Sample records for wave velocity variation

  1. Variation of type 1 plasma wave phase velocity with electron drift velocity in the equatorial electrojet

    NASA Astrophysics Data System (ADS)

    Ravindran, Sudha; Reddy, C. A.

    1993-12-01

    Using a 54.95-MHz coherent backscatter radar at Thumba (8.5 deg N, 77 deg E; 0.5 deg N dip angle), the phase velocity variations of type 1 plasma waves generated by the modified two-stream instability process in the equatorial electrojet have been measured on several occasions of large and rapid electric field flunctuations associated with geomagnetic substorms and storms. The measurements show a clear linear variation of type 1 wave phase velocity (VIp) over a considerable range with the simultaneously measured phase velocity (VIIp) of gradient drift instability-generated type 2 plasma waves. Since VIIp is porportional to the drift velocity of electrons, the observed variations of VIp with VIIp mean that VIp varies in step with the variations of the electron drift velocity Vey. The observed variation of VIp with Vey is consistent with the current theoretical understanding that the plasma wave-associated electric fields cause anomalous electron diffusion and heating which result in the stabilization of the type 1 wave phase velocity near the increased value of the ion-acoustic velocity. The enhanced electron temperatures estimated from the largest values of the observed VIp are found to be 2.0 - 2.4 times the ambient value in the absence of waves.

  2. 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.

  3. Lateral variations of Pn wave velocity in northwestern Italy

    Microsoft Academic Search

    S. Parolai; D. Spallarossa; C. Eva

    1997-01-01

    The Pn arrival times recorded from seismic networks operating throughout northwestern Italy and surrounding regions were inverted to map the structural variations of the uppermost mantle over the area and to estimate the crustal static delays at each station. By means of careful data selection a quality data set was obtained removing statistical outliers, poorly recorded events, and scantily sampled

  4. The group velocity variation of Lamb wave in fiber reinforced composite plate

    Microsoft Academic Search

    Sang-Ho Rhee; Jeong-Ki Lee; Jung-Ju Lee

    2007-01-01

    Experimentally measured Lamb wave group velocities in composite materials with anisotropic characteristics are not the same as the theoretical group velocities which is calculated with the Lamb wave dispersion equation. This discrepancy arises from the fact that the angle between the group velocity direction and the phase velocity direction in anisotropic materials exists. Wave propagation in a composite material with

  5. Apparent changes in seismic wave velocity related to microseism noise source variations

    NASA Astrophysics Data System (ADS)

    Friderike Volk, Meike; Bean, Christopher; Lokmer, Ivan; Craig, David

    2014-05-01

    Currently there is a strong interest of using cross correlation of ambient noise for imaging of the subsurface or monitoring of various geological settings where we expect rapid changes (e.g. reservoirs or volcanoes). Through cross correlation retrieved Green's function is usually used to calculate seismic velocities of the subsurface. The assumption of this method is that the wavefields which are correlated must be diffuse. That means that the ambient noise sources are uniformly distributed around the receivers or the scattering in the medium is high enough to mitigate any source directivity. The location of the sources is usually unknown and it can change in time. These temporal and spatial variations of the microseism noise sources may lead to changes in the retrieved Green's functions. The changed Green's functions will then cause apparent changes in the calculated seismic velocity. We track the spatial and temporal distribution of the noise sources using seismic arrays, located in Ireland. It is a good location in which to study these effects, as it is tectonically very quiet and is relatively close to large microseism noise sources in the North Atlantic, allowing a quantification of noise source heterogeneity. Temporal variations in seismic wave velocity are calculated using data recorded in Ireland. The results are compared to the variations in microseism source locations. We also explore the minimum noise trace length required in Ireland for the Green's functions to converge. We quantify the degree to which apparent velocity variations using direct arrivals are caused by changes in the sources and assess if and at what frequencies the scattering of the medium in Ireland is high enough to homogenise the coda wavefield.

  6. Lateral variations of the upper mantle structure in Eurasia from group velocities of surface waves

    Microsoft Academic Search

    T. B Yanovskaya; L. M Antonova; V. M Kozhevnikov

    2000-01-01

    Group velocities of both Rayleigh and Love waves in the 20–70s period range along paths across Asia and the Eastern Europe are used to obtain group velocity maps of the region. For this purpose, we developed a method for tomographic inversion on spherical surface, which is practically free of a priori assumptions. Checker-board test shows that velocity anomalies of 10°×10°

  7. Lateral variations of the upper mantle structure in Eurasia from group velocities of surface waves

    Microsoft Academic Search

    T. B. Yanovskaya; L. M. Antonova; V. M. Kozhevnikov

    2000-01-01

    Group velocities of both Rayleigh and Love waves in the 20-70s period range along paths across Asia and the Eastern Europe are used to obtain group velocity maps of the region. For this purpose, we developed a method for tomographic inversion on spherical surface, which is practically free of a priori assumptions. Checker-board test shows that velocity anomalies of \\/10°×10°

  8. Variation of seismic-wave velocities in westerly granite under stress 

    E-print Network

    Al-Shaibani, Abdulaziz Muhareb

    1994-01-01

    stresses and about 3% along the direction of the minimum stresses and showed an anisotropy of about 6%. The shear-wave velocity increased by different amounts in different directions. The amount of increase ranged from 3.4% to about 6%. The anisotropy in S...

  9. Variation of Rayleigh and Love Wave Fundamental Mode Group Velocity Dispersion Across India and Surrounding Regions

    Microsoft Academic Search

    C. E. Acton; K. Priestley; S. Mitra; V. K. Gaur; S. S. Rai

    2007-01-01

    We present group velocity dispersion results from a study of regional fundamental mode Rayleigh and Love waves propagating across India and surrounding regions. Data used in this study comes from broadband stations operated in India by us in addition to data from seismograms in the region whose data is archived at the IRIS Data Management Centre. The large amount of

  10. Variation of Fundamental Mode Surface Wave Group Velocity Dispersion in Iran and the Surrounding Region

    Microsoft Academic Search

    D. J. Rham; K. Preistley; M. Tatar; A. Paul

    2006-01-01

    We present group velocity dispersion results from a study of regional fundamental mode Rayleigh and Love waves propagating across Iran and the surrounding region. Data for these measurements comes from field deployments within Iran by the University of Cambridge (GBR) and the Universite Joseph-Fourier (FRA) in conjunction with International Institute of Earthquake Engineering and Seismology (Iran), in addition to data

  11. Variation of fundamental mode Rayleigh wave group velocity dispersion in Iran and the surrounding region

    Microsoft Academic Search

    D. Rham; K. Priestley; M. Tatar; A. Paul; D. Hatzfeld; A. Radjaee; G. Nowrouzi; A. Kaviani; C. Tiberi

    2005-01-01

    We present group velocity dispersion results from a study of regional fundamental mode Rayleigh waves propagating across Iran and the surrounding region. Data for these measurements come from field deployments within Iran by the University of Cambridge (UK) and the Universite Joseph-Fourier (FRA) in conjunction with International Institute of Earthquake Engineering and Seismology (Iran), within Oman by the Universite Pierre

  12. 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.

  13. Velocities under Water Waves

    NSDL National Science Digital Library

    Robert A. Dalrymple

    This site from the Center of Applied Coastal Research at the University of Delaware features an interactive animation of wave form that users can modify then watch the results of their input. Parameters include wave height, wave period, and local depth. The resulting animation shows the associated water particle motion, plus the velocity vector of the user's chosen wave.

  14. Spatial variation in coda Q around the Nobi fault zone, central Japan: relation to S-wave velocity and seismicity

    NASA Astrophysics Data System (ADS)

    Tsuji, Sugane; Hiramatsu, Yoshihiro

    2014-12-01

    We investigate the spatial variation in coda Q around the Nobi fault zone in a high strain rate zone to assess the relation between coda Q, shear wave velocity, and seismicity. Waveform data were obtained from dense seismic observations. Low coda Q that follows the Niigata-Kobe Tectonic Zone in the high strain rate zone is distinct at the lowest frequency band of 1 to 2 Hz. However, at higher frequencies, such a spatial pattern in coda Q is unclear. A good positive correlation was found between coda Q at the 1- to 2-Hz frequency band and the S-wave velocity perturbation at 25-km depth, which suggests that the coda Q reflects the ductile deformation below the brittle-ductile transition zone. Furthermore, coda Q at the 1- to 2-Hz frequency band correlates negatively with seismicity at 10- to 15-km depth, which implies that there is a high stressing rate in the low coda Q area. These facts, together with results of previous studies, imply that a high deformation rate below the brittle-ductile transition zone produces the high strain rate observed by the Global Positioning System (GPS) on the surface in this region.

  15. A preliminary investigation of the effect of compositional variation on compressional-wave velocity in transversely isotropic media

    E-print Network

    Melia, Patrick John

    1983-01-01

    , transversely isotropic models, the effect of compositional varia- tion on compressional-wave veloci. ties in the layered samples has been evaluated. The theoretical equations derived by Levin (1979) for predicting elastic moduli and acoustic velocities... is that of elastic isotropy. Along with the field and laboratory observations which have demonstrated the anisotropic behavior in layezed media, theoretical discussions have been developed (Backus, 1962; Levin, 1979) to ad- dress the effect of compositional...

  16. Tomographic inversion of R sub g wave group velocities for regional near-surface velocity structure

    Microsoft Academic Search

    Argun H. Kocaoglu; Leland T. Long

    1993-01-01

    Mapping lateral variations in the lithology of sedimentary basins may be done using the technique of tomographic inversion of the group velocities of R sub g waves. The velocity structure is determined by first using the moving-window maximum entropy spectral analysis to measure the average R sub g wave group travel times. Tomographic inversion is then used to determine the

  17. Microwave velocity measurements of marginal detonation waves

    Microsoft Academic Search

    D H Edwards; G Hooper; R J Meddins

    1970-01-01

    A prerequisite to a study of a detonation wave structure is the establishment of an equilibrium frontal configuration, which is repeatable at equi-spaced distances along the detonation tube, together with a constant average wave velocity. A microwave interferometer is described which is capable of giving a continuous monitor of the velocity of a marginal planar detonation wave propagating in a

  18. Velocity and Q of mantle waves

    Microsoft Academic Search

    Hiroo Kanamori

    1970-01-01

    Phase velocity and Q of long-period waves have been determined for 13 great-circle paths for Rayleigh waves and 12 great-circle paths for Love waves. Group velocities are also determined by band-pass filtering technique. Some of the preexisting data are incorporated to obtain representative sets of data for Q, phase and group velocities. With these sets of data stringent tests of

  19. Relativistic Hydromagnetic Waves and Group Velocity

    Microsoft Academic Search

    Albert C. Giere

    1966-01-01

    The velocities of relativistic hydromagnetic waves in a compressible, perfect fluid of infinite conductivity are calculated in the framework of general relativity. In the absence of viscuous and Joule heat losses, the flow is isentropic, and, therefore, the wave surfaces are propagated without change of shape. The velocities are first obtained in terms of the four-vector magnetic field and then

  20. Global Models of Surface Wave Group Velocity

    Microsoft Academic Search

    E. W. F. Larson; G. Ekström

    2001-01-01

    v--vMeasurements of group velocity are derived from phase-velocity dispersion curves and modeled with global laterally-varying isotropic structure. Maps for both Love and Rayleigh waves are created in the period range 35 s to 175 s. The data set of group-velocity measurements includes over 50,000 minor-arc observations and 5,000 major-arc observations. The errors in the measurements are estimated by an empirical

  1. Wave Measurements Using GPS Velocity Signals

    PubMed Central

    Doong, Dong-Jiing; Lee, Beng-Chun; Kao, Chia Chuen

    2011-01-01

    This study presents the idea of using GPS-output velocity signals to obtain wave measurement data. The application of the transformation from a velocity spectrum to a displacement spectrum in conjunction with the directional wave spectral theory are the core concepts in this study. Laboratory experiments were conducted to verify the accuracy of the inversed displacement of the surface of the sea. A GPS device was installed on a moored accelerometer buoy to verify the GPS-derived wave parameters. It was determined that loss or drifting of the GPS signal, as well as energy spikes occurring in the low frequency band led to erroneous measurements. Through the application of moving average skill and a process of frequency cut-off to the GPS output velocity, correlations between GPS-derived, and accelerometer buoy-measured significant wave heights and periods were both improved to 0.95. The GPS-derived one-dimensional and directional wave spectra were in agreement with the measurements. Despite the direction verification showing a 10° bias, this exercise still provided useful information with sufficient accuracy for a number of specific purposes. The results presented in this study indicate that using GPS output velocity is a reasonable alternative for the measurement of ocean waves. PMID:22346618

  2. Group Velocities of Atmospheric Gravity Waves

    Microsoft Academic Search

    T. J. Herron

    1971-01-01

    Atmospheric gravity waves generated by low-altitude nuclear explosions have been detected by ground-level microbarographs and by ionospheric instruments. Group velocity dispersion curves have been computed for propagation over the short and long great-circle paths. Apparent lower velocities over the short paths are interpreted as due to the `rise time' of the nuclear disturbances to ionospheric levels with subsequent generation of

  3. Measurements of the Gravity Waves Velocity

    E-print Network

    V. A. Dubrovskiy

    2001-06-20

    Some results are presented of the Earth's microseismic background. It is assumed that background peaks should correspond to the resonance gravity-wave exchange in the system of two gravity-connected bodies. The microseismic spectrum is compared with the distribution of gravity potential of the nearest stars. A close peak-to-peak correspondence is found. This correspondence and resonance condition lead to an evaluation of the gravity-wave velocity. The resulting value is nine orders of magnitude more than the velocity of light. Some consequences of such result are discussed.

  4. Eurasian surface wave tomography: Group velocities

    Microsoft Academic Search

    Michael H. Ritzwoller; Anatoli L. Levshin

    1998-01-01

    This paper presents the results of a study of the dispersion characteristics of broadband fundamental surface waves propagating across Eurasia. The study is broader band, displays denser and more uniform data coverage, and demonstrates higher resolution than previous studies of Eurasia performed on this scale. In addition, the estimated group velocity maps reveal the signatures of geological and tectonic features

  5. S-wave velocity structure of the North China from inversion of Rayleigh wave phase velocity

    NASA Astrophysics Data System (ADS)

    Chen, Hao-peng; Zhu, Liang-bao; Wang, Qing-dong; Zhang, Pan; Yang, Ying-hang

    2014-07-01

    We constructed the S-wave velocity structure of the crust and uppermost mantle (10-100 km) beneath the North China based on the teleseismic data recorded by 187 portable broadband stations deployed in this region. The traditional two-step inversion scheme was adopted. Firstly, we measured the interstation fundamental Rayleigh wave phase velocity of 10-60 s and imaged the phase velocity distributions using the Tarantola inversion method. Secondly, we inverted the 1-D S-wave velocity structure with a grid spacing of 0.25° × 0.25° and constructed the 3-D S-wave velocity structure of the North China. The 3-D S-wave velocity model provides valuable information about the destruction mechanism and geodynamics of the North China Craton (NCC). The S-wave velocity structures in the northwestern and southwestern sides of the North-South Gravity Lineament (NSGL) are obviously different. The southeastern side is high velocity (high-V) while the northeastern side is low velocity (low-V) at the depth of 60-80 km. The upwelling asthenosphere above the stagnated Pacific plate may cause the destruction of the Eastern Block and form the NSGL. A prominent low-V anomaly exists around Datong from 50 to 100 km, which may due to the upwelling asthenosphere originating from the mantle transition zone beneath the Western Block. The upwelling asthenosphere beneath the Datong may also contribute to the destruction of the Eastern Block. The Zhangjiakou-Penglai fault zone (ZPFZ) may cut through the lithosphere and act as a channel of the upwelling asthenosphere. A noticeable low-V zone also exists in the lower crust and upper mantle lid (30-50 km) beneath the Beijing-Tianjin-Tangshan (BTT) region, which may be caused by the upwelling asthenosphere through the ZPFZ.

  6. SURFACE WAVE PHASE VELOCITY DISTRIBUTION OF TURKEY

    Microsoft Academic Search

    Kazunori YOSHIZAWA

    The crustal and upper mantle structure beneath Turkey is investgated by using phase velocity of fundamental-mode Rayleigh waves working with a two-station method. We used vertical component seismograms of 72 broad-band seismic stations in Turkey and surrounding areas from 172 teleseismic events from April 2005 to June 2007. The average dispersion curve of the entire region of Turkey is estimated

  7. Tomographic imaging of P and S wave velocity structure beneath northeastern Japan

    Microsoft Academic Search

    Dapeng Zhao; Akira Hasegawa; Shigeki Horiuchi

    1992-01-01

    The seismic body wave tomography method has been improved and extended to adapt to a general velocity structure with a number of complexity shaped seismic velocity discontinuities and with three-dimensional variations in the velocities in the modeling space. This method is applied to 18,679 arrival times from 470 shallow and intermediate-depth earthquakes in order to study P and S wave

  8. Propagation of a constant velocity fission wave

    NASA Astrophysics Data System (ADS)

    Deinert, Mark

    2011-10-01

    The ideal nuclear fuel cycle would require no enrichment, minimize the need fresh uranium, and produce few, if any, transuranic elements. Importantly, the latter goal would be met without the reprocessing. For purely physical reasons, no reactor system or fuel cycle can meet all of these objectives. However, a traveling-wave reactor, if feasible, could come remarkably close. The concept is simple: a large cylinder of natural (or depleted) uranium is subjected to a fast neutron source at one end, the neutrons would transmute the uranium downstream and produce plutonium. If the conditions were right, a self-sustaining fission wave would form, producing yet more neutrons which would breed more plutonium and leave behind little more than short-lived fission products. Numerical studies have shown that fission waves of this type are also possible. We have derived an exact solution for the propagation velocity of a fission wave through fertile material. The results show that these waves fall into a class of traveling wave phenomena that have been encountered in other systems. The solution places a strict conditions on the shapes of the flux, diffusive, and reactive profiles that would be required for such a phenomenon to persist. The results are confirmed numerically.

  9. Investigation of gravity waves using horizontally resolved radial velocity measurements

    NASA Astrophysics Data System (ADS)

    Stober, G.; Sommer, S.; Rapp, M.; Latteck, R.

    2013-10-01

    The Middle Atmosphere Alomar Radar System (MAARSY) on the island of Andøya in Northern Norway (69.3° N, 16.0° E) observes polar mesospheric summer echoes (PMSE). These echoes are used as tracers of atmospheric dynamics to investigate the horizontal wind variability at high temporal and spatial resolution. MAARSY has the capability of pulse-to-pulse beam steering allowing for systematic scanning experiments to study the horizontal structure of the backscatterers as well as to measure the radial velocities for each beam direction. Here we present a method to retrieve gravity wave parameters from these horizontally resolved radial wind variations by applying velocity azimuth display and volume velocity processing. Based on the observations a detailed comparison of the two wind analysis techniques is carried out in order to determine the zonal and meridional wind as well as to measure first-order inhomogeneities. Further, we demonstrate the possibility to resolve the horizontal wave properties, e.g., horizontal wavelength, phase velocity and propagation direction. The robustness of the estimated gravity wave parameters is tested by a simple atmospheric model.

  10. Investigation of gravity waves using horizontally resolved radial velocity measurements

    NASA Astrophysics Data System (ADS)

    Stober, G.; Sommer, S.; Rapp, M.; Latteck, R.

    2013-06-01

    The Middle Atmosphere Alomar Radar System (MAARSY) on the island Andøya in Northern Norway (69.3° N, 16.0° E) observes polar mesospheric summer echoes (PMSE). These echoes are used as tracers of atmospheric dynamics to investigate the horizontal wind variability at high temporal and spatial resolution. MAARSY has the capability of a pulse-to-pulse beam steering allowing for systematic scanning experiments to study the horizontal structure of the backscatterers as well as to measure the radial velocities for each beam direction. Here we present a method to retrieve gravity wave parameters from these horizontally resolved radial wind variations by applying velocity azimuth display and volume velocity processing. Based on the observations a detailed comparison of the two wind analysis techniques is carried out in order to determine the zonal and meridional wind as well as to measure first order inhomogeneities. Further, we demonstrate the possibility to resolve the horizontal wave properties, e.g. horizontal wavelength, phase velocity and propagation direction. The robustness of the estimated gravity wave parameters is tested by a simple atmospheric model.

  11. Diffraction correction for precision surface acoustic wave velocity measurements

    E-print Network

    Nagy, Peter B.

    Diffraction correction for precision surface acoustic wave velocity measurements Alberto Ruiz M wave dispersion measurements can be used to nondestructively characterize shot-peened, laser shock dispersion measurements. A simple diffraction correction model was developed for surface waves

  12. 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

    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.

  13. Effects of horizontal velocity variations on ultrasonic velocity measurements in open channels

    USGS Publications Warehouse

    Swain, E.D.

    1992-01-01

    Use of an ultrasonic velocity meter to determine discharge in open channels involves measuring the velocity in a line between transducers in the stream and relating that velocity to the average velocity in the stream. The standard method of calculating average velocity in the channel assumes that the velocity profile in the channel can be represented by the one-dimensional von Karman universal velocity profile. However, the velocity profile can be described by a two-dimensional equation that accounts for the horizontal velocity variations induced by the channel sides. An equation to calculate average velocity accounts for the two-dimensional variations in velocity within a stream. The use of this new equation to calculate average velocity was compared to the standard method in theoretical trapezoidal cross sections and in the L-31N and Snapper Creek Extension Canals near Miami, Florida. These comparisons indicate that the two-dimensional variations have the most significant effect in narrow, deep channels. Also, the two-dimensional effects may be significant in some field situations and need to be considered when determining average velocity and discharge with an ultrasonic velocity meter.

  14. Diffraction correction for precision surface acoustic wave velocity measurements

    NASA Astrophysics Data System (ADS)

    Ruiz M., Alberto; Nagy, Peter B.

    2002-09-01

    Surface wave dispersion measurements can be used to nondestructively characterize shot-peened, laser shock-peened, burnished, and otherwise surface-treated specimens. In recent years, there have been numerous efforts to separate the contribution of surface roughness from those of near-surface material variations, such as residual stress, texture, and increased dislocation density. As the accuracy of the dispersion measurements was gradually increased using state-of-the-art laser-ultrasonic scanning and sophisticated digital signal processing methods, it was recognized that a perceivable dispersive effect, similar to the one found on rough shot-peened specimens, is exhibited by untreated smooth surfaces as well. This dispersion effect is on the order of 0.1%, that is significantly higher than the experimental error associated with the measurements and comparable to the expected velocity change produced by near-surface compressive residual stresses in metals below their yield point. This paper demonstrates that the cause of this apparent dispersion is the diffraction of the surface acoustic wave (SAW) as it travels over the surface of the specimen. The results suggest that a diffraction correction may be introduced to increase the accuracy of surface wave dispersion measurements. A simple diffraction correction model was developed for surface waves and this correction was subsequently validated by laser-interferometric velocity measurements on aluminum specimens. copyright 2002 Acoustical Society of America.

  15. Surface wave group velocity tomography of East Asia, part 1

    Microsoft Academic Search

    Francis T. Wu

    1993-01-01

    Group velocities of both Rayleigh and Love waves are used in a tomographic inversion to obtain group velocity maps of East Asia (60 deg E-140 deg E and 20 deg N-50 deg N). The period range studied is 30-70 seconds. For periods longer than 40 seconds, a high group velocity gradient clearly exists along longitude 105 deg E; the velocities

  16. Velocity variations in the high-latitude solar wind

    SciTech Connect

    Neugebauer, M.; Goldstein, B.E. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109 (United States); McComas, D.J. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Suess, S.T. [Marshall Space Flight Center, Huntsville, Alabama 35812 (United States); Balogh, A. [Imperial College, London (United Kingdom)

    1996-07-01

    Velocity variations of the solar wind from a south polar coronal hole registered by the Ulysses spacecraft in 1994 are analyzed. Power spectra of hourly averages in the Hz range are presented. {copyright} {ital 1997 American Institute of Physics.}

  17. Surface wave phase-velocity tomography based on multichannel cross-correlation

    NASA Astrophysics Data System (ADS)

    Jin, Ge; Gaherty, James B.

    2015-06-01

    We have developed a new method to retrieve seismic surface wave phase velocity using dense seismic arrays. The method measures phase variations between nearby stations based on waveform cross-correlation. The coherence in waveforms between adjacent stations results in highly precise relative phase estimates. Frequency-dependent phase variations are then inverted for spatial variations in apparent phase velocity via the Eikonal equation. Frequency-dependent surface wave amplitudes measured on individual stations are used to correct the apparent phase velocity to account for multipathing via the Helmholtz equation. By using coherence and other data selection criteria, we construct an automated system that retrieves structural phase-velocity maps directly from raw seismic waveforms for individual earthquakes without human intervention. The system is applied to broad-band seismic data from over 800 events recorded on EarthScope's USArray from 2006 to 2014, systematically building up Rayleigh-wave phase-velocity maps between the periods of 20 and 100 s for the entire continental United States. At the highest frequencies, the resulting maps are highly correlated with phase-velocity maps derived from ambient noise tomography. At all frequencies, we observe a significant contrast in Rayleigh-wave phase velocity between the tectonically active western US and the stable eastern US, with the phase velocity variations in the western US being 1-2 times greater. The Love wave phase-velocity maps are also calculated. We find that overtone contamination may produce systemic bias for the Love-wave phase-velocity measurements.

  18. The shear wave velocity underneath Bucharest city, Romania, from the analysis of Love waves

    NASA Astrophysics Data System (ADS)

    Sèbe, Olivier; Forbriger, Thomas; Ritter, Joachim R. R.

    2009-03-01

    From the dispersion of Love waves, we infer models of shear wave velocity structure underneath Bucharest (Romania) at depths down to 2km that can contribute to seismic hazard estimation. Waves from eight regional events recorded during 10months with a network of 34 seismic broad-band stations of the URban Seismology (URS) experiment are used. Although these events provide poor azimuthal coverage the data reliably constrain a shear wave velocity model with an interface between the Neogene and the Cretaceous sediments that is dipping northwards towards the Carpathian mountains. Array processing techniques that account for non-uniform wave propagation are used to estimate the dispersion of structural phase velocity. From this, we infer subsurface structure at three different latitudes. The Neogene sediments are represented by a gradient layer with no significant lateral variation. Shear wave velocity increases from approximately 400ms-1 near the surface to 1kms-1 at 1km depth and 5km in the south, and to 1.35kms-1 at 1.5km depth and 5km in the north from the centre of Bucharest, respectively. For the half-space representing the Cretaceous sediments, we obtain shear wave velocities of 2.7-2.9kms-1. The results are consistent with results from boreholes and shallow seismics for the near-surface structure and results from receiver function studies and crustal refraction seismic studies for the deeper structure. The details of the Neogene layer comprising a vertical gradient fill a gap in existing models of the subsurface structure of Bucharest and can contribute to modelling of seismic hazard for the city. Since the signal-to-noise ratio restricted useful data to the frequency range from 90 to 290mHz, the inversion could not constrain the near-surface velocity independently. Due to strong trade-off between near-surface velocity and depth of half-space, the latter had to be introduced as a priori data from previous studies.

  19. S wave velocity structure below central Mexico using highresolution surface wave tomography

    E-print Network

    Clayton, Robert W.

    ), S wave velocity structure below central Mexico using highresolution surface wave tomography, J. Geophys of group velocity dispersion curves of nine earthquakes located near the Guerrero coast that were recordedClick Here for Full Article S wave velocity structure below central Mexico using highresolution

  20. Determining wave velocities in polymer fibers using electromagnetic radiation

    Microsoft Academic Search

    I. V. Simonov; I. M. Smirnov

    2008-01-01

    We have developed a new technique for determining wave velocities in fibers by measuring an electric response signal. Using this method, the velocities of longitudinal elastic unloading waves and the corresponding instantaneous Young modules have been studied as functions of the initial tensile strain in copolymer fibers of various diameters ( d = 60, 100, and 280 µ m). The

  1. Longshore sediment transport rate calculated incorporating wave orbital velocity fluctuations

    E-print Network

    Smith, Ernest Ray

    2006-10-30

    of the requirements for the degree of DOCTOR OF PHILOSOPHY August 2006 Major Subject: Ocean Engineering LONGSHORE SEDIMENT TRANSPORT RATE CALCULATED INCORPORATING WAVE ORBITAL VELOCITY FLUCTUATIONS A Dissertation by ERNEST.... Edge Achim St?ssel Steven A. Hughes Head of Department, David V. Rosowsky August 2006 Major Subject: Ocean Engineering iii ABSTRACT Longshore Sediment Transport Rate Calculated Incorporating Wave Orbital Velocity Fluctuations...

  2. Crustal P and Pn Wave Velocity Perturbations Beneath Caucasus Region

    NASA Astrophysics Data System (ADS)

    Mumladze, T.; Wu, Y. M.

    2012-04-01

    In presented study we invert crustal P and Pn velocities as well as Moho depth simultaneously applying the joint inversion method developed by Zhen et al. (2009). In this method all those three parameters are jointly inverted. It's using a spherical pseudo-bending ray tracing method and includes secondary Pg wave data at large distances. We applied the method to the Caucasus region and adjusted territories for reconstruction of the crust structure and uppermost mantle. New digital seismic network in Georgia was developed from 2003 and because of that we selected data from 2004 to 2010. Also we add data of past earthquakes from the time interval 1960-1990, with local magnitude more than 3.5. Before 1960 and during 1990-2004 seismic station coverage and hypocenter determination were very poor, so it was better not to use data from this time windows to avoid big errors in hypocenter locations. Final data set includes information about more than six thousand earthquakes. It includes Pg and Pn wave arrivals from the seismograms recorded by seismic stations of the regional seismic network of Georgia, Central Caucasus Local Network (installed in 2007), regional seismic networks of Turkey, Azerbaijan and Armenia. We applied the checkerboard resolution test to estimate the spatial resolution of the tomographic images. The results of the checkerboard test indicate that the initial model with passive and negative values is well reconstructed for all depths. The results of tomography show some significant features, well seen heterogeneities in upper crust, high and low Pn velocity zones. The depth of Moho discontinuity is relatively big in northern and southern part of Georgia, beneath the Greater and Smaller Caucasus, it has relatively large variations in this region. We can see the similar results in previous studies. Our tomography results in upper crust also show correlation among the velocity variations, seismicity, active faults and quaternary volcanic centers. At shallow depth are visible low velocity zones, which may be related to the thick sedimentary layer. The biggest depth of earthquakes in this region is about 40 kilometers, from our study is clearly shown that they are related with high velocity area at that depth.

  3. Group velocity of cylindrical guided waves in anisotropic laminate composites.

    PubMed

    Glushkov, Evgeny; Glushkova, Natalia; Eremin, Artem; Lammering, Rolf

    2014-01-01

    An explicit expression for the group velocity of wave packets, propagating in a laminate anisotropic composite plate in prescribed directions, is proposed. It is based on the cylindrical guided wave asymptotics derived from the path integral representation for wave fields generated in the composites by given localized sources. The expression derived is theoretically confirmed by the comparison with a known representation for the group velocity vector of a plane guided wave. Then it is experimentally validated against laser vibrometer measurements of guided wave packets generated by a piezoelectric wafer active sensor in a composite plate. PMID:24437754

  4. 3d S-wave Velocity Structure of The Upper Mantle In Asia From Group Velocities of Rayleigh Waves

    Microsoft Academic Search

    T. B. Yanovskaya; V. M. Kozhevnikov

    2002-01-01

    Group velocities of Rayleigh waves in the 10-150 s period range along more than 1200 paths across the continent of Asia are used to obtain group velocity maps of the re- gion. The method for 2D tomographic inversion on spherical surface developed earlier by one of the authors is applied for mapping the locally averaged group velocities for each period.

