results demonstrate a trade-off between CNRasse and the resolution with respect to pitch.

  16. Signal-to-noise ratio, contrast-to-noise ratio and their trade-offs with resolution in axial-shear strain elastography.

    PubMed

    Thitaikumar, Arun; Krouskop, Thomas A; Ophir, Jonathan

    2007-01-07

    In axial-shear strain elastography, the local axial-shear strain resulting from the application of quasi-static axial compression to an inhomogeneous material is imaged. In this paper, we investigated the image quality of the axial-shear strain estimates in terms of the signal-to-noise ratio (SNR(asse)) and contrast-to-noise ratio (CNR(asse)) using simulations and experiments. Specifically, we investigated the influence of the system parameters (beamwidth, transducer element pitch and bandwidth), signal processing parameters (correlation window length and axial window shift) and mechanical parameters (Young's modulus contrast, applied axial strain) on the SNR(asse) and CNR(asse). The results of the study show that the CNR(asse) (SNR(asse)) is maximum for axial-shear strain values in the range of 0.005-0.03. For the inclusion/background modulus contrast range considered in this study (<10), the CNR(asse) (SNR(asse)) is maximum for applied axial compressive strain values in the range of 0.005%-0.03%. This suggests that the RF data acquired during axial elastography can be used to obtain axial-shear strain elastograms, since this range is typically used in axial elastography as well. The CNR(asse) (SNR(asse)) remains almost constant with an increase in the beamwidth while it increases as the pitch increases. As expected, the axial shift had only a weak influence on the CNR(asse) (SNR(asse)) of the axial-shear strain estimates. We observed that the differential estimates of the axial-shear strain involve a trade-off between the CNR(asse) (SNR(asse)) and the spatial resolution only with respect to pitch and not with respect to signal processing parameters. Simulation studies were performed to confirm such an observation. The results demonstrate a trade-off between CNR(asse) and the resolution with respect to pitch.

  17. The shear wave velocity of the upper mantle beneath the Bay of Bengal, Northeast Indian Ocean from interstation phase velocities of surface waves

    NASA Astrophysics Data System (ADS)

    Bhattacharya, S. N.; Mitra, Supriyo; Suresh, G.

    2013-06-01

    The Bay of Bengal evolved along the eastern margin of the Indian subcontinent about 130 Ma with the breakup of India from eastern Gondwanaland. Since then the Indian lithospheric Plate has moved northward, along with the Bay of Bengal, and eventually collided with the Eurasian Plate. The age of the lithosphere beneath the central Bay of Bengal is ˜110 Ma. We evaluate the shear wave velocity structure of the upper mantle beneath the central Bay through inversion of phase velocities of fundamental mode Rayleigh and Love waves along two wave paths: (i) between Port Blair (PBA) and VIS (Visakhapatnam) and (ii) between DGPR (Diglipur) and VIS. The seismological observatories PBA and DGPR are located on the Andaman Island and to the east of the Bay and the observatory at VIS in located on the eastern coast of India to the west of the Bay. Using broad-band records of earthquakes, which lie along the great circle arc joining each pair of observatories, we obtain phase velocities between 20 and 240 s periods for Rayleigh waves and between 23 and 170 s for Love waves. These phase velocities are inverted to find the S-wave velocity structure of the upper mantle down to 400 km. The crustal structure is based on previous studies of the Bay and kept fixed in the inversion. We obtain a radially anisotropic upper-mantle structure, where the SH-wave velocity (VSH) is greater than the SV-wave velocity (VSV) down to 400 km. The S-wave velocity decreases sharply by ˜4.5 per cent for VSV and ˜1.5 per cent for VSH at a depth 110 km, which is considered as the Lithosphere-Asthenosphere boundary (LAB), that is, the bottom of the mantle lid. Based on recent studies, such sharp fall of S-wave velocity below the mantle lid appears to indicate a partially molten thin layer (G-discontinuity) at this depth. The thickness of the mantle lid is intermediate between oceanic and continental regions. The lid is also characterized

  18. Study of the dynamic behavior of earthflows through the analysis of shear wave velocity in the landslide's body

    NASA Astrophysics Data System (ADS)

    Bertello, Lara

    2015-04-01

    Over the first year of my PhD, I carried out a literature search about earthflows features and dynamics and conducted periodic ReMi-MASW campaigns to assess the temporal variation of shear velocity for several landslides that were recently reactivated. Literature search was conducted to review recent works related to shear wave velocity as an indicator for rheological changes in clay materials (Mainsant et al., 2012). From January to August 2014 I carried out numerous ReMi-MASW surveys to characterize several active earthflows in the Emilia-Romagna Apennines. I did these measures both inside and outside the landslide's bodies, usually during the first ten days after the reactivation. At first, these measures indicate low shear waves velocity inside the landslide and high velocity outside. This is due to the different consistence of the materials, to the different water content and to the void index. Then I repeated the measures over time in the same places on the same landslide, in order to detect the variability of Vs over time in correlations with the landslide's movements. Periodic ReMi-MASW survey were conducted on the following landslides: • The Montevecchio (FC) earthflow was reactivated the 1th of February 2014 (estimated volume of 240.000 m³) and increased the movement's velocity around the 7th of February 2014, after intense precipitations. Analyzing the data collected inside the landslide's body, I observed an increase of Vs over time, due to the decrease of landslide velocity; • The Silla (BO) complex landslide reactivated the 10th of February 2014 (estimated volume of 900.000 m³), and moved downslope with a maximum velocity in the order of several m/hour. Studying the data, it is possible to notice how the Vs increase over time only in the lower portion of the landslide. In fact the upper portion is still active, so the Vs remained unchanged over time. • the Puzzola-Grizzana Morandi (BO) complex landslide. This landslide was reactivated the 10th

  19. Electrostatic drift-wave instability in a nonuniform quantum magnetoplasma with parallel velocity shear flows

    SciTech Connect

    Tariq, Sabeen; Mirza, Arshad M.; Masood, W.

    2010-10-15

    The propagation of high and low frequency (in comparison with the cyclotron frequency) electrostatic drift-waves is investigated in a nonuniform, dense magnetoplasma (composed of electrons and ions), in the presence of parallel shear flow, by employing the quantum magnetohydrodynamic (QMHD) model. Using QMHD model, a new set of equations is presented in order to investigate linear properties of electrostatic drift-waves with sheared plasma flows for dense plasmas. In this regard, dispersion relations for coupled electron-thermal and drift-ion acoustic modes are derived and several interesting limiting cases are discussed. For instance, it is found that sheared ion flow parallel to the external magnetic field can drive the quantum drift-ion acoustic wave unstable, etc. The present investigation may have relevance in dense astrophysical environments where quantum effects are significant.

  20. Feasibility of waveform inversion of Rayleigh waves for shallow shear-wave velocity using a genetic algorithm

    USGS Publications Warehouse

    Zeng, C.; Xia, J.; Miller, R.D.; Tsoflias, G.P.

    2011-01-01

    Conventional surface wave inversion for shallow shear (S)-wave velocity relies on the generation of dispersion curves of Rayleigh waves. This constrains the method to only laterally homogeneous (or very smooth laterally heterogeneous) earth models. Waveform inversion directly fits waveforms on seismograms, hence, does not have such a limitation. Waveforms of Rayleigh waves are highly related to S-wave velocities. By inverting the waveforms of Rayleigh waves on a near-surface seismogram, shallow S-wave velocities can be estimated for earth models with strong lateral heterogeneity. We employ genetic algorithm (GA) to perform waveform inversion of Rayleigh waves for S-wave velocities. The forward problem is solved by finite-difference modeling in the time domain. The model space is updated by generating offspring models using GA. Final solutions can be found through an iterative waveform-fitting scheme. Inversions based on synthetic records show that the S-wave velocities can be recovered successfully with errors no more than 10% for several typical near-surface earth models. For layered earth models, the proposed method can generate one-dimensional S-wave velocity profiles without the knowledge of initial models. For earth models containing lateral heterogeneity in which case conventional dispersion-curve-based inversion methods are challenging, it is feasible to produce high-resolution S-wave velocity sections by GA waveform inversion with appropriate priori information. The synthetic tests indicate that the GA waveform inversion of Rayleigh waves has the great potential for shallow S-wave velocity imaging with the existence of strong lateral heterogeneity. ?? 2011 Elsevier B.V.

  1. Pressure tensor in the presence of velocity shear: Stationary solutions and self-consistent equilibria

    SciTech Connect

    Cerri, S. S.; Pegoraro, F.; Califano, F.; Jenko, F.

    2014-11-15

    Observations and numerical simulations of laboratory and space plasmas in almost collisionless regimes reveal anisotropic and non-gyrotropic particle distribution functions. We investigate how such states can persist in the presence of a sheared flow. We focus our attention on the pressure tensor equation in a magnetized plasma and derive analytical self-consistent plasma equilibria which exhibit a novel asymmetry with respect to the magnetic field direction. These results are relevant for investigating, within fluid models that retain the full pressure tensor dynamics, plasma configurations where a background shear flow is present.

  2. Sperm dilution ratio affects post-thaw motility rate and velocity of Prochilodus lineatus (Characiformes) sperm.

    PubMed

    Viveiros, Ana T M; Leal, Marcelo C

    2016-10-01

    There is a lack of standardization in sperm cryopreservation of aquatic organisms and, thus, a necessity of more accurate investigations in all steps of this process. In this study, the effects of sperm dilution ratio on post-thaw sperm quality of Prochilodus lineatus were evaluated. Sperm was diluted in a standard freezing medium (glucose and methyl glycol) at four different ratios (sperm to final volume = 1:5, 1:10, 1:50 or 1:100), frozen in a nitrogen vapour vessel at -170°C and then stored in liquid nitrogen vessel at -196°C. Post-thaw motility rate and velocities (curvilinear = VCL; average path = VAP; straight line = VSL) were determined using a Computer-Assisted Sperm Analyzer (CASA) at 10 and 40 s post-activation. The highest motility rates were observed when sperm was frozen at a ratio of 1:5 (76%) and 1:10 (75%). The highest VCL (225 μm/s) and VAP (203 μm/s) were observed at a ratio of 1:10, while VSL was similar among samples frozen at 1:5, 1:10 and 1:50 (97-124 μm/s). When those parameters were evaluated again 30 s later, motility decreased significantly in samples frozen at a ratio of 1:5 (57%) and 1:10 (61%), while velocities decreased significantly in all samples regardless of dilution ratio (75-85 μm/s of VCL, 38-53 μm/s of VAP and 25-39 μm/s of VSL). P. lineatus sperm should be frozen at a ratio of 1:10, where both the number of loaded sperm per straw and the post-thaw quality are maximized.

  3. Shallow Shear Wave Velocity Structure of Adapazari (Turkey) Region by MASW And MAM Measurements and Some Implications

    NASA Astrophysics Data System (ADS)

    Ozcep, T.; Ozcep, F.; Ozel, O.

    2009-04-01

    Wave-propagation method to generate the near-surface Vs profile are called spectral analysis of surface waves that uses the spectral analysis of ground roll generated by an impulsive source and recorded by a pair of receivers. This method has been widely and effectively used in many shallow shear wave velocity structure. The 17 August 1999 Izmit earthquake (Mw=7.4) ruptured a 140 km segment of the North Anatolian Fault, extending from the Izmit bay in the west to Akyazi in the east, and caused about 20,000 loss of life and totally 20,000 collapsed buildings. In the study area, the shear wave velocities are obtained by multi channel analysis of surface wave for 100 points in study area. The phase velocity-dispersion curve for each point and shear wave velocity are obtained by inversion distance profile for first 50 meters of soil. The records that are depending on field conditions with different geophone intervals are taken. Passive source when it is compared by active source reaches deeper parts of soils, because the lower frequency of natural noises are recorded different noises that are given more information from the deeply distance. After the data are collected from the field, data-processing are carried out, the phase velocities for the different frequency are obtained by using a computer program and after the process dispersion curve is obtained. During the field studies, the seismic refraction data are also collected. The initial model that obtained from these data is used the initial model data. By using both forward and inverse solutions algorithm, S wave velocities are calculated and drown depending on distance. For 100 sites, soil classifications are mapped according to the Eurocode-8, UBC (NEHRP) and the Turkish Seismic Design Code. The site classification, based on Vs30 in seismic design codes, are compared with fundamental periods and amplification values that obtained by using real earthquake data obtained from region. This study was supported by

  4. A combined analysis of basaltic melting and shear wave velocity anomalies to constrain dynamic support of western North America

    NASA Astrophysics Data System (ADS)

    Klöcking, Marthe; White, Nicky; Maclennan, John; Fitton, Godfrey

    2017-04-01

    The region of western North America that encompasses the Basin and Range Province, the Snake River Plain and the Colorado Plateau is about 2 km higher than cratonic North America. This topographic difference broadly coincides with variations in lithospheric thickness (i.e. <120 km beneath Colorado Plateau, 220 km beneath the Great Plain). Thermochronologic observations from the Grand Canyon area, sedimentary flux estimates from the Gulf of Mexico, and inverse modeling of regional drainage networks together suggest that this regional uplift occurred during Cenozoic time in at least two discrete phases. Earthquake tomographic models have imaged low velocity material beneath the bulk of western North America, including a ring-shaped anomaly encompassing the Colorado Plateau itself. Basaltic magmatism coincides with these low velocity zones and indicates an overall increase in melt volume at 40 Ma, as well as an abrupt change from lithospheric to asthenospheric signatures at 5 Ma. To investigate the quantitative relationship between seismic velocity anomalies and basaltic magmatism, we have analyzed >260 samples from volcanic centers throughout western North America for major, trace and rare earth elements using ICP-MS and XRF techniques. For asthenospheric samples, we observe a correlation between slow shear wave velocity anomalies and basaltic geochemistry. Using a combination of petrologic observations, forward and inverse modeling of major and rare earth elements, and shear wave velocity anomalies from tomographic models, we determine depth of melting and melt fraction. We explore the possibility that volatiles, anomalous source composition and/or temperature can give rise to basaltic magmatism and regional uplift. We then calculate mantle temperatures from shear wave velocity profiles beneath each volcanic field. In this way, we exploit a variety of approaches to constrain lithospheric thickness and mantle potential temperature. Our combined geochemical and

  5. Ambient noise surface wave tomography to determine the shallow shear velocity structure at Valhall: depth inversion with a Neighbourhood Algorithm

    NASA Astrophysics Data System (ADS)

    Mordret, A.; Landès, M.; Shapiro, N. M.; Singh, S. C.; Roux, P.

    2014-09-01

    This study presents a depth inversion of Scholte wave group and phase velocity maps obtained from cross-correlation of 6.5 hr of noise data from the Valhall Life of Field Seismic network. More than 2 600 000 vertical-vertical component cross-correlations are computed from the 2320 available sensors, turning each sensor into a virtual source emitting Scholte waves. We used a traditional straight-ray surface wave tomography to compute the group velocity map. The phase velocity maps have been computed using the Eikonal tomography method. The inversion of these maps in depth are done with the Neighbourhood Algorithm. To reduce the number of free parameters to invert, geological a priori information are used to propose a power-law 1-D velocity profile parametrization extended with a gaussian high-velocity layer where needed. These parametrizations allowed us to create a high-resolution 3-D S-wave model of the first 600 m of the Valhall subsurface and to precise the locations of geological structures at depth. These results would have important implication for shear wave statics and monitoring of seafloor subsidence due to oil extraction. The 3-D model could also be a good candidate for a starting model used in full-waveform inversions.

  6. Factors governing hole expansion ratio of steel sheets with smooth sheared edge

    NASA Astrophysics Data System (ADS)

    Yoon, Jae Ik; Jung, Jaimyun; Lee, Hak Hyeon; Kim, Gyo-Sung; Kim, Hyoung Seop

    2016-11-01

    Stretch-flangeability measured using hole expansion test (HET) represents the ability of a material to form into a complex shaped component. Despite its importance in automotive applications of advanced high strength steels, stretch-flangeability is a less known sheet metal forming property. In this paper, we investigate the factors governing hole expansion ratio (HER) by means of tensile test and HET. We correlate a wide range of tensile properties with HERs of steel sheet specimens because the stress state in the hole edge region during the HET is almost the same as that of the uniaxial tensile test. In order to evaluate an intrinsic HER of steel sheet specimens, the initial hole of the HET specimen is produced using a milling process after punching, which can remove accumulated shearing damage and micro-void in the hole edge region that is present when using the standard HER evaluation method. It was found that the intrinsic HER of steel sheet specimens was proportional to the strain rate sensitivity exponent and post uniform elongation.

  7. Competing mechanisms of plasma transport in inhomogeneous configurations with velocity shear: the solar-wind interaction with earth's magnetosphere.

    PubMed

    Faganello, M; Califano, F; Pegoraro, F

    2008-01-11

    Two-dimensional simulations of the Kelvin-Helmholtz instability in an inhomogeneous compressible plasma with a density gradient show that, in a transverse magnetic field configuration, the vortex pairing process and the Rayleigh-Taylor secondary instability compete during the nonlinear evolution of the vortices. Two different regimes exist depending on the value of the density jump across the velocity shear layer. These regimes have different physical signatures that can be crucial for the interpretation of satellite data of the interaction of the solar wind with the magnetospheric plasma.

  8. The Maryland Centrifugal Experiment (MCX): Centrifugal Confinement and Velocity Shear Stabilization of Plasmas in Shaped Open Magnetic Systems

    SciTech Connect

    Hassam, Adil; Ellis, Richard F.

    2012-01-01

    The Maryland Centrifugal Experiment (MCX) Project has investigated the concepts of centrifugal plasma confinement and stabilization of instabilities by velocity shear. The basic requirement is supersonic plasma rotation about a shaped, open magnetic field. Overall, the MCX Project attained three primary goals that were set out at the start of the project. First, supersonic rotation at Mach number up to 2.5 was obtained. Second, turbulence from flute interchange modes was found considerably reduced from conventional. Third, plasma pressure was contained along the field, as evidenced by density drops of x10 from the center to the mirror throats.

  9. The effect of shearing strain-rate on the ultimate shearing resistance of clay

    NASA Technical Reports Server (NTRS)

    Cheng, R. Y. K.

    1975-01-01

    An approach for investigating the shearing resistance of cohesive soils subjected to a high rate of shearing strain is described. A fast step-loading torque apparatus was used to induce a state of pure shear in a hollow cylindrical soil specimen. The relationship between shearing resistance and rate of shear deformation was established for various soil densities expressed in terms of initial void ratio or water content. For rate of shearing deformation studies, the shearing resistance increases initially with shearing velocity, but subsequently reaches a terminal value as the shearing velocity increases. The terminal shearing resistance is also found to increase as the density of the soil increases. The results of this investigation are useful in the rheological study of clay. It is particularly important for mobility problems of soil runways, since the soil resistance is found to be sensitive to the rate of shearing.

  10. Comparison of shear wave velocity measurements assessed with two different ultrasound systems in an ex-vivo tendon strain phantom.

    PubMed

    Rosskopf, Andrea B; Bachmann, Elias; Snedeker, Jess G; Pfirrmann, Christian W A; Buck, Florian M

    2016-11-01

    The purpose of this study is to compare the reliability of SW velocity measurements of two different ultrasound systems and their correlation with the tangent traction modulus in a non-static tendon strain model. A bovine tendon was fixed in a custom-made stretching device. Force was applied increasing from 0 up to 18 Newton. During each strain state the tangent traction modulus was determined by the stretcher device, and SW velocity (m/s) measurements using a Siemens S3000 and a Supersonic Aixplorer US machine were done for shear modulus (kPa) calculation. A strong significant positive correlation was found between SW velocity assessed by the two ultrasound systems and the tangent traction modulus (r = 0.827-0.954, p < 0.001), yet all SW velocity-based calculations underestimated the reference tissue tangent modulus. Mean difference of SW velocities with the S3000 was 0.44 ± 0.3 m/s (p = 0.002) and with the Aixplorer 0.25 ± 0.3 m/s (p = 0.034). Mean difference of SW velocity between the two US-systems was 0.37 ± 0.3 m/s (p = 0.012). In conclusion, SW velocities are highly dependent on mechanical forces in the tendon tissue, but for controlled mechanical loads appear to yield reproducible and comparable measurements using different US systems.

  11. Modeling a Propagating Sawtooth Flare Ribbon Structure as a Tearing Mode in the Presence of Velocity Shear

    NASA Astrophysics Data System (ADS)

    Parker, Jacob; Longcope, Dana

    2017-09-01

    On 2014 April 18 (SOL2014-04-18T13:03), an M-class flare was observed by IRIS. The associated flare ribbon contained a quasi-periodic sawtooth pattern that was observed to propagate along the ribbon, perpendicular to the IRIS spectral slit, with a phase velocity of ∼15 km s‑1. This motion resulted in periodicities in both intensity and Doppler velocity along the slit. These periodicities were reported by Brannon et al. to be approximately ±0.″5 in position and ±20 km s‑1 in velocity and were measured to be ∼180° out of phase with one another. This quasi-periodic behavior has been attributed by others to bursty or patchy reconnection and slipping occurring during three-dimensional magnetic reconnection. Though able to account for periodicities in both intensity and Doppler velocity, these suggestions do not explicitly account for the phase velocity of the entire sawtooth structure or the relative phasing of the oscillations. Here we propose that the observations can be explained by a tearing mode (TM) instability occurring at a current sheet across which there is also a velocity shear. Using a linear model of this instability, we reproduce the relative phase of the oscillations, as well as the phase velocity of the sawtooth structure. We suggest a geometry and local plasma parameters for the April 18 flare that would support our hypothesis. Under this proposal, the combined spectral and spatial IRIS observations of this flare may provide the most compelling evidence to date of a TM occurring in the solar magnetic field.