  5. Microwave acoustics handbook. Volume 2: Surface wave velocities, numerical data

    Microsoft Academic Search

    A. J. Slobodnik Jr.; R. T. Delmonico; E. D. Conway

    1974-01-01

    Information essential for the accurate design of advanced acoustic surface wave filters, signal processors, and other miniature low-cost reliable devices for use in communications and electronic sensing is given. Numerical data on surface wave velocity, electromechanical power flow angle, mechanical displacement, electric potential, and estimates of surface wave coupling to interdigital transducers are given for various orientations of the following

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

    Microsoft Academic Search

    Jianghai Xia; Richard D. Miller; Choon B. Park; James A. Hunter; James B. Harris; Julian Ivanov

    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

  7. Blood characteristics effect on pulse wave velocity.

    PubMed

    Kim, Jong Youn; Yoon, Jihyun; Cho, Minhee; Lee, Byoung-Kwon; Karimi, Ali; Shin, Sehyun

    2013-01-01

    PWV, a surrogate marker for vascular stiffness, can be also expressed by the Bramwell-Hill equation. The effect of blood density to PWV has been ignored, because variation of blood density is assumed to be negligible. In some clinical situation, blood density could be changed, and blood density as a mechanical property of blood flow might affect to PWV. While the elastic property plays an important role in determining the wave propagation in an elastic tube, our assumption is that there might be some relation between blood flow and vascular wall, and that the characteristics of blood flow might influence PWV. This study was objected to investigate the role of mechanical and hemorheologic parameters on PWV in subjects with cardiovascular disease. We have measured and analyzed the PWV, hemorheologic parameters, and other clinical parameters in 814 patients with coronary arterial disease scheduled for coronary angiography. There is no commercial method for measuring whole blood density. So, we defined the density score, which is sum of hemoglobin and total protein. And the hemorheologic parameters were measured within 4 hours after sampling by automated microfluidic hemorheometer. And the effect of all the clinical and hemorheologic parameter on PWV was analyzed by multiple linear regression analysis. Many clinical parameters including age and blood pressure, high shear WBV and ESR as hemorheologic parameters, and density score were correlated well with ba-PWV. However, many clinical variables, high shear WBV and ESR lost the independent significance on multivariable regression analysis. Only age, SBP, and density score were independent variables (p < 0.001). In conclusion, density score as a mechanical property of blood might be suggested as an independent variable influencing PWV in addition to age and blood pressure, but hemorheologic parameters, such as RBC deformability, aggregation, and whole blood viscosity do not affect PWV independently. PMID:23445636

  8. Implications of elastic wave velocities for Apollo 17 rock powders

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

    Ultrasonic P- and S-wave velocities of lunar rock powders 172701, 172161, 170051, and 175081 were measured at room temperature and to 2.5 kb confining pressure. The results compare well with those of terrestrial volcanic ash and powdered basalt. P-wave velocity values up to pressures corresponding to a lunar depth of 1.4 km preclude cold compaction alone as an explanation for the observed seismic velocity structure at the Apollo 17 site. Application of small amounts of heat with simultaneous application of pressure causes rock powders to achieve equivalence of seismic velocities for competent rocks.

  9. Rayleigh wave group velocity dispersion across Northern Africa, Southern Europe and the Middle East

    SciTech Connect

    McNamara, D.E.; Walter, W.R.

    1997-07-15

    THis report presents preliminary results from a large scale study of surface wave group velocity dispersion throughout Northern Africa, the Mediterranean, Southern Europe and the Middle East. Our goal is to better define the 3D lithospheric shear-wave velocity structure within this region by improving the resolution of global surface wave tomographic studies. We hope to accomplish this goal by incorporating regional data at relatively short periods (less than 40 sec), into the regionalization of lateral velocity variation. Due to the sparse distributions of stations and earthquakes throughout the region (Figure 1) we have relied on data recorded at both teleseismic and regions; distances. Also, to date we have concentrated on Rayleigh wave group velocity measurements since valuable measurements can be made without knowledge of the source. In order to obtain Rayleigh wave group velocity throughout the region, vertical component teleseismic and regional seismograms were gathered from broadband, 3-component, digital MEDNET, GEOSCOPE and IRIS stations plus the portable PASSCAL deployment in Saudi Arabia. Figure 1 shows the distribution of earthquakes (black circles) and broadband digital seismic stations (white triangles) throughout southern Europe, the middle east and northern Africa used in this study. The most seismicly active regions of northern Africa are the Atlas mountains of Morocco and Algeria as well as the Red Sea region to the east. Significant seismicity also occurs in the Mediterranean, southern Europe and throughout the high mountains and plateaus of the middle-east. To date, over 1300 seismograms have been analyzed to determine the individual group velocities of 10-150 second Rayleigh waves. Travel times, for each period, are then inverted in a back projection tomographic method in order to determine the lateral group velocity variation throughout the region. These results are preliminary, however, Rayleigh wave group velocity maps for a range of periods (10-95 sec) are presented and initial interpretations are discussed. Significant lateral group velocity variation is apparent at all periods. In general, shorted periods (10-45 sec) are sensitive to crustal structure as seen by the relatively low velocities associated with large sedimentary features (eastern Arabian shield, Persian Gulf, Eastern Mediterranean, Caspian Sea). At longer periods (50-95 sec), Rayleigh waves are most sensitive to topography on the Moho and upper mantle shear-wave velocity structure. This is observed in the group velocity maps as low velocities associated with features such as the Zagros Mountains, Iranian Plateau and the Red Sea. Analysis will eventually be expanded to include Love wave group and phase velocity. Knowledge of the lateral variation of group velocity and phase velocity will allow us to invert for shear velocity at each grid point. A detailed regionalization of shear-wave velocity will potentially lower the threshold for Ms determinations and improve event location capabilities throughout the region. Better Ms estimates and locations will improve our ability to reliably monitor the Comprehensive Test Ban Treaty (CTBT).

  10. Longitudinal Variation and Waves in Jupiter's South Equatorial Wind Jet

    NASA Technical Reports Server (NTRS)

    Simon-Miller, Amy A.; Choi, David; Rogers, John H.; Gierasch, Peter J.; Allison, Michael D.; Adamoli, Gianluigi; Mettig, Hans-Joerg

    2012-01-01

    A detailed study of the chevron-shaped dark spots on the strong southern equatorial wind jet near 7.5 S planetographic latitude shows variations in velocity with longitude and time. The presence of the large anticyclonic South Equatorial Disturbance (SED) has a profound effect on the chevron velocity, causing slower velocities to its east and accelerations over distance from the disturbance. The chevrons move with velocities near the maximum wind jet velocity of approx 140 m/s, as deduced by the history of velocities at this latitude and the magnitude of the symmetric wind jet near 7 N latitude. Their repetitive nature is consistent with a gravity-inertia wave (n = 75 to 100) with phase speed up to 25 m/s, relative to the local flow, but the identity of this wave mode is not well constrained. However, for the first time, high spatial resolution movies from Cassini images show that the chevrons oscillate in latitude with a 6.7 +/- 0.7-day period. This oscillating motion has a wavelength of approx 20 and a speed of 101 +/- 3 m/s, following a pattern similar to that seen in the Rossby wave plumes of the North Equatorial Zone, and possibly reinforced by it. All dates show chevron latitude variability, but it is unclear if this larger wave is present during other epochs, as there are no other suitable time series movies that fully delineate it. In the presence of mUltiple wave modes, the difference in dominant cloud appearance between 7 deg N and 7.5 deg S is likely due to the presence of the Great Red Spot, either through changes in stratification and stability or by acting as a wave boundary.

  11. Calculating wave-generated bottom orbital velocities from surface-wave parameters

    USGS Publications Warehouse

    Wiberg, P.L.; Sherwood, C.R.

    2008-01-01

    Near-bed wave orbital velocities and shear stresses are important parameters in many sediment-transport and hydrodynamic models of the coastal ocean, estuaries, and lakes. Simple methods for estimating bottom orbital velocities from surface-wave statistics such as significant wave height and peak period often are inaccurate except in very shallow water. This paper briefly reviews approaches for estimating wave-generated bottom orbital velocities from near-bed velocity data, surface-wave spectra, and surface-wave parameters; MATLAB code for each approach is provided. Aspects of this problem have been discussed elsewhere. We add to this work by providing a method for using a general form of the parametric surface-wave spectrum to estimate bottom orbital velocity from significant wave height and peak period, investigating effects of spectral shape on bottom orbital velocity, comparing methods for calculating bottom orbital velocity against values determined from near-bed velocity measurements at two sites on the US east and west coasts, and considering the optimal representation of bottom orbital velocity for calculations of near-bed processes. Bottom orbital velocities calculated using near-bed velocity data, measured wave spectra, and parametric spectra for a site on the northern California shelf and one in the mid-Atlantic Bight compare quite well and are relatively insensitive to spectral shape except when bimodal waves are present with maximum energy at the higher-frequency peak. These conditions, which are most likely to occur at times when bottom orbital velocities are small, can be identified with our method as cases where the measured wave statistics are inconsistent with Donelan's modified form of the Joint North Sea Wave Project (JONSWAP) spectrum. We define the 'effective' forcing for wave-driven, near-bed processes as the product of the magnitude of forcing times its probability of occurrence, and conclude that different bottom orbital velocity statistics may be appropriate for different problems. ?? 2008 Elsevier Ltd.

  12. Elastic wave velocities of peridotite KLB-1 at mantle pressures and implications for mantle velocity modeling

    NASA Astrophysics Data System (ADS)

    Wang, Xuebing; Chen, Ting; Zou, Yongtao; Liebermann, Robert C.; Li, Baosheng

    2015-05-01

    Compressional (VP) and shear (VS) wave velocities of a synthetic KLB-1 peridotite were measured for the first time up to 10 GPa using ultrasonic interferometry. Analysis of the P and S wave velocities yielded K0 = 123(1) GPa, K0' = 5.1(2), G0 = 75(1) GPa, and G0'= 1.3(1) for the bulk and shear moduli and their pressure derivatives. Comparison with Voigt-Reuss-Hill (VRH) calculations based on literature elasticity data for its constituent minerals indicates that the experimentally measured P and S wave velocities, densities, bulk sound velocities, and VP/VS ratios fall close to the lower limit of VRH averages associated with the uncertainties of the mineral elasticity data. A comparison with previous modeling of mantle compositions implies that the velocities for an aggregate with the pyrolitic composition of KLB-1 are in close agreement with seismic data at the depths of the Earth's upper mantle.

  13. Helioseismic Measurements in the Solar Envelope Using Group Velocities of Surface Waves

    E-print Network

    Vorontsov, S V; Ayukov, S V; Gryaznov, V K

    2014-01-01

    At intermediate and high degree $l$, solar p- and f modes can be considered as surface waves. Using variational principle, we derive an integral expression for the group velocities of the surface waves in terms of adiabatic eigenfunctions of normal modes, and address the benefits of using group-velocity measurements as a supplementary diagnostic tool in solar seismology. The principal advantage of using group velocities, when compared with direct analysis of the oscillation frequencies, comes from their smaller sensitivity to the uncertainties in the near-photospheric layers. We address some numerical examples where group velocities are used to reveal inconsistencies between the solar models and the seismic data. Further, we implement the group-velocity measurements to the calibration of the specific entropy, helium abundance Y and heavy-element abundance Z in the adiabatically-stratified part of the solar convective envelope, using different recent versions of the equation of state. The results are in close ...

  14. Tomographic imaging of local earthquake delay times for three-dimensional velocity variation in western Washington

    Microsoft Academic Search

    Jonathan M. Lees; Robert S. Crosson

    1990-01-01

    Tomographic inversion is applied to delay times from local earthquakes to image three dimensional velocity variations in the Puget Sound region of western Washington. The 37,500 square km region is represented by nearly cubic blocks of 5 km per side. P-wave arrival time observations from 4,387 crustal earthquakes, with depths of 0 to 40 km, were used as sources producing

  15. Tomographic imaging of local earthquake delay times for three-dimensional velocity variation in Western Washington

    Microsoft Academic Search

    Jonathan M. Lees; Roberts S. Crosson

    1990-01-01

    Tomographic inversion is applied to delay times from local earthquakes to image three dimensional velocity variations in the Puget Sound region of Western Washington. The 37,500 square km region is represented by nearly cubic blocks of 5 km per side. P-wave arrival time observations from 4,387 crustal earthquakes, with depths of 0 to 40 km, were used as sources producing

  16. Ultrasonic Velocity and Attenuation of Longitudinal Waves in Rocks

    Microsoft Academic Search

    Michel Auberger; John S. Rinehart

    1961-01-01

    Hughes' pulse technique for measuring longitudinal velocities has been adapted and extended to measure attenuation of longitudinal waves in the frequency range from 250 to 1000 kc\\/s. Data for velocity and attenuation in eight different rocks (three granites, one porphyry, two sandstones, one limestone, and one marble) are given at eight different frequencies ranging from 250 to 1000 kc\\/s. The

  17. Polarization, phase velocity and NMO velocity of qP waves in arbitrary weakly anisotropic media

    E-print Network

    Cerveny, Vlastislav

    ). Accuracy of presented formulae is tested on two examples of anisotropic media with relatively strongPolarization, phase velocity and NMO velocity of qP waves in arbitrary weakly anisotropic media) in isotropic media, the WA parameters are zero and the corresponding equations reduce to equations

  18. Minimizers with discontinuous velocities for the electromagnetic variational method

    E-print Network

    Jayme De Luca

    2011-02-01

    The electromagnetic two-body problem has \\emph{neutral differential delay} equations of motion that, for generic boundary data, can have solutions with \\emph{discontinuous} derivatives. If one wants to use these neutral differential delay equations with \\emph{arbitrary} boundary data, solutions with discontinuous derivatives must be expected and allowed. Surprisingly, Wheeler-Feynman electrodynamics has a boundary value variational method for which minimizer trajectories with discontinuous derivatives are also expected, as we show here. The variational method defines continuous trajectories with piecewise defined velocities and accelerations, and electromagnetic fields defined \\emph{by} the Euler-Lagrange equations \\emph{% on} trajectory points. Here we use the piecewise defined minimizers with the Li{\\'{e}}nard-Wierchert formulas to define generalized electromagnetic fields almost everywhere (but on sets of points of zero measure where the advanced/retarded velocities and/or accelerations are discontinuous). Along with this generalization we formulate the \\emph{generalized absorber hypothesis} that the far fields vanish asymptotically \\emph{almost everywhere%} and show that localized orbits with far fields vanishing almost everywhere \\emph{must} have discontinuous velocities on sewing chains of breaking points. We give the general solution for localized orbits with vanishing far fields by solving a (linear) neutral differential delay equation for these far fields. We discuss the physics of orbits with discontinuous derivatives stressing the differences to the variational methods of classical mechanics and the existence of a spinorial four-current associated with the generalized variational electrodynamics.

  19. Surface-wave group velocity tomography of East Asia

    Microsoft Academic Search

    Francis T. Wu; Anatoli Levshin

    1994-01-01

    Group velocities of both Rayleigh and Love waves are used in a tomographic inversion to obtain group velocity maps of East Asia (60-140°E and 20-60°N). The period range studied is 30-70 s. The Tibetan plateau, a region undergoing intense north-south compression, appears as a prominent low-velocity (about -15% from the average) structure in this area; central Tibet appears as the

  20. Shear velocity structure of central Eurasia from inversion of surface wave velocities

    Microsoft Academic Search

    A. Villaseñor; M. H. Ritzwoller; A. L. Levshin; M. P. Barmin; E. R. Engdahl; W. Spakman; J. Trampert

    2001-01-01

    We present a shear velocity model of the crust and upper mantle beneath central Eurasia by simultaneous inversion of broadband group and phase velocity maps of fundamental-mode Love and Rayleigh waves. The model is parameterized in terms of velocity depth profiles on a discrete 2°×2° grid. The model is isotropic for the crust and for the upper mantle below 220km

  1. Shear-wave attenuation and velocity studies in southeastern Asia

    NASA Astrophysics Data System (ADS)

    Jemberie, Alemayehu Lakew

    Models of shear-wave Q (Qmu) have been obtained for southeastern Asia using two methods. The first method inverts attenuation coefficients of the fundamental Rayleigh mode obtained using a standard two-station technique. The second method matches theoretical amplitude spectra for the fundamental and higher-mode Rayleigh waves computed for previously obtained velocity and assumed Qmu models, and earthquakes with known source depths and focal mechanisms, to observed spectra. The latter method provides much better regional coverage than the first and allows us to map lateral variations of Qmu at various levels in the crust and uppermost mantle. For the single-station, multi-mode method, I assumed an Earth model consisting of three layers, layer 1 being 10 km, layer 2 being 20 km, and layer 3 being 30 km in thickness. Qmu in layer 1 achieves lowest values (about 40) in the southern part of the Tibetan Plateau and in the Tarim basin and is highest (about 250) in southeastern China. The Qmu map of layer 2 indicates that the highest Qmu values (about 150) he in the central part of China and in parts of the Sino-Korean platform. The lowest Q mu value (about 50) occurs in Tibet and the Pamir thrust system. Layer 2 exhibits an overall increase in Qmu going from south to north. For layer 3 the resolution of crustal variations in Qmu, is poorer than layers 1 and 2. Available results, however, indicate that Qmu, is highest (about 180) under southern Mongolia and the Tarim basin, somewhat lower (100) beneath the southern portion of the Baikal Rift, and lowest (80) under the Pamir thrust system.

  2. Improving surface-wave group velocity measurements by energy reassignment

    Microsoft Academic Search

    Helle A. Pedersen; Pierre-Olivier Amblard

    2003-01-01

    Surface waves are increasingly used for shallow seis- mic surveys—in particular, in acoustic logging, environ- mental, and engineering applications. These waves are dispersive, and their dispersion curves are used to ob- tain shear velocity profiles with depth. The main obsta- cle to their more widespread use is the complexity of the associated data processing and interpretation of the re- sults.

  3. Constraints on Shear Velocity in the Cratonic Upper Mantle From Rayleigh Wave Phase Velocity

    NASA Astrophysics Data System (ADS)

    Hirsch, A. C.; Dalton, C. A.

    2014-12-01

    In recent years, the prevailing notion of Precambrian continental lithosphere as a thick boundary layer (200-300 km), defined by a depleted composition and a steady-state conductively cooled temperature structure, has been challenged by several lines of seismological evidence. One, profiles of shear velocity with depth beneath cratons exhibit lower wave speed at shallow depths and higher wave speed at greater depths than can be explained by temperature alone. These profiles are also characterized by positive or flat velocity gradients with depth and anomalously high attenuation in the uppermost mantle, both of which are difficult to reconcile with the low temperatures and large thermal gradient expected with a thermal boundary layer. Two, body-wave receiver-function studies have detected a mid-lithospheric discontinuity that requires a large and abrupt velocity decrease with depth in cratonic regions that cannot be achieved by thermal gradients alone. Here, we used forward-modeling to identify the suite of shear-velocity profiles that are consistent with phase-velocity observations made for Rayleigh waves that primarily traversed cratons in North America, South America, Africa, and Australia. We considered two approaches; with the first, depth profiles of shear velocity were predicted from thermal models of the cratonic upper mantle that correspond to a range of assumed values of mantle potential temperature, surface heat flow, and radiogenic heat production in the crust and upper mantle. With the second approach, depth profiles of shear velocity were randomly generated. In both cases, Rayleigh wave phase velocity was calculated from the Earth models and compared to the observed values. We show that it is very difficult to match the observations with an Earth model containing a low-velocity zone in the upper mantle; instead, the best-fit models contain a flat or positive velocity gradient with depth. We explore the implications of this result for the thermal and compositional properties and long-term stability of the cratonic upper mantle.

  4. The ''phase velocity'' of nonlinear plasma waves in the laser beat-wave accelerator

    SciTech Connect

    Spence, W.L.

    1985-04-01

    A calculational scheme for beat-wave accelerators is introduced that includes all orders in velocity and in plasma density, and additionally accounts for the influence of plasma nonlinearities on the wave's phase velocity. The main assumption is that the laser frequencies are very large compared to the plasma frequency - under which it is possible to sum up all orders of forward Raman scattering. It is found that the nonlinear plasma wave does not have simply a single phase velocity, but that the beat-wave which drives it is usefully described by a non-local ''effective phase velocity'' function. A time-space domain approach is followed. (LEW)

  5. 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.

  6. Group velocity of Rayleigh waves in the Antarctic region

    Microsoft Academic Search

    S. Danesi; A. Morelli

    2000-01-01

    We analyzed dispersion of intermediate and long period surface waves, recorded at permanent observatories in the Antarctic region, in a tomographic study based on group velocity. We considered Rayleigh waves from available records of all events which occurred during years 1991–1995, with latitude lower than 40°S and magnitude M?5.0. We performed classic single-station dispersion analysis on the surface wave train

  7. Velocity regularities of p and s-waves in formations

    SciTech Connect

    Li, Q. (Bureau of Oil Geophysical Prospecting, P.O. Box 11, Zhouzhou City, Hebei Province (CN))

    1992-01-01

    This paper reports on the velocity regularities of seismic waves in sandstone that are emphatically studied by comprehensively analyzing previous authors' velocity results of P and S-waves in various rocks. The velocity regularities of P and S-waves in water-saturated and gas-saturated sandstones have been derived from the comprehensive analysis and study. They can be expressed as two parabolas and four empiric V{sub p}-V{sub s} formulas. It is pointed out that some researchers; linear fitting of velocity data is only applied to a particular area or a particular formation while the parabola formulas have wide adaptability. Four empiric formulas and the relevant figures in this paper favor AVO analysis, lithology regularity recognition in multiwave exploration, and the discovery of hydrocarbon accumulation area.

  8. Rayleigh Wave Phase Velocity and Shear Wave Velocities in the Western Branch of the East African Rift System

    Microsoft Academic Search

    A. N. Adams; A. Nyblade

    2009-01-01

    In this study we present phase velocities and a quasi-three dimensional model of shear wave velocities in the western branch of the East African Rift System and the Tanzania Craton. We incorporate data from a temporary Africa Array broadband network (2007-2009), the Tanzania Broadband Seismic Network (1994-1995), and GSN stations. We employ these datasets to solve for phase velocities using

  9. CONFIGURATION OF NEAR-SURFACE SHEAR-WAVE VELOCITY BY INVERTING SURFACE WAVE

    Microsoft Academic Search

    Jianghai Xia; Richard D. Miller; Choon B. Park

    The shear (S)-wave velocity of near-surface materials (such as soil, rocks, and pavement) and its effect on seismic wave propagation are of fundamental interest in many groundwater, engineering, and environmental studies. Ground roll is a Rayleigh-type surface wave that travels along or near the surface of the ground. Rayleigh wave phase velocity of a layered earth model is a function

  10. Laboratory study of wave and turbulence velocities in a broad-banded irregular wave surf zone

    Microsoft Academic Search

    Francis C. K. Ting

    2001-01-01

    The characteristics of wave and turbulence velocities created by a broad-banded irregular wave train breaking on a 1:35 slope were studied in a laboratory wave flume. Water particle velocities were measured simultaneously with wave elevations at three cross-shore locations inside the surf zone. The measured data were separated into low-frequency and high-frequency time series using a Fourier filter. The measured

  11. Linking sperm length and velocity: the importance of intramale variation

    PubMed Central

    Fitzpatrick, John L.; Garcia-Gonzalez, Francisco; Evans, Jonathan P.

    2010-01-01

    Selection imposed through sperm competition is commonly thought to promote the evolution of longer sperm, since sperm length is assumed to be positively associated with sperm swimming velocity. Yet, the basis for this assumption remains controversial, and there is surprisingly little intraspecific evidence demonstrating such a link between sperm form and function. Here, we show that sperm length and velocity are highly correlated in the sea urchin Heliocidaris erythrogramma, but importantly we report that failure to account for within-male variation in these sperm traits can obscure this relationship. These findings, in conjunction with the mounting evidence for extremely high levels of intra-specific variance in sperm traits, suggest that a functional link between sperm morphology and velocity may be more prevalent than what current evidence suggests. Our findings also suggest that selection for faster swimming sperm may promote the evolution of longer sperm, thereby supporting recent findings from macroevolutionary studies. PMID:20484233

  12. An upper-mantle S-wave velocity model for Northern Europe from Love and Rayleigh group velocities

    Microsoft Academic Search

    Christian Weidle; Valérie Maupin

    2008-01-01

    A model of upper-mantle S-wave velocity and transverse anisotropy beneath northwestern Europe is presented, based on regional surface wave observations. Group velocities for both Love and Rayleigh surface waves are measured on waveform data from international and regional data archives (including temporary deployments) and then inverted for group velocity maps, using a method accounting for Fresnel zone sensitivity. The group

  13. Anisotropic changes in P-wave velocity and attenuation during deformation and fluid infiltration of granite

    USGS Publications Warehouse

    Stanchits, S.A.; Lockner, D.A.; Ponomarev, A.V.

    2003-01-01

    Fluid infiltration and pore fluid pressure changes are known to have a significant effect on the occurrence of earthquakes. Yet, for most damaging earthquakes, with nucleation zones below a few kilometers depth, direct measurements of fluid pressure variations are not available. Instead, pore fluid pressures are inferred primarily from seismic-wave propagation characteristics such as Vp/Vs ratio, attenuation, and reflectivity contacts. We present laboratory measurements of changes in P-wave velocity and attenuation during the injection of water into a granite sample as it was loaded to failure. A cylindrical sample of Westerly granite was deformed at constant confining and pore pressures of 50 and 1 MPa, respectively. Axial load was increased in discrete steps by controlling axial displacement. Anisotropic P-wave velocity and attenuation fields were determined during the experiment using an array of 13 piezoelectric transducers. At the final loading steps (86% and 95% of peak stress), both spatial and temporal changes in P-wave velocity and peak-to-peak amplitudes of P and S waves were observed. P-wave velocity anisotropy reached a maximum of 26%. Transient increases in attenuation of up to 483 dB/m were also observed and were associated with diffusion of water into the sample. We show that velocity and attenuation of P waves are sensitive to the process of opening of microcracks and the subsequent resaturation of these cracks as water diffuses in from the surrounding region. Symmetry of the orientation of newly formed microcracks results in anisotropic velocity and attenuation fields that systematically evolve in response to changes in stress and influx of water. With proper scaling, these measurements provide constraints on the magnitude and duration of velocity and attenuation transients that can be expected to accompany the nucleation of earthquakes in the Earth's crust.

  14. Optical guiding and beat wave phase velocity control in the plasma beat wave accelerator

    Microsoft Academic Search

    E. Esarey; A. Ting; P. Sprangle

    1989-01-01

    Relativistic optical guiding allows two colinear short pulse radiation beams, provided they are of sufficiently high power, to propagate through a plasma without diffracting. By further accounting for finite radial beam geometry, it is possible for the phase velocity of the radiation beat (ponderomotive) wave to equal the speed of light. Provided the plasma wave phase velocity remains equal to

  15. Constraints on shear velocity in the cratonic upper mantle from Rayleigh wave phase velocity

    NASA Astrophysics Data System (ADS)

    Hirsch, Aaron C.

    The standard model of the thermal and chemical structure of cratons has been scrutinized in recent years as additional data have been collected. Recent seismological and petrological studies indicate that the notion of cratonic lithosphere as a thick thermal boundary layer with a very depleted and dehydrated composition may be too simplistic and does not fully explain all aspects of the seismological and petrological observations. We hypothesized that the cratonic lithosphere may be more complicated and designed an experiment to investigate its thermal, chemical, and mineralogical properties using a global database of fundamental mode Rayleigh surface waves. To test this hypothesis, the phase velocities of Rayleigh wave that travel paths primarily over cratons were selected. A 1-D global craton phase velocity profile was generated from these observations and compared to predicted phase-velocity curves using two different forward modeling techniques. With the first approach, profiles of shear velocity were generated based on educated guesses of upper mantle temperatures using geotherms. With the second approach, profiles of shear velocity were generated using random permutations about 1-D global model STW105. In total 5,625 geotherm and 80,000 random 1-D forward models were generated for comparison. Each shear velocity model was converted to phase velocity and compared to the observed range of cratonic phase velocities, defined as within one standard deviation of the mean. This method was able to constrain shear velocity in cratons relatively well though the 1-D profiles deviate at depths shallower than 100 km. Shear velocity is faster than PREM/STW105 to depths greater than 200 km with constantly increasing velocity with depth in the random model and a low velocity layer at 100-150 km.

  16. 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., III

    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.

  17. Rock critical porosity inversion and S-wave velocity prediction

    NASA Astrophysics Data System (ADS)

    Zhang, Jia-Jia; Li, Hong-Bing; Yao, Feng-Chang

    2012-03-01

    A critical porosity model is often used to calculate the dry frame elastic modulus by the rock critical porosity value which is affected by many factors. In practice it is hard for us to obtain an accurate critical porosity value and we can generally take only an empirical critical porosity value which often causes errors. In this paper, we propose a method to obtain the rock critical porosity value by inverting P-wave velocity and applying it to predict S-wave velocity. The applications of experiment and log data both show that the critical porosity inversion method can reduce the uncertainty resulting from using an empirical value in the past and provide the accurate critical porosity value for predicting S-wave velocity which significantly improves the prediction accuracy.

  18. Adaptive Simulated Annealing Velocity Modeling for Rayleigh Wave Dispersion

    Microsoft Academic Search

    Donghong Pei; Satish Pullammanappallil; John Louie

    2005-01-01

    We first implemented a new forward computation of Rayleigh dispersion curves from 1-d velocity profiles. Based on the reflectivity method in terms of generalized reflection and transmission coefficients, we compute the phase velocities of fundamental and higher modes and corresponding eigen-functions for shallow surface-wave dispersion curves. The significant small of relative traction residuals at the free surface and comparisons with

  19. Reconfigurable Wave Velocity Transmission Lines for Phased Arrays

    NASA Technical Reports Server (NTRS)

    Host, Nick; Chen, Chi-Chih; Volakis, John L.; Miranda, Felix

    2013-01-01

    Phased array antennas showcase many advantages over mechanically steered systems. However, they are also more complex, heavy and most importantly costly. This presentation paper presents a concept which overcomes these detrimental attributes by eliminating all of the phase array backend (including phase shifters). Instead, a wave velocity reconfigurable transmission line is used in a series fed array arrangement to allow phase shifting with one small (100mil) mechanical motion. Different configurations of the reconfigurable wave velocity transmission line are discussed and simulated and experimental results are presented.

  20. Performance of velocity sensor for flexural wave reduction

    SciTech Connect

    Ko, S.H. [Naval Undersea Warfare Center Detachment, New London, Connecticut 06320 (United States)

    1996-04-01

    This paper presents the analysis (mathematical modeling) for the reduction of flexural wave (structure-borne) noise that is generated by a line force on a steel plate. The steel plate is covered with a baffle (elastomer layer) to reduce the flexural wave noise. The main objective is to evaluate the performance of a velocity sensor located at the outer surface of the baffle layer. Toward this objective, the transmissibility of the plate displacement (velocity) through the baffle structure has been evaluated. {copyright} {ital 1996 American Institute of Physics.}

  1. An inexpensive instrument for measuring wave exposure and water velocity

    USGS Publications Warehouse

    Figurski, J.D.; Malone, D.; Lacy, J.R.; Denny, M.

    2011-01-01

    Ocean waves drive a wide variety of nearshore physical processes, structuring entire ecosystems through their direct and indirect effects on the settlement, behavior, and survivorship of marine organisms. However, wave exposure remains difficult and expensive to measure. Here, we report on an inexpensive and easily constructed instrument for measuring wave-induced water velocities. The underwater relative swell kinetics instrument (URSKI) is a subsurface float tethered by a short (<1 m) line to the seafloor. Contained within the float is an accelerometer that records the tilt of the float in response to passing waves. During two field trials totaling 358 h, we confirmed the accuracy and precision of URSKI measurements through comparison to velocities measured by an in situ acoustic Doppler velocimeter and those predicted by a standard swell model, and we evaluated how the dimensions of the devices, its buoyancy, and sampling frequency can be modified for use in a variety of environments.

  2. Constant Group Velocity Ultrasonic Guided Wave Inspection for Corrosion and Erosion Monitoring in Pipes

    NASA Astrophysics Data System (ADS)

    Instanes, Geir; Pedersen, Audun; Toppe, Mads; Nagy, Peter B.

    2009-03-01

    This paper describes a novel ultrasonic guided wave inspection technique for the monitoring of internal corrosion and erosion in pipes, which exploits the fundamental flexural mode to measure the average wall thickness over the inspection path. The inspection frequency is chosen so that the group velocity of the fundamental flexural mode is essentially constant throughout the wall thickness range of interest, while the phase velocity is highly dispersive and changes in a systematic way with varying wall thickness in the pipe. Although this approach is somewhat less accurate than the often used transverse resonance methods, it smoothly integrates the wall thickness over the whole propagation length, therefore it is very robust and can tolerate large and uneven thickness variations from point to point. The constant group velocity (CGV) method is capable of monitoring the true average of the wall thickness over the inspection length with an accuracy of 1% even in the presence of one order of magnitude larger local variations. This method also eliminates spurious variations caused by changing temperature, which can cause fairly large velocity variations, but do not significantly influence the dispersion as measured by the true phase angle in the vicinity of the CGV point. The CGV guided wave CEM method was validated in both laboratory and field tests.

  3. Microwave acoustics handbook. Volume 4: Bulk wave velocities: Numerical data

    Microsoft Academic Search

    A. J. Slobodnik Jr.; R. T. Delmonico; E. D. Conway

    1980-01-01

    Information useful for the design of acoustic delay lines, resonators, and other miniature, low-cost devices for use in communications and electronic sensing is given. Numerical data on bulk acoustic wave velocities and power flow angles are given for longitudinal, and two shear waves for various orientations of the following single crystalline materials: Ba2NaNb5O15, Bi12\\/geO20, CdS, Diamond, Eu3Fe5O15, GaAs, Gadolinium Gallium

  4. Azimuthal anisotropy and 3-D shear-wave velocity structures of North Island, New Zealand.

    NASA Astrophysics Data System (ADS)

    Fry, B.; Yin, Y.; Deschamps, F.; Reyners, M.

    2014-12-01

    We invert Rayleigh-wave group-velocity dispersion data to calculate isotropic and anisotropic anisotropy of wavespeeds between 6 50 second periods in North Island, New Zealand. This is a region with a subduction system including back-arc spreading as well as upper plate block rotation. We generate interstation empirical Green's Functions from stacked ambient noise cross-correlations recorded from station pairs of the GeoNet network and temporary experiments. Measurements of fundamental-mode Rayleigh-wave dispersion are made using multiple-filtering and frequency-time analysis and manual selection of the dispersion curves. This collection of dispersion curves is then inverted for lateral variations in both isotropic and azimuthally anisotropic wavespeeds at discrete periods using an LSQR method with lateral smoothing and slight norm and gradient damping. Each discrete period provides a different depth sensitivity range, yielding information on depth dependence of the velocity variations. We then use the isotropic solutions to develop a 3D shear wave velocity model for each node of a 50 km triangular grid. We define an anomalous region of slow velicities accompanying trench-perpendicular fast-propagation under the east coast, near the shallow Hikurangi subduction zone. The structure appears at periods of about 21 seconds and is most prominent at periods of about 28 seconds. Toward the western North Island, farther from the trench, the isotropic group velocity and shear-wave velocity is relatively fast with the fast-propagating axis parallel to the trench direction. The isotropic dispersion curves extract from our model are strongly suggestive of a thin (<10km) low-velocity zone within or above the subducting slab which is also present in our 3D shear-wave model.

  5. Formula for the phase velocity of electromagnetic waves

    NASA Astrophysics Data System (ADS)

    Huang, Shihua; Wu, Fengmin; Hu, Bo

    2009-04-01

    A new formula for the phase velocity of electromagnetic waves presented by Chen [Appl. Phys. Lett. 88, 121125 (2006)] is investigated and discussed here. The difference between the result obtained with the new formula and that obtained directly using the phase term is small for a fundament-mode Gaussian laser beam. However, this difference is qualitative in some high-order Gaussian-mode laser beams. Using the new formula for such beams, discontinuities arise in the distribution of the phase velocity. This distribution is not rotationally symmetric with respect to the optical axis, and an imaginary phase velocity may appear near these discontinuities.

  6. Simultaneous measurement of group velocities of various mode's Lamb wave

    NASA Astrophysics Data System (ADS)

    Murase, Morimasa; Kawashima, Koichiro

    2001-04-01

    Multimode's Lamb waves in stainless steel plates of 0.490 and 5.042 mm thickness were generated by 2.25 or 5 MHz broadband transducers with three plastic wedges of different angles. With the time domain signals received at two different positions, the group velocities of various modes (S0-S6,A1-A7) were calculated by using the phase spectrum. The measured dispersion curves of the group velocity agree well with a certain part of each theoretical curves in velocity range of 2000-4000 m/s and in frequency x thickness range of 2.5-22.5 MHz mm.

  7. Fast magnetosonic waves driven by shell velocity distributions

    NASA Astrophysics Data System (ADS)

    Min, Kyungguk; Liu, Kaijun

    2015-04-01

    Using linear dispersion theory and particle-in-cell simulations, we explore the ion Bernstein instability driven by the shell-type ion velocity distribution which is related to the excitation of fast magnetosonic waves in the terrestrial magnetosphere. We first demonstrate a novel idea to construct the shell velocity distribution out of multiple Maxwellian ring-beam velocity distributions. Applying this technique, we find that the convergence of the linear theory instability can be achieved with only a moderate number of ring-beam components. In order to prove that such an approximation is legitimate and the linear theory instabilities evaluated are indeed valid, we use the exact shell distribution to carry out a number of one dimensional particle-in-cell simulations corresponding to multiple wave propagation angles adjacent to the direction at which the most unstable waves are expected to grow. The agreement between the linear dispersion analysis and the simulation results is generally very good: enhanced waves are organized along the linear theory dispersion curves in the frequency-wave number space, and relative wave amplitudes are ordered as the linear theory growth rates very well. However, the simulations show a few extra branches that are not expected from the linear dispersion analysis. A close examination of these extra branches suggests that they are not simulation artifacts and particularly related to the ring/shell-type distributions with large ring/shell speed (v>˜1.5 vA, where vA is the Alfvén speed). In addition, our results show that substantial wave growth can occur at nonintegral harmonics of the proton cyclotron frequency at wave normal angles substantially far away from the perpendicular direction, which may provide an alternative explanation of the off-harmonic peaks of some fast magnetosonic waves observed in space.

  8. A1. Synthetic surface wave phase velocities The azimuthal dependence of phase velocities were computed based on the perturbation

    E-print Network

    Ito, Garrett

    APPENDIX A1. Synthetic surface wave phase velocities The azimuthal dependence of phase velocitiessin4cos2sin2cos 2 1 , 4321 TATATATA U Tc , (1) where T is period, U is group velocity) and the displacement eigenfunctions of the isotropic model. Phase velocity values were calculated for Rayleigh wave

  9. Lithospheric structure beneath the East China Sea revealed by Rayleigh-wave phase velocities

    NASA Astrophysics Data System (ADS)

    Legendre, C. P.; Chen, Q.-F.; Zhao, L.

    2014-12-01

    We explore the variations of Rayleigh-wave phase-velocity beneath the East China Sea in a broad period range (5-200 s). Rayleigh-wave dispersion curves are measured by the two-station technique for a total of 373 interstation paths using vertical-component broad-band waveforms at 32 seismic stations around the East China Sea from 6891 global earthquakes. The resulting maps of Rayleigh-wave phase velocity and azimuthal anisotropy provide a high resolution model of the lithospheric mantle beneath the East China Sea. The model exhibits four regions with different isotropic and anisotropic patterns: the Bohai Sea, belonging to the North China Craton, displays a continental signature with fast velocities at short periods; the Yellow Sea, very stable unit associated with low deformation, exhibits fast velocities and limited anisotropy; the southern part of the East China Sea, with high deformation and many fractures and faults, is related to slow velocities and high anisotropic signature; and the Ryukyu Trench shows high-velocity perturbations and slab parallel anisotropy.

  10. 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

  11. Compositional variation versus partial melting: What is the cause of low velocity and high conductivity?

    NASA Astrophysics Data System (ADS)

    Karato, Shun-ichiro

    2013-04-01

    The causes for low velocity, high conductivity regions of Earth (asthenosphere in the upper mantle, some regions of the D" layer at the bottom of the mantle) are controversial. I will discuss two possible causes: anomalies in chemical composition and presence of liquids (e.g., partial melt). Based on the thermodynamics and the physics of melt generation and migration, I will discuss the difficulties of partial melt model to explain geophysical anomalies. A brief review will be presented about the hydrogen-based model for geophysical anomalies including a new theory on the relationship between isotope diffusion and conductivity, and the role of grain-boundary sliding to affect seismic wave velocities. I conclude that the variation in hydrogen content is the most plausible explanation for the anomalies in the upper mantle and the transition zone. However, hydrogen model unlikely explains the observed very large velocity reduction in the ultra-low velocity regions in the D" layer. Fe-enrichment is a possible cause for low velocity and high conductivity. However, difficulties with this model are (i) the core is under-saturated with oxygen and hence the mantle next to the core must be depleted with FeO, and (ii) previously proposed mechanisms of Fe penetration are inefficient. A new finding in my lab shows that FeO-depletion at the bottom of the mantle likely promotes the penetration of molten iron leading to the low velocity and high conductivity.

  12. Velocity of Shear Waves in Rocks to 10 Kilobars, 1

    Microsoft Academic Search

    Gene Simmons; Dallas Seismological

    1964-01-01

    The velocity of shear waves is reported as a function of pressure for several rocks previously used by Birch in his measurements of ¾. AC-cut quartz transducers with resonant frequencies of I to 5 Mc\\/s were used with the usual ultrasonic technique. In fine-grained, low porosity rocks, very little compressional energy precedes $ and there is no ambiguity in ar-

  13. Continuous subsurface velocity measurement with coda wave interferometry

    E-print Network

    Niu, Fenglin

    to 10À8 PaÀ1 [e.g., Birch, 1960, 1961; Simmons, 1964]. Such dependence is attributed to the opening, and B. Wang (2008), Continuous subsurface velocity measurement with coda wave interferometry, J. Geophys/closing of micro- cracks in response to changes in the stress normal to the crack surface [e.g., Walsh, 1965; Nur

  14. Studies on the determination of shear wave velocity in sands

    Microsoft Academic Search

    P. P. Bartake; D. N. Singh

    2007-01-01

    Laboratory investigations such as resonant column, cyclic triaxial, and torsional shear tests are usually conducted on undisturbed and reconstituted sand samples in order to determine their shear modulus, which can be used to compute shear wave velocity. However, these methods are extremely cumbersome and indirect, they employ cost-intensive instrumentation, and they require trained manpower. These problems can be overcome by

  15. The Velocity of Radio Waves over Short Paths

    Microsoft Academic Search

    R. C. Colwell; H. Atwood; J. E. Bailey; C. O. Marsh

    1942-01-01

    The velocity of radio waves was measured directly in the following manner. Two radio stations were set up on frequencies of 3492.5 and 2398 kilocycles, respectively. One station was fixed while the other was portable. The fixed station sent out pulses which were received at the portable station. A thyratron control set off return pulses which came back to the

  16. Surface Wave Group Velocity Tomography and Lithospheric S-velocity Structure of South American Continent

    Microsoft Academic Search

    M. Feng; M. Assumpcao; S. van der Lee

    2003-01-01

    A new group velocity tomography is presented for the South American continent including additional stations deployed in the northern and northeastern part of the continent, which had not been covered by previous works. More than 10,000 seismograms were examined with paths principally propagating across the continent of South America. 4000 Rayleigh- and 2270 Love-wave dispersion curves with good quality were

  17. Analysis of sediment particle velocity in wave motion based on wave flume experiments

    NASA Astrophysics Data System (ADS)

    Krupi?ski, Adam

    2012-10-01

    The experiment described was one of the elements of research into sediment transport conducted by the Division of Geotechnics of West-Pomeranian University of Technology. The experimental analyses were performed within the framework of the project "Building a knowledge transfer network on the directions and perspectives of developing wave laboratory and in situ research using innovative research equipment" launched by the Institute of Hydroengineering of the Polish Academy of Sciences in Gda?sk. The objective of the experiment was to determine relations between sediment transport and wave motion parameters and then use the obtained results to modify formulas defining sediment transport in rivers, like Ackers-White formula, by introducing basic parameters of wave motion as the force generating bed material transport. The article presents selected results of the experiment concerning sediment velocity field analysis conducted for different parameters of wave motion. The velocity vectors of particles suspended in water were measured with a Particle Image Velocimetry (PIV) apparatus registering suspended particles in a measurement flume by producing a series of laser pulses and analysing their displacement with a high-sensitivity camera connected to a computer. The article presents velocity fields of suspended bed material particles measured in the longitudinal section of the wave flume and their comparison with water velocity profiles calculated for the definite wave parameters. The results presented will be used in further research for relating parameters essential for the description of monochromatic wave motion to basic sediment transport parameters and "transforming" mean velocity and dynamic velocity in steady motion to mean wave front velocity and dynamic velocity in wave motion for a single wave.

  18. P, S wave velocity model of the crust and upper most mantle of Albania region

    NASA Astrophysics Data System (ADS)

    Ormeni, Rrapo

    2011-01-01

    This paper describes the one-dimensional (1D) velocity model computed by VELEST in the SEISAN seismic analysis system, inverting re-picked P-wave and S-wave arrival times recorded during 2002-2006 by the Albanian, Montenegro, Thessalonica and Macedonia seismic networks. The re-picked data yield P-wave and S-wave velocities proved to be more suitable compared to bulletin data for this detailed inversion study. Seismic phases recorded by the Albania seismic network and integrated with data from the Montenegro, Thessalonica and Macedonia networks are used to prepare the Albanian seismic bulletin. Earthquake hypocenters from the Albanian bulletins have also location errors that are negligible for civil protection purposes, large scale seismotectonic analyses and more accurate hypocentral determinations which are necessary for detailed seismotectonic and geodynamic studies. It was noted that the smoothness of the velocity variation increased with depth. A velocity of 5.5 km/s was calculated for the upper crust, 6.1 km/s was calculated for the middle crust and 6.9 km/s was computed for the lower crust. P wave velocity was 7.85 km/s at depth of 50 km and for the upper mantle it is 8.28 km/s. Using the improved velocity model, the earthquakes which occurred in Albania in the past 5 years were able to be relocated, achieving constrained hypocentral determinations for events in Albania. The interpretation of the 1 D velocity models infers interesting features of the deep structure of Albania. These results represent an important step towards more detailed seismotectonic analyses.

  19. Crustal and upper mantle velocity structure beneath central Tibet by P-wave teleseismic tomography

    NASA Astrophysics Data System (ADS)

    Zhang, Heng; Zhao, Junmeng; Xu, Qiang

    2012-09-01

    A detailed 3-D P-wave velocity model beneath central Tibet was obtained using 26 741 arrival times from 1025 teleseismic events recorded by the portable stations of the Hi-CLIMB project. In the crustal correction, we consider both vertical and lateral velocity variations. Our teleseismic P-wave tomography result reveals that the Indian lithospheric mantle underthrusts no further than 32.5°N. In addition, the presence of low velocity anomalies under the Indus-Tsangpo suture suggests that subduction is not a simple and continuous process. We suggest that the delamination of Indian mantle lithosphere induces mantle upwelling beneath the rifts, which in turn created cracks or a break in the subducted plate. Moreover, the formation of active rifts near the profile is related to the mantle upwelling.

  20. Accurate seismic phase-velocities from interfering surface-waves using homomorphic deconvolution 

    E-print Network

    Szerbiak, Robert Bruce

    1981-01-01

    . This velocity structure determines the surface-waves's phase-velocity, which is the velocity of a particular frequency of the surface-wave. Phase-velocity is computed from the alpha spectrum of a surface-wave (Toksoz and Ben-Menahem, 1963). 1. 0 O I 0. 0...

  1. Variations in the relationship of seismic velocities before two earthquakes in Imbria (Italy)

    Microsoft Academic Search

    P. F. Biagi; G. Della Monica; A. Ermini; V. Sgrigna

    1981-01-01

    Summary  The variation of thev\\u000a \\u000a P\\u000a \\/v\\u000a \\u000a S\\u000a relationship between the velocities of longitudinal and transverse seismic waves in an area of Central Italy has been examined\\u000a between January 1979 and March 1980. SP seimograms, recorded by a three-station network, have been used duringM?4.2 earthquakes. Such events took place along an active zone which included the epicentre areas of the two

  2. 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.

  3. PRACTICAL USE OF VARIATIONAL PRINCIPLES FOR MODELING WATER WAVES

    E-print Network

    Paris-Sud XI, Université de

    formulations for surface waves can be found in review papers, e.g., [47, 48, 61]. The water wave problem references. Key words and phrases. water waves; variational principle; Lagrangian; Hamiltonian; relaxationPRACTICAL USE OF VARIATIONAL PRINCIPLES FOR MODELING WATER WAVES DIDIER CLAMOND AND DENYS DUTYKH

  4. Surface Waves: Concept of Stationary Phase Velocities of a Non-Stationary Signal

    E-print Network

    Laske, Gabi

    ;Surface Waves: Dispersion Curves Yuck! Overtones have same group velocity! Even worse! Same as fundamentalSurface Waves: Concept of Stationary Phase Velocities of a Non-Stationary Signal stationary phase gives phase velocity energy transport of wave packet of similar frequencies #12;Surface Waves: Concept

  5. Correcting Radial Velocities for Long-Term Magnetic Activity Variations.

    PubMed

    Saar; Fischer

    2000-05-01

    We study stars in the Lick planetary survey for correlations between simultaneous measurements of high-precision radial velocities vr and magnetic activity (as measured in an SIR emission index from Ca ii lambda8662). We find significant correlations in approximately 30% of the stars. After removing linear trends between SIR and vr, we find that the dispersion in vr in these stars is decreased by an average of 17%, or approximately 45% of the dispersion above the measurement noise. F stars and less active stars with variable Ca ii H and K lines are the most successfully corrected. The magnitude of the slope of the SIR versus vr relations increases proportional to vsini and (excepting M dwarfs) tends to decrease with decreasing Teff. We argue that the main cause of these effects is modification of the mean line bisector shape brought on by long-term, magnetic activity-induced changes in the surface brightness and convective patterns. The correlations can be used to partially correct vr data for the effects of long-term activity variations, potentially permitting study of planets around some (higher mass) younger stars and planets producing smaller stellar reflex velocities. PMID:10790082

  6. Phase Velocity Method for Guided Wave Measurements in Composite Plates

    NASA Astrophysics Data System (ADS)

    Moreno, E.; Galarza, N.; Rubio, B.; Otero, J. A.

    Carbon Fiber Reinforced Polymer is a well-recognized material for aeronautic applications. Its plane structure has been widely used where anisotropic characteristics should be evaluated with flaw detection. A phase velocity method of ultrasonic guided waves based on a pitch-catch configuration is presented for this purpose. Both shear vertical (SV) and shear horizontal (SH) have been studied. For SV (Lamb waves) the measurements were done at different frequencies in order to evaluate the geometrical dispersion and elastic constants. The results for SV are discussed with an orthotropic elastic model. Finally experiments with lamination flaws are presented.

  7. Whistler Waves Driven by Anisotropic Strahl Velocity Distributions: Cluster Observations

    NASA Technical Reports Server (NTRS)

    Vinas, A.F.; Gurgiolo, C.; Nieves-Chinchilla, T.; Gary, S. P.; Goldstein, M. L.

    2010-01-01

    Observed properties of the strahl using high resolution 3D electron velocity distribution data obtained from the Cluster/PEACE experiment are used to investigate its linear stability. An automated method to isolate the strahl is used to allow its moments to be computed independent of the solar wind core+halo. Results show that the strahl can have a high temperature anisotropy (T(perpindicular)/T(parallell) approximately > 2). This anisotropy is shown to be an important free energy source for the excitation of high frequency whistler waves. The analysis suggests that the resultant whistler waves are strong enough to regulate the electron velocity distributions in the solar wind through pitch-angle scattering

  8. Collisional and wave-particle interactions in critical velocity ionization

    Microsoft Academic Search

    William J. McNeil; Shu T. Lai; Edmond Murad

    1990-01-01

    Alfven's critical ionization velocity (CIV) process involves collective and collisional interactions of a magnetoplasma streaming through a neutral gas. Numerical simulations of CIV using particle-in-cell plasma codes including various collisional interactions are given. Fast electron heating is observed. The interplay between collisional and collective interactions renders the hot electron tail shorter than in non-CIV situations with collisionless wave-particle interactions without

  9. Microwave acoustics handbook. Volume 3: Bulk wave velocities

    Microsoft Academic Search

    A. J. Slobodnik Jr.; R. T. Delmonico; E. D. Conway

    1980-01-01

    Information useful for the design of acoustic delay lines, resonators, and other miniature, low cost, reliable devices for use in communications and electronic sensing is given in this report. Computations of bulk acoustic wave velocities, power flow angles, and coupling to electric fields are plotted for various orientations of the following single crystalline materials: Ba2NaNb5O15, Bi12GeO20, CdS, Diamond, Eu3Fe5O15, Gadolinium

  10. Accuracy of arterial pulse-wave velocity measurement using MR

    Microsoft Academic Search

    Bradley D. Bolster; Ergin Atalar; Christopher J. Hardy; Elliot R. McVeigh

    1998-01-01

    The performance of a one-dimensional MR technique for the estimation of pulse-wave velocity in the aorta was evaluated. An expression for the error in this es- timate was formulated and veri5ed both by simulation and by experiment. On the basis of this formulation. guidelines for increasing the emciency of the acquisi- tion were established. The technique was further vali- dated

  11. One-dimensional Shear Velocity Structure of Northern Africa from Rayleigh Wave Group Velocity Dispersion

    Microsoft Academic Search

    S. E. Hazler; A. F. Sheehan; D. E. McNamara; W. R. Walter

    2001-01-01

    ABSTRACT Provide a concise summary,of the whole paper. You can draw from your fall 1998 AGU abstract in part. Here’s some text you can use if you wish. Rayleigh wave group velocity dispersion measurements,from 7s to 200s period have been made for paths traversing Northern Africa. Data were accumulated from the IRIS DMC, GEOSCOPE, and MEDNET seismic networks covering the

  12. Group velocity and characteristic wave curves of Lamb waves in composites: Modeling and experiments

    Microsoft Academic Search

    Lei Wang; F. G. Yuan

    2007-01-01

    The propagation characteristics of Lamb waves in composites, with emphasis on group velocity and characteristic wave curves, are investigated theoretically and experimentally. In particular, the experimental study focuses on the existence of multiple higher-order Lamb wave modes that can be observed from piezoelectric sensors by the excitation of ultrasonic frequencies. Using three-dimensional (3-D) elasticity theory, the exact dispersion relations governed

  13. Analysis of group-velocity dispersion of high-frequency Rayleigh waves for near-surface applications

    Microsoft Academic Search

    Yinhe Luo; Jianghai Xia; Yixian Xu; Chong Zeng

    2011-01-01

    The Multichannel Analysis of Surface Waves (MASW) method is an efficient tool to obtain the vertical shear (S)-wave velocity profile using the dispersive characteristic of Rayleigh waves. Most MASW researchers mainly apply Rayleigh-wave phase-velocity dispersion for S-wave velocity estimation with a few exceptions applying Rayleigh-wave group-velocity dispersion. Herein, we first compare sensitivities of fundamental surface-wave phase velocities with group velocities

  14. The upper mantle shear wave velocity structure of East Africa derived from Rayleigh wave tomography

    NASA Astrophysics Data System (ADS)

    O'Donnell, J.; Nyblade, A.; Adams, A. N.; Weeraratne, D. S.; Mulibo, G.; Tugume, F.

    2012-12-01

    An expanded model of the three-dimensional shear wave velocity structure of the upper mantle beneath East Africa has been developed using data from the latest phases of the AfricaArray East African Seismic Experiment in conjunction with data from preceding studies. The combined dataset consists of 331 events recorded on a total of 95 seismic stations spanning Kenya, Uganda, Tanzania, Zambia and Malawi. In this latest study, 149 events were used to determine fundamental mode Rayleigh wave phase velocities at periods ranging from 20 to 182 seconds using the two-plane-wave method. These were subsequently combined with the similarly processed published measurements and inverted for an updated upper mantle three-dimensional shear wave velocity model. Newly imaged features include a substantial fast anomaly in eastern Zambia that may have exerted a controlling influence on the evolution of the Western Rift Branch. Furthermore, there is a suggestion that the Eastern Rift Branch trends southeastward offshore eastern Tanzania.

  15. Stress-wave velocity of wood-based panels: Effect of moisture,

    E-print Network

    Stress-wave velocity of wood-based panels: Effect of moisture, product type, and material direction Guangping Han Qinglin Wu Xiping Wang Abstract The effect of moisture on longitudinal stress-wave veloc- ity, particleboard, and southern pine lumber was evaluated. It was shown that the stress-wave velocity decreased

  16. Experimental study of Love wave sensor response by phase and group velocity measurement

    Microsoft Academic Search

    Fabrice Martin; Glen McHale; Michael I. Newton

    2004-01-01

    The effect of dispersion on acoustic wave sensors is considered experimentally. A recent theoretical prediction that the phase velocity mass sensitivity of guided shear horizontal surface acoustic wave devices can be obtained using measurements of phase and group velocity, and that the group velocity is highly sensitive to mass loading, is investigated. Experimental data for a polymer-coated surface-skimming bulk wave

  17. Group velocity and power flow relations for surface waves in plane-stratified anisotropic media

    Microsoft Academic Search

    H. Bertoni; A. Hessel

    1966-01-01

    Two aspects of power flow associated with electromagnetic waves in plane-stratified, dispersive, anisotropic media that are also lossless and linear are considered. One aspect is the relation between group velocity and the velocity of energy transport of surface waves in such media. It is shown that the group velocity of surface waves is equal to the ratio of the real

  18. Near surface shear wave velocity in Bucharest, Romania

    NASA Astrophysics Data System (ADS)

    von Steht, M.; Jaskolla, B.; Ritter, J. R. R.

    2008-12-01

    Bucharest, the capital of Romania with nearly 2 1/2 million inhabitants, is endangered by the strong earthquakes in the Vrancea seismic zone. To obtain information on the near surface shear-wave velocity Vs structure and to improve the available microzonations we conducted seismic refraction measurements in two parks of the city. There the shallow Vs structure is determined along five profiles, and the compressional-wave velocity (Vp) structure is obtained along one profile. Although the amount of data collected is limited, they offer a reasonable idea about the seismic velocity distribution in these two locations. This knowledge is useful for a city like Bucharest where seismic velocity information so far is sparse and poorly documented. Using sledge-hammer blows on a steel plate and a 24-channel recording unit, we observe clear shear-wave arrivals in a very noisy environment up to a distance of 300 m from the source. The Vp model along profile 1 can be correlated with the known near surface sedimentary layers. Vp increases from 320 m/s near the surface to 1280 m/s above 55 65 m depth. The Vs models along all five profiles are characterized by low Vs (<350 m/s) in the upper 60 m depth and a maximum Vs of about 1000 m/s below this depth. In the upper 30 m the average Vs30 varies from 210 m/s to 290 m/s. The Vp-Vs relations lead to a high Poisson's ratio of 0.45 0.49 in the upper ~60 m depth, which is an indication for water-saturated clayey sediments. Such ground conditions may severely influence the ground motion during strong Vrancea earthquakes.

  19. Advantages of Using Multichannel Analysis of Love Waves (MALW) to Estimate Near-Surface Shear-Wave Velocity

    NASA Astrophysics Data System (ADS)

    Xia, Jianghai; Xu, Yixian; Luo, Yinhe; Miller, Richard D.; Cakir, Recep; Zeng, Chong

    2012-09-01

    As theory dictates, for a series of horizontal layers, a pure, plane, horizontally polarized shear (SH) wave refracts and reflects only SH waves and does not undergo wave-type conversion as do incident P or Sv waves. This is one reason the shallow SH-wave refraction method is popular. SH-wave refraction method usually works well defining near-surface shear-wave velocities. Only first arrival information is used in the SH-wave refraction method. Most SH-wave data contain a strong component of Love-wave energy. Love waves are surface waves that are formed from the constructive interference of multiple reflections of SH waves in the shallow subsurface. Unlike Rayleigh waves, the dispersive nature of Love waves is independent of P-wave velocity. Love-wave phase velocities of a layered earth model are a function of frequency and three groups of earth properties: SH-wave velocity, density, and thickness of layers. In theory, a fewer parameters make the inversion of Love waves more stable and reduce the degree of nonuniqueness. Approximating SH-wave velocity using Love-wave inversion for near-surface applications may become more appealing than Rayleigh-wave inversion because it possesses the following three advantages. (1) Numerical modeling results suggest the independence of P-wave velocity makes Love-wave dispersion curves simpler than Rayleigh waves. A complication of "Mode kissing" is an undesired and frequently occurring phenomenon in Rayleigh-wave analysis that causes mode misidentification. This phenomenon is less common in dispersion images of Love-wave energy. (2) Real-world examples demonstrated that dispersion images of Love-wave energy have a higher signal-to-noise ratio and more focus than those generated from Rayleigh waves. This advantage is related to the long geophone spreads commonly used for SH-wave refraction surveys, images of Love-wave energy from longer offsets are much cleaner and sharper than for closer offsets, which makes picking phase velocities of Love waves easier and more accurate. (3) Real-world examples demonstrated that inversion of Love-wave dispersion curves is less dependent on initial models and more stable than Rayleigh waves. This is due to Love-wave's independence of P-wave velocity, which results in fewer unknowns in the MALW method compared to inversion methods of Rayleigh waves. This characteristic not only makes Love-wave dispersion curves simpler but also reduces the degree of nonuniqueness leading to more stable inversion of Love-wave dispersion curves.

  20. An estimation technique of Rayleigh wave phase velocities using arrays with arbitrary geometry

    Microsoft Academic Search

    H. Shiraishi; H. Asanuma

    2008-01-01

    The mictotremor survey method (MSM) is one of the most practical techniques to estimate velocity structure of shear waves in sedimentary layers. In the MSM, the velocity models are determined by inversion analysis of the Rayleigh wave phase velocity dispersion curve observed from microtremors. In most of the cases, the phase velocity dispersion curve is obtained by either the spatial

  1. Adhesion Molecule Polymorphisms and Pulse Wave Velocity in American Youth

    PubMed Central

    Zhu, Haidong; Yan, Weili; Tan, Yuande; Li, Ke; Kapuku, Gaston; Treiber, Frank A.; Su, Shaoyong; Harshfield, Gregory A.; Snieder, Harold; Dong, Yanbin

    2013-01-01

    Background Our research group recently reported that aorto-radial (radial) and aorto-dorsalis-pedis (foot) pulse wave velocity (PWV) as proxies of arterial stiffness are substantially heritable in healthy youth. This paper aimed at uncovering the genetic contributions of adhesion molecules, key members in the inflammatory process, to PWV in these young individuals. Methods Radial and foot PWV were non-invasively measured with applanation tonometry in 702 black and white subjects (42% blacks, mean age 17.7 ±3.3 years) from the Georgia Cardiovascular Twin Study. Eight functional polymorphisms from genes for E-selectin (SELE), P-selectin (SELP), intercellular adhesion molecules-1 (ICAM1), and vascular cell adhesion molecules-1 (VCAM1) were genotyped. Results Youth with Ser290Asn or Asn290Asn genotype (SELP) compared to those with Ser290Ser had an increase in both radial and foot PWV (6.61±0.07 vs. 6.41±0.05 m/s, p=0.026; 7.22±0.05 vs. 7.04±0.04 m/s, p=0.007). TT homozygotes of rs2244529 (SELP) had higher foot PWV (7.28±0.07 vs. 7.06±0.03 m/s, p=0.002) than CT heterozygotes and CC homozygotes. There appeared to be a decrease in foot PWV in youth with the 241Arg allele (ICAM1) as compared to those without (6.96±0.08 vs. 7.14±0.03 m/s, p=0.005). For the Asp693Asp (C to T) polymorphism (VCAM1), CC genotype had higher foot PWV than CT and TT genotypes (7.18±0.04 vs. 6.95±0.06 m/s, p<0.0001). There was an epistatic interaction between Ser290Asn, Gly241Arg, and Asp693Asp on foot PWV (p=0.017), explaining 3.6% variance of the foot PWV. Conclusion Genetic variation of adhesion molecules may be implicated in the development of arterial stiffness. Screening for adhesion molecule polymorphisms may help identify high-risk youth. PMID:18828734

  2. Searching for Radial Velocity Variations in eta Carinae

    NASA Technical Reports Server (NTRS)

    Iping, R. C.; Sonneborn, G.; Gull, T. R.; Ivarsson, S.; Nielsen, K.

    2006-01-01

    A hot companion of eta Carinae has been detected using high resolution spectra (905 - 1180 A) obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite (see poster by Sonneborn et al.). Analysis of the far-UV spectrum shows that eta Car B is a luminous hot star. The N II 1084-86 emission feature indicates that the star may be nitrogen rich. The FUV continuum and the S IV 1073 P-Cygni wind line suggest that the effective temperature of eta Car B is at least 25,000 K. FUV spectra of eta Carinae were obtained with the FUSE satellite at 9 epochs between 2000 February and 2005 July. The data consists of 12 observations taken with the LWRS aperture (30x30 arcsec), three with the HIRS aperture (1.25x20 arcsec), and one MRDS aperture (4x20 arcsec). In this paper we discuss the analysis of these spectra to search for radial velocity variations associated with the 5.54-year binary orbit of Eta Car AB.

  3. A continuous record of intereruption velocity change at Mount St. Helens from coda wave interferometry

    NASA Astrophysics Data System (ADS)

    Hotovec-Ellis, A. J.; Gomberg, J.; Vidale, J. E.; Creager, K. C.