  12. Shear wave velocity structure in North America from large-scale waveform inversions of surface waves

    NASA Astrophysics Data System (ADS)

    Alsina, D.; Woodward, R. L.; Snieder, R. K.

    1996-07-01

    A two-step nonlinear and linear inversion is carried out to map the lateral heterogeneity beneath North America using surface wave data. The lateral resolution for most areas of the model is of the order of several hundred kilometers. The most obvious feature in the tomographic images is the rapid transition between low velocities in the tectonically active region west of the Rocky Mountains and high velocities in the stable central and eastern shield of North America. The model also reveals smaller-scale heterogeneous velocity structures. A high-velocity anomaly is imaged beneath the state of Washington that could be explained as the subducting Juan de Fuca plate beneath the Cascades. A large low-velocity structure extends along the coast from the Mendocino to the Rivera triple junction and to the continental interior across the southwestern United States and northwestern Mexico. Its shape changes notably with depth. This anomaly largely coincides with the part of the margin where no lithosphere is consumed since the subduction has been replaced by a transform fault. Evidence for a discontinuous subduction of the Cocos plate along the Middle American Trench is found. In central Mexico a transition is visible from low velocities across the Trans-Mexican Volcanic Belt (TMVB) to high velocities beneath the Yucatan Peninsula. Two elongated low-velocity anomalies beneath the Yellowstone Plateau and the eastern Snake River Plain volcanic system and beneath central Mexico and the TMVB seem to be associated with magmatism and partial melting. Another low-velocity feature is seen at depths of approximately 200 km beneath Florida and the Atlantic Coastal Plain. The inversion technique used is based on a linear surface wave scattering theory, which gives tomographic images of the relative phase velocity perturbations in four period bands ranging from 40 to 150 s. In order to find a smooth reference model a nonlinear inversion based on ray theory is first performed. After

  13. Shear wave velocity structure in North America from large-scale waveform inversions of surface waves

    USGS Publications Warehouse

    Alsina, D.; Woodward, R.L.; Snieder, R.K.

    1996-01-01

    A two-step nonlinear and linear inversion is carried out to map the lateral heterogeneity beneath North America using surface wave data. The lateral resolution for most areas of the model is of the order of several hundred kilometers. The most obvious feature in the tomographic images is the rapid transition between low velocities in the technically active region west of the Rocky Mountains and high velocities in the stable central and eastern shield of North America. The model also reveals smaller-scale heterogeneous velocity structures. A high-velocity anomaly is imaged beneath the state of Washington that could be explained as the subducting Juan de Fuca plate beneath the Cascades. A large low-velocity structure extends along the coast from the Mendocino to the Rivera triple junction and to the continental interior across the southwestern United States and northwestern Mexico. Its shape changes notably with depth. This anomaly largely coincides with the part of the margin where no lithosphere is consumed since the subduction has been replaced by a transform fault. Evidence for a discontinuous subduction of the Cocos plate along the Middle American Trench is found. In central Mexico a transition is visible from low velocities across the Trans-Mexican Volcanic Belt (TMVB) to high velocities beneath the Yucatan Peninsula. Two elongated low-velocity anomalies beneath the Yellowstone Plateau and the eastern Snake River Plain volcanic system and beneath central Mexico and the TMVB seem to be associated with magmatism and partial melting. Another low-velocity feature is seen at depths of approximately 200 km beneath Florida and the Atlantic Coastal Plain. The inversion technique used is based on a linear surface wave scattering theory, which gives tomographic images of the relative phase velocity perturbations in four period bands ranging from 40 to 150 s. In order to find a smooth reference model a nonlinear inversion based on ray theory is first performed. After

  14. Amplitude Anomalies of S Waves Caused by Low Shear Velocity Structures at the Base of the Mantle

    NASA Astrophysics Data System (ADS)

    To, A.; Capdeville, Y.; Romanowicz, B. A.

    2015-12-01

    Previous studies have shown that the direct S and Sdiff waveforms of earthquakes in Papua New Guinea region recorded by seismographs in Northern America are distorted due to sampling slow shear velocity anomalies at the base of the mantle. The emergence of postcursours to the S/Sdiff waves and the travel time anomalies have been reasonably explained by placing a ultra low velocity zone (ULVZ) in southwest of Hawaii. In this study, we focused on the amplitude anomalies of the S/Sdiff waveforms. The direct S phase show very low amplitude at stations in Southern California, at the distance and azimuth around 90 and 55 degrees from the earthquake. The amplitude is as low as 10% of the synthetic amplitude of a standard 1D model, especially at higher frequency range above 0.025 Hz. We first checked and confirmed that the anomalies are not due to errors in the focal mechanism, which is used to calculate the reference synthetic waveforms. Also we checked that the amplitude anomalies are unlikely to be caused by the structures near the earthquake or near the stations, by looking at the amplitude of the depth phases or waveforms of other earthquakes. We assumed that the anomalies are produced by the focusing and defocusing effect of sampling 3D heterogeneous at the base of the mantle, and searched for the causal structures. Full 3D synthetic waveforms are calculated down to 8 seconds for tens of structural models with slow anomalies of different size and velocity reduction placed on the core-mantle boundary (CMB). The result shows that existing tomographic models do not fully explain the observed amplitude anomalies. Stronger shear velocity anomalies are required. The previously proposed thin large ULVZ placed on the CMB southwest of Hawaii partly explains the observed amplitude reduction, even at the distance as short as 90 degrees from the earthquake. This result indicates the significance of finite frequency effect of the ULVZ structure to the S waves, since the ray

  15. Site response, shallow shear-wave velocity, and wave propagation at the San Jose, California, dense seismic array

    USGS Publications Warehouse

    Hartzell, S.; Carver, D.; Williams, R.A.; Harmsen, S.; Zerva, A.

    2003-01-01

    Ground-motion records from a 52-element dense seismic array near San Jose, California, are analyzed to obtain site response, shallow shear-wave velocity, and plane-wave propagation characteristics. The array, located on the eastern side of the Santa Clara Valley south of the San Francisco Bay, is sited over the Evergreen basin, a 7-km-deep depression with Miocene and younger deposits. Site response values below 4 Hz are up to a factor of 2 greater when larger, regional records are included in the analysis, due to strong surface-wave development within the Santa Clara Valley. The pattern of site amplification is the same, however, with local or regional events. Site amplification increases away from the eastern edge of the Santa Clara Valley, reaching a maximum over the western edge of the Evergreen basin, where the pre-Cenozoic basement shallows rapidly. Amplification then decreases further to the west. This pattern may be caused by lower shallow shear-wave velocities and thicker Quaternary deposits further from the edge of the Santa Clara Valley and generation/trapping of surface waves above the shallowing basement of the western Evergreen basin. Shear-wave velocities from the inversion of site response spectra based on smaller, local earthquakes compare well with those obtained independently from our seismic reflection/refraction measurements. Velocities from the inversion of site spectra that include larger, regional records do not compare well with these measurements. A mix of local and regional events, however, is appropriate for determination of site response to be used in seismic hazard evaluation, since large damaging events would excite both body and surface waves with a wide range in ray parameters. Frequency-wavenumber, plane-wave analysis is used to determine the backazimuth and apparent velocity of coherent phases at the array. Conventional, high-resolution, and multiple signal characterization f-k power spectra and stacked slowness power spectra are

  16. Towards a new tool to develop a 3-D shear-wave velocity model from converted waves

    NASA Astrophysics Data System (ADS)

    Colavitti, Leonardo; Hetényi, György

    2017-04-01

    The main target of this work is to develop a new method in which we exploit converted waves to construct a fully 3-D shear-wave velocity model of the crust. A reliable 3-D model is very important in Earth sciences because geological structures may vary significantly in their lateral dimension. In particular, shear-waves provide valuable complementary information with respect to P-waves because they usually guarantee a much better correlation in terms of rock density and mechanical properties, reducing the interpretation ambiguities. Therefore, it is fundamental to develop a new technique to improve structural images and to describe different lithologies in the crust. In this study we start from the analysis of receiver functions (RF, Langston, 1977), which are nowadays largely used for structural investigations based on passive seismic experiments, to map Earth discontinuities at depth. The RF technique is also commonly used to invert for velocity structure beneath single stations. Here, we plan to combine two strengths of RF method: shear-wave velocity inversion and dense arrays. Starting from a simple 3-D forward model, synthetic RFs are obtained extracting the structure along a ray to match observed data. During the inversion, thanks to a dense stations network, we aim to build and develop a multi-layer crustal model for shear-wave velocity. The initial model should be chosen simple to make sure that the inversion process is not influenced by the constraints in terms of depth and velocity posed at the beginning. The RFs inversion represents a complex problem because the amplitude and the arrival time of different phases depend in a non-linear way on the depth of interfaces and the characteristics of the velocity structure. The solution we envisage to manage the inversion problem is the stochastic Neighbourhood Algorithm (NA, Sambridge, 1999a, b), whose goal is to find an ensemble of models that sample the good data-fitting regions of a multidimensional parameter

  17. Prediction of the Peak Shear Strength of Sandstone and Mudstone Joints Infilled with High Water-Cement Ratio Grouts

    NASA Astrophysics Data System (ADS)

    Ma, Hao; Liu, Quansheng

    2017-08-01

    There are very few studies on the peak shear strength of cement-infilled joints, despite it being a key parameter in the grouting technique. To quantify this strength, the average elastic modulus of hardened cement pastes with a high water-cement ratio (w/c) has been determined by using a homogenization method, in which the bleeding ratio is includes. Based on a scanning electron microscope analysis of the micromorphology of the rock joint surface and study of the interfacial transition zone, the mechanisms of the microscopic bond shear failure at the interfaces between the cement pastes and rocks have been deduced, in which the effect of the macroscopic roughness has not been taken into consideration. Based on the JRC-JCS model of unfilled joints, which takes the macroscopic roughness into consideration, together with the microscopic bond shear model, a model has been developed that can predict the peak shear strength of cement-infilled joints of sandstone and mudstone. The predictions have been verified by experimental results. The results show that if the w/ c is too low, then the grouting can weaken the rock mass. If the w/ c is appropriate, then the increase to the peak shear strength can be determined by the model.

  18. Shear wave velocity profile estimation by integrated analysis of active and passive seismic data from small aperture arrays

    NASA Astrophysics Data System (ADS)

    Lontsi, A. M.; Ohrnberger, M.; Krüger, F.

    2016-07-01

    We present an integrated approach for deriving the 1D shear wave velocity (Vs) information at few tens to hundreds of meters down to the first strong impedance contrast in typical sedimentary environments. We use multiple small aperture seismic arrays in 1D and 2D configuration to record active and passive seismic surface wave data at two selected geotechnical sites in Germany (Horstwalde & Löbnitz). Standard methods for data processing include the Multichannel Analysis of Surface Waves (MASW) method that exploits the high frequency content in the active data and the sliding window frequency-wavenumber (f-k) as well as the spatial autocorrelation (SPAC) methods that exploit the low frequency content in passive seismic data. Applied individually, each of the passive methods might be influenced by any source directivity in the noise wavefield. The advantages of active shot data (known source location) and passive microtremor (low frequency content) recording may be combined using a correlation based approach applied to the passive data in the so called Interferometric Multichannel Analysis of Surface Waves (IMASW). In this study, we apply those methods to jointly determine and interpret the dispersion characteristics of surface waves recorded at Horstwalde and Löbnitz. The reliability of the dispersion curves is controlled by applying strict limits on the interpretable range of wavelengths in the analysis and further avoiding potentially biased phase velocity estimates from the passive f-k method by comparing to those derived from the SPatial AutoCorrelation method (SPAC). From our investigation at these two sites, the joint analysis as proposed allows mode extraction in a wide frequency range (~ 0.6-35 Hz at Horstwalde and ~ 1.5-25 Hz at Löbnitz) and consequently improves the Vs profile inversion. To obtain the shear wave velocity profiles, we make use of a global inversion approach based on the neighborhood algorithm to invert the interpreted branches of the

  19. Application of high-velocity friction experiments to the shear rupture of a fault in an elastic half-space

    NASA Astrophysics Data System (ADS)

    Liao, Zonghu; Reches, Zeev

    2013-04-01

    We developed a physics-based model for earthquake rupture by numerically simulating shear rupture along a 2D vertical fault with the dynamic frictional strength of granite under high slip velocity. Recent experimental observations indicated that the steady-state frictional strength of silica-rich igneous rocks (granite, syenite, diorite) alternate between dynamic-weakening under low velocity (V < 0.03 m/s) and dynamic-strengthening under higher velocities (V > 0.03 m/s). This strength alternation was attributed to powder-lubrication (weakening), and powder dehydration (strengthening) (Sammis et al., 2011). We used the dynamic friction law which was determined on samples of Sierra White granite under experimental velocities approaching 1 m/s (Reches and Lockner, 2010). We converted their observed friction-distance-velocity relations into an empirical friction model referred to as WEST (WEakening - STrengthening). For the simulation calculations, we used the spectral element code of Ampuero (web.gps.caltech.edu/~ampuero/software), which computes the spontaneous rupture propagation along an anti-plane shear (mode III) fracture in an elastic half-space. In the present analysis, the WEST friction model is used as the fault strength while keeping all other parameters (crust properties and stresses) the same as Version 3 of the Southern California Earthquake Center (SCEC) benchmark problem (Harris et al., 2004). This approach allows for direct comparison between the WEST rupture and the benchmark rupture with a fault of slip-weakening friction model (Rojas et al., 2008). We found the following differences between the ruptures of the two models: (1) WEST-based rupture occurs earlier at all observation points away from the nucleation zone; (2) WEST-based model has lower (~ 35%) peak velocity and shorter rise-time; and (3) WEST-based rupture shows rich, frequent alteration of slip velocity, and consequently, the simulated rupture is more complex in stress drop, displacements

  20. Shear-wave velocity structure of the south-eastern part of the Iberian Peninsula from Rayleigh wave analysis

    NASA Astrophysics Data System (ADS)

    Corchete, V.; Chourak, M.

    2011-10-01

    In this study, we present the lithospheric structure of the south-eastern part of the Iberian Peninsula by means of a set of 2D images of shear velocity, for depths ranging from 0 to 50 km. This goal will be attained by means of the inversion of the Rayleigh wave dispersion. For it, the traces of 25 earthquakes occurred on the neighbouring of the study area, from 2001 to 2003, will be considered. These earthquakes have been registered by 11 broadband stations located on Iberia. All seismic events have been grouped in source zones to get an average dispersion curve for each source-station path. The dispersion curves have been measured for periods between 2 and 45 s, by combination of two digital filtering techniques: Multiple Filter Technique and Time Variable Filtering. The resulting set of source-station averaged dispersion curves has been inverted according to the generalized inversion theory, to get S-wave velocity models for each source-station path. Later, these models have been interpolated using the method of kriging, to obtain a 2D mapping of the S-wave velocity structure for the south-eastern part of Iberia. The results presented in this paper show that the techniques used here are a powerful tool to investigate the crust and upper mantle structure, through the dispersion analysis and its inversion to obtain shear velocity distributions with depth. By means of this analysis, principal structural features of the south-eastern part of Iberia, such as the existence of lateral and vertical heterogeneity in the whole study area, or the location of the Moho discontinuity at 30 km of depth (with an average S-velocity of uppermost mantle of 4.7 km/s), have been revealed. Other important structural features revealed by this analysis have been that the uppermost of Iberian massif shows higher velocity values than the uppermost of the Alpine domain, indicating that the massif is old and tectonically stable. The average velocity of the crust in Betic cordillera is of

  1. Reynolds number effects on the fluctuating velocity distribution in wall-bounded shear layers

    NASA Astrophysics Data System (ADS)

    Li, Wenfeng; Roggenkamp, Dorothee; Jessen, Wilhelm; Klaas, Michael; Schröder, Wolfgang

    2017-01-01

    The streamwise turbulence intensity and wall-shear stress fluctuations of zero pressure gradient (ZPG) turbulent boundary layers are investigated for seven Reynolds numbers based on the momentum thickness in the range of 1009  ⩽  Re θ   ⩽  4070 by particle-image velocimetry (PIV) and micro-particle tracking velocimetry (µ-PTV) at a spatial resolution up to 0.06-0.23 wall units such that the viscous sublayer is well resolved. The statistics evidence good agreement with direct numerical simulations (DNS) and experimental results from the literature. The experimental results show the streamwise turbulence intensity and wall-shear stress fluctuation to grow at increasing Reynolds numbers.

  2. A joint inversion for shear velocity and anisotropy: the Woodlark Rift, Papua New Guinea

    NASA Astrophysics Data System (ADS)

    Eilon, Zachary; Abers, Geoffrey A.; Gaherty, James B.

    2016-08-01

    Trade-offs between velocity and anisotropy heterogeneity complicate the interpretation of differential traveltime data and have the potential to bias isotropic tomographic models. By constructing a simple parametrisation to describe an elastic tensor with hexagonal symmetry, we find analytic solutions to the Christoffel equations in terms of fast and slow horizontal velocities that allow us to simultaneously invert differential traveltime data and splitting data from teleseismic S arrivals to recover 3-D velocity and anisotropy structure. This technique provides a constraint on the depth-extent of shallow anisotropy, otherwise absent from interpretations based on SKS splitting alone. This approach is well suited to the young Woodlark Rift, where previous studies have found strong velocity variation and substantial SKS splitting in a continental rift with relatively simple geometry. This study images a low-velocity rift axis with ≤4 per cent spreading-parallel anisotropy at 50-100 km depth that separates regions of pre-existing lithospheric fabric, indicating the synchronous development of extensional crystallographic preferred orientation and lithospheric thinning. A high-velocity slab fragment north of the rift axis is associated with strike-parallel anisotropic fast axes, similar to that seen in the shallow mantle of some subduction zones. In addition to the insights provided by the anisotropy structure, the improvement in fit to the differential traveltime data demonstrates the merit to a joint inversion that accounts for anisotropy.

  3. Fabric-related velocity anisotropy and shear wave splitting in rocks from the Santa Rosa Mylonite Zone, California

    SciTech Connect

    Kern, H. ); Wenk, H.R. )

    1990-07-10

    The directional dependence of P and S wave velocities have been measured at pressures (up to 600 MPa) and temperatures (up to 700C) in rocks from the Santa Rosa Mylonite Zone (southern California). During tectonism, these were progressively deformed from granodiorite protolith to mylonite and ultimately phyllonite. The mineralogical and chemical composition of protolith and mylonite is nearly identical. Thus these rocks provide excellent material for documenting the effect of microstructural and textural changes on rock anisotropy. Velocity anisotropy increases significantly with the degree of deformation, whereas average velocities and densities do not change. At low pressure (50 MPa) the velocity anisotropy ranges from 1.7% in granodiorite up to 19% in phyllonite and is due to both oriented microfractures and crystallographic preferred orientation. At high pressure (600 MPa), the residual anisotropy up to 12% is mainly due to preferred mineral orientation, in particular of biotite. Significant shear wave splitting is measured parallel to the foliation plane and shows a good correlation with the biotite texture. These observations confirm that oriented microcracks and preferred orientation of minerals should be taken into account in the interpretation of seismic reflection and refraction data in terranes with deformed rocks.

  4. The shear wave velocity structure of the heterogeneous alluvial plain of Beirut (Lebanon): combined analysis of geophysical and geotechnical data

    NASA Astrophysics Data System (ADS)

    Salloum, Nancy; Jongmans, Denis; Cornou, Cécile; Youssef Abdel Massih, Dalia; Hage Chehade, Fadi; Voisin, Christophe; Mariscal, Armand

    2014-11-01

    A geotechnical and geophysical campaign was performed at sites located in the alluvial plain of the river of Beirut (Lebanon), which is characterized by a significant lateral and vertical geological variability, along with anthropogenic disturbances in the first metres. The method combination has allowed detecting a shallow conductive low velocity layer of varying depth and thickness, corresponding to a soft clay layer embedded in coarser formations. This layer was found to exert strong control on the experimental dispersion curves (estimated from both active and passive experiments) characterized by a continuous mode superposition at high frequency, associated with an increase in phase velocity. Vs profiles in boreholes turned out to be of prime importance for adequately defining the parametrization before inversion and for ensuring the reliability of the inversion dispersive estimates at low frequency. A major output of this study is also to show that this low velocity layer, along with the strong shear velocity contrast at its bottom, significantly contributes to the site seismic response, and could make it difficult to use the measured H/V peak frequency as a proxy for the soil thickness over bedrock.