    2014-03-01

    In September 2004, Mount St. Helens volcano erupted after nearly 18 years of quiescence. However, it is unclear from the limited geophysical observations when or if the magma chamber replenished following the 1980-1986 eruptions in the years before the 2004-2008 extrusive eruption. We use coda wave interferometry with repeating earthquakes to measure small changes in the velocity structure of Mount St. Helens volcano that might indicate magmatic intrusion. By combining observations of relative velocity changes from many closely located earthquake sources, we solve for a continuous function of velocity changes with time. We find that seasonal effects dominate the relative velocity changes. Seismicity rates and repeating earthquake occurrence also vary seasonally; therefore, velocity changes and seismicity are likely modulated by snow loading, fluid saturation, and/or changes in groundwater level. We estimate hydrologic effects impart stress changes on the order of tens of kilopascals within the upper 4 km, resulting in annual velocity variations of 0.5 to 1%. The largest nonseasonal change is a decrease in velocity at the time of the deep Mw = 6.8 Nisqually earthquake. We find no systematic velocity changes during the most likely times of intrusions, consistent with a lack of observable surface deformation. We conclude that if replenishing intrusions occurred, they did not alter seismic velocities where this technique is sensitive due to either their small size or the finite compressibility of the magma chamber. We interpret the observed velocity changes and shallow seasonal seismicity as a response to small stress changes in a shallow, pressurized system.

  4. Lithospheric Velocity Structure Along the Dead Sea Transform From the Joint Inversion of P- and S-Wave Receiver Functions and Dispersion Velocities

    NASA Astrophysics Data System (ADS)

    Julia, J.; Nyblade, A.; Pasyanos, M. E.; Matzel, E.; Rodgers, A.; Al-Amri, A. M.

    2012-12-01

    The Dead Sea Transform (DST) is a ~1000 km long fault system that separates the Arabian and African plates and links the active spreading center of the Red Sea with the continental collision zone in the Zagros mountains. Independent thermo-mechanical modeling had suggested that a mantle plume intruding from the south might have eroded the lithosphere East of the DST, but recent results from a number of temporary seismic deployments in the area have found little variation in lithospheric thickness to support it and proposed that such geodynamic processes might have operated on both sides of the DST. Those lithospheric thickness estimates have been obtained through the stack and migration of Sp conversions in S-receiver functions, which assumes a global background velocity model to calibrate the depth-scale that might not represent mantle structure under the DST accurately. In this study, we obtain lithospheric and sub-lithospheric S-velocity structure under several permanent broadband stations along the DST from the joint inversion of P- and S-wave receiver functions and tomographic surface-wave dispersion velocities. The joint inversion approach simultaneously models S-P times and Ps amplitudes in P-receiver functions, P-S times and Sp amplitudes in S-receiver functions, and fundamental-mode, Rayleigh-wave group velocities, providing local 1D models of S-velocity under individual recording stations. Our velocity models display interesting variations in crustal thickness along the DST, with values under 40 km in the southern portions and values well over 40 km more to the North, near Lebanon. The models also display S-velocity values in the lithospheric mantle that are generally slow, in the 4.3-4.4 km/s range, sometimes overlaying a relatively shallow asthenospheric low velocity channel, above 150 km depth.

  5. Imaging Rayleigh Wave Attenuation and Phase Velocity beneath North America with USArray

    NASA Astrophysics Data System (ADS)

    Bao, X.; Dalton, C. A.; Jin, G.; Gaherty, J. B.

    2014-12-01

    The EarthScope USArray provides an opportunity to obtain detailed images of the continental upper mantle of United States at a novel scale. The majority of mantle models derived from USArray data contain spatial variations in velocity; however, little is known about the attenuation structure of the North American upper mantle. Joint interpretation of seismic attenuation and velocity models can improve upon the interpretations based only on velocity, and provide important constraints on the temperature, composition, melt content, and volatile content of the mantle. In this study, Rayleigh wave travel time and amplitude are measured using an interstation cross-correlation version of the Generalized Seismological Data Functional algorithm, which takes advantage of waveform similarity at nearby stations. Our data are from 670 large teleseismic earthquakes that occurred from 2006 to 2014 and were recorded by 1,764 Transportable Array stations. More than 4.8 million measurements at periods between 20 and 100 s are collected into our database. Isolating the signal of attenuation in the amplitude observations is challenging because amplitudes are sensitive to a number of factors in addition to attenuation, such as focusing/defocusing and local site amplification. We generate several Rayleigh wave attenuation maps at each period, using several different approaches to account for source and receiver effects on amplitude. This suite of attenuation maps allows us to distinguish between the robust features in the maps and the features that are sensitive to the treatment of source and receiver effects. We apply Helmholtz surface-wave tomography (Lin et al., 2012) to determine velocity and attenuation maps. A significant contrast in velocity and attenuation is observed in the transition between the western and central United States along the Rocky Mountain front. We find low Q values in the western US, along the eastern coast, and the Gulf plain. These areas are also characterized by low wave speed in the phase-velocity maps. The lateral variations in Q may indicate possible temperature variations in the upper mantle of the continental interior. Our Q maps in the western US show good agreement with those presented by Lin et al. (2012). Both models contain low Q (< 100) beneath the Colorado Plateau and the West Coast for 60 s.

  6. Shear Wave Velocity Structure beneath the African-Anatolian Subduction Zone in Southwestern Turkey from Inversions of Rayleigh Waves

    NASA Astrophysics Data System (ADS)

    Teoman, U. M.; Sandvol, E. A.; Kahraman, M.; Sahin, S.; Turkelli, N.

    2011-12-01

    The ongoing subduction of the African Plate under western Anatolia results in a highly complex tectonic structure especially beneath Isparta Angle (IA) and the surroundings where the Hellenic and Cyprian slabs with different subduction geometries intersect. The primary objective is to accurately image the lithospheric structure at this convergent plate boundary and further understand the reasons responsible for the active deformation. Data was gathered from a temporary seismic network consisting of 10 broadband stations that was installed in August 2006 with the support from University of Missouri and nine more stations deployed in March 2007 with the support from Bogazici Research Fund (project ID:07T203). In addition, 21 permanent stations of Kandilli Observatory and Earthquake Research Institute (KOERI) and two from Süleyman Demirel University (SDU) together with five stations from IRIS/Geofon Network were also included to extend the station coverage. We used earthquakes in a distance range of 30-120 degrees with body wave magnitudes larger than 5.5. Depending on the signal to noise ratio, azimuthal coverage of events, and coherence from station, 81 events provided high-quality data for our analysis. The distribution of events shows a good azimuthal coverage, which is important for resolving both lateral heterogeneity and azimuthal anisotropy. We adopted a two-plane-wave inversion technique of Forsyth and Li (2003) to simultaneously solve for the incoming wave field and phase velocity. This relatively simpler representation of a more complex wavefield provided quite stable patterns of amplitude variations in many cases. To begin with, an average phase velocity dispersion curve was obtained and used as an input for tomographic inversions. Two-dimensional tomographic maps of isotropic and azimuthally anisotropic phase velocity variations were generated. Phase velocities can only tell us integrated information about the upper mantle. Furthermore, we inverted phase velocities for shear wave velocities (Saito,1988) in order to obtain direct information at a depth range of 30-300 km that can be interpreted in terms of major tectonic processes such as extension, slab detachment/tearing, STEP faults, volcanism, temperature anomalies, the presence of melt or dissolved water, etc. Resulting tomograms along horizontal and vertical depth sections provided valuable insights on the crustal and upper mantle structure beneath Southwestern Turkey down to almost 300 km.

  7. Properties of seismic fault zone waves and their utility for imaging low-velocity structures

    Microsoft Academic Search

    Yehuda Ben-Zion

    1998-01-01

    A two-dimensional solution for the scalar wave equation in a model of two vertical layers between two quarter spaces is used to study properties of seismic waves in a laterally heterogeneous low-velocity structure. The waves, referred to as seismic fault zone waves, include head waves, internal fault zone reflections, and trapped waves. The analysis aims to clarify the dependency of

  8. Predicting S-wave velocities for unconsolidated sediments at low effective pressure

    USGS Publications Warehouse

    Lee, Myung W.

    2010-01-01

    Accurate S-wave velocities for shallow sediments are important in performing a reliable elastic inversion for gas hydrate-bearing sediments and in evaluating velocity models for predicting S-wave velocities, but few S-wave velocities are measured at low effective pressure. Predicting S-wave velocities by using conventional methods based on the Biot-Gassmann theory appears to be inaccurate for laboratory-measured velocities at effective pressures less than about 4-5 megapascals (MPa). Measured laboratory and well log velocities show two distinct trends for S-wave velocities with respect to P-wave velocity: one for the S-wave velocity less than about 0.6 kilometer per second (km/s) which approximately corresponds to effective pressure of about 4-5 MPa, and the other for S-wave velocities greater than 0.6 km/s. To accurately predict S-wave velocities at low effective pressure less than about 4-5 MPa, a pressure-dependent parameter that relates the consolidation parameter to shear modulus of the sediments at low effective pressure is proposed. The proposed method in predicting S-wave velocity at low effective pressure worked well for velocities of water-saturated sands measured in the laboratory. However, this method underestimates the well-log S-wave velocities measured in the Gulf of Mexico, whereas the conventional method performs well for the well log velocities. The P-wave velocity dispersion due to fluid in the pore spaces, which is more pronounced at high frequency with low effective pressures less than about 4 MPa, is probably a cause for this discrepancy.

  9. Monitoring stress related velocity variation in concrete with a 2 x 10(-5) relative resolution using diffuse ultrasound.

    PubMed

    Larose, Eric; Hall, Stephen

    2009-04-01

    Ultrasonic waves propagating in solids have stress-dependent velocities. The relation between stress (or strain) and velocity forms the basis of non-linear acoustics. In homogeneous solids, conventional time-of-flight techniques have measured this dependence with spectacular precision. In heterogeneous media such as concrete, the direct (ballistic) wave around 500 kHz is strongly attenuated and conventional techniques are less efficient. In this manuscript, the effect of weak stress changes on the late arrivals constituting the acoustic diffuse coda is tracked. A resolution of 2 x 10(-5) in relative velocity change is attained which corresponds to a sensitivity to stress change of better than 50 kPa. Therefore, the technique described here provides an original way to measure the non-linear parameter with stress variations on the order of tens of kPa. PMID:19354358

  10. Monitoring stress related velocity variation in concrete with a 2.10-5 relative resolution using diffuse ultrasound

    NASA Astrophysics Data System (ADS)

    Larose, E. F.; Hall, S.

    2009-12-01

    Ultrasonic waves propagating in solids have stress-dependent velocities. The relation between stress (or strain) and velocity forms the basis of non-linear acoustics. In homogeneous solids, conventional time-of-flight techniques have measured this dependence with spectacular precision. In heterogeneous media like concrete, the direct (ballistic) wave around 500 kHz is strongly attenuated and conventional techniques are less efficient. In this manuscript, the effect of weak stress changes on the late arrivals constituting the acoustic diffuse coda is tracked. A resolution of 2.10-5 in relative velocity change is attained which corresponds to a sensitivity to stress change of better than 50 kPa. Therefore the technique described here provides an original way to measure the non-linear parameter with stress variations on the order of tens of kPa. From E. Larose and Stephen Hall, J. Acoust. Soc. Am. 125 1853-1857 (2009)

  11. Microwave acoustics handbook. Volume 4: Bulk wave velocities: Numerical data

    NASA Astrophysics Data System (ADS)

    Slobodnik, A. J., Jr.; Delmonico, R. T.; Conway, E. D.

    1980-06-01

    Information useful for the design of acoustic delay lines, resonators, and other miniature, low-cost devices for use in communications and electronic sensing is given. Numerical data on bulk acoustic wave velocities and power flow angles are given for longitudinal, and two shear waves for various orientations of the following single crystalline materials: Ba2NaNb5O15, Bi12/geO20, CdS, Diamond, Eu3Fe5O15, GaAs, Gadolinium Gallium Garnet, Germanium, InSb, InAs, Lead Molybdate, PbS, LiNbO3, LiTaO3, MgO, Quartz, Rutile, Sapphire, Silicon, Spinel, TeO2, YAG, YGaG, YIG, and ZnO. This present volume is intended to be used as a supplement to Volume 3 whenever accurate numerical data is required rather than the more convenient graphical information.

  12. Relationship between macro-fracture density, P-wave velocity, and permeability of coal

    NASA Astrophysics Data System (ADS)

    Wang, Haichao; Pan, Jienan; Wang, Sen; Zhu, Haitao

    2015-06-01

    This study was undertaken to determine the quantitative relationship between macro-fracture density, P-wave velocity, porosity and permeability of different coal rank samples from mining areas in North China. The coal sample permeability shows an exponential growth with increasing fracture density. The relation between P-wave velocity and porosity is power function and P-wave velocity decreases with the increasing porosity. P-wave velocity linearly or nonlinearly decreases with the increase of fracture density in the selected coal samples (0.73-3.59% Ro). However, the overall trend is that P-wave velocity decreases with an increase in macro-fracture density. The permeability of coal samples linearly decreases with the increase of P-wave velocity. The quantitative relationship between P-wave velocity and permeability could provide reference for the further study of permeability predicting.

  13. Shear Wave Velocity Structure of the Sinai Peninsula from Rayleigh Wave Analysis

    Microsoft Academic Search

    V. Corchete; M. Chourak; H. M. Hussein

    2007-01-01

    The lithospheric structure of the Sinai Peninsula is shown by means of nine shear velocity profiles for depths ranging from\\u000a zero to 50 km, determined from the Rayleigh wave analysis. The traces of 30 earthquakes, which occurred from 1992 to 1999\\u000a in and around the study area, have been used to obtain Rayleigh wave dispersion. These earthquakes were registered by a

  14. Interannual variations of total ozone and their relationship to variations of planetary wave activity

    Microsoft Academic Search

    Andrew C. Fusco; Murry L. Salby

    1999-01-01

    Interannual variations of total ozone at midlatitudes of the Northern Hemisphere are shown to operate coherently wit h variations of upwelling planetary wave activity from the troposphere. Variations of upwelling wave activity, which modulate ozone transport and chemical production by the diabatic mean circulation of the stratosphere, account for much of the interannual variance of total ozone, including its systematic

  15. Estimation of seismic velocity in the subducting crust of the Pacific slab beneath Hokkaido, northern Japan by using guided waves

    NASA Astrophysics Data System (ADS)

    Shiina, T.; Nakajima, J.; Toyokuni, G.; Kita, S.; Matsuzawa, T.

    2014-12-01

    A subducting crust contains a large amount of water as a form of hydrous minerals (e.g., Hacker et al., 2003), and the crust plays important roles for water transportation and seismogenesis in subduction zones at intermediate depths (e.g., Kirby et al., 1996; Iwamori, 2007). Therefore, the investigation of seismic structure in the crust is important to understand ongoing physical processes with subduction of oceanic lithosphere. A guided wave which propagates in the subducting crust is recorded in seismograms at Hokkaido, northern Japan (Shiina et al., 2014). Here, we estimated P- and S-wave velocity in the crust with guided waves, and obtained P-wave velocity of 6.6-7.3 km/s and S-wave velocity of 3.6-4.2 km/s at depths of 50-90 km. Moreover, Vp/Vs ratio in the crust is calculated to be 1.80-1.85 in that depth range. The obtained P-wave velocity about 6.6km/s at depths of 50-70 km is consistent with those estimated in Tohoku, northeast Japan (Shiina et al., 2013), and this the P-wave velocity is lower than those expected from models of subducting crustal compositions, such as metamorphosed MORB model (Hacker et al., 2003). In contrast, at greater depths (>80 km), the P-wave velocity marks higher velocity than the case of NE Japan and the velocity is roughly comparable to those of the MORB model. The obtained S-wave velocity distribution also shows characteristics similar to P waves. This regional variation may be caused by a small variation in thermal regime of the Pacific slab beneath the two regions as a result of the normal subduction in Tohoku and oblique subduction in Hokkaido. In addition, the effect of seismic anisotropy in the subducting crust would not be ruled out because rays used in the analysis in Hokkaido propagate mostly in the trench-parallel direction, while those in Tohoku are sufficiently criss-crossed.

  16. Waveform modeling of short-scale shear-wave splitting variations across the Dead Sea basin

    NASA Astrophysics Data System (ADS)

    Kaviani, A.; Rumpker, G.

    2010-12-01

    The Dead Sea basin forms the largest pull-apart basin along the Dead Sea transform fault. As part of the DESIRE project, we investigate the seismic anisotropy across the Dead Sea basin to study mantle deformation processes. We examine shear-wave splitting of SKS waveforms collected by a temporary array of 68 stations along the Dead Sea basin. The observed splitting parameters (i.e. the delay time between the fast and slow shear waves and the polarization direction of the fast shear wave) exhibit systematic variations along an EW-trending profile across the basin. The delay times vary between 1.0 and 2.8 seconds and are among the largest observed in the world. The fast polarizations are oriented more-or-less parallel to the strike of the Dead Sea transform fault and vary between -10 and 20 degrees with respect to North. Full finite-difference waveform modeling reveals that the source-region of the small-scale lateral variations is likely located within the crust. The modeling further shows that purely isotropic velocity variations can affect shear-wave splitting. To a large degree, the observed variations of splitting parameters can be explained by the sedimentary fill of the basin and its low seismic velocities. Our study indicates that precaution must be taken when interpreting short-scale lateral variations of shear wave splitting in terms of anisotropic structures in the crust or upper mantle.

  17. Relativistic focusing and beat wave phase velocity control in the plasma beat wave accelerator

    Microsoft Academic Search

    E. Esarey; A. Ting; P. Sprangle

    1988-01-01

    Relativistic focusing allows two collinear short pulse radiation beams, provided they are of sufficiently high power, to propagate through a plasma without diffracting. By further accounting for finite radial beam geometry, it is possible for the phase velocity of the radiation beat (ponderomotive) wave to equal to the speed of light. This removes one of the limiting factors, phase detuning

  18. Relativistic focusing and beat wave phase velocity control in the plasma beat wave accelerator

    Microsoft Academic Search

    E. Esarey; A. Ting; P. Sprangle

    1988-01-01

    Relativistic focusing allows two colinear short pulse radiation beams, provided they are of sufficiently high power, to propagate through a plasma without diffracting. By further accounting for finite radial beam geometry, it is possible for the phase velocity of the radiation beat (ponderomotive) wave to equal the speed of light. This removes one of the limiting factors, phase detuning between

  19. Variation of the upper mantle velocity structure along the central-south Andes

    NASA Astrophysics Data System (ADS)

    Liang, Xiaofeng; Sandvol, Eric; Shen, Yang; Gao, Haiying

    2014-05-01

    Variations in the subduction angle of the Nazca plate beneath the South American plate has lead to different modes of deformation and volcanism along the Andean active margin. The volcanic gap between the central and southern Andean volcanic zones is correlated with the Pampean flat-slab subduction zone, where the subducting Nazca slab changes from a 30-degree dipping slab beneath the Puna plateau to a horizontal slab beneath the Sierras Pampeanas, and then to a 30-degree dipping slab beneath the south Andes from north to south. The Pampean flat-slab subduction correlates spatially with the track of the Juan Fernandez Ridge, and is associated with the inboard migration of crustal deformation. A major Pliocene delamination event beneath the southern Puna plateau has previously been inferred from geochemical and geological and preliminary geophysical data. The mechanisms for the transition between dipping- and flat-subduction slab and the mountain building process of the central Andean plateau are key issues to understanding the Andean-type orogenic process. We use a new frequency-time normalization approach with non-linear stacking to extract very-broadband (up to 300 second) empirical Green's functions (EGFs) from continuous seismic records. The long-period EGFs provide the deeper depth-sensitivity needed to constrain the mantle structure. The broadband waveform data are from 393 portable stations of four temporary networks: PUNA, SIEMBRA, CHARGE, RAMP, East Sierras Pampeanas, BANJO/SEDA, REFUCA, ANCORP, and 31 permanent stations accessed from both the IRIS DMC and GFZ GEOFON DMC. A finite difference waveform propagation method is used to generate synthetic seismograms from 3-D velocity model. We use 3-D traveltime sensitivity kernels, and traveltime residuals measurement by waveform cross-correlation to directly invert the upper mantle shear-wave velocity structure. The preliminary model shows strong along-strike velocity variations within in the mantle wedge and the subducting NAZCA slab. Low upper mantle velocities are north of 29°S and south of 35°S, corresponding to the low velocity mantle wedge of dipping-subduction. The upper mantle beneath the Sierras Pampeanas has a higher velocity than that beneath the central and south volcanic zones, which is consistent with the Pampeanas flat-slab. Though we observe substantial heterogenity within this flat-slab zone.

  20. 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 correcting for the crustal thickness the phase velocity perturbations obtained from the subsequent linear waveform inversion for the different period bands are converted to a three-layer model of S velocity perturbations (layer 1, 25-100 km; layer 2, 100-200 km) layer 3, 200-300 km). We have applied this method on 275 high-quality Rayleigh waves recorded by a variety of instruments in North America (IRIS/USGS, IRIS/IDA, TERRAscope, RSTN). Sensitivity tests indicate that the lateral resolution is especially good in the densely sampled western continental United States, Mexico, and the Gulf of Mexico.

  1. Flow of concentrated suspensions through fractures: Significant in-plane velocity variations caused by small variations in solid concentration

    NASA Astrophysics Data System (ADS)

    Medina, R.; Detwiler, R. L.; Morris, J. P.; Prioul, R.; Desroches, J.

    2014-12-01

    Flow of fluids containing large concentrations of suspended solids through narrow fractures is important in subsurface processes where the permeability of the fracture is greater than the surrounding matrix (i.e. sand intrusion, environmental remediation, hydraulic fracturing, magma flow, and mud volcanoes). We present results from experiments in which a high concentration (50% by volume) of granular solids suspended in a non-Newtonian carrier fluid (0.75% guar gum in water) flowed through a transparent parallel-plate fracture. Digital particle-image-velocimetry analysis demonstrates the development of a strongly heterogeneous velocity field within the fracture that persists for the length of the fracture. The highest velocities were observed along the no-flow boundaries and the lowest velocities along the centerline; we carried out numerical simulations and additional experiments to elucidate this surprising result. Depth-averaged (2D) simulations using a rheological model of concentrated suspensions of mono-disperse solids in Newtonian fluids reproduced experimental observations of the velocity field when small (3%) variations in solid concentration were introduced. Such concentration variability led to significant (factor of two) velocity variations within the fracture yet negligible changes in observed pressure gradients. Two plausible explanations for solid-concentration variability are: (i) shearing of the fluid at the no-flow boundaries induced these concentration variations or (ii) they were induced by upstream boundary conditions. A second set of experiments was performed to identify which of the two phenomena caused the observed velocity variations. A narrow obstruction was placed along the centerline of the same cell; reduced velocities along the obstruction were observed, indicating that the observed velocity variations are the result of solid concentration heterogeneities that occurred in the upstream boundary and not from concentration heterogeneities developing inside the fracture. Our results suggest that small variations in solid concentration can lead to significant velocity variations such that a simple fracture-averaged conductivity may not reliably predict transport of suspended solids within fractures.

  2. Note on the velocity and related fields of steady irrotational two-dimensional surface gravity waves.

    PubMed

    Clamond, Didier

    2012-04-13

    The velocity and other fields of steady two-dimensional surface gravity waves in irrotational motion are investigated numerically. Only symmetric waves with one crest per wavelength are considered, i.e. Stokes waves of finite amplitude, but not the highest waves, nor subharmonic and superharmonic bifurcations of Stokes waves. The numerical results are analysed, and several conjectures are made about the velocity and acceleration fields. PMID:22393109

  3. Direct Observations of Atmospheric Boundary Layer Response to SST Variations Associated with Tropical Instability Waves over the Eastern Equatorial Pacific

    Microsoft Academic Search

    Hiroshi Hashizume; Shang-Ping Xie; Masatomo Fujiwara; Masato Shiotani; Tomowo Watanabe; Youichi Tanimoto; W. Timothy Liu; Kensuke Takeuchi

    2002-01-01

    Tropical instability waves (TIWs), with a typical wavelength of 1000 km and period of 30 days, cause the equatorial front to meander and result in SST variations on the order of 1°-2°C. Vertical soundings of temperature, humidity, and wind velocity were obtained on board a Japanese research vessel, which sailed through three fully developed SST waves from 140° to 110°W

  4. New constraints on the arctic crust and uppermost mantle: surface wave group velocities, Pn, and Sn

    Microsoft Academic Search

    A. L. Levshin; M. H. Ritzwoller; M. P. Barmin; A. Villaseñor; C. A. Padgett

    2001-01-01

    We present the results of a study of surface wave dispersion across the Arctic region (>60°N) and compare the estimating group velocity maps with new maps of the body wave phases Pn and Sn. Data recorded at about 250 broadband digital stations from several global and regional networks were used to obtain Rayleigh and Love wave group velocity measurements following

  5. 3-D surface wave group velocity distribution in Central-Southern Africa

    Microsoft Academic Search

    V. Midzi

    2001-01-01

    Group velocities estimated from fundamental mode Love and Rayleigh waves are used in a tomography process in central-southern Africa. The waves were generated by eighteen earthquakes, which occurred along the East African Rift and recorded at BOSA, LBTB and SLR seismic stations in southern Africa. The group velocities from Love and Rayleigh waves were isolated using the Multiple Filter Technique

  6. Rayleigh wave group velocity dispersion across Northern Africa, Southern Europe and the Middle East

    Microsoft Academic Search

    D. E. McNamara; W. R. Walter

    1997-01-01

    THis report presents preliminary results from a large scale study of surface wave group velocity dispersion throughout Northern Africa, the Mediterranean, Southern Europe and the Middle East. Our goal is to better define the 3D lithospheric shear-wave velocity structure within this region by improving the resolution of global surface wave tomographic studies. We hope to accomplish this goal by incorporating

  7. One year variations in the near earth solar wind ion density and bulk flow velocity

    NASA Technical Reports Server (NTRS)

    Bolton, Scott J.

    1990-01-01

    One-year periodic variations in the near earth solar wind ion density and bulk flow velocity are reported. The variations show an inverse relationship between the ion velocity and density. The peak strength of the observed density variation ranges from 50-100 percent over the background. These variations imply either large scale mass loading inside the earth's orbit or intrinsic solar modulations. Analyses of both near earth and Pioneer Venus Orbiter spacecraft data provide a comparison at two different heliocentric distances. Several explanations for these variations are discussed.

  8. Illumination Profile & Dispersion Variation Effects on Radial Velocity Measurements

    NASA Astrophysics Data System (ADS)

    Grieves, Nolan; Ge, Jian; Thomas, Neil B.; Ma, Bo; Li, Rui; SDSS-III

    2015-01-01

    The Multi-object APO Radial-Velocity Exoplanet Large-Area Survey (MARVELS) measures radial velocities using a fiber-fed dispersed fixed-delay interferometer (DFDI) with a moderate dispersion spectrograph. This setup allows a unique insight into the 2D illumination profile from the fiber on to the dispersion grating. Illumination profile investigations show large changes in the profile over time and fiber location. These profile changes are correlated with dispersion changes and long-term radial velocity offsets, a major problem within the MARVELS radial velocity data. Characterizing illumination profiles creates a method to both detect and correct radial velocity offsets, allowing for better planet detection. Here we report our early results from this study including improvement of radial velocity data points from detected giant planet candidates. We also report an illumination profile experiment conducted at the Kitt Peak National Observatory using the EXPERT instrument, which has a DFDI mode similar to MARVELS. Using profile controlling octagonal-shaped fibers, long term offsets over a 3 month time period were reduced from ~50 m/s to within the photon limit of ~4 m/s.

  9. Temporal pattern of pulse wave velocity during brachial hyperemia reactivity

    NASA Astrophysics Data System (ADS)

    Graf, S.; Valero, M. J.; Craiem, D.; Torrado, J.; Farro, I.; Zócalo, Y.; Valls, G.; Bía, D.; Armentano, R. L.

    2011-09-01

    Endothelial function can be assessed non-invasively with ultrasound, analyzing the change of brachial diameter in response to transient forearm ischemia. We propose a new technique based in the same principle, but analyzing a continuous recording of carotid-radial pulse wave velocity (PWV) instead of diameter. PWV was measured on 10 healthy subjects of 22±2 years before and after 5 minutes forearm occlusion. After 59 ± 31 seconds of cuff release PWV decreased 21 ± 9% compared to baseline, reestablishing the same after 533 ± 65 seconds. There were no significant changes observed in blood pressure. When repeating the study one hour later in 5 subjects, we obtained a coefficient of repeatability of 4.8%. In conclusion, through analysis of beat to beat carotid-radial PWV it was possible to characterize the temporal profiles and analyze the acute changes in response to a reactive hyperemia. The results show that the technique has a high sensitivity and repeatability.

  10. Mineralization, crystallography, and longitudinal seismic wave velocity of speleothems

    SciTech Connect

    Williams, R.S.; Grant, S.K. (Univ. of Missouri, Rolla, MO (United States). Dept. of Geology and Geophysics); Haas, C.J. (Univ. of Missouri, Rolla, MO (United States). Dept. of Mining Engineering)

    1993-03-01

    Speleothems, or cave deposits, of Fisher Cave in Sullivan, Missouri, display unique arrangements of overlapping and interwoven crystals that provide the foundation for intricate shapes and patterns. Research has found that the deposition of such forms are affected by many variables associated with carbonate petrology. An active cave system having a consistent yearly rate of water flow will deposit trace, non-carbonate mineralization at locations of initial contact with the cave environment. Deposit specimens were tested using X-ray diffraction methods resulting in the identification of a manganese oxide coating of a psilomelane. Speleothems, considered a natural resource, are protected along with the cave from industrial advancements outside the cave environment. When the detonation of explosives during the construction of a highway near Crystal Cave in Springfield, Missouri threatened the speleothegenic decoration, a study of the damaging resonant frequency of the speleothems was instigated. To calculate this frequency, the longitudinal and transverse seismic wave velocity was measured by geophysical techniques.

  11. The influence of velocity-changing collisions on resonant degenerate four-wave mixing

    NASA Technical Reports Server (NTRS)

    Richardson, W. H.; Maleki, L.; Garmire, Elsa

    1989-01-01

    The phase-conjugate signal observed in resonant degenerate four-wave mixing on the 6 3P2 to 7 3S1 transition of atomic Hg in an Hg-Ar discharge is investigated. At a fixed Ar pressure the variation of the signal with pump powers is explained by a model that includes the effects of velocity-changing collisions (VCCs). As the Ar pressure was varied from 0 to 1 torr, an increase in the phase-conjugate signal was observed and is ascribed to a change in the discharge dynamics with Ar pressure and to the influence of VCCs. To further clarify the role of collisions and optical pumping, degenerate four-wave mixing spectra are examined as a function of pump power. Line shapes are briefly discussed.

  12. 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.

  13. Effect of gravity wave temperature variations on homogeneous ice nucleation

    NASA Astrophysics Data System (ADS)

    Dinh, Tra; Podglajen, Aurélien; Hertzog, Albert; Legras, Bernard; Plougonven, Riwal

    2015-04-01

    Observations of cirrus clouds in the tropical tropopause layer (TTL) have shown various ice number concentrations (INC) (e.g., Jensen et al. 2013), which has lead to a puzzle regarding their formation. In particular, the frequently observed low numbers of ice crystals seemed hard to reconcile with homogeneous nucleation knowing the ubuquity of gravity waves with vertical velocity of the order of 0.1 m/s. Using artificial time series, Spichtinger and Krämer (2013) have illustrated that the variation of vertical velocity during a nucleation event could terminate it and limit the INC. However, their study was limited to constructed temperature time series. Here, we carry out numerical simulations of homogeneous ice nucleation forced by temperature time series data collected by isopycnic balloon flights near the tropical tropopause. The balloons collected data at high frequency (30 s), so gravity wave signals are well resolved in the temperature time series. With the observed temperature time series, the numerical simulations with homogeneous freezing show a full range of ice number concentrations (INC) as previously observed in the tropical upper troposphere. The simulations confirm that the dynamical time scale of temperature variations (as seen from observations) can be shorter than the nucleation time scale. They show the existence of two regimes for homogeneous ice nucleation : one limited by the depletion of water vapor by the nucleated ice crystals (those we name vapor events) and one limited by the reincrease of temperature after its initial decrease (temperature events). Low INC may thus be obtained for temperature events when the gravity wave perturbations produce a non-persistent cooling rate (even with large magnitude) such that the absolute change in temperature remains small during nucleation. This result for temperature events is explained analytically by a dependence of the INC on the absolute drop in temperature (and not on the cooling rate). This work supports the hypothesis that even acting alone homogeneous ice nucleation is not necessarily inconsistent with observations of low INC. Spichtinger, P. and Krämer, M.: Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers, Atmos. Chem. Phys., 13, 9801-9818, doi:10.5194/acp-13-9801-2013, 2013. Jensen, E. J., Diskin, G., Lawson, R. P., Lance, S., Bui, T. P., Hlavka, D., McGill, M., Pfister, L., Toon, O. B., and Gao, R.: Ice nucleation and dehydration in the Tropical Tropopause Layer, Proc. Nat. Acad. Sci., 110, 2041-2046, doi:10.1073/pnas.1217104110, 2013.