  5. Shear wave velocity estimation of the near-surface materials of Chittagong City, Bangladesh for seismic site characterization

    NASA Astrophysics Data System (ADS)

    Rahman, Md. Zillur; Siddiqua, Sumi; Kamal, A. S. M. Maksud

    2016-11-01

    The average shear wave velocity of the near-surface materials down to a depth of 30 m (Vs30) is essential for seismic site characterization to estimate the local amplification factor of the seismic waves during an earthquake. Chittagong City is one of the highest risk cities of Bangladesh for its seismic vulnerability. In the present study, the Vs30 is estimated for Chittagong City using the multichannel analysis of surface waves (MASW), small scale microtremor measurement (SSMM), downhole seismic (DS), and correlation between the shear wave velocity (Vs) and standard penetration test blow count (SPT-N). The Vs30 of the near-surface materials of the city varies from 123 m/s to 420 m/s. A Vs30 map is prepared from the Vs30 of each 30 m grid using the relationship between the Holocene soil thickness and the Vs30. Based on the Vs30, the near-surface materials of Chittagong City are classified as site classes C, D, and E according to the National Earthquake Hazards Reduction Program (NEHRP), USA and as site classes B, C, and D according to the Eurocode 8. The Vs30 map can be used for seismic microzonation, future planning, and development of the city to improve the earthquake resiliency of the city.

  6. Modeling a Propagating Sawtooth Flare Ribbon Structure as a Tearing Mode in the Presence of Velocity Shear

    NASA Astrophysics Data System (ADS)

    Parker, Jacob; Longcope, Dana

    2017-08-01

    On April 18, 2014 (SOL2014-04-18T13:03) an M-class flare was observed by IRIS. The associated flare ribbon contained a quasi-periodic sawtooth pattern that was observed to propagate perpendicular the the IRIS spectral slit with a phase velocity of approximately 15 km/s (Brannon et al. 2015). This motion resulted in periodicities in both intensity and Doppler velocity along the slit. These periodicities were reported by Brannon et al. (2015) to be approximately plus-minus .5 arcseconds in position and plus-minus 20 km/s in velocity and were measured to be approximately 180 degrees out of phase with one another. This quasi-periodic behavior has been attributed by others to bursty or patchy reconnection (Brosius & Daw 2015; Brosius et al. 2016) and slipping occurring during three-dimensional magnetic reconnection (Li & Zhang 2015; Li et al. 2016). While able to account for periodicities in both intensity and Doppler velocity these suggestions do not explicitly account for the phase velocity of the entire sawtooth structure, or for the relative phasing of the oscillations. Here we propose that the observations can be explained by a tearing mode instability occurring at a current sheet across which there is also a velocity shear. We suggest a geometry and local plasma parameters for the April 18 flare which would support our hypothesis. Under this proposal the IRIS observations of this flare may provide the most compelling evidence to date of a tearing mode occurring in the solar magnetic field.

  7. a Global Shear Velocity Model of the Upper Mantle from New Fundamental and Higher Rayleigh Mode Measurements

    NASA Astrophysics Data System (ADS)

    Debayle, E.; Ricard, Y. R.

    2011-12-01

    We present a global SV-wave tomographic model of the upper mantle, built from a new dataset of fundamental and higher mode Rayleigh waveforms. We use an extension of the automated waveform inversion approach of Debayle (1999) designed to improve the extraction of fundamental and higher mode information from a single surface wave seismogram. The improvement is shown to be significant in the transition zone structure which is constrained by the higher modes. The new approach is fully automated and can be run on a Beowulf computer to process massive surface wave dataset. It has been used to match successfully over 350 000 fundamental and higher mode Rayleigh waveforms, corresponding to about 20 millions of new measurements extracted from the seismograms. For each seismogram, we obtain a path average shear velocity and quality factor model, and a set of fundamental and higher mode dispersion and attenuation curves compatible with the recorded waveform. The set of dispersion curves provides a global database for future finite frequency inversion. Our new 3D SV-wave tomographic model takes into account the effect of azimuthal anisotropy and is constrained with a lateral resolution of several hundred kilometers and a vertical resolution of a few tens of kilometers. In the uppermost 200 km, our model shows a very strong correlation with surface tectonics. The slow velocity signature of mid-oceanic ridges extend down to ~100 km depth while the high velocity signature of cratons vanishes below 200 km depth. At depth greater than 400 km, the pattern of seismic velocities appear relatively homogeneous at large scale, except for high velocity slabs which produce broad high velocity regions within the transition zone. Although resolution is still good, the region between 200 and 400 km is associated with a complex pattern of seismic heterogeneities showing no simple correlation with the shallower or deeper structure.

  8. Upper mantle shear wave velocity structure of the east Anatolian-Caucasus region

    NASA Astrophysics Data System (ADS)

    Skobeltsyn, Gleb Anatolyevich

    The Eastern Anatolian-Caucasus region is a relatively young part of the Alpine- Himalayan orogenic belt and has been formed as the result of the ongoing continental collision of Arabia and Eurasia. In spite of a number of geological studies that have been conducted in this area, there is still no consensus within the geoscience community about the regional tectonic settings and a model for the late Cenozoic tectonic evolution of the Anatolian Plateau. Knowledge of the upper mantle velocity structure in this region can provide the geological community with important constraints that are crucial for developing an understanding of the regional geology and the processes associated with early stages of mountain building. In the present dissertation, I describe two studies of the regional upper mantle S wave velocity structure. In order to derive the absolute velocity structure of the upper mantle, I have applied surface wave tomography to model Rayleigh wave phase velocities as a function of period. Then I inverted the Rayleigh phase velocities to obtain S wave velocities as a function of depth. The resulted high-resolution 3-D S wave velocity model of the regional upper mantle is characterized by a better depth resolution than any preexisting tomographic models. I also conducted an S wave splitting analysis using traditional methods and developed a two-layer grid search algorithm in order to infer the upper mantle anisotropic structure. The results of the S wave splitting analysis for the stations located in Azerbaijan are the first in the region. (Abstract shortened by ProQuest.).

  9. General measurement of optical system aberrations with a continuously variable lateral shear ratio by a randomly encoded hybrid grating.

    PubMed

    Ling, Tong; Yang, Yongying; Liu, Dong; Yue, Xiumei; Jiang, Jiabin; Bai, Jian; Shen, Yibing

    2015-10-20

    A general lateral shearing interferometry method to measure the wavefront aberrations with a continuously variable shear ratio by the randomly encoded hybrid grating (REHG) is proposed. The REHG consists of a randomly encoded binary amplitude grating and a phase chessboard. Its Fraunhofer diffractions contain only four orders which are the ±1 orders in two orthogonal directions due to the combined modulation of the amplitude and phase. As a result, no orders selection mask is needed for the REHG and the shear ratio is continuously variable, which is beneficial to the variation of sensitivity and testing range for different requirements. To determine the fabrication tolerance of this hybrid grating, the analysis of the effects of different errors on the diffraction intensity distributions is carried out. Experiments have shown that the testing method can achieve a continuously variable shear ratio with the same REHG, and the comparison with a ZYGO GPI interferometer exhibits that the aberration testing method by the REHG is highly precise and also has a good repeatability. This testing method by the REHG is available for general use in testing the aberrations of different optical systems in situ.

  10. Shear wave velocities in the upper mantle of the Western Alps: new constraints using array analysis of seismic surface waves

    NASA Astrophysics Data System (ADS)

    Lyu, Chao; Pedersen, Helle A.; Paul, Anne; Zhao, Liang; Solarino, Stefano

    2017-07-01

    It remains challenging to obtain absolute shear wave velocities of heterogeneities of small lateral extension in the uppermost mantle. This study presents a cross-section of Vs across the strongly heterogeneous 3-D structure of the western European Alps, based on array analysis of data from 92 broad-band seismic stations from the CIFALPS experiment and from permanent networks in France and Italy. Half of the stations were located along a dense sublinear array. Using a combination of these stations and off-profile stations, fundamental-mode Rayleigh wave dispersion curves were calculated using a combined frequency-time beamforming approach. We calculated dispersion curves for seven arrays of approximately 100 km aperture and 14 arrays of approximately 50 km aperture, the latter with the aim of obtaining a 2-D vertical cross-section of Vs beneath the western Alps. The dispersion curves were inverted for Vs(z), with crustal interfaces imposed from a previous receiver function study. The array approach proved feasible, as Vs(z) from independent arrays vary smoothly across the profile length. Results from the seven large arrays show that the shear velocity of the upper mantle beneath the European plate is overall low compared to AK135 with the lowest velocities in the internal part of the western Alps, and higher velocities east of the Alps beneath the Po plain. The 2-D Vs model is coherent with (i) a ∼100 km thick eastward-dipping European lithosphere west of the Alps, (ii) very high velocities beneath the Po plain, coherent with the presence of the Alpine (European) slab and (iii) a narrow low-velocity anomaly beneath the core of the western Alps (from the Briançonnais to the Dora Maira massif), and approximately colocated with a similar anomaly observed in a recent teleseismic P-wave tomography. This intriguing anomaly is also supported by traveltime variations of subvertically propagating body waves from two teleseismic events that are approximately located on

  11. Shear wave transmissivity measurement by color Doppler shear wave imaging

    NASA Astrophysics Data System (ADS)

    Yamakoshi, Yoshiki; Yamazaki, Mayuko; Kasahara, Toshihiro; Sunaguchi, Naoki; Yuminaka, Yasushi

    2016-07-01

    Shear wave elastography is a useful method for evaluating tissue stiffness. We have proposed a novel shear wave imaging method (color Doppler shear wave imaging: CD SWI), which utilizes a signal processing unit in ultrasound color flow imaging in order to detect the shear wave wavefront in real time. Shear wave velocity is adopted to characterize tissue stiffness; however, it is difficult to measure tissue stiffness with high spatial resolution because of the artifact produced by shear wave diffraction. Spatial average processing in the image reconstruction method also degrades the spatial resolution. In this paper, we propose a novel measurement method for the shear wave transmissivity of a tissue boundary. Shear wave wavefront maps are acquired by changing the displacement amplitude of the shear wave and the transmissivity of the shear wave, which gives the difference in shear wave velocity between two mediums separated by the boundary, is measured from the ratio of two threshold voltages required to form the shear wave wavefronts in the two mediums. From this method, a high-resolution shear wave amplitude imaging method that reconstructs a tissue boundary is proposed.

  12. Three-dimensional particle-in-cell simulation of whistler wave generated by strong velocity shear

    NASA Astrophysics Data System (ADS)

    Lin, D.; Scales, W.

    2016-12-01

    Inhomogeneous transverse flows are generated in plasma that contains a static electric field perpendicular to the magnetic field, which is a configuration that may naturally arise in the boundary layer between plasmas of different characteristics. The magnetized plasma layer with a velocity gradient is shown to be unstable to waves in the Very Low Frequency band that spans the ion and electron gyrofrequencies. With a three-dimensional electromagnetic PIC model, we are going to numerically reproduce the generation of whistler waves by strong velocity gradient. The simulation results will be compared with phenomena found in laboratory experiments. Velocity distribution function of will be investigated for possible acceleration of electrons by whistlers. Implications are for the dynamics in the radiation belt.

  13. Generation of a pseudo-2D shear-wave velocity section by inversion of a series of 1D dispersion curves

    USGS Publications Warehouse

    Luo, Y.; Xia, J.; Liu, J.; Xu, Y.; Liu, Q.

    2008-01-01

    Multichannel Analysis of Surface Waves utilizes a multichannel recording system to estimate near-surface shear (S)-wave velocities from high-frequency Rayleigh waves. A pseudo-2D S-wave velocity (vS) section is constructed by aligning 1D models at the midpoint of each receiver spread and using a spatial interpolation scheme. The horizontal resolution of the section is therefore most influenced by the receiver spread length and the source interval. The receiver spread length sets the theoretical lower limit and any vS structure with its lateral dimension smaller than this length will not be properly resolved in the final vS section. A source interval smaller than the spread length will not improve the horizontal resolution because spatial smearing has already been introduced by the receiver spread. In this paper, we first analyze the horizontal resolution of a pair of synthetic traces. Resolution analysis shows that (1) a pair of traces with a smaller receiver spacing achieves higher horizontal resolution of inverted S-wave velocities but results in a larger relative error; (2) the relative error of the phase velocity at a high frequency is smaller than at a low frequency; and (3) a relative error of the inverted S-wave velocity is affected by the signal-to-noise ratio of data. These results provide us with a guideline to balance the trade-off between receiver spacing (horizontal resolution) and accuracy of the inverted S-wave velocity. We then present a scheme to generate a pseudo-2D S-wave velocity section with high horizontal resolution using multichannel records by inverting high-frequency surface-wave dispersion curves calculated through cross-correlation combined with a phase-shift scanning method. This method chooses only a pair of consecutive traces within a shot gather to calculate a dispersion curve. We finally invert surface-wave dispersion curves of synthetic and real-world data. Inversion results of both synthetic and real-world data demonstrate that

  14. Shear wave velocity measurements of thin epoxy adhesive samples using broadband EMATs

    NASA Astrophysics Data System (ADS)

    Dixon, S.; Edwards, C.; Palmer, S. B.

    2002-05-01

    This paper describes an ultrasonic analysis of thin epoxy resin samples using normal incidence radially polarized shear wave ElectroMagnetic Acoustic Transducers (EMATs). The adhesive thickness in the first set of experiments was approximately 0.5 mm. The adhesive used in the first set of experiments was obtained from a 2 component cartridge and it was found that adhesive extruded from such cartridges can be inhomogeneous within the same cartridge. The second experiment described here demonstrated how material property changes of a thin adhesive layer (70 μm) could be ultrasonically measured during cure via spectral analysis.

  15. Gas Excitation in ULIRGs: Maps of Diagnostic Emission-line Ratios in Space and Velocity

    NASA Astrophysics Data System (ADS)

    Soto, Kurt T.; Martin, Crystal L.

    2012-11-01

    Emission-line spectra extracted at multiple locations across 39 ultraluminous infrared galaxies have been compiled into a spectrophotometric atlas. Line profiles of Hα, [N II], [S II], [O I], Hβ, and [O III] are resolved and fit jointly with common velocity components. Diagnostic ratios of these line fluxes are presented in a series of plots, showing how the Doppler shift, line width, gas excitation, and surface brightness change with velocity at fixed position and also with distance from the nucleus. One general characteristic of these spectra is the presence of shocked gas extending many kiloparsecs from the nucleus. In some systems, the rotation curves of the emitting gas indicate motions that suggest gas disks, which are most frequent at early merger stages. At these early merger stages, the emission line ratios indicate the presence of shocked gas, which may be triggered by the merger event. We also report the general characteristics of the integrated spectra. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

  16. 3D shear-wave velocity structure of the eastern Tennessee seismic zone from ambient noise correlation data

    NASA Astrophysics Data System (ADS)

    Arroucau, Pierre; Kuponiyi, Ayodeji; Vlahovic, Gordana; Powell, Chris

    2013-04-01

    The Eastern Tennessee Seismic Zone (ETSZ) is an intraplate seismic region characterized by frequent but low magnitude earthquakes and is the second most active seismic area in the United States east of the Rocky Mountains. One key question in the ETSZ is the actual relationship between earthquake distribution and geological structure at depth. Seismicity is mostly confined in the Precambrian basement, below the Paleozoic cover of the southern Appalachian foreland fold-and-thrust belt and shows little to no correlation with surface geological features. Since the middle of the seventies, the Center for Earthquake Research and Information (CERI) has installed and maintained several seismic networks in central and eastern United States. In this work, we use Rayleigh wave group and phase velocity dispersion information obtained from cross-correlation of seismic ambient noise at 24 short-period stations located in the vicinity of the ETSZ. The 3D velocity structure is estimated in four steps. First, dispersion curves are obtained for simultaneously recording station pairs for periods ranging from 2 to 20 s. Then, 2D group and phase velocity maps are determined for each period. Those maps are further used to reconstruct dispersion curves at fixed, regularly spaced locations. For each of these locations, a 1D shear-wave velocity profile is finally inverted for, that takes velocity information from previous studies into account. By providing new information about the upper crustal structure of this region, this work is a contribution to the understanding of the seismic activity of the ETSZ, and -to a broader extent- of the structure and evolution of the North American lithosphere.

  17. Near-Surface Shear Wave Velocity Versus Depth Profiles, VS30, and NEHRP Classifications for 27 Sites in Puerto Rico

    USGS Publications Warehouse

    Odum, Jack K.; Williams, Robert A.; Stephenson, William J.; Worley, David M.; von Hillebrandt-Andrade, Christa; Asencio, Eugenio; Irizarry, Harold; Cameron, Antonio

    2007-01-01

    In 2004 and 2005 the Puerto Rico Seismic Network (PRSN), Puerto Rico Strong Motion Program (PRSMP) and the Geology Department at the University of Puerto Rico-Mayaguez (UPRM) collaborated with the U.S. Geological Survey to study near-surface shear-wave (Vs) and compressional-wave (Vp) velocities in and around major urban areas of Puerto Rico. Using noninvasive seismic refraction-reflection profiling techniques, we acquired velocities at 27 locations. Surveyed sites were predominantly selected on the premise that they were generally representative of near-surface materials associated with the primary geologic units located within the urbanized areas of Puerto Rico. Geologic units surveyed included Cretaceous intrusive and volcaniclastic bedrock, Tertiary sedimentary and volcanic units, and Quaternary unconsolidated eolian, fluvial, beach, and lagoon deposits. From the data we developed Vs and Vp depth versus velocity columns, calculated average Vs to 30-m depth (VS30), and derived NEHRP (National Earthquake Hazards Reduction Program) site classifications for all sites except one where results did not reach 30-m depth. The distribution of estimated NEHRP classes is as follows: three class 'E' (VS30 below 180 m/s), nine class 'D' (VS30 between 180 and 360 m/s), ten class 'C' (VS30 between 360 and 760 m/s), and four class 'B' (VS30 greater than 760 m/s). Results are being used to calibrate site response at seismograph stations and in the development of regional and local shakemap models for Puerto Rico.

  18. Velocity field of a round jet in a cross flow for various jet injection angles and velocity ratios. [Langley V/STOL tunnel

    NASA Technical Reports Server (NTRS)

    Fearn, R. L.; Weston, R. P.

    1979-01-01

    A subsonic round jet injected from a flat plate into a subsonic crosswind of the same temperature was investigated. Velocity and pressure measurements in planes perpendicular to the path of the jet were made for nominal jet injection angles of 45 deg, 60 deg, 75 deg, 90 deg, and 105 deg and for jet/cross flow velocity ratios of four and eight. The velocity measurements were obtained to infer the properties of the vortex pair associated with a jet in a cross flow. Jet centerline and vortex trajectories were determined and fit with an empirical equation that includes the effects of jet injection angle, jet core length, and jet/cross flow velocity ratios.

  19. Influence of the aspect ratio on Buoyant-Thermocapillary convection stability by the velocity field measurements

    NASA Astrophysics Data System (ADS)

    Chen, C.; Duan, D.; Li, L.; Zhou, Z.; Shen, S.; Kang, K.

    This paper describes an experimental study on the influence of the aspect ratio of the buoyant-thermocapillary convection in silicon oil which is subjected to a horizontal temperature difference The flow pattern of liquid layer in a rectangular cavity will change from steady convection to unstable convection when the temperature gradient is increasing between the two sidewalls The thickness of the liquid layer more exactly speaking the aspect ratio of the liquid layer is an important parameter in the flow state transition For the experiment on ground the convection is mainly controlled by thermocapillary effect for thin layer however the convection is mainly controlled by buoyancy effect for thick layer It is necessary to do some experiments to get the clear correlation between the aspect ratio and state transition Beside a space experiment of thermocapillary convection will be completed on board the Chinese recoverable satellite in 2006 It is a good chance to understand the difference between buoyant-thermocapillary convection and pure thermocapillary convection An open rectangular cavity is designed for the experiment The heat pipe technology is applied in the cold sidewall of the test cell in order to get a permanent and steady temperature difference Thus the multiplicate temperature gradient 0 sim 60 o C of the liquid layer will come true by simply increasing or decreasing the temperature of hot sidewall Making use of PIV Particle Image Velocity measurement technology and FlowManager software the flow

  20. Particle-in-cell simulation of two-dimensional electron velocity shear driven instability in relativistic domain

    SciTech Connect

    Shukla, Chandrasekhar Das, Amita; Patel, Kartik

    2016-08-15

    We carry out particle-in-cell simulations to study the instabilities associated with a 2-D sheared electron flow configuration against a neutralizing background of ions. Both weak and strong relativistic flow velocities are considered. In the weakly relativistic case, we observe the development of electromagnetic Kelvin-Helmholtz instability with similar characteristics as that predicted by the electron Magnetohydrodynamic (EMHD) model. On the contrary, in a strong relativistic case, the compressibility effects of electron fluid dominate and introduce upper hybrid electrostatic oscillations transverse to the flow which are very distinct from EMHD fluid behavior. In the nonlinear regime, both weak and strong relativistic cases lead to turbulence with broad power law spectrum.

  1. Particle-in-cell simulation of two-dimensional electron velocity shear driven instability in relativistic domain

    NASA Astrophysics Data System (ADS)

    Shukla, Chandrasekhar; Das, Amita; Patel, Kartik

    2016-08-01

    We carry out particle-in-cell simulations to study the instabilities associated with a 2-D sheared electron flow configuration against a neutralizing background of ions. Both weak and strong relativistic flow velocities are considered. In the weakly relativistic case, we observe the development of electromagnetic Kelvin-Helmholtz instability with similar characteristics as that predicted by the electron Magnetohydrodynamic (EMHD) model. On the contrary, in a strong relativistic case, the compressibility effects of electron fluid dominate and introduce upper hybrid electrostatic oscillations transverse to the flow which are very distinct from EMHD fluid behavior. In the nonlinear regime, both weak and strong relativistic cases lead to turbulence with broad power law spectrum.

  2. Bending and shear stresses developed by the instantaneous arrest of the root of a cantilever beam rotating with constant angular velocity about a transverse axis through the root

    NASA Technical Reports Server (NTRS)

    Stowell, Elbridge Z; Schwartz, Edward B; Houbolt, John C

    1945-01-01

    A theoretical investigation was made of the behavior of a cantilever beam in rotational motion about a transverse axis through the root determining the stresses, the deflections, and the accelerations that occur in the beam as a result of the arrest of motion. The equations for bending and shear stress reveal that, at a given percentage of the distance from root to tip and at a given trip velocity, the bending stresses for a particular mode are independent of the length of the beam and the shear stresses vary inversely with the length. When examined with respect to a given angular velocity instead of a given tip velocity, the equations reveal that the bending stress is proportional to the length of the beam whereas the shear stress is independent of the length. Sufficient experimental verification of the theory has previously been given in connection with another problem of the same type.

  3. Asymptotic solution of the turbulent mixing layer for velocity ratio close to unity

    NASA Technical Reports Server (NTRS)

    Higuera, F. J.; Jimenez, J.; Linan, A.

    1996-01-01

    The equations describing the first two terms of an asymptotic expansion of the solution of the planar turbulent mixing layer for values of the velocity ratio close to one are obtained. The first term of this expansion is the solution of the well-known time-evolving problem and the second, which includes the effects of the increase of the turbulence scales in the stream-wise direction, obeys a linear system of equations. Numerical solutions of these equations for a two-dimensional reacting mixing layer show that the correction to the time-evolving solution may explain the asymmetry of the entrainment and the differences in product generation observed in flip experiments.

  4. Reconstructions of shear modulus, Poisson's ratio, and density using approximate mean normal stress lambda epsilon alpha alpha as unknown.

    PubMed

    Sumi, Chikayoshi

    2006-12-01

    As a differential diagnosis technique for living soft tissues, we are developing ultrasonic-strain-measurement-based shear modulus reconstruction methods. Previously, we reported three-dimensional (3-D) and 2-D reconstruction methods utilizing a typical Poisson's ratio very close to 0.5 (nearly-incompressible). However, because a decrease in the accuracy of the reconstructed value was confirmed to be due to the difference between the original value and the set value, we proposed 3-D and 2-D methods of reconstructing Poisson's ratio as well. Furthermore, we proposed methods of reconstructing density and dealing with dynamic deformation. However, due to tissue incompressibility, the reconstructions of shear modulus, Poisson's ratio, and density became unstable. In this report, to obtain stable, unique reconstructions, we describe a new reconstruction method using mean normal stress approximated by the product of one of Lame's constants X and volume strain epsilon alpha alpha as an unknown. Regularization is simultaneously applied to the respective distributions to decrease the instability of the reconstructions due to measurement errors of the deformation. This method also enables stable, unique reconstructions of shear modulus and density under the condition that the mean normal stress remains unknown. We also verify the effectiveness of this method through 3-D simulations, while showing erroneous artifacts occurring when 2-D and 1-D reconstructions are performed.

  5. The stabilizing effect of collision-induced velocity shear on the ionospheric feedback instability in Earth's magnetosphere

    NASA Astrophysics Data System (ADS)

    Sydorenko, D.; Rankin, R.

    2017-07-01

    The feedback instability in the ionospheric Alfvén resonator in Earth's magnetosphere is examined using a two-dimensional multifluid numerical model of coupled ionosphere and magnetosphere. Two simulation configurations are used to demonstrate that the instability occurs under an assumption that is unrealistic for Earth's ionosphere. In the first configuration, a flat sheet height-integrated conducting boundary replaces the ionospheric E layer. In the second configuration, plasma dynamics in a simplified E layer is resolved ignoring ion production, loss, and diffusion. For the same parameters (plasma and neutral density profiles and convection electric field), the instability develops only with the flat sheet boundary. When the E layer is resolved, the variation of ion-neutral collision frequencies with altitude produces vertical shear in the horizontal ion flow velocity. The shear prevents density perturbations from remaining field aligned, causing them to decay rather than grow. It is suggested that the instability cannot occur in Earth's ionosphere because ion-neutral collision frequencies always have a significant variation with altitude through the E layer.

  6. Velocity and attenuation of shear waves in the phantom of a muscle-soft tissue matrix with embedded stretched fibers

    NASA Astrophysics Data System (ADS)

    Rudenko, O. V.; Tsyuryupa, S. N.; Sarvazyan, A. P.

    2016-09-01

    We develop a theory of the elasticity moduli and dissipative properties of a composite material: a phantom simulating muscle tissue anisotropy. The model used in the experiments was made of a waterlike polymer with embedded elastic filaments imitating muscle fiber. In contrast to the earlier developed phenomenological theory of the anisotropic properties of muscle tissue, here we obtain the relationship of the moduli with characteristic sizes and moduli making up the composite. We introduce the effective elasticity moduli and viscosity tensor components, which depend on stretching of the fibers. We measure the propagation velocity of shear waves and the shear viscosity of the model for regulated tension. Waves were excited by pulsed radiation pressure generated by modulated focused ultrasound. We show that with increased stretching of fibers imitating muscle contraction, an increase in both elasticity and viscosity takes place, and this effect depends on the wave propagation direction. The results of theoretical and experimental studies support our hypothesis on the protective function of stretched skeletal muscle, which protects bones and joints from trauma.

  7. Kinetic effects on the Kelvin–Helmholtz instability in ion-to-magnetohydrodynamic scale transverse velocity shear layers: Particle simulations

    PubMed Central

    Nakamura, T. K. M.; Hasegawa, H.; Shinohara, I.

    2010-01-01

    Ion-to-magnetohydrodynamic scale physics of the transverse velocity shear layer and associated Kelvin–Helmholtz instability (KHI) in a homogeneous, collisionless plasma are investigated by means of full particle simulations. The shear layer is broadened to reach a kinetic equilibrium when its initial thickness is close to the gyrodiameter of ions crossing the layer, namely, of ion-kinetic scale. The broadened thickness is larger in B⋅Ω<0 case than in B⋅Ω>0 case, where Ω is the vorticity at the layer. This is because the convective electric field, which points out of (into) the layer for B⋅Ω<0 (B⋅Ω>0), extends (reduces) the gyrodiameters. Since the kinetic equilibrium is established before the KHI onset, the KHI growth rate depends on the broadened thickness. In the saturation phase of the KHI, the ion vortex flow is strengthened (weakened) for B⋅Ω<0 (B⋅Ω>0), due to ion centrifugal drift along the rotational plasma flow. In ion inertial scale vortices, this drift effect is crucial in altering the ion vortex size. These results indicate that the KHI at Mercury-like ion-scale magnetospheric boundaries could show clear dawn-dusk asymmetries in both its linear and nonlinear growth. PMID:20838425

  8. Comparison of shear wave velocities on ultrasound elastography between different machines, transducers, and acquisition depths: a phantom study.

    PubMed

    Shin, Hyun Joo; Kim, Myung-Joon; Kim, Ha Yan; Roh, Yun Ho; Lee, Mi-Jung

    2016-10-01

    To investigate consistency in shear wave velocities (SWVs) on ultrasound elastography using different machines, transducers and acquisition depths. The SWVs were measured using an elasticity phantom with a Young's modulus of 16.9 kPa, with three recently introduced ultrasound elastography machines (A, B and C from different vendors) and two transducers (low and high frequencies) at four depths (2, 3, 4 and 5 cm). Mean SWVs from 15 measurements and coefficient of variations (CVs) were compared between three machines, two transducers and four acquisition depths. The SWVs using the high frequency transducer were not acquired at 5 cm depth in machine B, and a high frequency transducer was not available in machine C. The mean SWVs in the three machines were different (p ≤ 0.002). The CVs were 0-0.09 in three machines. The mean SWVs between the two transducers were different (p < 0.001) except at 4 and 5 cm depths in machine A. The SWVs were affected by the acquisition depths in all conditions (p < 0.001). There is considerable difference in SWVs on ultrasound elastography depending on different machines, transducers and acquisition depths. Caution is needed when using the cutoff values of SWVs in different conditions. • The shear wave velocities (SWVs) are different between different ultrasound elastography machines • The SWVs are also different between different transducers and acquisition depths • Caution is needed when using the cutoff SWVs measured under different conditions.

  9. VELOCITY-SHEAR-INDUCED MODE COUPLING IN THE SOLAR ATMOSPHERE AND SOLAR WIND: IMPLICATIONS FOR PLASMA HEATING AND MHD TURBULENCE

    SciTech Connect

    Hollweg, Joseph V.; Chandran, Benjamin D. G.; Kaghashvili, Edisher Kh. E-mail: ekaghash@aer.com

    2013-06-01

    We analytically consider how velocity shear in the corona and solar wind can cause an initial Alfven wave to drive up other propagating signals. The process is similar to the familiar coupling into other modes induced by non-WKB refraction in an inhomogeneous plasma, except here the refraction is a consequence of velocity shear. We limit our discussion to a low-beta plasma, and ignore couplings into signals resembling the slow mode. If the initial Alfven wave is propagating nearly parallel to the background magnetic field, then the induced signals are mainly a forward-going (i.e., propagating in the same sense as the original Alfven wave) fast mode, and a driven signal propagating like a forward-going Alfven wave but polarized like the fast mode; both signals are compressive and subject to damping by the Landau resonance. For an initial Alfven wave propagating obliquely with respect to the magnetic field, the induced signals are mainly forward- and backward-going fast modes, and a driven signal propagating like a forward-going Alfven wave but polarized like the fast mode; these signals are all compressive and subject to damping by the Landau resonance. A backward-going Alfven wave, thought to be important in the development of MHD turbulence, is also produced, but it is very weak. However, we suggest that for oblique propagation of the initial Alfven wave the induced fast-polarized signal propagating like a forward-going Alfven wave may interact coherently with the initial Alfven wave and distort it at a strong-turbulence-like rate.

  10. Ratio of effective temperature to pressure controls the mobility of sheared hard spheres.

    PubMed

    Haxton, Thomas K

    2012-01-01

    Using molecular dynamics simulations, we calculate fluctuations and responses for steadily sheared hard spheres over a wide range of packing fractions φ and shear strain rates γ[over ̇], using two different methods to dissipate energy. To a good approximation, shear stress and density fluctuations are related to their associated response functions by a single effective temperature T(eff) that is equal to or larger than the kinetic temperature T(kin). We find a crossover in the relationship between the relaxation time τ and the the nondimensionalized effective temperature T(eff)/pσ(3), where p is the pressure and σ is the sphere diameter. In the solid response regime, the behavior at a fixed packing fraction satisfies τ ̇γ∝exp(-cpσ(3)/T(eff)), where c depends weakly on φ, suggesting that the average local yield strain is controlled by the effective temperature in a way that is consistent with shear transformation zone theory. In the fluid response regime, the relaxation time depends on T(eff)/pσ(3) as it depends on T(kin)/pσ(3) in equilibrium. This regime includes both near-equilibrium conditions where T(eff)≃T(kin) and far-from-equilibrium conditions where T(eff)≠T(kin). We discuss the implications of our results for systems with soft repulsive interactions.

  11. Shear wave velocity and radial anisotropy beneath the Wyoming craton: craton destruction and lithospheric layering

    NASA Astrophysics Data System (ADS)

    Dave, R.; Li, A.

    2016-12-01

    The Wyoming craton has evolved under an intriguing geological history with suture zones, accreted margins, flat-slab subduction, orogeny and an encroaching hotspot. Whether and how the cratonic root has been widely destroyed by the series of tectonic events remain controversial. Aiming to address these questions using a craton-wide model, we have analyzed Rayleigh and Love wave data from 75 earthquakes recorded by 103 USArray TA stations in the Wyoming craton. 2-D phase velocity maps are constructed for 18 periods from 20 s to 166 s using the two-plane-wave tomography. The Yellowstone hotspot and the Cheyenne belt are characterized by low velocity anomalies at all periods in both Rayleigh and Love wave models. The northern craton in Montana is broadly fast at periods < 70 s and is relatively slow at longer periods, suggesting a shallower lithosphere. The fast anomaly in Wyoming has a NE-SW trend and extends to more than 200 km in the VSV model. However, such a fast anomaly is largely absent in the Love wave images at long periods. The association of VSV>VSH with this deep fast anomaly indicates mantle downwelling beneath south-central Wyoming. Mantle upwelling likely happens in slow regions at the hotspot, the Cheyenne belt, and the northeastern craton. The overall pattern of velocity anomaly and radial anisotropy suggests that small-scale mantle convection is vigorously acting beneath the Wyoming craton and continuously destructing the cratonic lithosphere. In addition, the average VSV and VSH models show a strong positive radial anisotropy of 5% (VSH>VSV) above 100 km and a weak negative anisotropy (VSV>VSH) below 120 km. Such a significant change in radial anisotropy could contribute to the observed mid-lithosphere discontinuity (MLD) from receiver functions. Both VSV and VSH reveal a fast lid above 100 km and a large velocity reduction at the depths of 115-190 km, corresponding with a lithosphere-asthenosphere boundary (LAB) at 150 km. These observations

  12. Aortic-Brachial Pulse Wave Velocity Ratio: A Blood Pressure-Independent Index of Vascular Aging.

    PubMed

    Fortier, Catherine; Sidibé, Aboubacar; Desjardins, Marie-Pier; Marquis, Karine; De Serres, Sacha A; Mac-Way, Fabrice; Agharazii, Mohsen

    2017-01-01

    Aortic stiffness, a cardiovascular risk factor, depends on the operating mean arterial pressure (MAP). The impact of aortic stiffness on cardiovascular outcomes is proposed to be mediated by the attenuation or the reversal of the arterial stiffness gradient. We hypothesized that arterial stiffness gradient is less influenced by changes in MAP. We aimed to study the relationship between MAP and aortic stiffness, brachial stiffness, and arterial stiffness gradient. In a cross-sectional study of a dialysis cohort (group A, n=304) and a cohort of hypertensive or kidney transplant recipient with an estimated glomerular filtration rate of >45 mL/min/1.73 m(2) (group B, n=114), we assessed aortic and brachial stiffness by measuring carotid-femoral and carotid-radial pulse wave velocities (PWV). We used aortic-brachial PWV ratio as a measure of arterial stiffness gradient. Although there was a positive relationship between MAP and carotid-femoral PWV (R(2)=0.10 and 0.08; P<0.001 and P=0.003) and MAP and carotid-radial PWV (R(2)=0.22 and 0.12; P<0.001 and P<0.001), there was no statistically or clinically significant relationship between MAP and aortic-brachial PWV ratio (R(2)=0.0002 and 0.0001; P=0.8 and P=0.9) in group A and B, respectively. Dialysis status and increasing age increased the slope of the relationship between MAP and cf-PWV. However, we found no modifying factor (age, sex, dialysis status, diabetes mellitus, cardiovascular disease, and class of antihypertensive drugs) that could affect the lack of relationship between MAP and aortic-brachial PWV ratio. In conclusion, these results suggest that aortic-brachial PWV ratio could be considered as a blood pressure-independent measure of vascular aging. © 2016 American Heart Association, Inc.

  13. Mean velocity and temperature profiles in a sheared diabatic turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Li, Dan; Katul, Gabriel G.; Bou-Zeid, Elie

    2012-10-01

    In the atmospheric surface layer, modifications to the logarithmic mean velocity and air temperature profiles induced by thermal stratification or convection are accounted for via stability correction functions ϕm and ϕh, respectively, that vary with the stability parameter ς. These two stability correction functions are presumed to be universal in shape and independent of the surface characteristics. To date, there is no phenomenological theory that explains all the scaling laws in ϕh with ς, how ϕh relates to ϕm, and why ϕh ⩽ ϕm is consistently reported. To develop such a theory, the recently proposed links between the mean velocity profile and the Kolmogorov spectrum of turbulence, which were previously modified to account for the effects of buoyancy, are generalized here to include the mean air temperature profile. The resulting theory explains the observed scaling laws in ϕm and ϕh reported in many field and numerical experiments, predicts their behaviors across a wide range of atmospheric stability conditions, and elucidates why heat is transported more efficiently than momentum in certain stability regimes. In particular, it is shown that the enhancement in heat transport under unstable conditions is linked to a "scale-resonance" between turnover eddies and excursions in the instantaneous air temperature profiles. Excluding this scale-resonance results in the conventional Reynolds analogy with ϕm = ϕh across all stability conditions.

  14. Hydration of marginal basins and compositional variations within the continental lithospheric mantle inferred from a new global model of shear and compressional velocity

    NASA Astrophysics Data System (ADS)

    Tesoniero, Andrea; Auer, Ludwig; Boschi, Lapo; Cammarano, Fabio

    2015-11-01

    We present a new global model of shear and compressional wave speeds for the entire mantle, partly based on the data set employed for the shear velocity model savani. We invert Rayleigh and Love surface waves up to the sixth overtone in combination with major P and S body wave phases. Mineral physics data on the isotropic δlnVS/δlnVP ratio are taken into account in the form of a regularization constraint. The relationship between VP and VS that we observe in the top 300 km of the mantle has important thermochemical implications. Back-arc basins in the Western Pacific are characterized by large VP/VS and not extremely low VS at ˜150 km depth, consistently with presence of water. Most pronounced anomalies are located in the Sea of Japan, in the back-arc region of the Philippine Sea, and in the South China Sea. Our results indicate the effectiveness of slab-related processes to hydrate the mantle and suggest an important role of Pacific plate subduction also for the evolution of the South China Sea. We detect lateral variations in composition within the continental lithospheric mantle. Regions that have been subjected to rifting, collisions, and flood basalt events are underlain by relatively large VP/VS ratio compared to undeformed Precambrian regions, consistently with a lower degree of chemical depletion. Compositional variations are also observed in deep lithosphere. At ˜200 km depth, mantle beneath Australia and African cratons has comparable positive VS anomalies with other continental regions, but VP is ˜1% higher.

  15. The inviscid and viscous instability of an unbounded shear layer: Effect of surface tension, density, viscosity and velocity profile

    NASA Astrophysics Data System (ADS)

    Alabduljalil, Saad Abdulateef

    Parallel flows constitute prototypical configurations in many important applications in industry such as atomization and spraying of liquid fuels. A full description and understanding of the inviscid and viscous instability of realistic velocity profiles in unbounded two-phase shear layers without restriction on the range of the physical parameters of the flow are yet to be accomplished. The inviscid and viscous instability characteristics of unbounded parallel flows of two fluids with different viscosities and densities are extensively investigated by performing a full linear stability analysis. The effects of density and viscosity stratifications, surface tension, Reynolds number and velocity profile are determined. The neutral stability and the maximal growth rate for the instability modes are calculated for a wide range of flow parameters. The inviscid instability is first studied for the piecewise-linear profile and the error-function profile. Apart from the stabilizing effect observed in most of the cases, surface tension is found to destabilize the neutrally-stable waves that exist when surface tension is absent. A mathematical explanation and a physical explanation are given. The piecewise-linear profile does not match the more realistic results obtained with the error-function profile in the short-wavelength range, especially in nonhomogeneous shear layers. The viscous instability is then studied for the error-function profile. A numerical scheme which is efficiently capable of handling a broad range of flow configurations and parameters is developed. The inclusion of viscosity alters the inviscid perturbations and produces additional modes, most remarkably, the interfacial mode that arises at large wavenumbers. The coexistence of three distinct modes in gas-liquid systems is observed. The parameters that control the mode crossing between these modes are determined. Energy considerations and parametric properties are found to be efficient tools to identify

  16. Micromechanical poroelastic finite element and shear-lag models of tendon predict large strain dependent Poisson's ratios and fluid expulsion under tensile loading.