  14. Radial velocity variations in the young eruptive star EX Lupi

    NASA Astrophysics Data System (ADS)

    Kóspál, Á.; Mohler-Fischer, M.; Sicilia-Aguilar, A.; Ábrahám, P.; Curé, M.; Henning, Th.; Kiss, Cs.; Launhardt, R.; Moór, A.; Müller, A.

    2014-01-01

    Context. EX Lup-type objects (EXors) are low-mass pre-main sequence objects characterized by optical and near-infrared outbursts attributed to highly enhanced accretion from the circumstellar disk onto the star. Aims: The trigger mechanism of EXor outbursts is still debated. One type of theory requires a close (sub)stellar companion that perturbs the inner part of the disk and triggers the onset of the enhanced accretion. Here, we study the radial velocity (RV) variations of EX Lup, the prototype of the EXor class, and test whether they can be related to a close companion. Methods: We conducted a five-year RV survey, collecting 54 observations with HARPS and FEROS. We analyzed the activity of EX Lup by checking the bisector, the equivalent width of the Ca 8662 Å line, the asymmetry of the Ca II K line, the activity indicator SFEROS, the asymmetry of the cross-correlation function, the line depth ratio of the VI/FeI lines, and the TiO, CaH 2, CaH 3, CaOH, and H? indices. We complemented the RV measurements with a 14-day optical/infrared photometric monitoring to look for signatures of activity or varying accretion. Results: We found that the RV of EX Lup is periodic (P = 7.417 d), with stable period, semi-amplitude (2.2 km s-1), and phase over at least four years of observations. This period is not present in any of the above-mentioned activity indicators. However, the RVs of narrow metallic emission lines suggest the same period, but with an anti-correlating phase. The observed absorption line RVs can be fitted with a Keplerian solution around a 0.6 M? central star with msini = (14.7 ± 0.7) MJup and eccentricity of e = 0.24. Alternatively, we attempted to model the observations with a cold or hot stellar spot as well. We found that in our simple model, the spot parameters needed to reproduce the RV semi-amplitude are in contradiction with the photometric variability, making the spot scenario unlikely. Conclusions: We qualitatively discuss two possibilities to explain the RV data: a geometry with two accretion columns rotating with the star, and a single accretion flow synchronized with the orbital motion of the hypothetical companion; the second scenario is more consistent with the observed properties of EX Lup. In this scenario, the companion's mass would fall into the brown dwarf desert, which, together with the unusually small separation of 0.06 au would make EX Lup a unique binary system. The companion also has interesting implications on the physical mechanisms responsible for triggering the outburst. This work is based in part on observations made with ESO Telescopes at the La Silla Paranal Observatory under program IDs 079.A-9017, 081.A-9005, 081.A-9023, 081.C-0779, 082.C-0390, 082.C-0427, 083.A-9011, 083.A-9017, 084.A-9011, 085.A-9027, 086.A-9006, 086.A-9012, 087.A-9013, 087.A-9029, and 089.A-9007.Tables 2 and 3 are available in electronic form at http://www.aanda.org

  15. High-resolution surface wave tomography in oceanic and continental regions: Simultaneous inversion for shear wave velocity, azimuthal anisotropy and attenuation

    NASA Astrophysics Data System (ADS)

    Yang, Yingjie

    The primary goal of this thesis is to understand the structure, dynamics, deformation and evolution of the Earth's lithosphere and mantle in both oceanic and continental settings by surface wave tomography. In chapter 1, we revised 2-D Born-approximation sensitivity kernels of surface waves for the global case to that for a regional case. We found that the kernels can accurately predict the perturbation of the wavefield. Based on the 2-D sensitivity kernels, we developed a surface wave tomography method and tested the inversion method by using synthesized data obtained from numerical simulations. We found the method can almost completely recover the input checkerboard structure when the size of anomalies is larger than one wavelength. In chapter 2, we applied the tomography method developed in chapter 1 to fundamental mode Rayleigh waves in southern California. Two-dimensional phase velocities are used to invert for three-dimensional S-wave velocities of the upper mantle. The pattern of velocity anomalies indicates that there is active small-scale convection in the asthenosphere beneath southern California and that the dominant form of convection is 3-D lithospheric drips and asthenospheric upwellings, rather than 2-D sheets or slabs. Azimuthal anisotropy is obtained in a joint inversion including lateral variations of phase velocities. The strength of anisotropy is ˜1.7% at periods shorter than 67s and decreases to ˜1% at longer periods. In chapter 3, we invert Rayleigh waves recorded at ocean-bottom seismometers (OBSs) in very young (less than 10 Ma) seafloor for shear wave velocity (Vs) and attenuation (Qmu). A high velocity lid with negative gradient in the uppermost mantle overlying a low velocity zone is observed. Our Q mu models exhibit a sharp change over the depth range of 40 to 60 km with higher values above 40 km. The change of Qmu and S-wave velocity with depth is partly due to the sharp change of water content in the upper mantle as a result of the extraction of water by large fractional melting above ˜65 km. ˜1% partial melting in the low velocity zone is required to satisfy the minimum value of shear wave velocity.

  16. The correlations between the saturated and dry P-wave velocity of rocks.

    PubMed

    Kahraman, S

    2007-11-01

    Sometimes engineers need to estimate the wet-rock P-wave velocity from the dry-rock P-wave velocity. An estimation equation embracing all rock classes will be useful for the rock engineers. To investigate the predictability of wet-rock P-wave velocity from the dry-rock P-wave velocity, P-wave velocity measurements were performed on 41 different rock types, 11 of which were igneous, 15 of which were sedimentary and 15 of which was metamorphic. In addition to the dry- and wet-rock P-wave velocity measurements, the P-wave velocity changing as a function of saturation degree was studied. Moreover, dry-rock S-wave velocity measurements were conducted. The test results were modeled using Gassmann's and Wood's theory and it was seen that the measured data did not fit the theories. The unconformity is due to the fact that the theories are valid for high-porosity unconsolidated sediments at low frequencies. Gassmann's equation was modified for the rocks except high-porosity unconsolidated sediments. The dry- and wet-rock P-wave velocity values were evaluated using regression analysis. A strong linear correlation between the dry- and wet-rock P-wave velocities was found. Regression analyses were repeated for the rock classes and it was shown that correlation coefficients were increased. Concluding remark is that the derived equations can be used for the prediction of wet-rock P-wave velocity from the dry-rock P-wave velocity. PMID:17624388

  17. Stochastic simulation for the propagation of high-frequency acoustic waves through a random velocity field

    SciTech Connect

    Lu, B.; Darmon, M.; Leymarie, N.; Chatillon, S.; Potel, C. [CEA, LIST, F-91191 Gif-sur-Yvette (France); Laboratoire d'Acoustique de l'Universite du Maine (LAUM), UMR CNRS 6613, 72085 Le Mans Cedex 9 (France)

    2012-05-17

    In-service inspection of Sodium-Cooled Fast Reactors (SFR) requires the development of non-destructive techniques adapted to the harsh environment conditions and the examination complexity. From past experiences, ultrasonic techniques are considered as suitable candidates. The ultrasonic telemetry is a technique used to constantly insure the safe functioning of reactor inner components by determining their exact position: it consists in measuring the time of flight of the ultrasonic response obtained after propagation of a pulse emitted by a transducer and its interaction with the targets. While in-service the sodium flow creates turbulences that lead to temperature inhomogeneities, which translates into ultrasonic velocity inhomogeneities. These velocity variations could directly impact the accuracy of the target locating by introducing time of flight variations. A stochastic simulation model has been developed to calculate the propagation of ultrasonic waves in such an inhomogeneous medium. Using this approach, the travel time is randomly generated by a stochastic process whose inputs are the statistical moments of travel times known analytically. The stochastic model predicts beam deviations due to velocity inhomogeneities, which are similar to those provided by a determinist method, such as the ray method.

  18. Stochastic simulation for the propagation of high-frequency acoustic waves through a random velocity field

    NASA Astrophysics Data System (ADS)

    Lu, B.; Darmon, M.; Leymarie, N.; Chatillon, S.; Potel, C.

    2012-05-01

    In-service inspection of Sodium-Cooled Fast Reactors (SFR) requires the development of non-destructive techniques adapted to the harsh environment conditions and the examination complexity. From past experiences, ultrasonic techniques are considered as suitable candidates. The ultrasonic telemetry is a technique used to constantly insure the safe functioning of reactor inner components by determining their exact position: it consists in measuring the time of flight of the ultrasonic response obtained after propagation of a pulse emitted by a transducer and its interaction with the targets. While in-service the sodium flow creates turbulences that lead to temperature inhomogeneities, which translates into ultrasonic velocity inhomogeneities. These velocity variations could directly impact the accuracy of the target locating by introducing time of flight variations. A stochastic simulation model has been developed to calculate the propagation of ultrasonic waves in such an inhomogeneous medium. Using this approach, the travel time is randomly generated by a stochastic process whose inputs are the statistical moments of travel times known analytically. The stochastic model predicts beam deviations due to velocity inhomogeneities, which are similar to those provided by a determinist method, such as the ray method.

  19. Elastic wave velocities in anorthosite and anorthositic gabbros from Apollo 15 and 16 landing sites

    NASA Technical Reports Server (NTRS)

    Chung, D. H.

    1973-01-01

    Laboratory measurements of ultrasonic velocities in lunar samples 15065, 15555, 15415, 60015, and 61016 as well as in synthetic materials corresponding to compositions of anorthositic gabbros are presented as a function of hydrostatic pressure to about 7 kb. The author examined the seismic velocity distributions in the moon with reference to the variations to be expected in a homogeneous medium. The lunar mantle begins about 60 km, and the velocity of P waves in this area is about 7.7 km/sec. Variation of the seismic parameter with depth in the upper crust (about 20 km thick) is much too rapid to be explained by compression of a uniform material and the departure from expectation is so great that no reasonable adjustment of the material parameters can bring agreement; therefore, this author concludes that this result in this region of the moon is not due to self-compression but to textural gradients. In the lower crust (about 40 km thick), the region is shown to be relatively homogeneous, consisting probably of anorthositic rocks.

  20. Microwave acoustics handbook. Volume 3: Bulk wave velocities

    NASA Astrophysics Data System (ADS)

    Slobodnik, A. J., Jr.; Delmonico, R. T.; Conway, E. D.

    1980-05-01

    Information useful for the design of acoustic delay lines, resonators, and other miniature, low cost, reliable devices for use in communications and electronic sensing is given in this report. Computations of bulk acoustic wave velocities, power flow angles, and coupling to electric fields are plotted for various orientations of the following single crystalline materials: Ba2NaNb5O15, Bi12GeO20, CdS, Diamond, Eu3Fe5O15, Gadolinium Gallium Garnet, GaAs, Germanium, InSb, InAs, Lead Molybdate, PbS, LiNbO3, LiTaO3, MgO, Quartz, Rutile, Sapphire, Silicon, Spinel, TeO2, YAG, YGaG, YIG, and ZnO. Particular cuts of interest, including cases for common metals, are then chosen for more detailed numerical calculations of mechanical and electrical parameters governing acoustic wave propagation in these media. A list of material constants is also included.

  1. Shear Velocity Structure of the Tonga Arc and Lau Backarc Basin from Rayleigh Wave Tomography

    NASA Astrophysics Data System (ADS)

    Wei, S. S.; Wiens, D. A.; Webb, S. C.; Blackman, D. K.; Dunn, R.; Conder, J. A.

    2012-12-01

    We analyze seismic data from the 2009 - 2010 Ridge2000 Lau Spreading Center project using the two-plane wave method of Rayleigh wave tomography to investigate the spatial distribution of melt. This project consists of 50 ocean bottom seismographs (OBSs) and 17 land-based seismic stations deployed in Fiji, Tonga, and the Lau basin for about one year. 1-D results show that a low-velocity zone exists beneath the Lau basin at the depths of 20 - 70 km, whereas the relict Lau ridge and the Fiji plateau are characterized by a high-velocity lid, implying a ~80 km-thick lithosphere of an extinct island arc. Furthermore, 3-D results indicate that the slowest velocities are located in a ~100 km wide region beneath the Central Lau Spreading Center to the north, where the spreading rate is fastest. The slow anomalies form an inclined zone, dipping to the west away from the arc. Although temperature can significantly influence seismic velocities, it cannot explain the extremely low mantle velocities (less than 3.5 km/s). Therefore, we interpret the slow anomalies in terms of partial melting, which commences at about 70 km depth in accord with petrological constraints. The asymmetric and broad distribution of inferred melt in the mantle across the Lau basin implies the passive decompression melting process governed by the mantle wedge flow pattern. The variations of velocity anomalies along the spreading centers indicate varying depths and in-situ melt contents from north to south. Slow anomalies deeper than 80 km beneath the Lau ridge suggest minor initial partial melting during asymmetric upwelling supplied by the Indian-Australian asthenosphere from west. These anomalies become shallower beneath the active volcano of Taveuni in Fiji. Smaller amplitude slow anomalies along the subduction-influenced Valu Fa ridge may indicate less in-situ melt content due to low melt viscosity and more efficient transport of the water-rich melt.aps of isotropic shear wave velocity at depths of 38, 58, 78, 98 km. The black dots and triangles represent the OBSs and the island-based seismic stations, respectively. The black curves indicate the spreading centers. The extensional transform zone (ETZ), the central Lau spreading center (CLSC), the eastern Lau spreading center (ELSC), and the Valu Fa ridge (VFR) are labeled in the map of 78 km.

  2. Spectral analysis of surface waves method to assess shear wave velocity within centrifuge models

    NASA Astrophysics Data System (ADS)

    Murillo, Carol Andrea; Thorel, Luc; Caicedo, Bernardo

    2009-06-01

    The method of the spectral analysis of surface waves (SASW) is tested out on reduced scale centrifuge models, with a specific device, called the mini Falling Weight, developed for this purpose. Tests are performed on layered materials made of a mixture of sand and clay. The shear wave velocity VS determined within the models using the SASW is compared with the laboratory measurements carried out using the bender element test. The results show that the SASW technique applied to centrifuge testing is a relevant method to characterize VS near the surface.

  3. 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.

  4. Utility of automated brachial ankle pulse wave velocity measurements in hypertensive patients

    Microsoft Academic Search

    Masanori Munakata; Nobuhiko Ito; Tohru Nunokawa; Kaoru Yoshinaga

    2003-01-01

    BackgroundWe examined whether pulse wave velocity (PWV), determined by brachial ankle arterial pressure wave measurements, using a newly developed, fully automated device could be a surrogate measure for carotid femoral PWV.

  5. Signals embedded in the radial velocity noise. Periodic variations in the tau Ceti velocities

    E-print Network

    Tuomi, Mikko; Jenkins, James S; Tinney, Chris G; Butler, R Paul; Vogt, Steve S; Barnes, John R; Wittenmyer, Robert A; O'Toole, Simon; Horner, Jonathan; Bailey, Jeremy; Carter, Brad D; Wright, Duncan J; Salter, Graeme S; Pinfield, David

    2012-01-01

    The abilities of radial velocity exoplanet surveys to detect the lowest-mass extra-solar planets are currently limited by a combination of instrument precision, lack of data, and "jitter". Jitter is a general term for any unknown features in the noise, and reflects a lack of detailed knowledge of stellar physics (asteroseismology, starspots, magnetic cycles, granulation, and other stellar surface phenomena), as well as the possible underestimation of instrument noise. We study an extensive set of radial velocities for the star HD 10700 ($\\tau$ Ceti) to determine the properties of the jitter arising from stellar surface inhomogeneities, activity, and telescope-instrument systems, and perform a comprehensive search for planetary signals in the radial velocities. We perform Bayesian comparisons of statistical models describing the radial velocity data to quantify the number of significant signals and the magnitude and properties of the excess noise in the data. We reach our goal by adding artificial signals to t...

  6. The Crustal And Upper Mantle Shear Wave Velocity Structure Beneath Eastern Turkey Using Inversion of Surface Wave Dispersion

    Microsoft Academic Search

    B. Can; C. Gurbuz

    2005-01-01

    In this study, shear wave velocity structure model of the crust and upper mantle across a broad portion of Eastern Turkey was investigated using measurements of the group and phase velocity dispersion curves of fundamental mode Rayleigh and Love waves. The data used correspond to broadband 3 component records obtained during October 1999 to August 2001 Eastern Turkey Seismic Experiment

  7. Determinants of brachial-ankle pulse wave velocity and carotid-femoral pulse wave velocity in healthy Koreans.

    PubMed

    Jang, Shin Yi; Ju, Eun Young; Huh, Eun Hee; Kim, Jung Hyun; Kim, Duk-Kyung

    2014-06-01

    The aim of this study was to determine the normal value of brachial-ankle pulse wave velocity (baPWV) and carotid-femoral pulse wave velocity (cfPWV) according to age group, gender, and the presence of cardiovascular risk factors in healthy Koreans, and to investigate the association between PWV and risk factors such as prehypertension, dyslipidemia, smoking, and obesity. We measured an arterial stiffness in 110 normal subjects who were 20 to 69 yr-old with no evidence of cardiovascular disease, cerebrovascular accident or diabetes mellitus. The mean values of baPWV and cfPWV were 12.6 (± 2.27) m/sec (13.1 ± 1.85 in men, 12.1 ± 2.51 in women; P=0.019) and 8.70 (± 1.99) m/sec (9.34 ± 2.13 in men, 8.15 ± 1.69 in women; P=0.001), respectively. The distribution of baPWV (P<0.001) and cfPWV (P=0.006) by age group and gender showed an increase in the mean value with age. Men had higher baPWV and cfPWV than women (P<0.001). There was a difference in baPWV and cfPWV by age group on prehypertension, dyslipidemia, current smoking, or obesity (P<0.001). In multiple linear regression, age and prehypertension were highly associated with baPWV and cfPWV after adjustment for confounding factors (P<0.001). The present study showed that baPWV and cfPWV are associated with age, gender, and prehypertension in healthy Koreans. PMID:24932081

  8. Real-time vector velocity assessment through multigate Doppler and plane waves.

    PubMed

    Ricci, Stefano; Bassi, Luca; Tortoli, Piero

    2014-02-01

    Several ultrasound (US) methods have been recently proposed to produce 2-D velocity vector fields with high temporal and spatial resolution. However, the real-time implementation in US scanners is heavily hampered by the high calculation power required. In this work, we report a real-time vector Doppler imaging method which has been integrated in an open research system. The proposed approach exploits the plane waves transmitted from two sub-arrays of a linear probe to estimate the velocity vectors in 512 sample volumes aligned along the probe axis. The method has been tested for accuracy and reproducibility through simulations and in vitro experiments. Simulations over a 0° to 90° angle range of a 0.5 m/s peak parabolic flow have yielded 0.75° bias and 1.1° standard deviation for direction measurement, and 0.6 cm/s bias with 3.1% coefficient of variation for velocity assessment. In vitro tests have supported the simulation results. Preliminary measurements on the carotid artery of a volunteer have highlighted the real-time system capability of imaging complex flow configurations in an intuitive, easy, and quick way, as shown in a sample supplementary movie. These features have allowed reproducible peak velocity measurements to be obtained, as needed for quantitative investigations on patients. PMID:24474137

  9. P-wave velocity in granulites from South India: implications for the continental crust

    NASA Astrophysics Data System (ADS)

    Ramachandran, C.

    1992-01-01

    P-wave velocities ( Vp) were measured in 160 high-grade metamorphic rocks from the South Indian granulite terrain (SGT). The wide variations observed in the Vp of charnockites and gneisses could be due to the complex prograde and retrograde metamorphic histories of the two major rock types of the SGT. The velocity-density relation showed distinct trends for charnockites and gneisses. Initial stages of retrograde metamorphism in charnockites significantly affected their magnetic properties, however, its effect on velocity and density is not diagnostic. Contrasting physical properties on either side of the Palghat-Cauvery (P-C) shear zone lends support for the contention that the P-C shear zone is a major paleosuture. The laboratory mean Vpof the rocks from the northern SGT are comparable with the mid-crustal DSS velocity in the adjacent granite greenstone terrain (GGT), suggesting that the GGT is possibly underlain by a felsic granulite basement. The physical properties of the high-grade metamorphic rocks from SGT are significantly lower than that of the lower crust. The physical properties and tectonic considerations show that the granulites of South India may not be of lower crustal origin and hence not representative of the lower crust, as generally thought. A simplified two-layer crustal model with a predominantly felsic granulite upper crust and a mafic granulite lower crust, is suggested for the SGT.

  10. Upper mantle structure of the European and Mediterranean region from inversion of surface wave group velocity

    Microsoft Academic Search

    R. Schivardi; A. Morelli

    2007-01-01

    We present a new transversely isotropic shear wave velocity model of the upper mantle in the European and Mediterranean region, obtained by analysis of surface wave group speed. Our data set consists of fundamental mode Love and Rayleigh wave group speed measurements, taken by multi-filter analysis on wave groups isolated by phase matched filtering on seismograms recorded at regional distance.

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

    E-print Network

    Rickards, Benjamin Thomas

    2011-05-31

    ¬channel Analysis of Surface Waves (MASW), S-wave tomography, and downhole seismic for measuring S-wave velocities, investigates and identi¬fies the differences among the methods' results, and pri¬oritizes the different methods for S-wave use at the U. S. Army...

  12. Three-dimensional shear velocity structure of the African lithosphere from Rayleigh wave tomography

    NASA Astrophysics Data System (ADS)

    Raveloson, A.; Nyblade, A.; Mangongolo, A.

    2013-12-01

    We investigate the lithospheric structure beneath Africa using a shear wave velocity model of the upper mantle derived from an inversion of Rayleigh wave group velocity measurements. Our data set consists of a large number of regional seismic events recorded from 1990 until present on many available stations belonging to permanent or temporary networks. To minimize contribution from outside structure, we only use seismic events within the African plate or along the African plate boundary. With magnitude greater than 4.5 and depths shallower than 100 km Rayleigh wave group velocity measurements from 10s to 125s periods have been made using multiple narrow band filter and phase matching method. First, we measure group velocities of fundamental mode Rayleigh waves. Secondly, for each pair station events, we extract the group velocity value at each period to obtain dispersion curves and inverted them to obtain maps of Rayleigh wave group velocities. To evaluate the resolution of the group velocity tomography, the standard checkerboard resolution technique was performed. Finally, we inverted the dispersion curves, using a linear tomographic inversion over a grid of 1o x 1o cells to create 1-D shear wave velocity models. Our 3D shear wave velocity model is then obtained from combining these 1-D models at a regular spatial interval. Prominent features in our 3D model include a newly identified center of deposition in the northern part of the Congo Basin, fast cratonic keels, and slower uppermost mantle velocities beneath the Proterozoic mobile belts.

  13. Velocity shear effect on the longitudinal wave in a strongly coupled dusty plasma

    NASA Astrophysics Data System (ADS)

    Garai, S.; Banerjee, D.; Janaki, M. S.; Chakrabarti, N.

    2014-02-01

    The characteristics of longitudinal dust acoustic wave (DAW) in presence of velocity shear have been investigated in a strongly coupled dusty plasma using the generalized hydrodynamic (GH) model. In the hydrodynamic regime ( ?? m ?1), i.e. when characteristic time ? m is slower than inverse of wave frequency, the viscosity in the GH model plays the usual role of wave damping, whereas in the kinetic regime ( ?? m ?1), i.e. when characteristic time ? m is larger than inverse of wave frequency, viscosity shows energy storing property in the wave. In the kinetic regime, we have studied the longitudinal mode (where ? is the frequency, k is the wave number, c d is the dust acoustic velocity and c l is the longitudinal velocity that arises due to viscosity) in presence of velocity shear. It is shown that velocity shear can destabilize this mode. Both nonmodal and modal techniques are employed to demonstrate the growth rate of the instability.

  14. 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.

  15. A Variational Property of the Velocity Distribution in a System of Material Particles

    ERIC Educational Resources Information Center

    Siboni, S.

    2009-01-01

    A simple variational property concerning the velocity distribution of a set of point particles is illustrated. This property provides a full characterization of the velocity distribution which minimizes the kinetic energy of the system for prescribed values of linear and angular momentum. Such a characterization is applied to discuss the kinetic…

  16. Hemispherical variations in seismic velocity at the top of the Earth's inner core

    Microsoft Academic Search

    Fenglin Niu; Lianxing Wen

    2001-01-01

    Knowledge of the seismic velocity structure at the top of the Earth's inner core is important for deciphering the physical processes responsible for inner-core growth. Previous global seismic studies have focused on structures found 100km or deeper within the inner core, with results for the uppermost 100km available for only isolated regions. Here we present constraints on seismic velocity variations

  17. An evaluation of effective radiuses of bulk-wave ultrasonic transducers as circular piston sources for accurate velocity measurements

    Microsoft Academic Search

    Mototaka Arakawa; Jun-ichi Kushibiki; Naoya Aoki

    2004-01-01

    The effective radius of a bulk-wave ultrasonic transducer as a circular piston source, fabricated on one end of a synthetic silica (SiO2) glass buffer rod, was evaluated for accurate velocity measurements of dispersive specimens over a wide frequency range. The effective radius was determined by comparing measured and calculated phase variations due to diffraction in an ultrasonic transmission line of

  18. Estimation of near-surface shear-wave velocities and quality factors using multichannel analysis of surface-wave methods

    NASA Astrophysics Data System (ADS)

    Xia, Jianghai

    2014-04-01

    This overview article gives a picture of multichannel analysis of high-frequency surface (Rayleigh and Love) waves developed mainly by research scientists at the Kansas Geological Survey, the University of Kansas and China University of Geosciences (Wuhan) during the last eighteen years by discussing dispersion imaging techniques, inversion systems, and real-world examples. Shear (S)-wave velocities of near-surface materials can be derived from inverting the dispersive phase velocities of high-frequency surface waves. Multichannel analysis of surface waves—MASW used phase information of high-frequency Rayleigh waves recorded on vertical component geophones to determine near-surface S-wave velocities. The differences between MASW results and direct borehole measurements are approximately 15% or less and random. Studies show that inversion with higher modes and the fundamental mode simultaneously can increase model resolution and an investigation depth. Multichannel analysis of Love waves—MALW used phase information of high-frequency Love waves recorded on horizontal (perpendicular to the direction of wave propagation) component geophones to determine S-wave velocities of shallow materials. Because of independence of compressional (P)-wave velocity, the MALW method has some attractive advantages, such as 1) Love-wave dispersion curves are simpler than Rayleigh wave's; 2) dispersion images of Love-wave energy have a higher signal to noise ratio and more focused than those generated from Rayleigh waves; and 3) inversion of Love-wave dispersion curves is less dependent on initial models and more stable than Rayleigh waves.

  19. 3D P-Wave Velocity Structure of the Deep Galicia Rifted Margin

    NASA Astrophysics Data System (ADS)

    Bayrakci, Gaye; Minshull, Timothy; Davy, Richard; Sawyer, Dale; Klaeschen, Dirk; Papenberg, Cord; Reston, Timothy; Shillington, Donna; Ranero, Cesar

    2015-04-01

    The combined wide-angle reflection-refraction and multi-channel seismic (MCS) experiment, Galicia 3D, was carried out in 2013 at the Galicia rifted margin in the northeast Atlantic Ocean, west of Spain. The main geological features within the 64 by 20 km (1280 km²) 3D box investigated by the survey are the peridotite ridge (PR), the fault bounded, rotated basement blocks and the S reflector, which has been interpreted to be a low angle detachment fault. 44 short period four-component ocean bottom seismometers and 28 ocean bottom hydrophones were deployed in the 3D box. 3D MCS profiles sampling the whole box were acquired with two airgun arrays of 3300 cu.in. fired alternately every 37.5 m. We present the results from 3D first-arrival time tomography that constrains the P-wave velocity in the 3D box, for the entire depth sampled by reflection data. Results are validated by synthetic tests and by the comparison with Galicia 3D MCS lines. The main outcomes are as follows: 1- The 3.5 km/s iso-velocity contour mimics the top of the acoustic basement observed on MCS profiles. Block bounding faults are imaged as velocity contrasts and basement blocks exhibit 3D topographic variations. 2- On the southern profiles, the top of the PR rises up to 5.5 km depth whereas, 20 km northward, its basement expression (at 6.5 km depth) nearly disappears. 3- The 6.5 km/s iso-velocity contour matches the topography of the S reflector where the latter is visible on MCS profiles. Within a depth interval of 0.6 km (in average), velocities beneath the S reflector increase from 6.5 km/s to 7 km/s, which would correspond to a decrease in the degree of serpentinization from ~45 % to ~30 % if these velocity variations are caused solely by variations in hydration. At the intersections between the block bounding normal faults and the S reflector, this decrease happens over a larger depth interval (> 1 km), suggesting that faults act as conduit for the water flow in the upper mantle.

  20. 3D P-Wave Velocity Structure of the Deep Galicia Rifted Margin

    NASA Astrophysics Data System (ADS)

    Bayrakci, G.; Minshull, T. A.; Davy, R. G.; Sawyer, D. S.; Klaeschen, D.; Papenberg, C. A.; Reston, T. J.; Shillington, D. J.; Ranero, C. R.

    2014-12-01

    The combined wide-angle reflection-refraction and multi-channel seismic (MCS) experiment, Galicia 3D, was carried out in 2013 at the Galicia rifted margin in the northeast Atlantic Ocean, west of Spain. The main geological features within the 64 by 20 km (1280 km²) 3D box investigated by the survey are the peridotite ridge (PR), the fault bounded, rotated basement blocks and the S reflector, which has been interpreted to be a low angle detachment fault. 44 short period four-component ocean bottom seismometers and 28 ocean bottom hydrophones were deployed in the 3D box. 3D MCS profiles sampling the whole box were acquired with two airgun arrays of 3300 cu.in. fired alternately every 37.5 m. We present the results from 3D first-arrival time tomography that constrains the P-wave velocity in the 3D box, for the entire depth sampled by reflection data. Results are validated by synthetic tests and by the comparison with Galicia 3D MCS lines. The main outcomes are as follows: 1- The 3.5 km/s iso-velocity contour mimics the top of the acoustic basement observed on MCS profiles. Block bounding faults are imaged as velocity contrasts and basement blocks exhibit 3D topographic variations. 2- On the southern profiles, the top of the PR rises up to 5.5 km depth whereas, 20 km northward, its basement expression (at 6.5 km depth) nearly disappears. 3- The 6.5 km/s iso-velocity contour matches the topography of the S reflector where the latter is visible on MCS profiles. Within a depth interval of 0.6 km (in average), velocities beneath the S reflector increase from 6.5 km/s to 7 km/s, which would correspond to a decrease in the degree of serpentinization from ~45 % to ~30 % if these velocity variations are caused solely by variations in hydration. At the intersections between the block bounding normal faults and the S reflector, this decrease happens over a larger depth interval (> 1 km), suggesting that faults act as conduit for the water flow in the upper mantle.

  1. Signals embedded in the radial velocity noise. Periodic variations in the ? Ceti velocities

    NASA Astrophysics Data System (ADS)

    Tuomi, M.; Jones, H. R. A.; Jenkins, J. S.; Tinney, C. G.; Butler, R. P.; Vogt, S. S.; Barnes, J. R.; Wittenmyer, R. A.; O'Toole, S.; Horner, J.; Bailey, J.; Carter, B. D.; Wright, D. J.; Salter, G. S.; Pinfield, D.