    PubMed

    Ahmadzadeh, Hossein; Freedman, Benjamin R; Connizzo, Brianne K; Soslowsky, Louis J; Shenoy, Vivek B

    2015-08-01

    As tendons are loaded, they reduce in volume and exude fluid to the surrounding medium. Experimental studies have shown that tendon stretching results in a Poisson's ratio greater than 0.5, with a maximum value at small strains followed by a nonlinear decay. Here we present a computational model that attributes this macroscopic observation to the microscopic mechanism of the load transfer between fibrils under stretch. We develop a finite element model based on the mechanical role of the interfibrillar-linking elements, such as thin fibrils that bridge the aligned fibrils or macromolecules such as glycosaminoglycans (GAGs) in the interfibrillar sliding and verify it with a theoretical shear-lag model. We showed the existence of a previously unappreciated structure-function mechanism whereby the Poisson's ratio in tendon is affected by the strain applied and interfibrillar-linker properties, and together these features predict tendon volume shrinkage under tensile loading. During loading, the interfibrillar-linkers pulled fibrils toward each other and squeezed the matrix, leading to the Poisson's ratio larger than 0.5 and fluid expulsion. In addition, the rotation of the interfibrillar-linkers with respect to the fibrils at large strains caused a reduction in the volume shrinkage and eventual nonlinear decay in Poisson's ratio at large strains. Our model also predicts a fluid flow that has a radial pattern toward the surrounding medium, with the larger fluid velocities in proportion to the interfibrillar sliding. Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  17. Ground-motion site effects from multimethod shear-wave velocity characterization at 16 seismograph stations deployed for aftershocks of the August 2011 Mineral, Virginia earthquake

    USGS Publications Warehouse

    Stephenson, William J.; Odum, Jackson K.; McNamara, Daniel E.; Williams, Robert A.; Angster, Stephen J

    2014-01-01

    We characterize shear-wave velocity versus depth (Vs profile) at 16 portable seismograph sites through the epicentral region of the 2011 Mw 5.8 Mineral (Virginia, USA) earthquake to investigate ground-motion site effects in the area. We used a multimethod acquisition and analysis approach, where active-source horizontal shear (SH) wave reflection and refraction as well as active-source multichannel analysis of surface waves (MASW) and passive-source refraction microtremor (ReMi) Rayleigh wave dispersion were interpreted separately. The time-averaged shear-wave velocity to a depth of 30 m (Vs30), interpreted bedrock depth, and site resonant frequency were estimated from the best-fit Vs profile of each method at each location for analysis. Using the median Vs30 value (270–715 m/s) as representative of a given site, we estimate that all 16 sites are National Earthquake Hazards Reduction Program (NEHRP) site class C or D. Based on a comparison of simplified mapped surface geology to median Vs30 at our sites, we do not see clear evidence for using surface geologic units as a proxy for Vs30 in the epicentral region, although this may primarily be because the units are similar in age (Paleozoic) and may have similar bulk seismic properties. We compare resonant frequencies calculated from ambient noise horizontal:vertical spectral ratios (HVSR) at available sites to predicted site frequencies (generally between 1.9 and 7.6 Hz) derived from the median bedrock depth and average Vs to bedrock. Robust linear regression of HVSR to both site frequency and Vs30 demonstrate moderate correlation to each, and thus both appear to be generally representative of site response in this region. Based on Kendall tau rank correlation testing, we find that Vs30 and the site frequency calculated from average Vs to median interpreted bedrock depth can both be considered reliable predictors of weak-motion site effects in the epicentral region.

  18. Measuring ion velocity distribution functions through high-aspect ratio holes in inductively coupled plasmas

    NASA Astrophysics Data System (ADS)

    Cunge, G.; Darnon, M.; Dubois, J.; Bezard, P.; Mourey, O.; Petit-Etienne, C.; Vallier, L.; Despiau-Pujo, E.; Sadeghi, N.

    2016-02-01

    Several issues associated with plasma etching of high aspect ratio structures originate from the ions' bombardment of the sidewalls of the feature. The off normal angle incident ions are primarily due to their temperature at the sheath edge and possibly to charging effects. We have measured the ion velocity distribution function (IVDF) at the wafer surface in an industrial inductively coupled plasma reactor by using multigrid retarding field analyzers (RFA) in front of which we place 400 μm thick capillary plates with holes of 25, 50, and 100 μm diameters. The RFA then probes IVDF at the exit of the holes with Aspect Ratios (AR) of 16, 8, and 4, respectively. The results show that the ion flux dramatically drops with the increase in AR. By comparing the measured IVDF with an analytical model, we concluded that the ion temperature is 0.27 eV in our plasma conditions. The charging effects are also observed and are shown to significantly reduce the ion energy at the bottom of the feature but only with a "minor" effect on the ion flux and the shape of the IVDF.

  19. Measuring ion velocity distribution functions through high-aspect ratio holes in inductively coupled plasmas

    SciTech Connect

    Cunge, G. Darnon, M.; Dubois, J.; Bezard, P.; Mourey, O.; Petit-Etienne, C.; Vallier, L.; Despiau-Pujo, E.; Sadeghi, N.

    2016-02-29

    Several issues associated with plasma etching of high aspect ratio structures originate from the ions' bombardment of the sidewalls of the feature. The off normal angle incident ions are primarily due to their temperature at the sheath edge and possibly to charging effects. We have measured the ion velocity distribution function (IVDF) at the wafer surface in an industrial inductively coupled plasma reactor by using multigrid retarding field analyzers (RFA) in front of which we place 400 μm thick capillary plates with holes of 25, 50, and 100 μm diameters. The RFA then probes IVDF at the exit of the holes with Aspect Ratios (AR) of 16, 8, and 4, respectively. The results show that the ion flux dramatically drops with the increase in AR. By comparing the measured IVDF with an analytical model, we concluded that the ion temperature is 0.27 eV in our plasma conditions. The charging effects are also observed and are shown to significantly reduce the ion energy at the bottom of the feature but only with a “minor” effect on the ion flux and the shape of the IVDF.

  20. Mean velocity profile in a sheared and thermally stratified atmospheric boundary layer.

    PubMed

    Katul, Gabriel G; Konings, Alexandra G; Porporato, Amilcare

    2011-12-23

    A stability correction function φ(m)(ζ) that accounts for distortions to the logarithmic mean velocity profile (MVP) in the lower atmosphere caused by thermal stratification was proposed by Monin and Obukhov in the 1950s using dimensional analysis. Its universal character was established from many field experiments. However, theories that describe the canonical shape of φ(m)(ζ) are still lacking. A previous link between the spectrum of turbulence and the MVP is expanded here to include the effects of thermal stratification on the turbulent kinetic energy dissipation rate and eddy-size anisotropy. The resulting theory provides a novel explanation for the power-law exponents and coefficients already reported for φ(m)(ζ) from numerous field experiments.

  1. Velocity autocorrelation function in supercooled liquids: Long-time tails and anomalous shear-wave propagation

    NASA Astrophysics Data System (ADS)

    Peng, H. L.; Schober, H. R.; Voigtmann, Th.

    2016-12-01

    Molecular dynamic simulations are performed to reveal the long-time behavior of the velocity autocorrelation function (VAF) by utilizing the finite-size effect in a Lennard-Jones binary mixture. Whereas in normal liquids the classical positive t-3 /2 long-time tail is observed, we find in supercooled liquids a negative tail. It is strongly influenced by the transfer of the transverse current wave across the period boundary. The t-5 /2 decay of the negative long-time tail is confirmed in the spectrum of VAF. Modeling the long-time transverse current within a generalized Maxwell model, we reproduce the negative long-time tail of the VAF, but with a slower algebraic t-2 decay.

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

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

  4. Tetrahedral vs. polyhedral mesh size evaluation on flow velocity and wall shear stress for cerebral hemodynamic simulation.

    PubMed

    Spiegel, Martin; Redel, Thomas; Zhang, Y Jonathan; Struffert, Tobias; Hornegger, Joachim; Grossman, Robert G; Doerfler, Arnd; Karmonik, Christof

    2011-01-01

    Haemodynamic factors, in particular wall shear stresses (WSSs) may have significant impact on growth and rupture of cerebral aneurysms. Without a means to measure WSS reliably in vivo, computational fluid dynamic (CFD) simulations are frequently employed to visualise and quantify blood flow from patient-specific computational models. With increasing interest in integrating these CFD simulations into pretreatment planning, a better understanding of the validity of the calculations in respect to computation parameters such as volume element type, mesh size and mesh composition is needed. In this study, CFD results for the two most common aneurysm types (saccular and terminal) are compared for polyhedral- vs. tetrahedral-based meshes and discussed regarding future clinical applications. For this purpose, a set of models were constructed for each aneurysm with spatially varying surface and volume mesh configurations (mesh size range: 5119-258, 481 volume elements). WSS distribution on the model wall and point-based velocity measurements were compared for each configuration model. Our results indicate a benefit of polyhedral meshes in respect to convergence speed and more homogeneous WSS patterns. Computational variations of WSS values and blood velocities are between 0.84 and 6.3% from the most simple mesh (tetrahedral elements only) and the most advanced mesh design investigated (polyhedral mesh with boundary layer).

  5. Crustal shear wave velocity structure of the western United States inferred from ambient seismic noise and earthquake data

    NASA Astrophysics Data System (ADS)

    Moschetti, M. P.; Ritzwoller, M. H.; Lin, F.-C.; Yang, Y.

    2010-10-01

    Surface wave dispersion measurements from ambient seismic noise and array-based measurements from teleseismic earthquakes observed with the EarthScope/USArray Transportable Array (TA) are inverted using a Monte Carlo method for a 3-D VS model of the crust and uppermost mantle beneath the western United States. The combination of data from these methods produces exceptionally broadband dispersion information from 6 to 100 s period, which constrains shear wave velocity structures in the crust and uppermost mantle to a depth of more than 100 km. The high lateral resolution produced by the TA network and the broadbandedness of the dispersion information motivate the question of the appropriate parameterization for a 3-D model, particularly for the crustal part of the model. We show that a relatively simple model in which VS increases monotonically with depth in the crust can fit the data well across more than 90% of the study region, except in eight discrete areas where greater crustal complexity apparently exists. The regions of greater crustal complexity are the Olympic Peninsula, the MendocinoTriple Junction, the Yakima Fold Belt, the southern Cascadia back arc, the Great Central Valley of California, the Salton Trough, the Snake River Plain, and the Wasatch Mountains. We also show that a strong Rayleigh-Love discrepancy exists across much of the western United States, which can be resolved by introducing radial anisotropy in both the mantle and notably the crust. We focus our analysis on demonstrating the existence of crustal radial anisotropy and primarily discuss the crustal part of the isotropic model that results from the radially anisotropic model by Voigt averaging. Model uncertainties from the Monte Carlo inversion are used to identify robust isotropic features in the model. The uppermost mantle beneath the western United States is principally composed of four large-scale shear wave velocity features, but lower crustal velocity structure exhibits far greater

  6. A global horizontal shear velocity model of the upper mantle from multimode Love wave measurements

    NASA Astrophysics Data System (ADS)

    Ho, Tak; Priestley, Keith; Debayle, Eric

    2016-10-01

    Surface wave studies in the 1960s provided the first indication that the upper mantle was radially anisotropic. Resolving the anisotropic structure is important because it may yield information on deformation and flow patterns in the upper mantle. The existing radially anisotropic models are in poor agreement. Rayleigh waves have been studied extensively and recent models show general agreement. Less work has focused on Love waves and the models that do exist are less well-constrained than are Rayleigh wave models, suggesting it is the Love wave models that are responsible for the poor agreement in the radially anisotropic structure of the upper mantle. We have adapted the waveform inversion procedure of Debayle & Ricard to extract propagation information for the fundamental mode and up to the fifth overtone from Love waveforms in the 50-250 s period range. We have tomographically inverted these results for a mantle horizontal shear wave-speed model (βh(z)) to transition zone depths. We include azimuthal anisotropy (2θ and 4θ terms) in the tomography, but in this paper we discuss only the isotropic βh(z) structure. The data set is significantly larger, almost 500 000 Love waveforms, than previously published Love wave data sets and provides ˜17 000 000 constraints on the upper-mantle βh(z) structure. Sensitivity and resolution tests show that the horizontal resolution of the model is on the order of 800-1000 km to transition zone depths. The high wave-speed roots beneath the oldest parts of the continents appear to extend deeper for βh(z) than for βv(z) as in previous βh(z) models, but the resolution tests indicate that at least parts of these features could be artefacts. The low wave speeds beneath the mid-ocean ridges fade by ˜150 km depth except for the upper mantle beneath the East Pacific Rise which remains slow to ˜250 km depth. The resolution tests suggest that the low wave speeds at deeper depths beneath the East Pacific Rise are not solely due

  7. Upper mantle shear wave velocity structure beneath northern Victoria Land, Antarctica: Volcanism and uplift in the northern Transantarctic Mountains

    NASA Astrophysics Data System (ADS)

    Graw, Jordan H.; Adams, Aubreya N.; Hansen, Samantha E.; Wiens, Douglas A.; Hackworth, Lauren; Park, Yongcheol

    2016-09-01

    The Transantarctic Mountains (TAMs) are the largest non-compressional mountain range on Earth, and while a variety of uplift mechanisms have been proposed, the origin of the TAMs is still a matter of great debate. Most previous seismic investigations of the TAMs have focused on a central portion of the mountain range, near Ross Island, providing little along-strike constraint on the upper mantle structure, which is needed to better assess competing uplift models. Using data recorded by the recently deployed Transantarctic Mountains Northern Network, as well as data from the Transantarctic Mountains Seismic Experiment and from five stations operated by the Korea Polar Research Institute, we investigate the upper mantle structure beneath a previously unexplored portion of the mountain range. Rayleigh wave phase velocities are calculated using a two-plane wave approximation and are inverted for shear wave velocity structure. Our model shows a low velocity zone (LVZ; ∼4.24 km s-1) at ∼160 km depth offshore and adjacent to Mt. Melbourne. This LVZ extends inland and vertically upwards, with more lateral coverage above ∼100 km depth beneath the northern TAMs and Victoria Land. A prominent LVZ (∼4.16-4.24 km s-1) also exists at ∼150 km depth beneath Ross Island, which agrees with previous results in the TAMs near the McMurdo Dry Valleys, and relatively slow velocities (∼4.24-4.32 km s-1) along the Terror Rift connect the low velocity anomalies. We propose that the LVZs reflect rift-related decompression melting and provide thermally buoyant support for the TAMs uplift, consistent with proposed flexural models. We also suggest that heating, and hence uplift, along the mountain front is not uniform and that the shallower LVZ beneath northern Victoria Land provides greater thermal support, leading to higher bedrock topography in the northern TAMs. Young (0-15 Ma) volcanic rocks associated with the Hallett and the Erebus Volcanic Provinces are situated directly

  8. Shear-wave velocity and site-amplification factors for 50 Australian sites determined by the spectral analysis of surface waves method

    USGS Publications Warehouse

    Kayen, Robert E.; Carkin, Bradley A.; Allen, Trevor; Collins, Clive; McPherson, Andrew; Minasian, Diane L.

    2015-01-01

    One-dimensional shear-wave velocity (VS ) profiles are presented at 50 strong motion sites in New South Wales and Victoria, Australia. The VS profiles are estimated with the spectral analysis of surface waves (SASW) method. The SASW method is a noninvasive method that indirectly estimates the VS at depth from variations in the Rayleigh wave phase velocity at the surface.

  9. Inversion of surface wave data for shear wave velocity profiles: Case studies of thick buried low-velocity layers in Malta

    NASA Astrophysics Data System (ADS)

    Farrugia, Daniela; Paolucci, Enrico; D'Amico, Sebastiano; Galea, Pauline

    2015-04-01

    The islands composing the Maltese archipelago (Central Mediterranean) are characterised by a four layer sequence of limestones and clays, with the Lower Coralline Limestone being the oldest exposed layer. The hard Globigerina Limestone (GL) overlies this layer and is found outcropping in the eastern part of Malta and western part of Gozo. The rest of the islands are characterised by Upper Coralline Limestone (UCL) plateaus and hillcaps covering a soft Blue Clay (BC) layer which can be up to 75 m thick. Thus the BC layer introduces a velocity inversion in the stratigraphy, and makes the Vs30 parameter not always suitable for seismic microzonation purposes. Such a layer may still produce amplification effects, however would not contribute to the numerical mean of Vs in the upper 30m. Moreover, buildings are being increasingly constructed on this type of geological foundation. Obtaining the shear wave (Vs) profiles of the different layers around the islands is the first step needed for a detailed study of local seismic site response. A survey of Vs in each type of lithology and around the islands has never been undertaken. Array measurements of ambient noise using vertical geophones were carried out at six sites in Malta and one in Gozo, characterised by the buried low-velocity layer. The array was set up in an L-shaped configuration and the Extended Spatial Autocorrelation (ESAC) technique was used to extract Rayleigh wave dispersion curves. The effective dispersion curve obtained at all the sites exhibited a 'normal' dispersive trend (i.e. velocity decreases with increasing frequency) at low frequencies, followed by an inverse dispersive trend at high frequencies. Such a shape can be tentatively explained in terms of the presence of higher mode Rayleigh waves, which are generally present when a stiff layer overlies a softer layer. Additionally a series of three-component ambient noise measurements were taken at each of the sites and H/V curves obtained. The

  10. Influence of the tilt angle of Percutaneous Aortic Prosthesis on Velocity and Shear Stress Fields.

    PubMed

    Gomes, Bruno Alvares de Azevedo; Camargo, Gabriel Cordeiro; Santos, Jorge Roberto Lopes Dos; Azevedo, Luis Fernando Alzuguir; Nieckele, Ângela Ourivio; Siqueira-Filho, Aristarco Gonçalves; Oliveira, Glaucia Maria Moraes de

    2017-08-07

    Due to the nature of the percutaneous prosthesis deployment process, a variation in its final position is expected. Prosthetic valve placement will define the spatial location of its effective orifice in relation to the aortic annulus. The blood flow pattern in the ascending aorta is related to the aortic remodeling process, and depends on the spatial location of the effective orifice. The hemodynamic effect of small variations in the angle of inclination of the effective orifice has not been studied in detail. To implement an in vitro simulation to characterize the hydrodynamic blood flow pattern associated with small variations in the effective orifice inclination. A three-dimensional aortic phantom was constructed, reproducing the anatomy of one patient submitted to percutaneous aortic valve implantation. Flow analysis was performed by use of the Particle Image Velocimetry technique. The flow pattern in the ascending aorta was characterized for six flow rate levels. In addition, six angles of inclination of the effective orifice were assessed. The effective orifice at the -4° and -2° angles directed the main flow towards the anterior wall of the aortic model, inducing asymmetric and high shear stress in that region. However, the effective orifice at the +3° and +5° angles mimics the physiological pattern, centralizing the main flow and promoting a symmetric distribution of shear stress. The measurements performed suggest that small changes in the angle of inclination of the percutaneous prosthesis aid in the generation of a physiological hemodynamic pattern, and can contribute to reduce aortic remodeling. Devido à natureza do processo de liberação da prótese percutânea, é esperada uma variabilidade do posicionamento final da válvula. A localização da prótese irá definir a posição espacial do seu orifício efetivo em relação ao ânulo aórtico. O padrão do fluxo sanguíneo em aorta ascendente está relacionado ao processo de remodelamento a

  11. PKP Waveform Complexity and Its Implications to Fine Structure Near the Edge of African Large Low Shear Velocity Province

    NASA Astrophysics Data System (ADS)

    Song, Teh-Ru Alex; Tanaka, Satoru; Takeuchi, Nozomu

    2010-05-01

    and receiver-side structure do not play a predominant role in generating these anomalous PKPab waveforms. We then look into structural anomaly near the core-mantle-boundary (CMB) since PKPab grazes the CMB at a very shallow angle and it can effectively interact with it and possibly produce anomalous PKPab waveforms. We first explore 1-D model space by introducing velocity anomaly directly above the CMB, with a velocity perturbation up to a few tens of percents in S wave velocity and P wave velocity. We calculate synthetics up to 2 Hz by Direct Solution Method (DSM) and Reflectivity Method to examine waveform anomaly at long period band (0.01-0.2 Hz) as well as short-period band (0.5-2 Hz). Our preliminary result indicates that the model with a thin (~ 15 km) ultra-low velocity zone (ULVZ, 30% reduction in P wave and S wave velocity) is capable of reproducing characteristics of these anomalous PKPab waveforms at both frequency bands. The pierce points of PKPab in the source side at CMB are near the southeast Indian Ocean where S wave velocity is only slightly faster than PREM. On the other hand, the pierce points in the receiver side are at the eastern edge of the African Large Low Shear Velocity Province (LLSVP). One interesting feature of our ULVZ model is that dlnVs/dlnVp is about 1, which is different from most ULVZ models where dlnVs/dlnVp is about 3.

  12. Three-dimensional models of P wave velocity and P-to-S velocity ratio in the southern central Andes by simultaneous inversion of local earthquake data

    NASA Astrophysics Data System (ADS)

    Graeber, Frank M.; Asch, Günter

    1999-09-01

    The PISCO'94 (Proyecto de Investigatión Sismológica de la Cordillera Occidental, 1994) seismological network of 31 digital broad band and short-period three-component seismometers was deployed in northern Chile between the Coastal Cordillera and the Western Cordillera. More than 5300 local seismic events were observed in a 100 day period. A subset of high-quality P and S arrival time data was used to invert simultaneously for hypocenters and velocity structure. Additional data from two other networks in the region could be included. The velocity models show a number of prominent anomalies, outlining an extremely thickened crust (about 70 km) beneath the forearc region, an anomalous crustal structure beneath the recent magmatic arc (Western Cordillera) characterized by very low velocities, and a high-velocity slab. A region of an increased Vp/Vs ratio has been found directly above the Wadati-Benioff zone, which might be caused by hydration processes. A zone of lower than average velocities and a high Vp/Vs ratio might correspond to the asthenospheric wedge. The upper edge of the Wadati-Benioff zone is sharply defined by intermediate depth hypocenters, while evidence for a double seismic zone can hardly be seen. Crustal events between the Precordillera and the Western Cordillera have been observed for the first time and are mainly located in the vicinity of the Salar de Atacama down to depths of about 40 km.

  13. Upper mantle structure of shear-waves velocities and stratification of anisotropy in the Afar Hotspot region

    NASA Astrophysics Data System (ADS)

    Sicilia, D.; Montagner, J.-P.; Cara, M.; Stutzmann, E.; Debayle, E.; Lépine, J.-C.; Lévêque, J.-J.; Beucler, E.; Sebai, A.; Roult, G.; Ayele, A.; Sholan, J. M.

    2008-12-01

    The Afar area is one of the biggest continental hotspots active since about 30 Ma. It may be the surface expression of a mantle "plume" related to the African Superswell. Central Africa is also characterized by extensive intraplate volcanism. Around the same time (30 Ma), volcanic activity re-started in several regions of the African plate and hotspots such as Darfur, Tibesti, Hoggar and Mount Cameroon, characterized by a significant though modest volcanic production. The interactions of mantle upwelling with asthenosphere, lithosphere and crust remain unclear and seismic anisotropy might help in investigating these complex interactions. We used data from the global seismological permanent FDSN networks (GEOSCOPE, IRIS, MedNet, GEO- FON, etc.), from the temporary PASSCAL experiments in Tanzania and Saudi Arabia and a French deployment of 5 portable broadband stations surrounding the Afar Hotspot. A classical two-step tomographic inversion from surface waves performed in the Horn of Africa with selected Rayleigh wave and Love wave seismograms leads to a 3D-model of both S V velocities and azimuthal anisotropy, as well as radial SH/ SV anisotropy, with a lateral resolution of 500 km. The region is characterized by low shear-wave velocities beneath the Afar Hotspot, the Red Sea, the Gulf of Aden and East of the Tanzania Craton to 400 km depth. High velocities are present in the Eastern Arabia and the Tanzania Craton. The results of this study enable us to rule out a possible feeding of the Central Africa hotspots from the "Afar plume" above 150-200 km. The azimuthal anisotropy displays a complex pattern near the Afar Hotspot. Radial anisotropy, although poorly resolved laterally, exhibits S H slower than S V waves down to about 150 km depth, and a reverse pattern below. Both azimuthal and radial anisotropies show a stratification of anisotropy at depth, corresponding to different physical processes. These results suggest that the Afar hotspot has a different and

  14. Can Suspended Iron-Alloy Droplets Explain the Origin, Composition and Properties of Large Low Shear Velocity Provinces?

    NASA Astrophysics Data System (ADS)

    Zhang, Z.; Dorfman, S. M.; Labidi, J.; Zhang, S.; Manga, M.; Stixrude, L. P.; McDonough, W. F.; Williams, Q. C.

    2014-12-01

    The enigmatic large low shear velocity provinces (LLSVPs) identified by seismic tomography at the base of the Earth's mantle have been proposed to be reservoirs of primordial mantle composition tapped by hot spot volcanism. The LLSVPs are characterized by anomalously low shear wave speed, VS, slightly elevated bulk sound speed, VB, and high density, ρ, in piles as thick as 1000 km above the core-mantle boundary. This combination of properties could be explained by a few percent dense melt, but the solidus of the lower mantle silicate and oxide assemblage may be too high to produce melt over the large extent of these regions. Iron-rich sulfur-bearing alloy may be molten at the conditions of the LLSVPs and ~1-2% of this component could satisfy both constraints on VS and ρ. An Fe alloy phase in the LLSVPs also has the potential to explain geochemical anomalies associated with hot spot volcanism, and its existence can be constrained by geochemical mass balance. Primordial noble gases such as 3He would be preferentially dissolved in Fe-rich melt rather than crystalline silicates. The reconstructed abundances of the moderately siderophile/chalcophile elements S, Cu and Pb in iron-alloy-bearing LLSVPs do not exceed predicted losses from volatilization, though this depends on the S-content of the alloy. The alloy phase would also be expected to incorporate W, and W isotope anomalies associated with hot spots are thus expected to have important implications for the timing of LLSVP formation. We have developed a model, via CIDER-2014, for the origin and properties of LLSVPs incorporating geochemistry, mineral physics, and fluid dynamic constraints on the generation, capture, and thermoelastic properties of Fe-rich melt droplets. The solidification of a basal magma ocean would produce both solid silicates and metallic melt. The bulk of the alloy generated by this process would sink to merge with the core. However, once the density of the remnant liquid exceeds that of the

  15. New Hybridized Surface Wave Approach for Geotechnical Modeling of Shear Wave Velocity at Strong Motion Recording Stations

    NASA Astrophysics Data System (ADS)

    Kayen, R.; Carkin, B.; Minasian, D.

    2006-12-01

    Strong motion recording (SMR) networks often have little or no shear wave velocity measurements at stations where characterization of site amplification and site period effects is needed. Using the active Spectral Analysis of Surface Waves (SASW) method, and passive H/V microtremor method we have investigated nearly two hundred SMR sites in California, Alaska, Japan, Australia, China and Taiwan. We are conducting these studies, in part, to develop a new hybridized method of site characterization that utilizes a parallel array of harmonic-wave sources for active-source SASW, and a single long period seismometer for passive-source microtremor measurement. Surface wave methods excel in their ability to non-invasively and rapidly characterize the variation of ground stiffness properties with depth below the surface. These methods are lightweight, inexpensive to deploy, and time-efficient. They have been shown to produce accurate and deep soil stiffness profiles. By placing and wiring shakers in a large parallel circuit, either side-by-side on the ground or in a trailer-mounted array, a strong in-phase harmonic wave can be produced. The effect of arraying many sources in parallel is to increase the amplitude of waves received at far-away spaced seismometers at low frequencies so as to extend the longest wavelengths of the captured dispersion curve. The USGS system for profiling uses this concept by arraying between two and eight electro-mechanical harmonic-wave shakers. With large parallel arrays of vibrators, a dynamic force in excess of 1000 lb can be produced to vibrate the ground and produce surface waves. We adjust the harmonic wave through a swept-sine procedure to profile surface wave dispersion down to a frequency of 1 Hz and out to surface wave-wavelengths of 200-1000 meters, depending on the site stiffness. The parallel-array SASW procedure is augmented using H/V microtremor data collected with the active source turned off. Passive array microtremor data

  16. Shear viscosity to entropy density ratios and implications for (im)perfect fluidity in Fermionic and Bosonic superfluids

    NASA Astrophysics Data System (ADS)

    Boyack, Rufus; Guo, Hao; Levin, K.

    2015-03-01

    Recent experiments on both unitary Fermi gases and high temperature superconductors (arxiv:1410.4835 [cond-mat.quant-gas], arxiv:1409.5820 [cond-mat.str-el].) have led to renewed interest in near perfect fluidity in condensed matter systems. This is quantified by studying the ratio of shear viscosity to entropy density. In this talk we present calculations of this ratio in homogeneous bosonic and fermionic superfluids, with the latter ranging from BCS to BEC. While the shear viscosity exhibits a power law (for bosons) or exponential suppression (for fermions), a similar dependence is found for the respective entropy densities. As a result, strict BCS and (true) bosonic superfluids have an analogous viscosity to entropy density ratio, behaving linearly with temperature times the (T-dependent) dissipation rate; this is characteristic of imperfect fluidity in weakly coupled fluids. This is contrasted with the behavior of fermions at unitarity which we argue is a consequence of additional terms in the entropy density thereby leading to more perfect fluidity. (arXiv:1407.7572v1 [cond-mat.quant-gas])

  17. A New Potential Predictor of Coronary Artery Disease: The Ratio of Mitral Peak Filling Velocity to Mitral Annular Velocity in Early Diastole

    PubMed Central

    Ma, Li; Li, Yanhong; Wu, Zhisheng; Mu, Yuming

    2017-01-01

    Background The aim of this study was to explore the value of the ratio of mitral peak filling velocity (E) to mitral annular velocity (e’) in early diastole as a predictor of coronary artery disease (CAD). Material/Methods The study population consisted of 83 consecutive patients (aged 38–77 years, 22 women and 61 men) who received coronary angiography. The E/e’ ratio was estimated by echocardiographic examination. Statistical significance was determined by receiver operating characteristic (ROC) curve and multiple logistic regression analyses. Results ROC curve analysis showed that the optimal E/e’ ratio cut-off for predicting CAD was 8.153 with a specificity of 72.4% and sensitivity of 57.4%. The area under the ROC curve was 0.635 with a 95% confidence interval (CI) for normal distribution of 0.515–0.755 (p=0.043). Multivariate logistic regression analysis demonstrated that the E/e’ ratio was closely associated with CAD (odds ratio [OR], 1.350; 95% CI, 1.087–1.676, p=0.007). Conclusions The E/e’ ratio is a simple and practical predictor of CAD and may be an independent risk factor for CAD. Large-cohort and multi-center studies are required to confirm these observations. PMID:28267707

  18. Shear velocity model for the Kyrgyz Tien Shan from joint inversion of receiver function and surface wave data

    NASA Astrophysics Data System (ADS)

    Gilligan, Amy; Roecker, Steven W.; Priestley, Keith F.; Nunn, Ceri

    2014-10-01

    The Tien Shan is the largest active intracontinental orogenic belt on Earth. To better understand the processes causing mountains to form at great distances from a plate boundary, we analyse passive source seismic data collected on 40 broad-band stations of the MANAS project (2005-2007) and 12 stations of the permanent KRNET seismic network to determine variations in crustal thickness and shear wave speed across the range. We jointly invert P- and S-wave receiver functions with surface wave observations from both earthquakes and ambient noise to reduce the ambiguity inherent in the images obtained from the techniques applied individually. Inclusion of ambient noise data improves constraints on the upper crust by allowing dispersion measurements to be made at shorter periods. Joint inversion can also reduce the ambiguity in interpretation by revealing the extent to which various features in the receiver functions are amplified or eliminated by interference from multiples. The resulting wave speed model shows a variation in crustal thickness across the range. We find that crustal velocities extend to ˜75 km beneath the Kokshaal Range, which we attribute to underthrusting of the Tarim Basin beneath the southern Tien Shan. This result supports the plate model of intracontinental convergence. Crustal thickness elsewhere beneath the range is about 50 km, including beneath the Naryn Valley in the central Tien Shan where previous studies reported a shallow Moho. This difference apparently is the result of wave speed variations in the upper crust that were not previously taken into account. Finally, a high velocity lid appears in the upper mantle of the Central and Northern part of the Tien Shan, which we interpret as a remnant of material that may have delaminated elsewhere under the range.

  19. P- and S-wave boundaries of the north-western African Large Low Shear Velocity Province.

    NASA Astrophysics Data System (ADS)

    Smith, R.; Rost, S.

    2015-12-01

    Tomographic images of Earth's lowermost mantle are dominated by two large, nearly antipodal regions of strongly reduced seismic velocities. These areas, known as the Large Low Shear Velocity Provinces (LLSVPs), are located beneath the Pacific and Africa. This study focusses on the African LLSVP and mapping its northern and western boundaries using P- and S-waves and aims to infer the structural changes across this boundary. Tomographic models agree on the location and large-scale features of the lateral boundaries of the African LLSVP. However how to define the boundary of a LLSVP, commonly interpreted as a thermochemical pile, is still debated. Different tomographic models also disagree on the westward extent of the African LLSVP and its connection to the potential source region of the Icelandic hotspot. We analyse data from deep earthquakes in South America ( 5.5 magnitude and 100km depth) collected at broadband receivers across Africa and Europe to provide extensive coverage of the African LLSVP beneath the Atlantic ocean. The data-set provides the largest lateral coverage of the expected north-western boundary. Using Pdiff and PcP travel-time residuals we develop a model of the position of the western and north-western boundaries of the African LLSVP and detect smaller scale features located in the vicinity of the boundary. Pdiff results combined with P and PcP data allow us to constrain the height of the African LLSVP and the sharpness of the boundaries, allowing better characterisation of this dominant feature of the lowermost mantle.

  20. The ZH ratio method for long-period seismic data: inversion for S-wave velocity structure

    NASA Astrophysics Data System (ADS)

    Yano, Tomoko; Tanimoto, T.; Rivera, L.

    2009-10-01

    The particle motion of surface waves, in addition to phase and group velocities, can provide useful information for S-wave velocity structure in the crust and upper mantle. In this study, we applied a new method to retrieve velocity structure using the ZH ratio, the ratio between vertical and horizontal surface amplitudes of Rayleigh waves. Analysing data from the GEOSCOPE network, we measured the ZH ratios for frequencies between 0.004 and 0.05 Hz (period between 20 and 250s) and inverted them for S-wave velocity structure beneath each station. Our analysis showed that the resolving power of the ZH ratio is limited and final solutions display dependence on starting models; in particular, the depth of the Moho in the starting model is important in order to get reliable results. Thus, initial models for the inversion need to be carefully constructed. We chose PREM and CRUST2.0 in this study as a starting model for all but one station (ECH). The eigenvalue analysis of the least-squares problem that arises for each step of the iterative process shows a few dominant eigenvalues which explains the cause of the inversion's initial-model dependence. However, the ZH ratio is unique in having high sensitivity to near-surface structure and thus provides complementary information to phase and group velocities. Application of this method to GEOSCOPE data suggest that low velocity zones may exist beneath some stations near hotspots. Our tests with different starting models show that the models with low-velocity anomalies fit better to the ZH ratio data. Such low velocity zones are seen near Hawaii (station KIP), Crozet Island (CRZF) and Djibuti (ATD) but not near Reunion Island (RER). It is also found near Echery (ECH) which is in a geothermal area. However, this method has a tendency to produce spurious low velocity zones and resolution of the low velocity zones requires further careful study. We also performed simultaneous inversions for volumetric perturbation and

  1. A Three-Dimensional Shear-Velocity Model of the Atlantic Upper Mantle from Analysis of a Regional Dataset of Fundamental-Mode Rayleigh Waves

    NASA Astrophysics Data System (ADS)

    James, E.; Dalton, C. A.; Gaherty, J. B.

    2014-12-01

    We investigate the three-dimensional (3-D) shear-velocity structure of the upper mantle beneath the Atlantic Ocean. Phase velocity in the period range 30-130 seconds is measured for approximately 10,000 fundamental-mode Rayleigh waves traversing the Atlantic basin. In order to isolate the signal of the oceanic upper mantle, paths with >30% of their length through continental upper mantle are excluded. The lateral distribution of Rayleigh wave phase velocity in the Atlantic upper mantle is explored with two approaches. One, phase velocity is allowed to vary only as a function of seafloor age. Two, a general two-dimensional parameterization is utilized in order to capture perturbations to age-dependent structure. In both scenarios, phase velocity shows a strong dependence on seafloor age at all periods, with higher velocity associated with older seafloor. Removing age-dependent velocity from the 2-D phase-velocity maps highlights areas of anomalously low velocity, almost all of which are proximal to locations of hotspot volcanism. The age-dependent phase velocities for the Atlantic are not consistent with a half-space cooling model and are best explained by a plate cooling model with thickness of 75 km and mantle temperature of 1400oC. In contrast, age-dependent phase velocities for the Pacific basin determined by Nishimura and Forsyth [1989] can be fit reasonably well by a half-space cooling model with mantle temperature approximately 50oC warmer than the Atlantic. Comparison of Rayleigh wave phase velocity and fractionation-corrected Na concentrations in mid-ocean-ridge basalts erupted at 87 axial ridge segments reveals a positive correlation coefficient that increases with period, as expected if along-ridge variations in mantle potential temperature are controlling both quantities. Depth-dependent variations in vertically-polarized shear velocity are explored with a 3-D model and allow for comparison to previous whole-basin studies of the Atlantic [e.g., Moquet

  2. Multi-channel analysis of surface waves MASW of models with high shear-wave velocity contrast

    USGS Publications Warehouse

    Ivanov, J.; Miller, R.D.; Peterie, S.; Zeng, C.; Xia, J.; Schwenk, T.

    2011-01-01

    We use the multi-channel analysis of surface waves MASW method to analyze synthetic seismic data calculated using models with high shear-wave velocity Vs contrast. The MASW dispersion-curve images of the Rayleigh wave are obtained using various sets of source-offset and spread-size configurations from the synthetic seismic data and compared with the theoretically calculated fundamental- and higher-mode dispersion-curves. Such tests showed that most of the dispersion-curve images are dominated by higher-mode energy at the low frequencies, especially when analyzing data from long receiver offsets and thus significantly divert from numerically expected dispersion-curve trends, which can lead to significant Vs overestimation. Further analysis showed that using data with relatively short spread lengths and source offsets can image the desired fundamental-mode of the Rayleigh wave that matches the numerically expected dispersion-curve pattern. As a result, it was concluded that it might be possible to avoid higher-mode contamination at low frequencies at sites with high Vs contrast by appropriate selection of spread size and seismic source offset. ?? 2011 Society of Exploration Geophysicists.

  3. Shear wave velocities in the Pampean flat-slab region from Rayleigh wave tomography: Implications for slab and upper mantle hydration

    NASA Astrophysics Data System (ADS)

    Porter, Ryan; Gilbert, Hersh; Zandt, George; Beck, Susan; Warren, Linda; Calkins, Josh; Alvarado, Patricia; Anderson, Megan

    2012-11-01

    The Pampean flat-slab region, located in central Argentina and Chile between 29° and 34°S, is considered a modern analog for Laramide flat-slab subduction within western North America. Regionally, flat-slab subduction is characterized by the Nazca slab descending to ˜100 km depth, flattening out for ˜300 km laterally before resuming a more "normal" angle of subduction. Flat-slab subduction correlates spatially with the track of the Juan Fernandez Ridge, and is associated with the inboard migration of deformation and the cessation of volcanism within the region. To better understand flat-slab subduction we combine ambient-noise tomography and earthquake-generated surface wave measurements to calculate a regional 3D shear velocity model for the region. Shear wave velocity variations largely relate to changes in lithology within the crust, with basins and bedrock exposures clearly defined as low- and high-velocity regions, respectively. We argue that subduction-related hydration plays a significant role in controlling shear wave velocities within the upper mantle. In the southern part of the study area, where normal-angle subduction is occurring, the slab is visible as a high-velocity body with a low-velocity mantle wedge above it, extending eastward from the active arc. Where flat-slab subduction is occurring, slab velocities increase to the east while velocities in the overlying lithosphere decrease, consistent with the slab dewatering and gradually hydrating the overlying mantle. The hydration of the slab may be contributing to the excess buoyancy of the subducting oceanic lithosphere, helping to drive flat-slab subduction.

  4. The lower bound violation of shear viscosity to entropy ratio due to logarithmic correction in STU model

    NASA Astrophysics Data System (ADS)

    Pourhassan, Behnam; Faizal, Mir

    2017-02-01

    In this paper, we analyze the effects of thermal fluctuations on a STU black hole. We observe that these thermal fluctuations can affect the stability of a STU black hole. We will also analyze the effects of these thermal fluctuations on the thermodynamics of a STU black hole. Furthermore, in the Jacobson formalism such a modification will produce a deformation of the geometry of the STU black hole. Hence, we use the AdS/CFT correspondence to analyze the effect of such a deformation on the dual quark-gluon plasma. So, we explicitly analyze the effect of thermal fluctuations on the shear viscosity to entropy ratio in the quark-gluon plasma, and we analyze the effects of thermal fluctuations on this ratio.