    2013-03-01

    Context. The abilities of radial velocity exoplanet surveys to detect the lowest-mass extra-solar planets are currently limited by a combination of instrument precision, lack of data, and "jitter". Jitter is a general term for any unknown features in the noise, and reflects a lack of detailed knowledge of stellar physics (asteroseismology, starspots, magnetic cycles, granulation, and other stellar surface phenomena), as well as the possible underestimation of instrument noise. Aims: We study an extensive set of radial velocities for the star HD 10700 (? Ceti) to determine the properties of the jitter arising from stellar surface inhomogeneities, activity, and telescope-instrument systems, and perform a comprehensive search for planetary signals in the radial velocities. Methods: We performed Bayesian comparisons of statistical models describing the radial velocity data to quantify the number of significant signals and the magnitude and properties of the excess noise in the data. We reached our goal by adding artificial signals to the "flat" radial velocity data of HD 10700 and by seeing which one of our statistical noise models receives the greatest posterior probabilities while still being able to extract the artificial signals correctly from the data. We utilised various noise components to assess properties of the noise in the data and analyse the HARPS, AAPS, and HIRES data for HD 10700 to quantify these properties and search for previously unknown low-amplitude Keplerian signals. Results: According to our analyses, moving average components with an exponential decay with a timescale from a few hours to few days, and Gaussian white noise explains the jitter the best for all three data sets. Fitting the corresponding noise parameters results in significant improvements of the statistical models and enables the detection of very weak signals with amplitudes below 1 m s-1 level in our numerical experiments. We detect significant periodicities that have no activity-induced counterparts in the combined radial velocities. Three of these signals can be seen in the HARPS data alone, and a further two can be inferred by utilising the AAPS and Keck data. These periodicities could be interpreted as corresponding to planets on dynamically stable close-circular orbits with periods of 13.9, 35.4, 94, 168, and 640 days and minimum masses of 2.0, 3.1, 3.6, 4.3, and 6.6 M?, respectively. Radial velocities are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/551/A79

  2. Upper mantle structure of South America from joint inversion of waveforms and fundamental mode group velocities of Rayleigh waves

    Microsoft Academic Search

    Mei Feng; Suzan van der Lee; Marcelo Assumpção

    2007-01-01

    A new tomographic S wave velocity model for the upper mantle beneath South America is presented. We developed and applied a new method of simultaneously inverting regional S and Rayleigh waveforms and fundamental mode Rayleigh wave group velocities, to better constrain upper mantle S velocity structure and Moho depth. We used ?5700 Rayleigh wave group velocity dispersion curves and 1537

  3. Upper mantle structure of South America from joint inversion of waveforms and fundamental mode group velocities of Rayleigh waves

    Microsoft Academic Search

    Mei Feng; Suzan van der Lee; Marcelo Assumpção

    2007-01-01

    A new tomographic S wave velocity model for the upper mantle beneath South America is presented. We developed and applied a new method of simultaneously inverting regional S and Rayleigh waveforms and fundamental mode Rayleigh wave group velocities, to better constrain upper mantle S velocity structure and Moho depth. We used ~5700 Rayleigh wave group velocity dispersion curves and 1537

  4. A new method for estimating shear-wave velocity in marine sediments from radiation impedance measurements

    NASA Astrophysics Data System (ADS)

    Kimura, Masao

    2005-11-01

    Shear-wave velocity is one of the important parameters that characterize the physical properties of marine sediments. In this study, a new method is proposed for measuring shear-wave velocity in marine sediments by using radiation impedance. Shear-wave velocities for three kinds of urethane rubber with different Japanese Industrial Standards hardness values were obtained by radiation impedance and time-of-flight measurement techniques. It was shown that the values of the shear-wave velocity measured by the radiation impedance method were consistent with those of time-of-flight measurements. It was then shown that the shear-wave velocities for air- and water-saturated beach sands are different. It was also found that the indicated shear-wave velocity is dependent on the vibrating plate radius because the instrument measures an average shear-wave velocity within a depth window beneath the plate; the larger the plate radius, the deeper the averaging window. Finally, measurements were made on two-layered media in which air-saturated beach sand or urethane rubber was covered with air-saturated clay, and the relationship between the thickness of the clay layer and the indicated shear-wave velocity was investigated.

  5. Analysis of wave velocity patterns in black cherry trees and its effect on internal decay detection

    E-print Network

    Analysis of wave velocity patterns in black cherry trees and its effect on internal decay detection of black cherry trees, developed analytical models of stress wave velocity in sound healthy trees of the tree cross sections were collected from 12 black cherry trees at a production forest. Trees were

  6. The Influence of Permeability on Compressional Wave Velocity in Marine SEDIMENTS

    Microsoft Academic Search

    F. Hamdi; D. Taylor Smith

    1982-01-01

    To investigate the effect of permeability on the propagation of seismo-acoustic waves through marine sediments, a theoretical model based on Biot's equations is established which relates the compressional wave velocity measured at a fixed frequency to computed velocities at zero and infinite frequencies in terms of sediment porosity and permeability. The model is examined experimentally in a standard soil mechanics

  7. Magnetic plethysmograph transducers for local blood pulse wave velocity measurement.

    PubMed

    Nabeel, P M; Joseph, Jayaraj; Sivaprakasam, Mohanasankar

    2014-08-01

    We present the design of magnetic plethysmograph (MPG) transducers for detection of blood pulse waveform and evaluation of local pulse wave velocity (PWV), for potential use in cuffless blood pressure (BP) monitoring. The sensors utilize a Hall effect magnetic field sensor to capture the blood pulse waveform. A strap based design is performed to enable reliable capture of large number of cardiac cycles with relative ease. The ability of the transducer to consistently detect the blood pulse is verified by in-vivo trials on few volunteers. A duality of such transducers is utilized to capture the local PWV at the carotid artery. The pulse transit time (PTT) between the two detected pulse waveforms, measured along a small section of the carotid artery, was evaluated using automated algorithms to ensure consistency of measurements. The correlation between the measured values of local PWV and BP was also investigated. The developed transducers provide a reliable, easy modality for detecting pulse waveform on superficial arteries. Such transducers, used for measurement of local PWV, could potentially be utilized for cuffless, continuous evaluation of BP at various superficial arterial sites. PMID:25570363

  8. Pulse wave velocity and cognitive function in older adults.

    PubMed

    Zhong, Wenjun; Cruickshanks, Karen J; Schubert, Carla R; Carlsson, Cynthia M; Chappell, Richard J; Klein, Barbara E K; Klein, Ronald; Acher, Charles W

    2014-01-01

    Arterial stiffness may be associated with cognitive function. In this study, pulse wave velocity (PWV) was measured from the carotid to femoral (CF-PWV) and from the carotid to radial (CR-PWV) with the Complior SP System. Cognitive function was measured by 6 tests of executive function, psychomotor speed, memory, and language fluency. A total of 1433 participants were included (mean age 75 y, 43% men). Adjusting for age, sex, education, pulse rate, hemoglobin A1C, high-density lipoprotein cholesterol, hypertension, cardiovascular disease history, smoking, drinking, and depression symptoms, a CF-PWV>12 m/s was associated with a lower Mini-Mental State Examination score (coefficient: -0.31, SE: 0.11, P=0.005), fewer words recalled on Auditory Verbal Learning Test (coefficient: -1.10, SE: 0.43, P=0.01), and lower score on the composite cognition score (coefficient: -0.10, SE: 0.05, P=0.04) and marginally significantly associated with longer time to complete Trail Making Test-part B (coefficient: 6.30, SE: 3.41, P=0.06), CF-PWV was not associated with Trail Making Test-part A, Digit Symbol Substation Test, or Verbal Fluency Test. No associations were found between CR-PWV and cognitive performance measures. Higher large artery stiffness was associated with worse cognitive function, and longitudinal studies are needed to confirm these associations. PMID:23632267

  9. Radial Velocity Variations in Pulsating Ap Stars. II. 33 Librae

    E-print Network

    Mkrtichian, D E; Kanaan, A; Mkrtichian, David E.; Hatzes, Artie P.; Kanaan, Antonio

    2003-01-01

    We present precise relative radial velocity (RV) measurements for the rapidly oscillating Ap (roAp) star 33 Librae measured from high resolution data spanning the wavelength interval 5000--6200 A. We find that pulsational radial velocity amplitude determined over a broad wavelength range (~100 A) depends on the spectral region that is examined and can be as high as 60 m/s at 5600 A and as low as 7 m/s in the 5900 A region. RV measurements of individual spectral lines can show even higher RV amplitudes. The acoustic cross-sections of the atmosphere, i.e. the phase and amplitude of the pulsations, as a function of optical depth is found for spectral lines of Ca, Cr, Fe, La, Ce, Gd, Er and Nd. This analysis shows that pulsation phase is variable through the atmosphere and that Nd III lines pulsate almost 180 degrees out-of-phase with those of Nd II features and are formed significantly higher in the stellar atmosphere. This conclusively establishes the presence of at least one radial node to the pulsations in th...

  10. Compositional causes of velocity variations in garnet peridotite xenoliths from the Kaapvaal Craton, South Africa

    Microsoft Academic Search

    D. L. Schutt; C. E. Lesher

    2006-01-01

    To investigate the effects of compositional variations on the velocity and density of the upper mantle, we perform a principle component analysis on the modal variability of > 200 garnet peridotite xenoliths from the Archean Kaapvaal craton. Since peridotite melting relations change with depth, we consider xenolith compositional variations as a function of equilibration pressure, by examining all xenoliths that

  11. Three dimensional structure of correlations between intensity variation of cosmic rays and solar wind velocity

    Microsoft Academic Search

    H. Kojima; T. Fujii; Y. Hayashi; S. Kawakami; M. Minamino; H. Miyauchi; T. Nonaka; S. Ogio; H. Tanaka; E. Usui; Y. Yamashita; A. Oshima; H. M. Antia; S. R. Dugad; U. D. Goswami; S. K. Gupta; P. K. Mohanty; P. K. Nayak; P. Subramanian; S. C. Tonwar; S. Shibata; I. Morishita

    A three dimensional structure of a solar wind effect on the intensity variation of cosmic rays has been investigated by using the regression analysis method in this paper. The solar wind effect discussed here is represented by the regression coefficients between the intensity variation of cosmic rays and the solar wind velocity. The data of cosmic ray intensity used in

  12. Variational Structure of Inverse Problems in Wave Propagation and Vibration

    E-print Network

    Variational Structure of Inverse Problems in Wave Propagation and Vibration James G. Berryman in wave propagation (traveltime tomography) and two examples in vibration (the plucked string and free.'' For vibrating systems, the apparently very complex behavior of an excited string, drumhead, or the Earth can

  13. Variation of wave directional spread parameters along the Indian coast

    Microsoft Academic Search

    V. Sanil Kumar

    2006-01-01

    Directional spreading of wave energy is popularly modeled with the help of the Cosine Power model and it mainly depends on the spreading parameter. This paper describes the variation of the spreading parameter estimated based on the wave data collected at four locations along the East as well as the West side of the Indian coast. The directional spreading parameter

  14. S-wave velocity structures of the Taipei Basin, Taiwan, using microtremor array measurements

    NASA Astrophysics Data System (ADS)

    Huang, Huey-Chu; Wu, Cheng-Feng; Lee, Feng-Mei; Hwang, Ruey-Der

    2015-04-01

    The S-wave velocity structures of the Taipei Basin in Taiwan are investigated using the array records of microtremors at 15 sites. Dispersion curves at these sites are calculated using the frequency-wavenumber (F-K) spectrum method. The S-wave velocity structures in the Taipei Basin are then estimated by employing surface wave inversion technique. Harder strata sites have higher phase velocities than softer sites. If the S-wave velocity of the Tertiary Basement is assumed to be 1000 m/s, then the Quaternary alluvial thicknesses in the Taipei Basin are between about 100 m and 650 m. The thickness of the alluvium gradually increases from the southeast to the northwest. The inversion results are also in good agreement with well-logging data and seismic reflection studies of the Taipei Basin. The study concludes that microtremor array measurement is a useful tool for estimating S-wave velocity structure.

  15. Determination of Phase Velocity Dispersion Curves and Group Velocity in a Plate Using Backward Radiated Leaky Lamb Waves

    NASA Astrophysics Data System (ADS)

    Kim, Young H.; Song, Sung-Jin; Kwon, Sung-Duk

    2004-02-01

    The guided wave has been widely employed to characterize thin plates and layered media. The dispersion curves of phase and group velocities are essential for the quantitative application of guided waves. The technique using leaky Lamb wave (LLW) is one of the excellent methods to obtain dispersion curves. In the present work, a fully automated system for the measurement of backward radiation of LLW has been developed. The specimen moves in two dimensional planes as well as in angular rotation. The signals of backward radiation of LLW were measured from an elastic plate in which specific modes of Lamb wave were strongly generated. Phase velocity of the corresponding modes was determined from the incident angle. The generated Lamb waves propagated forward and backward with the leakage of energy into water. Backward radiated LLW was detected by the same transducer and its frequency components were analyzed to extract the related information to the dispersion curves. The dispersion curves of phase velocity were measured by varying the incident angle. Moving the specimen in the linear direction of LLW propagation, group velocity was determined by measuring the transit time shift in the rf waveform.

  16. Velocity width of the resonant domain in wave-particle interaction

    NASA Astrophysics Data System (ADS)

    Firpo, Marie-Christine; Doveil, Fabrice

    2002-01-01

    Wave-particle interaction is a ubiquitous physical mechanism exhibiting locality in velocity space. A single-wave Hamiltonian provides a rich model by which to study the self-consistent interaction between one electrostatic wave and N quasiresonant particles. For the simplest nonintegrable Hamiltonian coupling two particles to one wave, we analytically derive the particle velocity borders separating quasi-integrable motions from chaotic ones. These estimates are fully retrieved through computation of the largest Lyapunov exponent. For the large-N particle self-consistent case, we numerically investigate the localization of stochasticity in velocity space and test a qualitative estimate of the borders of chaos.

  17. Group velocity distribution of Rayleigh waves and crustal and upper mantle velocity structure of the Chinese mainland and its vicinity

    Microsoft Academic Search

    Zheng-Qin He; Zhi-Feng Ding; Tai-Lan Ye; Wei-Guo Sun; Nai-Ling Zhang

    2002-01-01

    Based on the long period digital surface wave data recorded by 11 CDSN stations and 11 IRIS stations, the dispersion curves\\u000a of the group velocities of fundamental mode Rayleigh waves along 647 paths, with the periods from 10 s to 92 s, were measured\\u000a by multi-filter. Their distribution at 25 central periods within the region of 18–54N, 70–140E was inverted

  18. A lithospheric velocity model for the flat slab region of Argentina from joint inversion of Rayleigh wave phase velocity dispersion and teleseismic receiver functions

    NASA Astrophysics Data System (ADS)

    Ammirati, Jean-Baptiste; Alvarado, Patricia; Beck, Susan

    2015-07-01

    In the central Andes, the Nazca plate displays large along strike variations in dip with a near horizontal subduction angle between 28 and 32°S referred to the Pampean flat slab segment. The upper plate above the Pampean flat slab has high rates of crustal seismicity and active basement cored uplifts. The SIEMBRA experiment, a 43-broad-band-seismic-station array was deployed to better characterize the Pampean flat slab region around 31°S. In this study, we explore the lithospheric structure above the flat slab as a whole and its relation to seismicity. We use the SIEMBRA data to perform a joint inversion of teleseismic receiver functions and Rayleigh wave phase velocity dispersion to constrain the shear wave velocity variations in the lithosphere. Our joint inversion results show: (1) the presence of several upper-plate mid-crustal discontinuities and their lateral extent that are probably related to the terrane accretion history; (2) zones of high shear wave velocity in the upper-plate lower crust associated with a weak Moho signal consistent with the hypothesis of partial eclogitization in the lower crust; (3) the presence of low shear-wave velocities at ˜100 km depth interpreted as the subducting oceanic crust. Finally, in order to investigate the relation of the lithospheric structure to seismicity, we determine an optimal velocity-depth model based on the joint inversion results and use it to perform regional moment tensor inversions (SMTI) of crustal and slab earthquakes. The SMTI for 18 earthquakes that occurred between 2007 and 2009 in the flat slab region below Argentina, indicates systematically shallower focal depths for slab earthquakes (compared with inversions using previous velocity models). This suggests that the slab seismicity is concentrated mostly between 90 and 110 km depths within the subducting Nazca plate's oceanic crust and likely related to dehydration. In addition, the slab earthquakes exhibit extensional focal mechanisms suggesting new faulting at the edges of the flat portion of the slab. SMTI solutions for upper-plate crustal earthquakes match well the geological observations of reactivated structures and agree with crustal shortening. Our new constraints on flat slab structure can aid earthquake characterization for regional seismic hazard assessment and efforts to help understand the mechanisms for slab flattening in the central Andes.

  19. Variational Water Wave Modelling: from Continuum to Experiment

    NASA Astrophysics Data System (ADS)

    Bokhove, Onno; Kalogirou, Anna

    2015-04-01

    Variational methods are investigated asymptotically and numerically to model water waves in tanks with wave generators. A modified Benney-Luke model is derived using variational techniques including a time-dependent gravitional potential mimicking a removable "sluice gate". As a validation, our modelling results using (dis)continuous Galerkin finite elements will be compared to a soliton splash event resulting after a sluice gate is removed during a finite time in a long water channel with a contraction at its end. Future work will explore these methods for wave-energy devices and ships in modest to heavy seas.

  20. 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 by low radial anisotropy, which decreases to near isotropy at the bottom of the lid. These two characteristics show a `continental-like' mantle lid beneath the Bay. Rapid northward motion of the Indian Plate before its collision with Eurasia might have caused the large radial anisotropy observed below the mantle lid.

  1. Accurate seismic phase-velocities from interfering surface-waves using homomorphic deconvolution

    E-print Network

    Szerbiak, Robert Bruce

    1981-01-01

    University Chairman of Advisory Committee: Dr. Anthony F. Gangi Phase-velocities computed from surface-wave data are normally contaminated by interference effects in the data. Several methods have been attempted to remove interference from surface...-waves so that accurate phase-velocities can be computed. Many filtering methods have attempted to remove interference from surface-waves. These methods have been partially successful in removing interference but have also caused a loss of signal content...

  2. Three dimensional Rayleigh wave velocity model using multimode surface wave tomography of Eastern Asia

    NASA Astrophysics Data System (ADS)

    Pandey, S.; Yuan, X.; Debayle, E.; Priestley, K. F.; Kind, R.; Li, X.

    2010-12-01

    The collision of the Eurasian plate, Indian plate and Philippine sea plate resulted in the tectonic feature of todays; like mountain ranges, fold belts, sedimentary basins and high plateaus in China and the surrounding region. In the Northern part this region is supposed to get some resistance from the Siberian shield. But the collision of Indian plate has left its major imprints and the consequence of this was the uplift of Himalayan Mountain and Tibetan Plateau. This triple junction scenario is the main cause for many inter and intra-plate earthquake in this region. It is generally agreed that the lithosphere is thick in west China while much of the lithospheric root was lost beneath some cratons in east China. Still it's an open debate whether the lithosphere beneath the Tibetan plateau has doubled its thickness as did the crust above or much of the thickened lithosphere was removed by mantle convection and delamination. In our study we try to determine the three dimensional Sv wave speed and azimuthal anisotropy model by analyzing the vertical component multimode Rayleigh wave seismogram. The data which we used are from broadband stations from in and around China. We construct the three dimensional model in two step procedure. In the first step we use the automated version of the Cara and Leveque [1987] waveform inversion technique in terms of secondary observables for modeling each multimode Rayleigh waveform to determine the path-average mantle Sv wave speed structure. In the second stage we combine the 1-D velocity models in a tomographic inversion to obtain the three dimensional Sv wave speed structure and the azimuthal anisotropy as a function of depth. We have taken a source region specific velocity structure from the three dimensional model 3SMAC to improve the source excitation computation. We analyzed the seismograms using a modified (smoothed) version of PREM for the upper mantle velocity structure both for the reference model used in extracting the modal information from the seismogram and for the starting inversion and a priori velocity models employed in determining the path-average mantle structure. However, each path has a path-specific crustal model determined by averaging the crustal part of 3SMAC along the path.

  3. Wave speed during maximal expiratory flow and phase velocity from forced oscillations

    Microsoft Academic Search

    Béla Suki; Ole f. Pedersen; Robert h. Habib; Andrew c. Jackson

    1995-01-01

    To test the hypothesis that pressure waves in the airways propagate at the speed obtained from maximal expiratory flow we compared wave speeds (WS) associated with flow limitation and phase velocities (PV) of oscillatory pressure waves in four excised calf tracheae for transmural pressures (Ptm) between 0 and — 10 kPa. WS was calculated from static area-Ptm curves using the

  4. Investigating the Anisotropic Shear Wave Velocity Structure of the Earth's Mantle

    Microsoft Academic Search

    A. M. Ferreira; J. H. Woodhouse; K. Visser; J. Trampert

    2007-01-01

    The principal tool by which we learn about the upper part of the mantle (the top 1000 km say) is through the study of surface waves and, importantly, surface wave overtones. In this study we combine a variety of existing databases of surface wave phase velocity measurements into a very large data set consisting of more than 9,500,000 dispersion measurements

  5. 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.

  6. Noninvasive Assessment of Pulse-Wave Velocity and Flow-Mediated Vasodilation in Anesthetized Göttingen Minipigs

    PubMed Central

    Ludvigsen, Trine P; Wiinberg, Niels; Jensen, Christina J; Callesen, Annemette T; Andersen, Regitze W; Jørgensen, Anne Sofie H; Christoffersen, Berit Ø; Pedersen, Henrik D; Moesgaard, Sophia G; Olsen, Lisbeth H

    2014-01-01

    Few methods for noninvasive assessment of arterial stiffness and endothelial dysfunction in porcine models are available. The aim of this study was to evaluate methods for assessment of arterial stiffness and endothelial dysfunction in anesthetized Göttingen minipigs. Pulse-wave velocity (PWV) was assessed in male Göttingen minipigs (n = 8; age approximately 60 wk) by using applanation tonometry of the carotid and femoral arteries. In addition, flow-mediated vasodilation (FMD) was assessed by using vascular ultrasonography of the brachial artery to evaluate endothelial dysfunction. To evaluate the reproducibility of the methods, minipigs were anesthetized by intravenous infusion of ketamine and midazolam and examined every other day for a total of 3 trials. Neither examination day nor systolic, diastolic, or mean arterial blood pressure statistically influenced PWV or FMD. The median interexamination coefficient of variation was 17% for PWV and 59% for FMD. Measured values of PWV corresponded largely to those in clinically healthy humans, but FMD values were lower than expected for lean, young animals. Although the ketamine–midazolam anesthesia we used has been associated with minor hemodynamic effects in vivo, in vitro studies suggest that both drugs are vasodilatory. Therefore anesthesia might have influenced the endothelial response, contributing to the modest FMD response and the concurrent high coefficients of variation that we noted. We conclude that PWV—but not FMD—showed acceptable interexamination variation for its potential application in porcine models. PMID:25527028

  7. Noninvasive assessment of pulse-wave velocity and flow-mediated vasodilation in anesthetized Göttingen minipigs.

    PubMed

    Ludvigsen, Trine P; Wiinberg, Niels; Jensen, Christina J; Callesen, Annemette T; Andersen, Regitze W; Jørgensen, Anne Sofie H; Christoffersen, Berit Ø; Pedersen, Henrik D; Moesgaard, Sophia G; Olsen, Lisbeth H

    2014-12-01

    Few methods for noninvasive assessment of arterial stiffness and endothelial dysfunction in porcine models are available. The aim of this study was to evaluate methods for assessment of arterial stiffness and endothelial dysfunction in anesthetized Göttingen minipigs. Pulse-wave velocity (PWV) was assessed in male Göttingen minipigs (n = 8; age approximately 60 wk) by using applanation tonometry of the carotid and femoral arteries. In addition, flow-mediated vasodilation (FMD) was assessed by using vascular ultrasonography of the brachial artery to evaluate endothelial dysfunction. To evaluate the reproducibility of the methods, minipigs were anesthetized by intravenous infusion of ketamine and midazolam and examined every other day for a total of 3 trials. Neither examination day nor systolic, diastolic, or mean arterial blood pressure statistically influenced PWV or FMD. The median interexamination coefficient of variation was 17% for PWV and 59% for FMD. Measured values of PWV corresponded largely to those in clinically healthy humans, but FMD values were lower than expected for lean, young animals. Although the ketamine-midazolam anesthesia we used has been associated with minor hemodynamic effects in vivo, in vitro studies suggest that both drugs are vasodilatory. Therefore anesthesia might have influenced the endothelial response, contributing to the modest FMD response and the concurrent high coefficients of variation that we noted. We conclude that PWV—but not FMD—showed acceptable interexamination variation for its potential application in porcine models. PMID:25527028

  8. Corrosion and erosion monitoring in plates and pipes using constant group velocity Lamb wave inspection.

    PubMed

    Nagy, Peter B; Simonetti, Francesco; Instanes, Geir

    2014-09-01

    Recent improvements in tomographic reconstruction techniques generated a renewed interest in short-range ultrasonic guided wave inspection for real-time monitoring of internal corrosion and erosion in pipes and other plate-like structures. Emerging evidence suggests that in most cases the fundamental asymmetric A0 mode holds a distinct advantage over the earlier market leader fundamental symmetric S0 mode. Most existing A0 mode inspections operate at relatively low inspection frequencies where the mode is highly dispersive therefore very sensitive to variations in wall thickness. This paper examines the potential advantages of increasing the inspection frequency to the so-called constant group velocity (CGV) point where the group velocity remains essentially constant over a wide range of wall thickness variation, but the phase velocity is still dispersive enough to allow accurate wall thickness assessment from phase angle measurements. This paper shows that in the CGV region the crucial issue of temperature correction becomes especially simple, which is particularly beneficial when higher-order helical modes are also exploited for tomography. One disadvantage of working at such relatively high inspection frequency is that, as the slower A0 mode becomes faster and less dispersive, the competing faster S0 mode becomes slower and more dispersive. At higher inspection frequencies these modes cannot be separated any longer based on their vibration polarization only, which is mostly tangential for the S0 mode while mostly normal for the A0 at low frequencies, as the two modes become more similar as the frequency increases. Therefore, we propose a novel method for suppressing the unwanted S0 mode based on the Poisson effect of the material by optimizing the angle of inclination of the equivalent transduction force of the Electromagnetic Acoustic Transducers (EMATs) used for generation and detection purposes. PMID:24582555

  9. Rayleigh wave phase velocity and error maps up to the fifth overtone

    NASA Astrophysics Data System (ADS)

    Durand, Stéphanie; Debayle, Eric; Ricard, Yanick

    2015-05-01

    We present a global data set of phase velocity maps for Rayleigh waves, with their errors. These maps are obtained from the tomographic inversion of phase velocity curves measured in the period range 40-250 s by Debayle and Ricard (2012), completed with new measurements at longer periods, between 150 and 360 s. The full data set includes ˜22,000,000 phase velocity measurements combined to build 60 phase velocity maps covering the period range 40-360 s for the fundamental mode and up to the fifth overtone. Each phase velocity map is provided with its a posteriori error, resulting in a unique data set which can be combined with other seismic measurements (surface waves, normal modes, and body waves) in regional and global tomographic studies. A preliminary inversion of this data set shows that it provides constraints on the shear velocity structure down to 1000 km depth.

  10. Kinetic theory for electrostatic waves due to transverse velocity shears

    Microsoft Academic Search

    G. Ganguli; Y. C. Lee; P. J. Palmadesso

    1988-01-01

    Shear in the flow velocity of a fluid leads to the low frequency and long wavelength Kelvin-Helmholtz (K-H) instability. The velocity shear can be generated in a number of ways. In a plasma the existence of an inhomogeneous electric field component transverse to the ambient uniform magnetic field can provide a transverse velocity shear. The evolution of the K-H instability

  11. Thermal dehydration reactions characterized by combined measurements of electrical conductivity and elastic wave velocities

    NASA Astrophysics Data System (ADS)

    Popp, T.; Kern, H.

    1993-11-01

    Combined laboratory measurements of seismic velocities and electrical conductivity as a function of PT and drainage conditions have been performed on various rocks containing hydrous minerals. This paper presents experimental results for evaporite rocks containing gypsum (CaSO4 x 2H2O) and carnallite (KMgCl3 x 6H2O) and for serpentinite. The experiments on the evaporite rocks were carried out in a triaxial cell in the range 20-130 C and 5.0-24.0 MPa confining pressure. The measurements on serpentinite covered the range 20-750 C at pressures of up to 200 MPa and were performed in a cubic pressure apparatus. The thermally induced onset of dehydration was indicated by the pronounced discontinuous behaviour of conductivity, corresponding to a marked drop in the elastic wave velocities. The respective Poisson ratios were inversely correlated with permeability and seem to be a sensitive parameter to describe the reaction-related variations of pore space. The seismic properties can be satisfactory modelled by using the self-consistent approximation of O'Connell and Budiansky, illustrating the effects of variations in pore space and saturation. The dehydration behavior of the various hydrous rock types was found to be different because the changes in the rock physical properties are closely linked to the internally created pore fluid, to the changes in the porosity and pore geometry, and to the resulting pore pressure. Progressive thermal dehydration reactions induce an opening of pore space accompanied by lowered saturation conditions whereby the rate of fluid release depends mainly on temperature and also on the drainage conditions of the system. Our findings, as reflected by the variations in the geophysical parameters, may be of importance for the interpretation of natural dehydration processes in the crust caused by prograde metamorphism.

  12. Effect of cracks on the pressure dependence of P wave velocities in crystalline rocks

    NASA Astrophysics Data System (ADS)

    Carlson, Richard L.; Gangi, Anthony F.

    1985-09-01

    To test the "bed of nails" model, we have made detailed measurements of P wave velocities in five low-porosity, crystalline rocks at effective pressures to 500 MPa and fit two equations based on the model to the laboratory data. The first equation, V(P) = V0(1 + P/ Pi)(1 - m)/2, applies at relatively low pressures because it assumes that the grain modulus is very much larger than the crack modulus. It can be fit to four of the five data sets. The fit to the data for a monomineralic epidote yields values for V0, Piand m of 8.02±0.02 km/s, 1.2±0.5 MPa, and 0.9845±0.0004, respectively, with a rms error of 6.28 m/s. The second equation, 1/V2 (P) = (1/Vc2 - Vg2)/(1 + P/Pi)1 - m + 1/Vg2 assigns a constant velocity to the grains and applies when the modulus of the cracks is of the order of the grain modulus at high pressures. This equation can be fit to three of the data sets; the fit to data for a diopside pyroxenite yields values of Vc, Vg, Pi, and m of 6.20±0.04 km/s, 8.28±0.02 km/s, 7±1 MPa, and 0.20±0.05, with a rms error of 17.9 m/s. For all seven fits to the laboratory data the rms errors range from 0.1 to 0.3% and are of the order of the limits of precision of the measurements. The "bed of nails" model explains the pressure dependence of P wave velocities in the samples remarkably well, as evidenced by the small rms errors. The variation with pressure of P wave velocities in these rocks clearly reflects the increasing stiffness of cracks. The fact that the first equation fits four of five data sets is one of several indications that cracks significantly affect the mechanical properties of the rocks even at 500 MPa. Finally, we note that different kinds of cracks have markedly different mechanical properties; the best fitting model parameters reflect the nature of the cracks which populate the samples.

  13. Longshore sediment transport rate calculated incorporating wave orbital velocity fluctuations 

    E-print Network

    Smith, Ernest Ray

    2006-10-30

    , and it is controlled by wave period, water depth, and local bottom slope (Weggel 1972; Smith and Kraus 1991). In addition, the manner in which waves break, i.e., the breaker type, has been found to be controlled by wave height, period, water depth, and local beach... crest becomes unstable and flows down the front face of the wave producing a foamy water surface; plunging breakers occur if the crest curls over the front face and falls into the base of the wave, resulting in a high splash; collapsing breakers occur...

  14. Spatial velocity distributions in pulse-wave propagation based on fluid-structure interaction.

    PubMed

    He, Fan; Hua, Lu; Gao, Li-Jian

    2014-09-01

    In this paper, spatial velocity distributions in pulse-wave propagation based on a fluid-structure interaction model are presented. The investigation is performed using the assumption of laminar flow and a linear-elastic wall. The fluid-structure interaction scheme is constructed using the finite element method. The results show that velocity distributions embody an obvious time delay in an elastic tube model. Further, the fully developed flow is delayed and the velocity values are increased in comparison with a rigid tube model. The increase in the wall thickness makes the time delay between the velocity peaks of different sites smaller while the time delay between the velocity minima is unchanged. Similarly, the time delay between the velocity bottoms is more easily found when decreasing the internal radius. The model gives valid results for spatial velocity distributions, which provide important information for wave propagation. PMID:24935118

  15. Spurious velocity changes caused by temporal variations in ambient noise frequency content

    NASA Astrophysics Data System (ADS)

    Zhan, Zhongwen; Tsai, Victor C.; Clayton, Robert W.

    2013-09-01

    Ambient seismic noise cross-correlations are now being used to detect temporal variations of seismic velocity, which are typically on the order of 0.1 per cent. At this small level, temporal variations in the properties of noise sources can cause apparent velocity changes. For example, the spatial distribution and frequency content of ambient noise have seasonal variations due to the seasonal hemispherical shift of storms. Here, we show that if the stretching method is used to measure time-shifts, then the temporal variability of noise frequency content causes apparent velocity changes due to the changes in both amplitude and phase spectra caused by waveform stretching. With realistic seasonal variations of frequency content in the Los Angeles Basin, our numerical tests produce about 0.05 per cent apparent velocity change, comparable to what Meier et al. observed in the Los Angeles Basin. We find that the apparent velocity change from waveform stretching depends on time windows and station-pair distances, and hence it is important to test a range of these parameters to diagnose the stretching bias. Better understanding of spatiotemporal noise source properties is critical for more accurate and reliable passive monitoring.

  16. P wave velocity structure in the Yucca Mountain, Nevada, region

    Microsoft Academic Search

    Leiph Preston; Ken Smith; David von Seggern

    2007-01-01

    We have performed a crustal tomographic inversion using over 250,000 P arrival times from local earthquake sources and surface explosions in the Yucca Mountain, Nevada, region. Within the shallowest 2–3 km, topographic features tend to dominate the structure with high velocities imaged under Bare Mountain, the Funeral Mountains, and higher terrain to the east of Yucca Mountain and low velocities

  17. A Note on Phase Velocity of VLF Radio Waves

    Microsoft Academic Search

    James R. Wait; Kenneth P. Spies

    1961-01-01

    end the quantity vc -- I is shown plotted in Figure I where c is the velocity of light in vacuo. The abscissa is frequency f in kilocycles and the curves are parametric in h, the height of the reflecting layer. It is interesting to observe, from the computed curves, that the phase velocity may actually be equal to c

  18. On measuring surface-wave phase velocity from station-station1 cross-correlation of ambient signal2

    E-print Network

    Boschi, Lapo

    -correlation, and phase and group velocities.22 1 Introduction23 The ability to observe coherent surface-wave signal fromOn measuring surface-wave phase velocity from station-station1 cross-correlation of ambient signal2¨urich)5 July 30, 20126 Abstract7 We apply two different algorithms to measure surface-wave phase velocity

  19. Radar measurement of the seasonal variation in the velocity of the sunrise terminator

    NASA Astrophysics Data System (ADS)

    Meehan, D. H.

    1990-03-01

    The HF phased-array radar at Bribie Island, Australia, used to measure horizontal movements of the ionosphere, has been calibrated using the known velocity of the sunrise terminator. The seasonal variation in the velocity of the terminator has been resolved, both in magnitud and direction. The technique uses single-station ionospheric sounding, and requires the angle of arrival and Doppler shift of ionospheric echoes to be measured as the terminator passes overhead. Pfister's (1971) theorem allows calculation of the velocity of the reflecting surface. The difference between theory and experiment is less than 3 percent in speed and 2 degrees in direction on average.

  20. Measurements of plasma temperature in indirect drive targets from the shock wave velocity in aluminum in the Iskra-5 facility

    SciTech Connect

    Vatulin, V. V.; Zhidkov, N. V.; Kravchenko, A. G.; Kuznetsov, P. G.; Litvin, D. N.; Mis'ko, V. V.; Pinegin, A. V.; Pleteneva, N. P.; Senik, A. V.; Starodubtsev, K. V.; Tachaev, G. V. [Russian Federal Nuclear Center, All-Russia Research Institute of Experimental Physics (Russian Federation)

    2010-05-15

    Results are presented from the development of a method for measuring plasma temperature in indirect (X-ray) drive targets by recording the shock wave velocity in the Iskra-5 facility. The samples under investigation were irradiated by X-rays in a converter box, and the shock wave velocity was determined from the time at which the wave reached the back surface of the sample and the surface began to emit visible radiation. This emission, in turn, was detected by a streak camera. The results of experiments on the interaction of X radiation with a hot dense plasma, as well as the accompanying gas-dynamic processes in aluminum samples, are analyzed both theoretically and numerically. In experiments with Al and Pb samples, the shock wave velocity was measured to vary in the range U = 8-35 km/s, and the range of variation of the temperature of the box walls was measured to be T{sub e} = 140-170 eV.

  1. 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.

  2. Simultaneous structure and elastic wave velocity measurement of SiO2 glass at high pressures and high temperatures in a Paris-Edinburgh cell

    NASA Astrophysics Data System (ADS)

    Kono, Yoshio; Park, Changyong; Sakamaki, Tatsuya; Kenny-Benson, Curtis; Shen, Guoyin; Wang, Yanbin

    2012-03-01

    An integration of multi-angle energy-dispersive x-ray diffraction and ultrasonic elastic wave velocity measurements in a Paris-Edinburgh cell enabled us to simultaneously investigate the structures and elastic wave velocities of amorphous materials at high pressure and high temperature conditions. We report the first simultaneous structure and elastic wave velocity measurement for SiO2 glass at pressures up to 6.8 GPa at around 500°C. The first sharp diffraction peak (FSDP) in the structure factor S(Q) evidently shifted to higher Q with increasing pressure, reflecting the shrinking of intermediate-range order, while the Si-O bond distance was almost unchanged up to 6.8 GPa. In correlation with the shift of FSDP position, compressional wave velocity (Vp) and Poisson's ratio increased markedly with increasing pressure. In contrast, shear wave velocity (Vs) changed only at pressures below 4 GPa, and then remained unchanged at ˜4.0-6.8 GPa. These observations indicate a strong correlation between the intermediate range order variations and Vp or Poisson's ratio, but a complicated behavior for Vs. The result demonstrates a new capability of simultaneous measurement of structures and elastic wave velocities at high pressure and high temperature conditions to provide direct link between microscopic structure and macroscopic elastic properties of amorphous materials.

  3. Observation of Wave Packet Distortion during a Negative-Group-Velocity Transmission

    PubMed Central

    Ye, Dexin; Salamin, Yannick; Huangfu, Jiangtao; Qiao, Shan; Zheng, Guoan; Ran, Lixin

    2015-01-01

    In Physics, causality is a fundamental postulation arising from the second law of thermodynamics. It states that, the cause of an event precedes its effect. In the context of Electromagnetics, the relativistic causality limits the upper bound of the velocity of information, which is carried by electromagnetic wave packets, to the speed of light in free space (c). In anomalously dispersive media (ADM), it has been shown that, wave packets appear to propagate with a superluminal or even negative group velocity. However, Sommerfeld and Brillouin pointed out that the “front” of such wave packets, known as the initial point of the Sommerfeld precursor, always travels at c. In this work, we investigate the negative-group-velocity transmission of half-sine wave packets. We experimentally observe the wave front and the distortion of modulated wave packets propagating with a negative group velocity in a passive artificial ADM in microwave regime. Different from previous literature on the propagation of superluminal Gaussian packets, strongly distorted sinusoidal packets with non-superluminal wave fronts were observed. This result agrees with Brillouin's assertion, i.e., the severe distortion of seemingly superluminal wave packets makes the definition of group velocity physically meaningless in the anomalously dispersive region. PMID:25631746

  4. Observation of wave packet distortion during a negative-group-velocity transmission.

    PubMed

    Ye, Dexin; Salamin, Yannick; Huangfu, Jiangtao; Qiao, Shan; Zheng, Guoan; Ran, Lixin

    2015-01-01

    In Physics, causality is a fundamental postulation arising from the second law of thermodynamics. It states that, the cause of an event precedes its effect. In the context of Electromagnetics, the relativistic causality limits the upper bound of the velocity of information, which is carried by electromagnetic wave packets, to the speed of light in free space (c). In anomalously dispersive media (ADM), it has been shown that, wave packets appear to propagate with a superluminal or even negative group velocity. However, Sommerfeld and Brillouin pointed out that the "front" of such wave packets, known as the initial point of the Sommerfeld precursor, always travels at c. In this work, we investigate the negative-group-velocity transmission of half-sine wave packets. We experimentally observe the wave front and the distortion of modulated wave packets propagating with a negative group velocity in a passive artificial ADM in microwave regime. Different from previous literature on the propagation of superluminal Gaussian packets, strongly distorted sinusoidal packets with non-superluminal wave fronts were observed. This result agrees with Brillouin's assertion, i.e., the severe distortion of seemingly superluminal wave packets makes the definition of group velocity physically meaningless in the anomalously dispersive region. PMID:25631746

  5. Observation of Wave Packet Distortion during a Negative-Group-Velocity Transmission

    NASA Astrophysics Data System (ADS)

    Ye, Dexin; Salamin, Yannick; Huangfu, Jiangtao; Qiao, Shan; Zheng, Guoan; Ran, Lixin

    2015-01-01

    In Physics, causality is a fundamental postulation arising from the second law of thermodynamics. It states that, the cause of an event precedes its effect. In the context of Electromagnetics, the relativistic causality limits the upper bound of the velocity of information, which is carried by electromagnetic wave packets, to the speed of light in free space (c). In anomalously dispersive media (ADM), it has been shown that, wave packets appear to propagate with a superluminal or even negative group velocity. However, Sommerfeld and Brillouin pointed out that the ``front'' of such wave packets, known as the initial point of the Sommerfeld precursor, always travels at c. In this work, we investigate the negative-group-velocity transmission of half-sine wave packets. We experimentally observe the wave front and the distortion of modulated wave packets propagating with a negative group velocity in a passive artificial ADM in microwave regime. Different from previous literature on the propagation of superluminal Gaussian packets, strongly distorted sinusoidal packets with non-superluminal wave fronts were observed. This result agrees with Brillouin's assertion, i.e., the severe distortion of seemingly superluminal wave packets makes the definition of group velocity physically meaningless in the anomalously dispersive region.

  6. Variations of atmospheric ozone according to millimeter-wave observations

    Microsoft Academic Search

    S. V. Solomonov; E. P. Kropotkina; A. N. Lukin; N. I. Ponomarenko; S. B. Rozanov

    1993-01-01

    The paper describes measurement instrumentation and methods and reports mm-wave observations of the vertical distribution of ozone in the stratosphere (above 27 km) and mesosphere during the colder part of the year over a period of the past several years. Short-term ozone variations were detected. Increased ozone content with small variations was observed mainly at altitudes of 27-37 km at

  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 determining the value of lithospheric VS and QS. At 100 km depth, where the resolution of seismic models is the highest, we compare observed seismic VS and QS with theoretical VST and QST values, respectively, that are calculated solely from temperature anomalies and constrained by experimental data on temperature dependencies of velocity and attenuation. This comparison shows that temperature variations alone are sufficient to explain seismic VS and QS in ca 50 per cent of continental regions. We hypothesize that compositional anomalies resulting from Fe depletion can explain the misfit between seismic and theoretical VS in cratonic lithosphere. In regions of active tectonics, temperature effects alone cannot explain seismic VS and QS in the lithosphere. It is likely that partial melts and/or fluids may affect seismic parameters in these regions. This study demonstrates that lithospheric temperature plays the dominant role in controlling VS and QS anomalies, but other physical parameters, such as compositional variations, fluids, partial melting and scattering, may also play a significant role in determining VS and QS variations in the continental mantle. ?? 2004 RAS.

  8. Energy velocity and quality factor of poroelastic waves in isotropic media.

    PubMed

    Gerasik, Vladimir; Stastna, Marek

    2011-05-01

    The energy velocity and Q factor of poroelastic acoustic waves in the context of classical isotropic Biot's theory are revisited. Special attention is paid to the high frequency regime when interphase interaction is viscoelastic. The analogy with viscoelastic behavior is emphasized in derivation of the energy balance equations which relate kinetic energy, potential energy, viscous power dissipation, and elastic energy stored associated with each wave. These lead to exact closed form expressions for the energy velocity and Q factor for both longitudinal and shear waves from energy principles. Most notably, the analysis of the resulting expressions reveals that the energy velocity of both longitudinal and shear waves equals (exceeds) the corresponding phase velocity in the case of the low (full) frequency range theory, and that the exact expression for the Q factor contains an additive correction due to viscoelastic interphase interaction. PMID:21568384

  9. Gravitation and electromagnetic wave propagation with negative phase velocity

    E-print Network

    Lakhtakia, Akhlesh

    with phase velocity directed opposite to the time-averaged Poynting vector is investigated for a generally. Electromagnetism in gravitationally affected vacuum 3 2.1. Noncovariant equations for vacuum . . . . . . . . . . . . . . . . . . . . . . . 3 2.2. Partitioning of spacetime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2

  10. Finite Frequency Group Velocity Sensitivity Kernels for Surface Wave Tomography

    Microsoft Academic Search

    M. P. Barmin; A. L. Levshin; M. H. Ritzwoller

    2005-01-01

    Surface wave tomography based on phase or group wave speeds have different strengths and limitations. Absolute phase speeds are strongly affected by source phase which may be poorly known and are subject to a 2-pi phase ambiguity, which together limit their use typically to periods above 40 sec. Group speeds do not suffer as strongly from these problems and measurements

  11. PARTICLE ACCELERATION BY ELECTROSTATIC WAVES WITH SPATIALLY VARYING PHASE VELOCITIES

    Microsoft Academic Search

    S. Peter Gary; David Montgomery; Daniel W. Swift

    1968-01-01

    We present here the results of numerical calculations connected with a mechanism recently proposed [Swift, 1968] for the acceleration of charged particles in a strong dc magnetic field. An electrostatic plasma wave propagates nearly perpendicularly to the magnetic field, and a weak density gradient exists parallel to the magnetic field. The wave propagates into the region of increasing plasma density

  12. Observation of an extrinsic critical velocity using matter wave interferometry

    SciTech Connect

    Sato, Yuki; Joshi, Aditya; Packard, Richard [Physics Department, University of California, Berkeley, California 94720 (United States)

    2007-08-01

    We report an experiment that uses a superfluid helium quantum interference device to probe the initial onset of the motion of a single vortex line driven by axial flow in a macroscopic channel. When the superfluid velocity reaches a temperature independent critical value (v{sub c}{approx}1 mm/s) periodic 2{pi} phase slippage occurs with a frequency of the order of a few Hz. As the axial flow velocity increases, the frequency increases, possibly stepwise.

  13. Analysis of group-velocity dispersion of high-frequency Rayleigh waves for near-surface applications

    USGS Publications Warehouse

    Luo, Y.; Xia, J.; Xu, Y.; Zeng, C.

    2011-01-01

    The Multichannel Analysis of Surface Waves (MASW) method is an efficient tool to obtain the vertical shear (S)-wave velocity profile using the dispersive characteristic of Rayleigh waves. Most MASW researchers mainly apply Rayleigh-wave phase-velocity dispersion for S-wave velocity estimation with a few exceptions applying Rayleigh-wave group-velocity dispersion. Herein, we first compare sensitivities of fundamental surface-wave phase velocities with group velocities with three four-layer models including a low-velocity layer or a high-velocity layer. Then synthetic data are simulated by a finite difference method. Images of group-velocity dispersive energy of the synthetic data are generated using the Multiple Filter Analysis (MFA) method. Finally we invert a high-frequency surface-wave group-velocity dispersion curve of a real-world example. Results demonstrate that (1) the sensitivities of group velocities are higher than those of phase velocities and usable frequency ranges are wider than that of phase velocities, which is very helpful in improving inversion stability because for a stable inversion system, small changes in phase velocities do not result in a large fluctuation in inverted S-wave velocities; (2) group-velocity dispersive energy can be measured using single-trace data if Rayleigh-wave fundamental-mode energy is dominant, which suggests that the number of shots required in data acquisition can be dramatically reduced and the horizontal resolution can be greatly improved using analysis of group-velocity dispersion; and (3) the suspension logging results of the real-world example demonstrate that inversion of group velocities generated by the MFA method can successfully estimate near-surface S-wave velocities. ?? 2011 Elsevier B.V.

  14. Group Velocity Measurement from the Propagation of the Ionization Front in a Surface-Wave Plasma

    Microsoft Academic Search

    J. Cotrino; A. Gamero; A. Sola; C. Lao

    1989-01-01

    During the first instant, previous to steady-state in a surface-wave-produced plasma, an ionization front advance front the launcher to the plasma column end. The velocity of the ionization front is much slower than the group velocity of the surface wave, this give a reflection of the incident signal on the moving ionization front. In this paper, we use this effect

  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. 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.

  17. Seasonal Variation in Conduction Velocity of Action Potentials in Squid Giant Axons

    E-print Network

    Bezanilla, Francisco

    Seasonal Variation in Conduction Velocity of Action Potentials in Squid Giant Axons JOSHUA J. C giant axon are seasonally acclimated, action potentials, recorded at different temperatures, were com of the action potential (e.g., maximum rate of rise, maximum rate of fall, and duration at half-peak) did

  18. Monitoring velocity variations in the crust using earthquake doublets: An application to the Calaveras fault, California

    Microsoft Academic Search

    G. Poupinet; V. L. Ellsworth; J. Frechet

    1984-01-01

    We present a technique that greatly improves the precision in measuring temporal variations of crustal velocities using an earthquake doublet, or pair of microearthquakes that have nearly identical waveforms and the same hypocenter and magnitude but occur on different dates. We compute differences in arrival times between seismograms recorded at the same station in the frequency domain by cross correlation

  19. Brachial artery flow velocity variation: another victory for hand-carried ultrasound?

    PubMed Central

    2009-01-01

    Dynamic predictors are clearly superior to static pressures in predicting whether a patient will respond to a fluid bolus. Hand-carried ultrasound (HCUS) can measure changes in blood flow velocity in the brachial artery that parallel arterial pulse pressure variation. The potential for HCUS to guide fluid therapy non-invasively must overcome problems of sensitivity and applicability. PMID:19849818

  20. Comparison of Phase Velocities from Array Measurements of Rayleigh Waves Associated with Microtremor and Results Calculated from Borehole Shear-Wave Velocity Profiles

    Microsoft Academic Search

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

    2000-01-01

    Shear-wave velocities (VS) are widely used for earthquake ground- motion site characterization. VS data are now largely obtained using borehole meth- ods. Drilling holes, however, is expensive. Nonintrusive surface methods are inex- pensive 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

  1. Electrostatic ion-cyclotron waves driven by parallel velocity shear R. L. Merlinoa)

    E-print Network

    Merlino, Robert L.

    treatment of the Kelvin­Helmholtz KH instability in a fully ionized plasma in a magnetic field of shear can, in some cases, drastically reduce the necessary critical drift velocities for the excitationElectrostatic ion-cyclotron waves driven by parallel velocity shear R. L. Merlinoa) Department

  2. The Velocity of Compressional Waves in Rocks to 10 Kilobars, Part 1

    Microsoft Academic Search

    Francis Birch

    1960-01-01

    The velocity of compressional waves has been determined by measurement of travel time of pulses in specimens of rock at pressures to 10 kilobars ad room temperature. Most of the samples, mainly igneous and metamorphic rocks, furnished three specimens ori- ented at right angles to one another. The present paper gives experimental details, modal analyses, and numerical tables of velocity

  3. Comment on the group velocity of surface waves on the plasma sheet boundary

    Microsoft Academic Search

    P. Nenovski

    1985-01-01

    In the recent estimation by Maltsev and Lyatsky (1984) of the group velocity of surface waves on the inner boundary of the plasma sheet, the effect of the curvature of the field lines of the ambient magnetic field of the earth on the spectrum has been assessed. The authors have not accounted for the fact, however, that the group velocity

  4. Energy Flow and Group Velocity of Electromagnetic Surface Wave in Hydrodynamic Approximation

    Microsoft Academic Search

    Etsuo Matsuo; Mikio Tsuji

    1978-01-01

    Expressions for the energy density and the energy flow are derived for the electromagnetic surface wave (surface plasmon) on a semi-infinite metal surface by using the hydrodynamic approximation. A proof is given for the equality between the group velocity and the energy velocity. It is also shown that the direction of the energy flow in the metal is the same

  5. Effect of wave boundary layer on sea-to-air dimethylsulfide transfer velocity during typhoon passage

    E-print Network

    Chu, Peter C.

    Effect of wave boundary layer on sea-to-air dimethylsulfide transfer velocity during typhoon and the sea-to-air transfer velocity of dimethylsulfide (DMS) during passage of Typhoon Wukong (September 5 Sea (SCS) during the passage of Typhoon Wukong (September 4­10, 2000). Journal of Marine Systems 66

  6. Vertical Energy Propagation of Inertial Waves: A Vector Spectral Analysis of Velocity Profiles

    Microsoft Academic Search

    KEVIN D. LEAMANAND; Thomas B. Sanford

    1975-01-01

    Vertical propagation of near-inertial period waves has been detected in a series of recent velocity profiles by a technique of vector spectral analysis. This method, previously applied to vector series in time, has been used to study the vertical spatial structure of velocity profiles obtained in the Mid-Ocean Dynamics Experiment (MODE). Prior to the use of spectral analysis, however, it

  7. Low Velocity Detonation of Nitromethane Affected by Precursor Shock Waves Propagating in Various Container Materials

    Microsoft Academic Search

    H. Hamashima; A. Osada; S. Itoh; Y. Kato

    2007-01-01

    It is well known that some liquid explosives have two detonation behaviors, high velocity detonation (HVD) or low velocity detonation (LVD) can propagate. A physical model to describe the propagation mechanism of LVD in liquid explosives was proposed that LVD is not a self-reactive detonation, but rather a supported-reactive detonation from the cavitation field generated by precursor shock waves. However,

  8. Properties of seismic fault zone waves and their utility for imaging low-velocity structures

    NASA Astrophysics Data System (ADS)

    Ben-Zion, Yehuda

    1998-06-01

    A two-dimensional solution for the scalar wave equation in a model of two vertical layers between two quarter spaces is used to study properties of seismic waves in a laterally heterogeneous low-velocity structure. The waves, referred to as seismic fault zone waves, include head waves, internal fault zone reflections, and trapped waves. The analysis aims to clarify the dependency of the waves on media velocities, media attenuation coefficients, layer widths, and source-receiver geometry. Additional calculations with extreme low-velocity layers provide examples that may be relevant for volcanic and geothermal domains. The interference patterns controlling seismic fault zone waves change with the number of internal reflections in the low-velocity structure. This number increases with propagation distance along the structure, decreases with fault zone width, and increases (for given length scales) with the velocity contrast. The relative lateral position of the source within the low-velocity layer modifies die length scales associated with internal reflections and influences the resulting interference pattern. Low values of Q affect considerably the dominant period and overall duration of the waves. Thus there are significant tradeoffs between propagation distance along the structure, fault zone width, velocity contrast, source location within the fault zone, and Q. The lateral and depth receiver coordinates determine the particular point where the interference pattern is sampled and observed motion is a strong function of both coordinates. The zone connecting sources generating fault zone waves and observation points with appreciable wave amplitude can be over an order of magnitude larger than the fault zone width. Calculations for cases with layer P wave velocity of ˜200 m s-1, modeling a vertical dike or crack with fluid and gas, show conspicuous persisting oscillations. The results resemble aspects of seismic data in volcanic domains. If these waves exist in observed records, their explicit recognition and modeling will help to separate source and structural effects and aid in the interpretation of volcano-seismology signals. Although the tradeoffs in parameters governing seismic fault zone waves are significant, each variable has its own signature, and the parameters may be constrained by additional geophysical data. Simultaneous modeling of many waveforms with an appropriate solution can resolve the various parameters and provide a high-resolution structural image.

  9. Shear wave velocity estimation of cover sediments by seismic array measurements (central Belgium)

    NASA Astrophysics Data System (ADS)

    Van Noten, Koen; Lecocq, Thomas; Camelbeeck, Thierry; Van Camp, Michel

    2015-04-01

    Since 1938, the Royal Observatory of Belgium has first held community inquiries and then online 'Did You Feel It' inquiries to gain information on the distribution of felt events in Belgium. For small magnitude events, mostly a circular macroseismic distribution pattern related to the energy decay by increasing hypocentral distance has been reported. However, few moderate-magnitude earthquakes (ML > 4) have caused an elliptical distribution pattern with higher macroseismic intensities in a consistent E-W direction and stronger intensity decay in a N-S direction. The macroseismic map of the 2011 ML 4.3 earthquake at Goch (Lower Rhine Embayment, Dutch-German border) also showed this E-W oriented distribution. Remarkably, in contrast to the NE of Belgium where this event was barely felt at close epicentral distances, many macroseismic reports were submitted in central Belgium at larger epicentral distances. This peculiar intensity distribution illustrates the important influence of the increasing thickness of the sedimentary cover above the basement rocks of the Brabant Massif from south to north. We will discuss the variation of S-wave velocity with depth of the sedimentary cover. Seismic noise array measurements were performed at different strategic sites at which the thickness of the sedimentary cover systematically increases. From south to north, the chosen sites vary from simple one-unit-over-halfspace configurations, with a clayey alluvium or sandy deposits covering the basement rocks (thickness < 20 m), to multilayer configurations (thickness up to 100 m) with a more complex sedimentary column. Wireless array measurements are performed by conducting CMG6TD Güralp seismometers in a rectangular array network. Subsequent surface wave analysis is executed in GEOPSY by conventional fk- and SPAC analysis to generate dispersion curves that are inverted in Dinver into depth profiles. Eventually, the resulting velocity profiles will help to evaluate the influence of sediments on strong ground motions experienced at the surface in Central Belgium.

  10. P-Wave Velocity Structure and Its Tectonics beneath Dabie-Sulu Region

    Microsoft Academic Search

    J. Xu; Z. Zhao

    2007-01-01

    The 3-D crustal structure of P-wave velocity in the Dabie-Sulu region and the vicinities was studied based on the data obtained by wide-angle seismic reflection and refraction surveys. The results suggest that the high velocity structure zones exist in the upper crust shallower than 20 km beneath the Sulu and Dabie regions. The cause of high velocity zones is attributable

  11. Three-dimensional P-wave velocity structure of Mt. Etna, Italy

    Microsoft Academic Search

    A. Villaseñor; H. M. Benz; L. Filippi; G. De Luca; R. Scarpa; G. Patanè; S. Vinciguerra

    1998-01-01

    The three-dimensional P-wave velocity structure of Mt. Etna is determined to depths of 15 km by tomographic inversion of first arrival times from local earthquakes recorded by a network of 29 permanent and temporary seismographs. Results show a near-vertical low-velocity zone that extends from beneath the central craters to a depth of 10 km. This low-velocity region is coincident with

  12. The chromospheric line-of-sight velocity variations in a solar microflare

    NASA Astrophysics Data System (ADS)

    Leiko, U. M.; Kondrashova, N. N.

    2015-02-01

    The variations of the chromospheric line-of-sight velocity in the active region NOAA 11024 are studied before, during, and after a solar microflare on 2009 July 4. At the day of the observations the main emergence phase was in this active region. The new emerging flux has interacted with the pre-existing magnetic field. The spectropolarimetric observations were carried out with the French-Italian THEMIS telescope (Spain, Tenerife). We used H? spectra of the high resolution obtained over 21 min. The spatial resolution was ?1 arcsec. The time interval between the spectra was 2.84 s. Doppler velocities were measured in the microflare location and its surroundings. We have revealed strong temporal variations of the line-of-sight velocity in the chromosphere. The velocities changed in the range -33-10 km/s. We revealed the velocity oscillations with the amplitude of 4-5 km/s. 12-14 min before the microflare both upward and downward motions with velocity values reaching about 20 km/s are found on the outer edge of the region studied. The amplitude of the oscillations increased. It may be the signature of the magnetic reconnection.

  13. Diurnal variations of mesospheric ozone using millimeter-wave measurements

    Microsoft Academic Search

    W. J. Wilson; P. R. Schwartz

    1981-01-01

    In March 1979, millimeter-wave observations of the ozone emission line at 101737 MHz were made to measure the diurnal variations in mesospheric ozone. Changes in mesospheric ozone were measured diurnally for a 10-day period. The ozone column above approximately 76 km rapidly decreased after sunrise to half value within 1 hour and was then followed by a slower (approximately 8

  14. Short-term velocity variations of three rock glaciers and their relationship with meteorological conditions

    NASA Astrophysics Data System (ADS)

    Wirz, V.; Gruber, S.; Purves, R. S.; Beutel, J.; Gärtner-Roer, I.; Gubler, S.; Vieli, A.

    2015-05-01

    In recent years, strong variations in the speed of rock glaciers have been detected, raising questions about their stability in a changed climate. In this study, we present continuous time series over three years of surface velocities of six GPS stations located on three rock glaciers in Switzerland. Intra-annual velocity variations are analyzed in relation to local meteorological factors, such as precipitation, snow(melt), as well as air and ground surface temperatures. A main focus of this study lies on the abrupt velocity peaks, which have been detected at two steep and fast moving rock glacier tongues. The continuous measurements with high temporal resolution revealed that all rock glaciers experience clear intra-annual variations in movement where the timing and the amplitude is rather similar between individual years. The seasonal decrease in velocity was typically smooth, starting one to three months after the seasonal decrease in temperatures, and was stronger in years with colder temperatures in mid winter. The seasonal acceleration always started during the zero curtain period, often was abrupt and rapid compared to the winter deceleration, and at two stations it was interrupted by short velocity peaks, occurring immediately after high water input from snowmelt or heavy precipitation. The findings of this study suggest that both, the seasonal acceleration and the short velocity peaks are strongly influenced by water infiltration, causing thermal advection and increase in pore water pressure, and that likely no velocity peak was solely caused by high temperatures. In contrast, the amount of deceleration in winter seems to be mainly controlled by winter temperatures.

  15. Determination of ultrasonic wave velocities and phase velocity dispersion curves of an Inconel 600 plate using resonant ultrasound spectroscopy and leaky Lamb waves.

    PubMed

    Kim, Young H; Song, Sung-Jin; Kwon, Sung-Duk; Cheong, Yong-Moo; Jung, Hyun-Kyu

    2004-04-01

    A plate of Inconel 600 was interrogated using the resonant ultrasound spectroscopy (RUS) and the reflected leaky Lamb waves (LLW). It was found that the plate used in the present work has anisotropy in its material properties by the RUS. The longitudinal and the transverse wave velocities of the Inconel 600 plate were determined by the RUS, ultrasonic pulse-echo method and cut-off frequencies of the LLWs. The wave velocities in the direction of thickness determined by the RUS under the assumption of the orthotropic symmetry were quite similar to those obtained by other methods, the pulse-echo method and from cut-off frequencies. The reflected LLW from the plate was measured with varying the incident angle. The dispersion curves obtained from the reflected LLWs show good agreement with the theoretical calculation in general. The mismatches may be caused by anisotropy of the plate. PMID:15047345

  16. An acoustic lens to measure wave velocities with the complex V( z) curve method

    Microsoft Academic Search

    Masahiro Nishida; Tomio Endo; Tadaharu Adachi; Hiroyuki Matsumoto

    1999-01-01

    In this paper, an acoustic lens is designed and built in order to determine wave velocities from measured critical angles of waves, using the complex V(z) curve method. The properties of the new lens are evaluated by the transfer function of the lens and the time-domain response of the transducer. The performance of the new lens is examined using specimens

  17. Worldwide distribution of group velocity of mantle Rayleigh waves as determined by spherical harmonic inversion

    Microsoft Academic Search

    ICHIRO NAKANISHI; D. L. Anderson

    1982-01-01

    We have determined the worldwide distribution of group velocity of mantle Rayleigh waves for periods between 100 and 300 sec without assuming any regionalization. Group slowness 1 \\/ u(0, ~) is expressed by spherical harmonics, and the coefficients, up to angular order 7, have been determined from travel times of Rayleigh waves by a least-squares method. From these, u(~, ~)

  18. Negative group velocity and three-wave mixing in dielectric crystals

    E-print Network

    Slabko, Vitaly V; Shalaev, Mikhail I; Popov, Alexander K

    2011-01-01

    Extraordinary features of optical parametric amplification of Stokes electromagnetic waves are investigated, which originate from three-wave mixing of two ordinary electromagnetic and one backward phonon wave with negative group velocity. A similarity with the counterpart in the negative-index plasmonic metamaterials and differences with those utilizing contra-propagating ordinary electromagnetic waves as well as electromagnetic and acoustic phonon waves are shown. They stem from backwardness of optical phonons with negative dispersion. Nonlinear-optical photonic devices with the properties similar to those predicted for the negative-index metamaterials are proposed.