  5. Isokinetic hamstrings-to-quadriceps peak torque ratio: the influence of sport modality, gender, and angular velocity.

    PubMed

    Andrade, Marilia Dos Santos; De Lira, Claudio Andre Barbosa; Koffes, Fabiana De Carvalho; Mascarin, Naryana Cristina; Benedito-Silva, Ana Amélia; Da Silva, Antonio Carlos

    2012-01-01

    The purpose of this study was to determine differences in hamstrings-to-quadriceps (H/Q) peak torque ratios evaluated at different angular velocities between men and women who participate in judo, handball or soccer. A total of 166 athletes, including 58 judokas (26 females and 32 males), 39 handball players (22 females and 17 males), and 69 soccer players (17 females and 52 males), were evaluated using an isokinetic dynamometer. The H/Q isokinetic peak torque ratios were calculated at angular velocities of 1.05 rad · s⁻¹ and 5.23 rad · s⁻¹. In the analysis by gender, female soccer players produced lower H/Q peak torque ratios at 1.05 rad · s⁻¹ than males involved in the same sport. However, when H/Q peak torque ratio was assessed at 5.23 rad · s⁻¹, there were no significant differences between the sexes. In the analysis by sport, there were no differences among females at 1.05 rad · s⁻¹. In contrast, male soccer players had significantly higher H/Q peak torque ratios than judokas (66 ± 12% vs. 57 ± 14%, respectively). Female handball players produced significantly lower peak torque ratios at 5.23 rad · s⁻¹ than judokas or soccer players, whereas males presented no ratio differences among sports At 5.23 rad · s⁻¹. In the analysis by velocity, women's muscular ratios assessed at 1.05 rad · s⁻¹ were significantly lower than at 5.23 rad · s⁻¹ for all sports; among men, only judokas presented lower ratios at 1.05 rad · s⁻¹ than at 5.23 rad · s⁻¹. The present results suggest that sport modality and angular velocity influence the isokinetic strength profiles of men and women.

  6. Comparison of Oceanic and Continental Lithosphere, Asthenosphere, and the LAB Through Shear Velocity Inversion of Rayleigh Wave Data from the ALBACORE Amphibious Array in Southern California

    NASA Astrophysics Data System (ADS)

    Amodeo, K.; Rathnayaka, S.; Weeraratne, D. S.; Kohler, M. D.

    2016-12-01

    Continental and oceanic lithosphere, which form in different tectonic environments, are studied in a single amphibious seismic array across the Southern California continental margin. This provides a unique opportunity to directly compare oceanic and continental lithosphere, asthenosphere, and the LAB (Lithosphere-Asthenosphere Boundary) in a single data set. The complex history of the region, including spreading center subduction, block rotation, and Borderland extension, allows us to study limits in the rigidity and strength of the lithosphere. We study Rayleigh wave phase velocities obtained from the ALBACORE (Asthenospheric and Lithospheric Broadband Architecture from the California Offshore Region Experiment) offshore seismic array project and invert for shear wave velocity structure as a function of depth. We divide the study area into several regions: continent, inner Borderland, outer Borderland, and oceanic seafloor categorized by age. A unique starting Vs model is used for each case including layer thicknesses, densities, and P and S velocities which predicts Rayleigh phase velocities and are compared to observed phase velocities in each region. We solve for shear wave velocities with the best fit between observed and predicted phase velocity data in a least square sense. Preliminary results indicate that lithospheric velocities in the oceanic mantle are higher than the continental region by at least 2%. The LAB is observed at 50 ± 20 km beneath 15-35 Ma oceanic seafloor. Asthenospheric low velocities reach a minimum of 4.2 km/s in all regions, but have a steeper positive velocity gradient at the base of the oceanic asthenosphere compared to the continent. Seismic tomography images in two and three dimensions will be presented from each study region.

  7. Pronounced Shear Velocity Asymmetry in the Mantle Across the Juan de Fuca Ridge and Curious Lack of Features at the Gorda Ridge

    NASA Astrophysics Data System (ADS)

    Bell, S. W.; Ruan, Y.; Forsyth, D. W.

    2015-12-01

    With new Rayleigh-wave tomography results, we have detected a clear and strong asymmetry in the shear velocity structure of the Juan de Fuca ridge. Concentrated in a relatively thin layer with a depth range of ~30-60km, there lies a region of very low shear velocity, with velocities ranging from ~3.8km/s to 4.0km/s. Such low velocities provide strong evidence for the presence of partial melt. This low-velocity region is highly asymmetric, extending much further west than east of the ridge. Especially at shallow depths of ~35 km, this low-velocity region is concentrated just west of the southern portion of the ridge. Peaking near the Axial Seamount, the youngest of the Cobb-Eickelberg Seamounts, it extends south to the region around the small Vance Seamounts just north of the junction with the Blanco Fracture Zone. The Juan de Fuca plate is relatively stationary in the hotspot reference frame, and the Juan de Fuca ridge migrates westward in the hotspot reference frame. Seamounts are overwhelmingly concentrated on the western flank of the ridge, and an asymmetric upwelling driven by migration in the hotspot reference frame has been proposed to explain the seamount asymmetry (i.e. Davis and Karsten, 1986). Our velocity asymmetry, which matches the seamount asymmetry, provides evidence for this asymmetric upwelling and its connection to migration in the absolute hotspot reference frame. In the shear velocity results, the Gorda ridge displays a remarkable lack of features, with no clearly identifiable expression in the subsurface velocity. There is evidence of a broad low-velocity feature beneath Gorda beginning at a depth of ~150 km, but no clear shallow features can be tied to the ridge. At the depths we can resolve (~25-250km), the anisotropy beneath and within the Juan de Fuca plate is small, indicating a deep source of the shear wave splitting results (Bodmer et al., in press), which indicate a fast axis aligned with the Juan de Fuca plate's absolute motion. Around

  8. Viscosity-ratio-based scaling for the rise velocity of a Taylor drop in a vertical tube.

    PubMed

    Quan, Shaoping; Lou, Jing

    2011-09-01

    Simulations of a silicon oil Taylor drop rising in a tube filled with a glycerol-water mixture are performed to investigate the viscosity ratio effects on the rise velocity of the Taylor drop. By varying the viscosity ratio λ between the drop and the suspending liquid from O(0.1) to O(10), a simple relationship of the nondimensional terminal velocity, the Froude number (Fr), is revealed as Fr ∝ λ(-0.27). This scaling is further confirmed by recently published experimental data [Hayashi, Kurimoto, and Tomiyama, Int. J. Multiphase Flow 37, 241 (2011)]. The simulated drop shapes also compare well with the experiments. Increasing the viscosity ratio elongates the drop and tends to make the tail bulge out. The correlation applies to small Reynolds numbers and finite viscosity ratios.

  9. Dependences of Ratio of the Luminosity to Ionization on Velocity and Chemical Composition of Meteors

    NASA Technical Reports Server (NTRS)

    Narziev, M.

    2011-01-01

    On the bases of results simultaneous photographic and radio echo observations, the results complex radar and television observations of meteors and also results of laboratory modeling of processes of a luminescence and ionization, correlation between of luminous intensity Ip to linear electronic density q from of velocities and chemical structure are investigated. It is received that by increasing value of velocities of meteors and decrease of nuclear weight of substance of particles, lg Ip/q decreased more than one order.

  10. Velocity ratio predicts outcomes in patients with low gradient severe aortic stenosis and preserved EF.

    PubMed

    Jander, Nikolaus; Hochholzer, Willibald; Kaufmann, Beat A; Bahlmann, Edda; Gerdts, Eva; Boman, Kurt; Chambers, John B; Nienaber, Christoph A; Ray, Simon; Rossebo, Anne; Pedersen, Terje R; Wachtell, Kristian; Gohlke-Bärwolf, Christa; Neumann, Franz-Josef; Minners, Jan

    2014-12-01

    To evaluate the usefulness of velocity ratio (VR) in patients with low gradient severe aortic stenosis (LGSAS) and preserved EF. LGSAS despite preserved EF represents a clinically challenging entity. Reliance on mean pressure gradient (MPG) may underestimate stenosis severity as has been reported in the context of paradoxical low flow, LGSAS. On the other hand, grading of stenosis severity by aortic valve area (AVA) may overrate stenosis severity due to erroneous underestimation of LV outflow tract (LVOT) diameter, small body size or inconsistencies in cut-off values for severe stenosis. We hypothesised that VR may have conceptual advantages over MPG and AVA, predict clinical outcomes and thereby be useful in the management of patients with LGSAS. Patients from the prospective Simvastatin and Ezetimibe in Aortic Stenosis (SEAS) study with an AVA<1.0 cm(2), MPG≤40 mm Hg and EF≥55% and asymptomatic at baseline were stratified according to VR with a cut-off value of 0.25. Outcomes were evaluated according to aortic valve-related events and cardiovascular death. Of 435 patients with LGSAS, 197 (45%) had VR<0.25 suggesting severe and 238 (55%) had VR≥0.25 suggesting non-severe stenosis. Aortic valve-related events (mean follow-up 42±14 months) were more frequent in patients with VR<0.25 (57% vs 41%; p<0.001) as was cardiovascular death within the first 24 months (p<0.05). In multivariable Cox regression analysis, MPG was the strongest independent predictor of aortic valve events (p<0.001) followed by VR (p<0.02). Adjusting AVA by VR increased predictive accuracy for aortic valve events (area under the receiver operating curve 0.62 (95% CI 0.57 to 0.67) vs 0.56 (95% CI 0.51 to 0.61) for AVA, p=0.02) with net reclassification improvement calculated at 0.36 (95% CI 0.17 to 0.54, p<0.001). VR did not improve the prediction of clinical events by MPG. In the difficult setting of LGSAS, VR shows a strong association with valve-related events and-although not

  11. Structure of turbulent flow at a river confluence with momentum and velocity ratios close to 1: Insight provided by an eddy-resolving numerical simulation

    NASA Astrophysics Data System (ADS)

    Constantinescu, George; Miyawaki, Shinjiro; Rhoads, Bruce; Sukhodolov, Alexander; Kirkil, Gokhan

    2011-05-01

    River confluences are complex hydrodynamic environments where convergence of incoming flows produces complicated patterns of fluid motion, including the development of large-scale turbulence structures. Accurately simulating confluence hydrodynamics represents a considerable challenge for numerical modeling of river flows. This study uses an eddy-resolving numerical model to simulate the mean flow and large-scale turbulence structure at an asymmetrical river confluence with a concordant bed when the momentum ratio between the two incoming streams is close to 1. Results of the simulation are compared with field data on mean flow and turbulence structure. The simulation shows that the mixing interface is populated by quasi-two-dimensional eddies. Successive eddies have opposing senses of rotation. The mixing layer structure resembles that of a wake behind a bluff body (wake mode). Strong streamwise-oriented vortical (SOV) cells form on both sides of the mixing layer, a finding consistent with patterns inferred from the field data. The predicted mean flow fields show that flow curvature has an important influence on streamwise variation of circulation within the cores of the two primary SOV cells. These SOV cells, along with vortices generated by flow over a submerged block of sediment at one of the banks, strongly influence distributions of the streamwise velocity and turbulent kinetic energy downstream of the junction. Comparison of the eddy-resolving simulation results with predictions from the steady Spalart-Allmaras RANS model shows that the latter fails to predict important features of the measured distributions of streamwise velocity and turbulent kinetic energy because the RANS model underpredicts the strength of the SOV cells. Analysis of instantaneous and mean bed shear stress distributions indicates that the SOV cells enhance bed shear stresses to a greater degree than the quasi-two-dimensional eddies in the mixing interface.

  12. Record of the Pacific Large Low Shear Velocity Province Upwellings Preserved in the Cretaceous Large Igneous Provinces

    NASA Astrophysics Data System (ADS)

    Madrigal, P.; Gazel, E.; Flores, K. E.; Bizimis, M.; Jicha, B. R.

    2015-12-01

    As the surface expression of deep mantle dynamics, Large Igneous Provinces (LIPs) are associated with the edges of large low shear velocity provinces (LLSVP) rooted at the core-mantle boundary. Instabilities in the LLSVP can cause periodic upwellings of material in the form of mantle plumes, which impact the lithosphere forming LIPs. However, the time frames of these massive lava outpourings are still uncertain. While continental LIPs are more readily accessible, oceanic LIPs have only been studied through drilling and sampling of fragments accreted to continental margins or island arcs, hence, they are relatively less understood. The impact of oceanic LIPs on oceanic biota is conspicuously recorded in global occurrences of black shale deposits that evidence episodes of anoxia and mass extinctions shortly after the formation of LIPs that ultimately can affect life on the entire planet. Our new geochemical and geochronological data of accreted Pacific LIPs found in the coasts of Nicoya Peninsula in Costa Rica record three LIP pulses possibly reflecting upwelling periods of the LLSVP at 140, 120 and 90 Ma. In order to test different models of origin of these LIPS, we created a complete reconstruction of the Pacific Plate configuration from the Mid-Jurassic to Upper-Cretaceous to show the existing correlation between upwelling pulses at edges of the Pacific LLSVP, oceanic anoxic events and the age from Pacific LIPs. We propose that since the formation of the Pacific plate at circa 175-180 Ma, a series of upwellings that interacted with mid-ocean ridge systems separated by 10-20 Ma have affected the planet periodically forming oceanic LIPs that still can be found today on the Pacific seafloor and accreted along the plate margins.

  13. Characteristics of Shear Wave Velocity Structures Beneath the Gulf of St. Lawrence, Eastern Canada from Ambient Seismic Noise Tomography

    NASA Astrophysics Data System (ADS)

    Kuponiyi, A.; Kao, H.; Cassidy, J. F.; Dosso, S. E.; Spence, G.

    2016-12-01

    Continuous ambient seismic noise waveforms collected from 2005-2008 at 24 broadband stations located in and around the Gulf St. Lawrence (GSL) are processed to derive Rayleigh wave dispersion curves. We conduct both surface wave tomography inversion and trans-dimensional Bayesian inversion to characterize the 3-D shear wave velocity (Vs) structure beneath the GSL up to 20 km depth. Our results indicate that the entire GSL region can be divided into three broad sections. In the northern GSL, the Grenville Province (i.e., the Proterozoic edge) is dominated by high Vs. However, scattered low Vs structures can be found to correspond to well-known anorthorsite sites. In contrast, the central section corresponds to a weak belt with generally low Vs. The southernmost section of the GSL is characterized by high Vs structures belonging to the Meguma and Avalon terranes. The basement structure at the eastern segment of the Appalachian Structural Front is characterized by relatively low-Vs. Prominent low Vs are found to coincide with locations of most graben structures and sedimentary basins in the GSL. Both the depth of the sedimentary basement and the geometry of major sedimentary basins are well imaged with the thickest sedimentary layer (over 15 km) found near the western edge of the Magdalen basin. At both shallow and mid-crust depths, prominent high Vs are found near the boundaries of the Ordovician-Silurian Anticosti and the Carboniferous Magdalen Basins. The deepest prominent low Vs structures correspond to displaced/deformed Humber zone sediments buried deep beneath Dunnage zone of Newfoundland. High Vs structures with variable thicknesses are found to overlie parts of the Canadian Maritime Basins. These top high Vs structures are generally very thin (<3 km) and can be explained as the manifestation of top volcanic layers in the region.

  14. Does Type 1 Diabetes Mellitus Affect the Shear Wave Velocity of the Thyroid Gland of Children Without Autoimmune Thyroiditis?

    PubMed

    Sağlam, Dilek; Ceyhan Bilgici, Meltem; Kara, Cengiz; Can Yilmaz, Gülay; Tanrivermiş Sayit, Asli

    2017-09-01

    The aim of this study is to evaluate the shear wave velocity (SWV) of the thyroid gland with acoustic radiation force impulse elastography in children with type 1 diabetes mellitus (T1D). Between November 2015 and April 2016, 35 T1D patients who were referred to our hospital's endocrinology outpatient clinic (mean age, 11.88 ± 4.1 years) and 30 children (mean age, 11.3 ± 3.08 years) in the control group were enrolled in the study. Five acoustic radiation force impulse elastography measurements from each lobe of the thyroid gland in m/s were recorded. Diabetes age, hemoglobin A1c, and C-peptide levels were recorded in T1D patients. Statistical analyses were performed using SPSS version 21 (IBM Corporation, Armonk, NY). The mean SWV of the thyroid gland in T1D patients and the control group was 1.11 ± 0.21 and 1.29 ± 0.23 m/s, respectively. The mean SWV of the thyroid gland in T1D patients was lower than that in the control group and this was significant (P = 0.002). The mean SWV of the thyroid gland was not correlated with hemoglobin A1c level, body mass index, or the insulin dose in T1D patients. The present study showed that T1D affects the thyroid gland stiffness even in patients without autoimmune thyroiditis. Acoustic radiation force impulse elastography may be a useful method in determining early changes in thyroid gland in T1D and may be used as a screening tool.

  15. Verification of the Velocity Structure in Mexico Basin Using the H/V Spectral Ratio of Microtremors

    NASA Astrophysics Data System (ADS)

    Matsushima, S.; Sanchez-Sesma, F. J.; Nagashima, F.; Kawase, H.

    2011-12-01

    The authors have been proposing a new theory to calculate the Horizontal-to-Vertical (H/V) spectral ratio of microtremors assuming that the wave field is completely diffuse and have attempted to apply the theory to understand the observed microtremor data. It is anticipated that this new theory can be applied to detect the subsurface velocity structure beneath urban area. Precise information about the subsurface velocity structure is essential for predicting strong ground motion accurately, which is necessary to mitigate seismic disaster. Mexico basin, who witnessed severe damage during the 1985 Michoacán Earthquake (Ms 8.1) several hundreds of kilometers away from the source region, is an interesting location in which the reassessment of soil properties is urgent. Because of subsidence, having improved estimates of properties is mandatory. In order to estimate possible changes in the velocity structure in the Mexico basin, we measured microtremors at strong motion observation sites in Mexico City. At those sites, information about the velocity profiles are available. Using the obtained data, we derive observed H/V spectral ratio and compare it with the theoretical H/V spectral ratio to gauge the goodness of our new theory. First we compared the observed H/V spectral ratios for five stations to see the diverse characteristics of this measurement. Then we compared the observed H/V spectral ratios with the theoretical predictions to confirm our theory. We assumed the velocity model of previous surveys at the strong motions observation sites as an initial model. We were able to closely fit both the peak frequency and amplitude of the observed H/V spectral ratio, by the theoretical H/V spectral ratio calculated by our new method. These results show that we have a good initial model. However, the theoretical estimates need some improvement to perfectly fit the observed H/V spectral ratio. This may be an indication that the initial model needs some adjustments. We

  16. [The radial velocity measurement accuracy of different spectral type low resolution stellar spectra at different signal-to-noise ratio].

    PubMed

    Wang, Feng-Fei; Luo, A-Li; Zhao, Yong-Heng

    2014-02-01

    The radial velocity of the star is very important for the study of the dynamics structure and chemistry evolution of the Milky Way, is also an useful tool for looking for variable or special objects. In the present work, we focus on calculating the radial velocity of different spectral types of low-resolution stellar spectra by adopting a template matching method, so as to provide effective and reliable reference to the different aspects of scientific research We choose high signal-to-noise ratio (SNR) spectra of different spectral type stellar from the Sloan Digital Sky Survey (SDSS), and add different noise to simulate the stellar spectra with different SNR. Then we obtain theradial velocity measurement accuracy of different spectral type stellar spectra at different SNR by employing a template matching method. Meanwhile, the radial velocity measurement accuracy of white dwarf stars is analyzed as well. We concluded that the accuracy of radial velocity measurements of early-type stars is much higher than late-type ones. For example, the 1-sigma standard error of radial velocity measurements of A-type stars is 5-8 times as large as K-type and M-type stars. We discuss the reason and suggest that the very narrow lines of late-type stars ensure the accuracy of measurement of radial velocities, while the early-type stars with very wide Balmer lines, such as A-type stars, become sensitive to noise and obtain low accuracy of radial velocities. For the spectra of white dwarfs stars, the standard error of radial velocity measurement could be over 50 km x s(-1) because of their extremely wide Balmer lines. The above conclusion will provide a good reference for stellar scientific study.

  17. Pseudo-3D shear velocity structure of the central North Island, New Zealand, determined from ambient noise analysis of temporary and permanent seismograph data

    NASA Astrophysics Data System (ADS)

    Behr, Y.; Townend, J.; Savage, M. K.; Bannister, S. C.

    2010-12-01

    The use of ambient seismic noise as a pervasive energy source has now become an established strand of seismology. It requires relatively short instrument deployment times and no artificial sources, thereby providing an economical and low-impact way of gaining new insights into crustal and upper mantle structure. The tectonics of the central North Island of New Zealand are dominated by the Taupo Volcanic Zone, a continental back-arc region characterized by extension, high heat flow and active volcanism, which has been the focus of several studies involving different geophysical methods. Information on the shear velocity structure derived from short-period surface wave analysis fills a gap in geophysical information from previous active and passive source studies. Furthermore the analysis of three-component data has revealed intriguing differences between vertically and horizontally polarized shear waves that can be related to melt bodies in the crust. Here we reprocess three-component data from four temporary seismic arrays that were deployed between 2001 and 2005 in the central North Island of New Zealand, combined with data from permanent seismic stations operational at the same time, using ambient noise correlation techniques. As the temporary deployments involved different types of broadband instruments and the necessary instrument response Information was in some cases incomplete or ambiguous, we use teleseismic events and the noise-correlation techniques suggested by Sens-Schoenfelder [GJI, 2008] to determine the correct instrument responses and timing errors. We then calculate Rayleigh and Love wave dispersion curves from ambient noise correlation and invert the dispersion curves for a pseudo-3D shear velocity model of the crust. Low shear velocities in the upper crust, as inferred from Rayleigh waves, coincide with regions of thick sediment deposits on the east coast of the North Island and presumed source regions for the rhyolitic volcanism in the Taupo

  18. Simulation comparison of a decoupled longitudinal control system and a velocity vector control wheel steering system during landings in wind shear

    NASA Technical Reports Server (NTRS)

    Kimball, G., Jr.

    1980-01-01

    A simulator comparison of the velocity vector control wheel steering (VCWS) system and a decoupled longitudinal control system is presented. The piloting task was to use the electronic attitude direction indicator (EADI) to capture and maintain a 3 degree glide slope in the presence of wind shear and to complete the landing using the perspective runway included on the EADI. The decoupled control system used constant prefilter and feedback gains to provide steady state decoupling of flight path angle, pitch angle, and forward velocity. The decoupled control system improved the pilots' ability to control airspeed and flight path angle during the final stages of an approach made in severe wind shear. The system also improved their ability to complete safe landings. The pilots preferred the decoupled control system in severe winds and, on a pilot rating scale, rated the approach and landing task with the decoupled control system as much as 3 to 4 increments better than use of the VCWS system.

  19. Phase-contrast magnetic resonance imaging measurements in intracranial aneurysms in vivo of flow patterns, velocity fields, and wall shear stress: comparison with computational fluid dynamics.

    PubMed

    Boussel, Loic; Rayz, Vitaliy; Martin, Alastair; Acevedo-Bolton, Gabriel; Lawton, Michael T; Higashida, Randall; Smith, Wade S; Young, William L; Saloner, David

    2009-02-01

    Evolution of intracranial aneurysms is known to be related to hemodynamic forces such as wall shear stress (WSS) and maximum shear stress (MSS). Estimation of these parameters can be performed using numerical simulations with computational fluid dynamics (CFD), but can also be directly measured with magnetic resonance imaging (MRI) using a time-dependent 3D phase-contrast sequence with encoding of each of the three components of the velocity vectors (7D-MRV). To study the accuracy of 7D-MRV in estimating these parameters in vivo, in comparison with CFD, 7D-MRV and patient-specific CFD modeling was performed for 3 patients who had intracranial aneurysms. Visual and quantitative analyses of the flow pattern and distribution of velocities, MSS, and WSS were performed using the two techniques. Spearman's coefficients of correlation between the two techniques were 0.56 for the velocity field, 0.48 for MSS, and 0.59 for WSS. Visual analysis and Bland-Altman plots showed good agreement for flow pattern and velocities but large discrepancies for MSS and WSS. These results indicate that 7D-MRV can be used in vivo to measure velocity flow fields and for estimating MSS and WSS. Currently, however, this method cannot accurately quantify the latter two parameters.

  20. Phase-Contrast MRI measurements in intra-cranial aneurysms in-vivo of flow patterns, velocity fields and wall shear stress: A comparison with CFD

    PubMed Central

    Boussel, Loic; Rayz, Vitaliy; Martin, Alastair; Acevedo-Bolton, Gabriel; Lawton, Michael T.; Higashida, Randall; Smith, Wade S.; Young, William L.; Saloner, David

    2010-01-01

    Evolution of intracranial aneurysms is known to be related to hemodynamic forces such as Wall Shear Stress (WSS) and Maximum Shear Stress (MSS). Estimation of these parameters can be performed using numerical simulations (computational fluid dynamics - CFD) but can also be directly measured with MRI using a time-dependent 3D phase-contrast sequence with encoding of each of the three components of the velocity vectors (7D-MRV). In order to study the accuracy of 7D-MRV in estimating these parameters in–vivo, in comparison with CFD, 7D-MRV and patient-specific CFD modeling was performed for three patients who had intracranial aneurysms. A visual and a quantitative analysis of the flow pattern and the distribution of velocities, MSS, and WSS were performed between the two techniques. Spearman's coefficients of correlation between the two techniques were 0.56 for the velocity field, 0.48 for MSS and 0.59 for WSS. Visual analysis and Bland-Altman plots showed a good agreement for flow pattern and velocities but large discrepancies for MSS and WSS. In conclusion, these results indicate that in-vivo 7D-MRV can be used to measure velocity flow fields and to estimate MSS and WSS but is not currently able to provide accurate quantification of these two last parameters. PMID:19161132

  1. Shear Wave Velocity and Site Amplification Factors for 25 Strong-Motion Instrument Stations Affected by the M5.8 Mineral, Virginia, Earthquake of August 23, 2011

    USGS Publications Warehouse

    Kayen, Robert; Carkin, Bradley; Corbett, Skye; Zangwill, Aliza; Estevez, Ivan; Lai, Lena

    2015-01-01

    Vertical one-dimensional shear wave velocity (Vs) profiles are presented for 25 strong-motion instrument sites along the Mid-Atlantic eastern seaboard, Piedmont region, and Appalachian region, which surround the epicenter of the M5.8 Mineral, Virginia, Earthquake of August 23, 2011. Testing was performed at sites in Pennsylvania, Maryland, West Virginia, Virginia, the District of Columbia, North Carolina, and Tennessee. The purpose of the study is to determine the detailed site velocity profile, the average velocity in the upper 30 meters of the profile (VS,30), the average velocity for the entire profile (VS,Z), and the National Earthquake Hazards Reduction Program (NEHRP) site classification. The Vs profiles are estimated using a non-invasive continuous-sine-wave method for gathering the dispersion characteristics of surface waves. A large trailer-mounted active source was used to shake the ground during the testing and produce the surface waves. Shear wave velocity profiles were inverted from the averaged dispersion curves using three independent methods for comparison, and the root-mean square combined coefficient of variation (COV) of the dispersion and inversion calculations are estimated for each site.

  2. Three-dimensional shear velocity anisotropic model of Piton de la Fournaise Volcano (La Réunion Island) from ambient seismic noise

    NASA Astrophysics Data System (ADS)

    Mordret, Aurélien; Rivet, Diane; Landès, Matthieu; Shapiro, Nikolaï M.

    2015-01-01

    We cross correlate 4 years of seismic noise from the seismic network of Piton de la Fournaise Volcano (La Réunion Island) to measure the group velocity dispersion curves of Rayleigh and Love waves. We average measurements from vertical and radial components to obtain 577 Rayleigh wave dispersion curves. The transverse components provided 395 Love wave dispersion curves. We regionalize the group velocities measurements into 2-D velocity maps between 0.4 and 8 s. Finally, we locally inverted these maps for a pseudo 3-D anisotropic shear-velocity model down to 3 km below the sea level using a Neighborhood Algorithm. The 3-D isotropic shear-wave model shows three distinct high-velocity anomalies surrounded by a low-velocity ring. The anomaly located below the present "Plaine des Sables" could be related to an old intrusive body at the location of the former volcanic center before it migrated toward its present location. The second high-velocity body located below the summit of the volcano likely corresponds to the actual preferential dyke intrusion zone as highlighted by the seismicity. The third high-velocity anomaly located below the "Grandes Pentes" and the "Grand Brûlé" areas and is an imprint of the solidified magma chamber of the dismantled "Les Alizés" Volcano. Radial anisotropy shows two main anomalies: positive anisotropy above sea level highlighting the recent edifice of Piton de la Fournaise with an accumulation of horizontal lava flows and the second one below the sea level with a negative anisotropy corresponding to the ancient edifice of Piton de la Fournaise dominated by intrusions of vertical dykes.

  3. Downhole Measurements of Shear- and Compression-Wave Velocities in Boreholes C4993, C4996, C4997 and C4998 at the Waste Treatment Plant DOE Hanford Site.

    SciTech Connect

    Redpath, Bruce B.

    2007-04-27

    This report describes the procedures and the results of a series of downhole measurements of shear- and compression-wave velocities performed as part of the Seismic Boreholes Project at the site of the Waste Treatment Plant (WTP). The measurements were made in several stages from October 2006 through early February 2007. Although some fieldwork was carried out in conjunction with the University of Texas at Austin (UT), all data acquired by UT personnel are reported separately by that organization.

  4. Explicit causal relations between material damping ratio and phase velocity from exact solutions of the dispersion equations of linear viscoelasticity

    NASA Astrophysics Data System (ADS)

    Meza-Fajardo, Kristel C.; Lai, Carlo G.

    2007-12-01

    The theory of linear viscoelasticity is the simplest constitutive model that can be adopted to accurately predict the small-strain mechanical response of materials exhibiting the ability to both store and dissipate strain energy. An important result implied by this theory is the relationship existing between material attenuation and the velocity of propagation of a mechanical disturbance. The functional dependence of these important parameters is represented by the Kramers-Kronig (KK) equations, also known as dispersion equations, which are nothing but a statement of the necessary and sufficient conditions to satisfy physical causality. This paper illustrates the derivation of exact solutions of the KK equations to provide explicit relations between frequency-dependent phase velocity and material damping ratio (or equivalently, quality factor). The assumptions that form the basis of the derivation are not beyond those established by the standard theory of viscoelasticity for a viscoelastic solid. The explicit expression for phase velocity as a function of damping ratio was derived by means of the theory of linear singular integral equations, and in particular by the solution of the associated Homogeneous Riemann Boundary Value Problem. It is shown that the same solution may be obtained also by using the implications of physical causality on the Fourier Transform. On the other hand, the explicit solution for damping ratio as a function of phase velocity was found through the components of the complex wavenumber. The exact solutions make it possible to obtain frequency-dependent material damping ratio solely from phase velocity measurements, and conversely. Hence, these relations provide an innovative and inexpensive tool to determine the small-strain dynamic properties of geomaterials. It is shown that the obtained rigorous solutions are in good agreement with well-known solutions based on simplifying assumptions that have been developed in the fields of seismology

  5. Laser induced fluorescence measurements of axial velocity, velocity shear, and parallel ion temperature profiles during the route to plasma turbulence in a linear magnetized plasma device

    NASA Astrophysics Data System (ADS)

    Chakraborty Thakur, S.; Adriany, K.; Gosselin, J. J.; McKee, J.; Scime, E. E.; Sears, S. H.; Tynan, G. R.

    2016-11-01

    We report experimental measurements of the axial plasma flow and the parallel ion temperature in a magnetized linear plasma device. We used laser induced fluorescence to measure Doppler resolved ion velocity distribution functions in argon plasma to obtain spatially resolved axial velocities and parallel ion temperatures. We also show changes in the parallel velocity profiles during the transition from resistive drift wave dominated plasma to a state of weak turbulence driven by multiple plasma instabilities.

  6. Scholte-wave Inversion for shallow 2D shear-wave velocity models at different locations in North- and Baltic sea using a hybrid particle swarm optimization scheme

    NASA Astrophysics Data System (ADS)

    Wilken, Dennis; Rabbel, Wolfgang

    2010-05-01

    In the years 2006 to 2008 we performed Airgun profiles to excite Scholte-waves at different locations in the North and Baltic sea. Scholte-wave energy was recorded using a specially developed Ocean-Bottom-Seismometer. The system is able to sample signals up to 11kHz and can thus be localised at seafloor with an accuracy of a few meters using traveltimes of high frequent seismic signals that are excited in the watercolumn. Scholte-wave recordings are added to common-receiver-gathers which are then inverted for shear-wave velocity structure by fitting modelled phase-slowness frequency dispersion spectra to spectra of the wavefield. By extracting local wavefields from the profile-gathers, multiple 1D Inversions of these fields at different offset-points lead to a 2D shear-wave velocity model of the profile. A new spectral misfit calculation was developed, working without the requirement of identification of the Scholte-wave dispersed modes in the spectra. For minimization of the misfit we implemented a new hybrid method using a combination of particle swarm optimization and a local downhill-simplex resulting in a resolution of global misfit minimum of about 7%. The method was used for shear-wave velocity inversion at four different locations in North and Baltic sea. Resulting models show very good coherence along each Profile and especially a very good correlation to high resolution reflection seismic sections of the same profiles.

  7. Very Broadband Rayleigh-Wave Dispersion (0.06 - 60 Hz) and Shear-Wave Velocity Structure Under Yucca Flat, Nevada Test Site

    NASA Astrophysics Data System (ADS)

    Schramm, K. A.; Bilek, S. L.; Patton, H. J.; Abbott, R. E.; Stead, R.; Pancha, A.; White, R.

    2009-12-01

    Earth structure plays an important role in the generation of seismic waves for all sources. Nowhere is this more evident than at near-surface depths where man-made sources, such as explosions, are conducted. For example, short-period Rayleigh waves (Rg) are excited and propagate in the upper 2 km of Earth's crust. The importance of Rg in the generation of S waves from explosion sources through near-source scattering depends greatly on the shear-wave velocity structure at very shallow depths. Using three distinct datasets, we present a very broadband Rayleigh-wave phase velocity dispersion curve for the Yucca Flat (YF) region of the Nevada Test Site (NTS). The first dataset consists of waveforms of historic NTS explosions recorded on regional seismic networks and will provide information for the lowest frequencies (0.06-0.3 Hz). The second dataset is comprised of waveforms from a non-nuclear explosion on YF recorded at near-local distances and will be used for mid-range frequencies (0.2-1.5 Hz). The third dataset contains high-frequency waveforms recorded from refraction microtremor surveys on YF. This dataset provides information between 1.5 and 60 Hz. Initial results from the high frequency dataset indicate velocities range from 0.45-0.9 km/s at 1.5 Hz and 0.25-0.45 km/s at 60 Hz. The broadband nature of the dispersion curve will allow us to invert for the shear-wave velocity structure to 10 km depth, with focus on shallow depths where nuclear tests were conducted in the YF region. The velocity model will be used by researchers as a tool to aid the development of new explosion source models that incorporate shear wave generation. The new model can also be used to help improve regional distance yield estimation and source discrimination for small events.

  8. Ultransonic velocity measurements in sheared granular layers: Implications for the evolution of dynamic elastic moduli of compositionally-diverse cataclastic fault gouges

    NASA Astrophysics Data System (ADS)

    Knuth, Matthew William

    The objective of this project was to investigate the mechanical and elastic evolution of laboratory fault gouge analogs during active shear. To do this, I designed, constructed, and implemented a new technique for measuring changes in the elastic properties of granular layers subjected to shear deformation. Granular layers serve as an experimental analog to gouge layers forming in cataclastic faults. The technique combines a double-direct shear configuration with a method of determining ultrasonic elastic compressional and shear wavespeed. Experimental results are divided into chapters based on application to fundamental mechanics or to field cases. The first set of experiments allowed us to develop the technique and apply it to a range of end- member materials including quartz sands, montmorillonite clays, and mixtures of sand and clay. Emphasis is placed on normal stress unload-reload cycles and the resulting behavior as clay content is varied within the layer. We observe consistent decrease in wavespeed with shear for sand, and nonlinear but increasing wavespeed for clay and the sand/clay mixture. The second set of experiments involves the application of this technique to measurements conducted under fluid saturation and controlled pressure conditions, examining the behavior of materials from the Nankai Trough Accretionary Prism under shear. I introduce the effects of variable displacement rate and hold time, with implications for fault stability and rate-and-state frictional sliding. The experiments demonstrate a consistent inverse relationship between sliding velocity and wavespeed, and an increase in wavespeed associated with holds. The third set of experiments deals with velocity through stick-slipping glass beads, which has implications for fundamental granular mechanics questions involving velocity-weakening materials. I find that wavespeed decreases in the time between events and increases at "slips", suggesting a strong control related to changes in

  9. Crustal and upper mantle shear velocities of Iberia, the Alboran Sea, and North Africa from ambient noise and ballistic finite-frequency Rayleigh wave tomography

    NASA Astrophysics Data System (ADS)

    Palomeras, I.; Villasenor, A.; Thurner, S.; Levander, A.; Gallart, J.; mimoun, H.

    2013-12-01

    The complex Mesozoic-Cenozoic Alpine deformation in the western Mediterranean extends from the Pyrenees in northern Spain to the Atlas Mountains in southern Morocco. The Iberian plate was accreted to the European plate in late Cretaceous, resulting in the formation of the Pyrenees. Cenozoic African-European convergence resulted in subduction of the Tethys oceanic plate beneath Europe. Rapid Oligocene slab rollback from eastern Iberia spread eastward and southward, with the trench breaking into three segments by the time it reached the African coast. One trench segment moved southwestward and westward creating the Alboran Sea, floored by highly extended continental crust, and building the encircling Betics Rif mountains comprising the Gibraltar arc, and the Atlas mountains, which formed as the inversion of a Jurassic rift. A number of recent experiments have instrumented this region with broad-band arrays (the US PICASSO array, Spanish IberArray and Siberia arrays, the University of Munster array), which, including the Spanish, Portuguese, and Moroccan permanent networks, provide a combined array of 350 stations having an average interstation spacing of ~60 km. Taking advantage of this dense deployment, we have calculated the Rayleigh waves phase velocities from ambient noise for short periods (4 s to 40 s) and teleseismic events for longer periods (20 s to 167 s). Approximately 50,000 stations pairs were used to measure the phase velocity from ambient noise and more than 160 teleseismic events to measure phase velocity for longer periods. The inversion of the phase velocity dispersion curves provides a 3D shear velocity for the crust and uppermost mantle. Our results show differences between the various tectonic regions that extend to upper mantle depths (~200 km). In Iberia we obtain, on average, higher upper mantle shear velocities in the western Variscan region than in the younger eastern part. We map high upper mantle velocities (>4.6 km/s) beneath the

  10. Joint tomographic inversion of surface wave and body wave data: shear wavespeed and Vp/Vs ratios in the mantle beneath the Continental US

    NASA Astrophysics Data System (ADS)

    Golos, E. M.; Fang, H.; Yao, H.; Zhang, H.; Schaeffer, A. J.; Lebedev, S.; Vernon, F.; Burdick, S.; van der Hilst, R. D.

    2016-12-01

    Ray-based traveltime tomography remains a powerful technique for generating models of seismic wavespeed variations. Such schemes are efficient, enabling the production of large numbers of models and allowing us to address the non-uniqueness problem inherent in geophysical inversion. However, distilling an entire waveform into one arrival time yields an incomplete picture of the earth's structure. In particular, if teleseismic body waves are used, the final result shows good resolution at depths where many ray paths intersect, but the crust and upper mantle experience vertical smearing. Meanwhile, if phase or group velocity traveltimes from surface waves are utilized, the result has good vertical resolution, because different frequencies are sensitivity to different depths; however, fundamental mode surface waves are only sensitive to the crust and shallow mantle. To address geological questions involving interaction of lithospheric and asthenospheric processes, it is necessary for both deep and shallow structures to be well-resolved. By combining both body wave and surface wave information in a ray-based tomographic inversion, we can generate a model that provides such resolution. Here we present an update of our model of shear wavespeed variations beneath the continental United States, using data from USArray and Schaeffer and Lebedev, 2013. We use the method of Fang et al., 2015 to construct a surface wave sensitivity matrix which linearly relates Rayleigh wave phase velocities to spatial Vs anomalies. We perform a least-squares inversion of these phase velocities alongside direct S arrival times. We discuss a method for determining the relative contribution of each data source, and we use statistical tests to compare the resolution and uncertainty of our model to those derived from only body waves and only surface waves. In addition, we extend this method to examine the Vp/Vs relationship. Exploiting the (small) sensitivity of Rayleigh wave phase velocity to Vp

  11. Shear-wave velocity anomalies in Southern Andes within latitudes 35°S and 37°S: model and interpretations from seismic ambient noise

    NASA Astrophysics Data System (ADS)

    González Vidal, Diego M.; Obermann, Anne; Bataille, Klaus; Miller, Stephen A.; Lupi, Matteo

    2017-04-01

    The volcanic arc of the Southern Andes is linked to the oblique convergence of Nazca plate beneath the South American plate (subduction velocity of ˜ 66 mm/yr). The volcanic arc accounts for about sixty active volcanoes of Pleistocene-to-Holocene ages. Here we present a regional-scale (i.e. 35°S and 37.5°S) Rayleigh surface-wave tomography from seismic ambient noise that highligths the three-dimensional shear-wave velocity structure at crustal depths. This study is, to the best of our knowledge, the first attempt of a regional-scale Ambient Noise Tomography of a volcanic arc. We find that velocity anomalies are in agreement with the geological setting and the spatial distribution of the present-day volcanoes. The crystalline Cenozoic basement, represented by the outcrop of Mio-Pliocene plutons shows high-velocity anomalies greater than 3%. On the other hand, Descabezado Grande, Puelche and Laguna del Maule volcanic fields show low-velocity anomalies ranging within 3 - 6% located at 5 - 10 km depth. Nevados de Longaví, Chillán and Antuco volcanoes also show strong low-velocity anomalies. We interpret that mid-crustal low-velocity anomalies are associated with a mechanically weakeaned regions, due to a high porous crust or, the presence of fluids an