  19. SIMULTANEOUS INVERSION FOR LATERAL VELOCITY VARIATIONS AND HYPOCENTERS IN THE YELLOWSTONE REGION USING EARTHQUAKE AND REFRACTION DATA

    Microsoft Academic Search

    Harley M. Benz; Robert B. Smith

    1984-01-01

    A three-dimensional upper crustal P shallow crustal ray paths across the Yellowstone wave velocity structure of the Yellowstone region caldera. Using a time term approach, Lehman et al. was determined by simultaneous inversion using Pg (1982) modeled lateral velocity decreases as great refracted arrival times and earthquake-generated- as 30% for the P_ refractor. However, due to direct P wave arrival

  20. Group velocity and energy propagation for three-dimensional waves

    Microsoft Academic Search

    G. B. Whitham

    1961-01-01

    This paper is a review and development of recent ideas on group velocity and energy propagation by Lighthill (l, 21, Landau and Lifshitz (3, $5 66 and 671, Ursell (7), and the present writer (a). Some of the ideas seem to be new but it is not always clear how much is implicit in the above references. A simple but

  1. Estimation of pseudo-2D shear-velocity section by inversion of high frequency surface waves

    USGS Publications Warehouse

    Luo, Y.; Liu, J.; Xia, J.; Xu, Y.; Liu, Q.

    2006-01-01

    A scheme to generate pseudo-2D shear-velocity sections with high horizontal resolution and low field cost by inversion of high frequency surface waves is presented. It contains six steps. The key step is the joint method of crossed correlation and phase shift scanning. This joint method chooses only two traces to generate image of dispersion curve. For Rayleigh-wave dispersion is most important for estimation of near-surface shear-wave velocity, it can effectively obtain reliable images of dispersion curves with a couple of traces. The result of a synthetic example shows the feasibility of this scheme. ?? 2005 Society of Exploration Geophysicists.

  2. Exploitation of SAR data for measurement of ocean currents and wave velocities

    NASA Technical Reports Server (NTRS)

    Shuchman, R. A.; Lyzenga, D. R.; Klooster, A., Jr.

    1981-01-01

    Methods of extracting information on ocean currents and wave orbital velocities from SAR data by an analysis of the Doppler frequency content of the data are discussed. The theory and data analysis methods are discussed, and results are presented for both aircraft and satellite (SEASAT) data sets. A method of measuring the phase velocity of a gravity wave field is also described. This method uses the shift in position of the wave crests on two images generated from the same data set using two separate Doppler bands. Results of the current measurements are pesented for 11 aircraft data sets and 4 SEASAT data sets.

  3. Negative group velocity Lamb waves on plates and applications to the scattering of sound by shells

    NASA Astrophysics Data System (ADS)

    Marston, Philip L.

    2003-05-01

    Symmetric Lamb waves on plates exhibit anomalies for certain regions of frequency. The phase velocity appears to be double-valued [M. F. Werby and H. Überall, J. Acoust. Soc. Am. 111, 2686-2691 (2002)] with one of the branches having a negative group velocity relative to the corresponding phase velocity. The classification of the symmetric plate modes for frequencies appearing to have a double-valued phase velocity is reviewed here. The complication of a double-valued velocity is avoided by examining mode orthogonality and the complex wave-number spectra. Various authors have noted an enhancement in the backscattering of sound by elastic shells in water that occurs for frequencies where symmetric leaky Lamb waves (generalized to case of a shell) have contra-directed group and phase velocities. The ray diagram for negative group velocity contributions to the scattering by shells [G. Kaduchak, D. H. Hughes, and P. L. Marston, J. Acoust. Soc. Am. 96, 3704-3714 (1994)] is unusual since for this type of mode the energy on the shell flows in the opposite direction of the wave vector. Circumnavigation of the shell is not required for the leaky ray to be backward directed.

  4. Negative group velocity Lamb waves on plates and applications to the scattering of sound by shells.

    PubMed

    Marston, Philip L

    2003-05-01

    Symmetric Lamb waves on plates exhibit anomalies for certain regions of frequency. The phase velocity appears to be double-valued [M. F. Werby and H. Uberall, J. Acoust. Soc. Am. 111, 2686-2691 (2002)] with one of the branches having a negative group velocity relative to the corresponding phase velocity. The classification of the symmetric plate modes for frequencies appearing to have a double-valued phase velocity is reviewed here. The complication of a double-valued velocity is avoided by examining mode orthogonality and the complex wave-number spectra. Various authors have noted an enhancement in the backscattering of sound by elastic shells in water that occurs for frequencies where symmetric leaky Lamb waves (generalized to case of a shell) have contra-directed group and phase velocities. The ray diagram for negative group velocity contributions to the scattering by shells [G. Kaduchak, D. H. Hughes, and P. L. Marston, J. Acoust. Soc. Am. 96, 3704-3714 (1994)] is unusual since for this type of mode the energy on the shell flows in the opposite direction of the wave vector. Circumnavigation of the shell is not required for the leaky ray to be backward directed. PMID:12765384

  5. Prediction of crack density in porous-cracked rocks from elastic wave velocities

    NASA Astrophysics Data System (ADS)

    Byun, Ji-Hwan; Lee, Jong-Sub; Park, Keunbo; Yoon, Hyung-Koo

    2015-04-01

    The stability of structures that are built over rock is affected by cracks in the rock that result from weathering, thawing and freezing processes. This study investigates a new method for determining rock crack densities using elastic wave velocities. The Biot-Gassmann model, which consists of several elastic moduli and Poisson's ratio, was used to determine a theoretical equation to predict the crack density of rocks. Ten representative specimens were extracted from ten boreholes to highlight the spatial variability. Each specimen was characterized using X-Ray Diffraction (XRD) analysis. The specimens were carved into cylinders measuring 50 mm in diameter and 30 mm in height using an abrasion process. A laboratory test was performed to obtain the elastic wave velocity using transducers that can transmit and receive compressional and shear waves. The measured compressional wave and shear wave velocities were approximately 2955 m/s-5209 m/s and 1652 m/s-2845 m/s, respectively. From the measured elastic wave velocities, the analyzed crack density and crack porosity were approximately 0.051-0.185 and 0.03%-0.14%, respectively. The calculated values were compared with the results of previous studies, and they exhibit similar values and trends. The sensitivity of the suggested theoretical equation was analyzed using the error norm technique. The results show that the compressional wave velocity and the shear modulus of a particle are the most influential factors in this equation. The study demonstrates that rock crack density can be estimated using the elastic wave velocities, which may be useful for investigating the stability of structures that are built over rock.

  6. Ultrasonic elastic wave velocity measurements of polycrystalline MgAl2O4 spinel at high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Irifune, T.; Zou, Y.; Greaux, S.; Zhou, C.; Whitaker, M. L.; Higo, Y.; Li, B.

    2012-12-01

    Magnesium aluminate (MgAl2O4) spinel is considered an important functional/structural material widely used at extreme conditions, due to its good mechanical strength, high resistance to chemical attack, good stability, and excellent optical and dielectric properties. Moreover, MgAl2O4 spinel also plays a significant role in geophysics as an important rock-forming mineral, which constitutes peridotites from the uppermost of the Earth's mantle. Therefore, understanding the elasticity and sound velocities of MgAl2O4 spinel are of great interest in the fields ranging from materials physics to geophysics by various experimental techniques. Previous experimental studies on MgAl2O4 spinel were carried out either at high temperature or high temperature. To date, there are no direct measurements of the elastic wave velocities of MgAl2O4 spinel at simultaneous high-pressure and high-temperature conditions. Recently, elasticity and sound velocities of polycrystalline MgAl2O4 spinel have been firstly measured up to 14 GPa and 900 K using ultrasonic interferometry in conjunction with energy-dispersive synchrotron X-ray diffraction. It is found that compressional wave velocity (VP) increases with pressure and decreases with temperature, whereas the shear wave velocity (VS) decreases with both pressure and temperature. Two-dimensional linear fittings of the present data give: KS0 =195 (1) GPa, dKs/dP = 4.4(1), dKs/dT = -0.023(1) GPa/K, G0 = 108(1) GPa, dG/dP = 0.38(1), dG/dT = -0.014(1) GPa/K. Moreover, the bulk modulus (KS) exhibits obvious increase with pressure, while the shear modulus (G) shows a weak variation with pressure, which may be due to the shear deformation relaxation by the coupling between atomic displacements and shear strains.

  7. Impact of desiccation on compressional and shear-wave velocities in clay-rocks: a laboratory study

    NASA Astrophysics Data System (ADS)

    Ghorbani, A.; Zamora, M.; Cosenza, Ph.

    2009-04-01

    The study of the impact of desiccation on the mechanical parameters of clay-rocks is of crucial importance to characterize the desaturated zone close to the walls of a deep underground repository, excavated into clay-rocks. Three core samples were taken from the Callovo-Oxfordian argillite formation located at the MHM-URL laboratory in Eastern France (40% of clay minerals in average); rich of illites/smectites. In order to desaturate the core samples, we followed two desiccation paths. In a first step (desaturation phase); each sample was dried at ambient air (relative humidity in the range 32 to 42 % and at average room temperature 20 ? C). In a second step (heating phase), the same samples were heated by four temperature levels from 65? C to 105? C. Velocity measurements were carried out on the core samples using an ultrasonic (1 MHz) pulse transmission technique to obtain P and perpendicularly polarized shear (Sv, Sh) wave velocities during both of desaturation and heating phases. The results show that when the degree of saturation decreased, both P and S wave velocities increased. During these desiccation paths, the initial anisotropy was not significantly enhanced. The increase in S wave velocity, by as much as 10% and the associated increase in dynamic shear modulus following desiccation, suggests the presence of desiccation-driven hardening, which is commonly observed in clay soils. The existence of a such a phenomenon proves that the classical models (e.g., the Gassmann equation) used to study the effect of saturating fluids, fail to correctly assess the influence of variations in water content on seismic velocities measured in clay-rocks. In the case of clay-rocks subjected to very low confining pressures and high desiccation conditions (high ventilation rates), new models which explicitly account for textural changes in clay will need to be developed.

  8. DETERMINING SUBSURFACE SHEAR-WAVE VELOCITIES: A REVIEW

    Microsoft Academic Search

    David M. Boore

    2006-01-01

    It is well known that the geologic materials beneath Earth's surface can have a first-order effect on ground motions from earthquakes. Fundamental to an understanding of the effects of geology on ground motion, and central to any prediction of these effects, is a description of the geologic materials that affect wave propagation. The material properties of interest include shear- and

  9. Crustal Structure in Greenland Using Surface Wave Group Velocities

    Microsoft Academic Search

    G. Joyal; F. A. Darbyshire; T. Dahl-Jensen; T. Larsen; P. Voss

    2009-01-01

    The objective of the project is to characterize the structure of the lower crust and upper lithospheric mantle across Greenland using regional earthquakes from the mid-Atlantic Ridge and northern Canada. We present Rayleigh wave dispersion curves for earthquake-station paths across Greenland using temporary stations operational for longer or shorter time periods during the last 10 years as well as the

  10. Shear wave velocities from noise correlation at local scale

    SciTech Connect

    De Nisco, G.; Nunziata, C. [Dipartimento di Scienze della Terra, Univ. Napoli Federico II (Italy); Vaccari, F. [Dipartimento di Scienze della Terra, Univ. Trieste (Italy); Panza, G. F. [Dipartimento di Scienze della Terra, Univ. Trieste (Italy); The Abdus Salam International Center for Theoretical Physics, ESP-SAND Group, Trieste (Italy)

    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.

  11. One-dimensional Shear Velocity Structure of Northern Africa from Rayleigh Wave Group Velocity Dispersion

    E-print Network

    Sheehan, Anne F.

    Africa. Data were accumulated from the IRIS DMC, GEOSCOPE, and MEDNET seismic networks covering the years will contribute to the mb:Ms discriminant important to the Comprehensive Nuclear-Test-Ban Treaty (CTBT, and identi®cation of seismic sources. Key words: Seismology, surface waves, Africa, mantle, crust

  12. Crust and upper mantle P wave velocity structure beneath Valles caldera, New Mexico: Results from the Jemez teleseismic tomography experiment

    SciTech Connect

    Steck, Lee K.; Fehler, Michael C.; Roberts, Peter M.; Baldridge, W. Scott; Stafford, Darrik G. [Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico (United States)] [Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico (United States); Lutter, William J.; Sessions, Robert [Department of Geology and Geophysics, University of Wisconsin-Madison (United States)] [Department of Geology and Geophysics, University of Wisconsin-Madison (United States)

    1998-10-01

    New results are presented from the teleseismic component of the Jemez Tomography Experiment conducted across Valles caldera in northern New Mexico. We invert 4872 relative {ital P} wave arrival times recorded on 50 portable stations to determine velocity structure to depths of 40 km. The three principle features of our model for Valles caldera are: (1) near-surface low velocities of {minus}17{percent} beneath the Toledo embayment and the Valle Grande, (2) midcrustal low velocities of {minus}23{percent} in an ellipsoidal volume underneath the northwest quadrant of the caldera, and (3) a broad zone of low velocities ({minus}15{percent}) in the lower crust or upper mantle. Crust shallower than 20 km is generally fast to the northwest of the caldera and slow to the southeast. Near-surface low velocities are interpreted as thick deposits of Bandelier tuff and postcaldera volcaniclastic rocks. Lateral variation in the thickness of these deposits supports increased caldera collapse to the southeast, beneath the Valle Grande. We interpret the midcrustal low-velocity zone to contain a minimum melt fraction of 10{percent}. While we cannot rule out the possibility that this zone is the remnant 1.2 Ma Bandelier magma chamber, the eruption history and geochemistry of the volcanic rocks erupted in Valles caldera following the Bandelier tuff make it more likely that magma results from a new pulse of intrusion, indicating that melt flux into the upper crust beneath Valles caldera continues. The low-velocity zone near the crust-mantle boundary is consistent with either partial melt in the lower crust or mafic rocks without partial melt in the upper mantle. In either case, this low-velocity anomaly indicates that underplating by mantle-derived melts has occurred. {copyright} 1998 American Geophysical Union

  13. Extensional wave attenuation and velocity in partially-saturated sand in the sonic frequency range

    SciTech Connect

    Liu, Z.; Rector, J.W.; Nihei, K.T.; Tomutsa, L.; Myer, L.R.; Nakagawa, S.

    2002-06-17

    Extensional wave attenuation and velocity measurements on a high permeability Monterey sand were performed over a range of gas saturations for imbibition and degassing conditions. These measurements were conducted using extensional wave pulse propagation and resonance over a 1 - 9 kHz frequency range for a hydrostatic confining pressure of 8.3 MPa. Analysis of the extensional wave data and the corresponding X-ray CT images of the gas saturation show strong attenuation resulting from the presence of the gas (QE dropped from 300 for the dry sand to 30 for the partially-saturated sand), with larger attenuation at a given saturation resulting from heterogeneous gas distributions. The extensional wave velocities are in agreement with Gassmann theory for the test with near-homogeneous gas saturation and with a patchy saturation model for the test with heterogeneous gas saturation. These results show that partially-saturated sands under moderate confining pressure can produce strong intrinsic attenuation for extensional waves.

  14. Noninvasive Method for Measuring Local Pulse Wave Velocity by Dual Pulse Wave Doppler: In Vitro and In Vivo Studies

    PubMed Central

    Wang, Zhen; Yang, Yong; Yuan, Li-jun; Liu, Jie; Duan, Yun-you; Cao, Tie-sheng

    2015-01-01

    Objectives To evaluate the validity and reproducibility of a noninvasive dual pulse wave Doppler (DPWD) method, which involves simultaneous recording of flow velocity of two independent sample volumes with a measurable distance, for measuring the local arterial pulse wave velocity (PWV) through in vitro and in vivo studies. Methods The DPWD mode of Hitachi HI Vision Preirus ultrasound system with a 5–13MHz transducer was used. An in vitro model was designed to compare the PWV of a homogeneous rubber tubing with the local PWV of its middle part measured by DPWD method. In the in vivo study, local PWV of 45 hypertensive patients (25 male, 49.8±3.1 years) and 45 matched healthy subjects (25 male, 49.3±3.0 years) were investigated at the left common carotid artery (LCCA) by DPWD method. Results In the in vitro study, the local PWV measured by DPWP method and the PWV of the homogeneous rubber tubing did not show statistical difference (5.16 ± 0.28 m/s vs 5.03 ± 0.15 m/s, p = 0.075). The coefficient of variation (CV) of the intra- and inter- measurements for local PWV were 3.46% and 4.96%, for the PWV of the homogeneous rubber tubing were 0.99% and 1.98%. In the in vivo study, a significantly higher local PWV of LCCA was found in the hypertensive patients as compared to that in healthy subjects (6.29±1.04m/s vs. 5.31±0.72m/s, P = 0.019). The CV of the intra- and inter- measurements in hypertensive patients were 2.22% and 3.94%, in healthy subjects were 2.07% and 4.14%. Conclusions This study demonstrated the feasibility of the noninvasive DPWD method to determine the local PWV, which was accurate and reproducible not only in vitro but also in vivo studies. This noninvasive echocardiographic method may be illuminating to clinical use. PMID:25786124

  15. Vertical structure of fluid velocity for flow through vegetation under waves

    NASA Astrophysics Data System (ADS)

    Yoon, H.; Cox, D.; Albert, D.; Mori, N.; Smith, H. D.

    2010-12-01

    Interaction between hydrodynamics (e.g., wave attenuation, fluid flow characteristics) and vegetation in coastal area is very important to develop strategies for maintenance of sustainable ecological systems. However, there are several difficulties in collecting and analyzing field data of wave attenuation and fluid flow characteristics in coastal vegetation owing to complexity of the various physical processes, such as changes in wind speed and direction, tides, wave refraction and shoaling. Furthermore, without understanding the impact of waves on real vegetation, it is difficult to develop scale-model tests. Therefore, a controlled laboratory environment at prototype scale with live plants is recommended to quantify the hydrodynamics and responses of vegetation. To account for this, a large-scale laboratory experiment was conducted during the summer of 2010 at the Large Wave Flume (104m long, 3.6m wide, and 4.6m deep) at O.H. Hinsdale Wave Research Laboratory (HWRL) at Oregon State University. Live plants (Schoenoplectus pungens or threesquare bulrush) were collected from the field (Tillamook, Oregon), and transplanted to twelve 8-ft long planters. The planters were placed into 4 channels with different plant densities. To our knowledge, this is the first test using live plants in a controlled, high energy wave environment. Observations of hydrodynamics under regular waves will be presented with an emphasis on the vertical structures of fluid velocity with different plant densities. The velocity data were measured using Acoustic Doppler Velocimeters (ADVs) and decomposed into mean current, wave-induced velocity and turbulence. Finally, the effect of the vegetation on the vertical structures of fluid velocity will be discussed. It is acknowledged that this work was conducted as part of Ecological modeling of emergent vegetation for sustaining wetlands in high wave energy coastal environments (NSF 0828549).

  16. Validity and reproducibility of arterial pulse wave velocity measurement using new device with oscillometric technique: A pilot study

    Microsoft Academic Search

    Madireddy Umamaheshwar Rao Naidu; Budda Reddy; Sridhar Yashmaina; Amar Narayana Patnaik; Pingali Usha Rani

    2005-01-01

    BACKGROUND: Availability of a range of techniques and devices allow measurement of many variables related to the stiffness of large or medium sized arteries. There is good evidence that, pulse wave velocity is a relatively simple measurement and is a good indicator of changes in arterial properties. The pulse wave velocity calculated from pulse wave recording by other methods like

  17. Seismic waves velocities and anisotropy in serpentinized peridotites from Xigaze ophiolite: Abundance of serpentine in slow spreading ridge

    Microsoft Academic Search

    H. Horen; M. Zamora; G. Dubuisson

    1996-01-01

    The effect of serpentinization on seismic wave velocity and anisotropy has been analyzed in 6 peridotite samples of the Xigaze ophiolite, having harzburgitic composition and a degree of serpentinization ranging from 3% to 70%. We found: i) P- and S-wave velocities are linearly correlated with serpentine content; ii) anisotropy of P- and S-waves decreases with increasing serpentinization (while in fresh

  18. New constraints on the arctic crust and uppermost mantle: surface wave group velocities, P n , and S n

    Microsoft Academic Search

    A. L. Levshin; M. H. Ritzwoller; M. P. Barmin; A. Villaseñor; C. A. Padgett

    2001-01-01

    We present the results of a study of surface wave dispersion across the Arctic region (>60°N) and compare the estimating group velocity maps with new maps of the body wave phases Pn and Sn. Data recorded at about 250 broadband digital stations from several global and regional networks were used to obtain Rayleigh and Love wave group velocity measurements following

  19. Physical modelling of a surface-wave survey over a laterally varying granular medium with property contrasts and velocity gradients

    NASA Astrophysics Data System (ADS)

    Bergamo, Paolo; Bodet, Ludovic; Socco, Laura Valentina; Mourgues, Régis; Tournat, Vincent

    2014-04-01

    Laboratory experiments using laser-based ultrasonic techniques can be used to simulate seismic surveys on highly controlled small-scale physical models of the subsurface. Most of the time, such models consist in assemblies of homogeneous and consolidated materials. To enable the physical modelling of unconsolidated, heterogeneous and porous media, the use of granular materials is suggested here. We describe a simple technique to build a two-layer physical model characterized by lateral variations, strong property contrasts and velocity gradients. We use this model to address the efficiency of an innovative surface-wave processing technique developed to retrieve 2-D structures from a limited number of receivers. A step by step inversion procedure of the extracted dispersion curves yields accurate results so that the 2-D structure of the physical model is satisfactorily reconstructed. The velocity gradients within each layer are accurately retrieved as well, confirming current theoretical and experimental studies regarding guided surface acoustic modes in unconsolidated granular media.

  20. Small-scale lateral variations in D'' attenuation and velocity structure

    NASA Astrophysics Data System (ADS)

    Fisher, Jesse L.; Wysession, Michael E.; Fischer, Karen M.

    2003-04-01

    Combined ScS-S differential attenuation and travel-time studies, with data from temporary and permanent arrays, produce quality factor, Q?(D''), estimates for D'' beneath Central America. Similarities between S and ScS ray paths through the upper mantle reduce the upper mantle elastic and anelastic contributions to differential studies. Differential attenuation correlates with ScS attenuation but not S attenuation, indicating that the attenuation primarily stems from lower mantle interactions. We image a ~250 km wide high-attenuation low-velocity anomaly within a ~600 km wide low-attenuation high-velocity region at the core-mantle boundary (CMB). The observed inverse exponential relationship between attenuation and velocity is consistent with a 200 +/- 50 km thermal anomaly, but does not preclude chemical, phase, or structural variations. Observation of a small-scale thermal anomaly within D'' may provide significant evidence in favor one kind of plume formation at the CMB.

  1. Measurements of wave-variance and velocity spectra in breaking waves

    Microsoft Academic Search

    H.-T. Liu; J.-T. Liu

    1987-01-01

    Displacements of mechanical waves superposed onto wind waves were measured with a laser displacement gauge in a wind-wave tank. The effects of wave breaking, especially the spilling breaking type, on the wave-variance spectra are investigated. In the absence of wave breaking, the quasi-equilibrium spectrum consists of an f -7\\/3 subrange in the capillary regime, and its spectral density increases with

  2. Measurements of wave-variance and velocity spectra in breaking waves

    Microsoft Academic Search

    H.-T. Liu; J.-T. Liu

    1987-01-01

    Displacements of mechanical waves superposed onto wind waves were measured with a laser displacement gauge in a wind-wave tank. The effects of wave breaking, especially the spilling breaking type, on the wave-variance spectra are investigated. In the absence of wave breaking, the quasi-equilibrium spectrum consists of an f-7\\/3 subrange in the capillary regime, and its spectral density increases with increasing

  3. A shear wave velocity model of the European upper mantle from automated inversion of seismic shear and surface waveforms

    NASA Astrophysics Data System (ADS)

    Legendre, C. P.; Meier, T.; Lebedev, S.; Friederich, W.; Viereck-Götte, L.

    2012-10-01

    We present a new, S-velocity model of the European upper mantle, constrained by inversions of seismic waveforms from broad-band stations in Europe and surrounding regions. We collected seismograms for the years 1990-2007 from all permanent stations in Europe for which data were available. In addition, we incorporated data from temporary experiments. Automated multimode inversion of surface and S-wave forms was applied to extract structural information from the seismograms, in the form of linear equations with uncorrelated uncertainties. The equations were then solved for seismic velocity perturbations in the crust and mantle with respect to a 3-D reference model with a realistic crust. We present two versions of the model: one for the entire European upper mantle and another, with the highest resolution, focused on the upper 200 km of the mantle beneath western and central Europe and the circum Mediterranean. The mantle lithosphere and asthenosphere are well resolved by both models. Major features of the lithosphere-asthenosphere system in Europe and the Mediterranean are indentified. The highest velocities in the mantle lithosphere of the East European Craton (EEC) are found at about 150 km depth. There are no indications for a deep cratonic root below about 330 km depth. Lateral variations within the cratonic mantle lithosphere are resolved as well. The locations of kimberlites correlate with reduced S-wave velocities in the shallow cratonic mantle lithosphere. This anomaly is present in regions of both Proterozoic and Archean crust, pointing to an alteration of the mantle lithosphere after the formation of the craton. Strong lateral changes in S-wave velocity are found at the northwestern margin of the EEC and may indicate erosion of cratonic mantle lithosphere beneath the Scandes by hot asthenosphere. The mantle lithosphere beneath western Europe and between the Tornquist-Teisseyre Zone and the Elbe Line shows moderately high velocities and is of an intermediate character, between cratonic lithosphere and the thin lithosphere of central Europe. In central Europe, Caledonian and Variscian sutures are not associated with strong lateral changes in the lithosphere-asthenosphere system. Cenozoic anorogenic intraplate volcanism in central Europe and the circum Mediterranean is found in regions of shallow asthenosphere and close to changes in the depth of the lithosphere-asthenosphere boundary. Very low velocities at shallow upper-mantle depths are present from eastern Turkey towards the Dead Sea transform fault system and Sinai, beneath locations of recent volcanism. Low-velocity anomalies extending vertically from shallow upper mantle down to the transition zone are found beneath the Massif Central, Sinai and the Dead Sea, the Canary Islands and Iceland.

  4. Velocity Spectrum Variation in Central Gulf of Mexico: 9Case Studies for the 2005 Hurricanes

    NASA Astrophysics Data System (ADS)

    Zhang, F.; Li, C.

    2012-12-01

    Significant near inertial oscillation caused by hurricanes is common in the ocean. The details of the vertical and temporal variations of hurricane induced near inertial oscillation are usually complicated. We have done a case study of such vertical and temporal variations of velocity spectrum focusing around the inertial frequency for the 2005 hurricane season. Data were from a deep water mooring chain containing a series of current meters and 2 ADCPs from June to November 2005. The velocity spectrum is obtained with a 10-day sliding window at different depths for the 40-hour high-passed data to exclude the low frequency Loop Current variations. This gives a temporal variation of the spectrum at different depths. Such variations in velocity spectrum are resulted from the ocean dynamics influenced by the passage of hurricanes. Our preliminary analysis of the results show that (1) right before the center of the hurricane gets closest to the mooring site, there always exists a 2-peak feature of energy at almost all depths; while during the passage of the hurricane these two peaks will merge Into one peak which has a corresponding period of 30.3 to 25.6 hours, encompassing that corresponding to the inertial frequency in this latitude; (2) after the passage of the hurricane, the decay process of energy is also complicated. It is found that the whole profile can be at least divided into 3 layers: surface to 800m, 800m to 1500m, and 1500m to the bottom, which is consistent with the stratification of the water column. It is also found that shift in the peak frequency to either side of the inertial frequency is very common. The main peak of energy can break into several parts during the decay stage, with blue shift and red shift.; ;

  5. Velocity-Space Diffusion Coefficients Due to Full-Wave ICRF Fields in Toroidal Geometry

    SciTech Connect

    Harvey, R.W. [CompX, P.O. Box 2672, Del Mar, CA 92014-5672 (United States); Jaeger, F.; Berry, L.A.; Batchelor, D.B.; D'Azevedo, E.; Carter, M.D. [ORNL, Oak Ridge, TN (United States); Ershov, N.M.; Smirnov, A.P. [Moscow State Univ. (Russian Federation); Bonoli, P.; Wright, J.C. [PSFC, MIT, Boston, MA (United States); Smithe, D.N. [ATK-Mission Research (United States)

    2005-09-26

    Jaeger et al. have calculated bounce-averaged QL diffusion coefficients from AORSA full-wave fields, based on non-Maxwellian distributions from CQL3D Fokker-Planck code. A zero banana-width approximation is employed. Complementing this calculation, a fully numerical calculation of ion velocity diffusion coefficients using the full-wave fields in numerical tokamak equilibria has been implemented to determine the finite orbit width effects. The un-approximated Lorentz equation of motion is integrated to obtain the change in velocity after one complete poloidal transit of the tokamak. Averaging velocity changes over initial starting gyro-phase and toroidal angle gives bounce-averaged diffusion coefficients. The coefficients from the full-wave and Lorentz orbit methods are compared for an ITER DT second harmonic tritium ICRF heating case: the diffusion coefficients are similar in magnitude but reveal substantial finite orbit effects.

  6. Detonation wave velocity and curvature of IRX-4 and PBXN-110

    SciTech Connect

    Lemar, E.R.; Forbes, J.W.; Sutherland, G.T. [Naval Surface Warfare Center, Indian Head Division, Silver Spring, Maryland 20903-5640 (United States)

    1996-05-01

    Detonation velocities and wave front curvatures were measured for bare cylindrical charges of IRX-4 and PBXN-110 charges. Steady detonation waves propagated in IRX-4 charges with diameters as small as 33 mm. The failure diameter of IRX-4 is between 25 and 33 mm. A fit of detonation velocity data gives 5.83 mm/{mu}s for IRX-4{close_quote}s infinite diameter velocity. Detonation wave curvature experiments have been done on 48 mm diameter cylindrical IRX-4 charges with lengths from 9 to 28 cm. The data have been fitted accurately over the entire charge diameters using the natural logarithm of a Bessel function. {copyright} {ital 1996 American Institute of Physics.}

  7. Velocity of sound behind strong shock waves in 2024 A1

    SciTech Connect

    McQueen, R.G.; Fritz, J.N.; Morris, C.E.

    1983-01-01

    Rarefaction waves were produced by impacting a target with a thin plate. An optical technique was used to determine where the rarefaction from the back surface of the impactor overtook the shock wave induced in a step wedge target. Bromoform was placed on the front surface. When the shock reached the liquid it radiated steadily until the rarefaction from the impactor overtakes it. The times when this occurred were used to determine where the rarefaction just overtook the shock in the target, and thus the sound velocity. The leading edge of this rarefaction wave travels at longitudinal sound velocity in solids. This velocity increases smoothly with pressure until shock heating causes the material to melt. The data indicate that melting on the Hugoniot of 2024 Al begins at about 125 GPa and is completed at 150 GPa.

  8. A lithospheric velocity model for the flat slab region of Argentina from joint inversion of Rayleigh-wave dispersion and teleseismic receiver functions

    NASA Astrophysics Data System (ADS)

    Ammirati, J. B.; Alvarado, P. M.; Beck, S. L.

    2014-12-01

    Receiver Function (RF) analyses using teleseismic P waveforms is a technique to isolate P to S conversions from seismic discontinuities in the lithosphere. Using earthquakes with a good azimuthal distribution, RFs recorded at a three-component seismic station can be inverted to obtain detailed lithospheric velocity structures. The technique, however presents a velocity-depth trade-off, which results in a non-unique model because RFs do not depend on the absolute seismic velocities but rather on relative velocity contrasts. Unlike RF, surface wave dispersion is sensitive to the average shear-wave velocity which makes it well suited for studying long period variations of the lithospheric seismic velocities. We performed a joint inversion of RF and Rayleigh-wave phase velocity dispersion to investigate the structure beneath the SIEMBRA network, a 43-broadband-seismic-station array deployed in the Pampean flat slab region of Argentina. Our results indicate: 1) The presence of several mid-crustal discontinuities probably related with terrane accretion; 2) A high seismic velocity in the lower crust suggesting partial eclogitization; 3) A thicker crust (> 50 km) beneath the western Sierras Pampeanas with an abrupt change in the relative timing of the Moho signal indicating a thinner crust to the east; 4) The presence of the subducting oceanic crust lying at ~100 km depth. We then built a 1D regional velocity model for the flat slab region of Argentina and used it for regional moment tensor inversions for local earthquakes. This technique is notably dependent on small-scale variations of Earth structure when modeling higher frequency seismic waveforms. Eighteen regional focal mechanisms have been determined. Our solutions are in good agreement with GCMT source estimations although our solutions for deep earthquakes systematically resulted in shallower focal depths suggesting that the slab seismicity could be concentrated at the top of the subducting Nazca plate. Solutions corresponding to crustal events match well the geological observations from other studies.

  9. Characterizing Rayleigh Wave Velocity and Amplitude Anisotropy in an Alpine Glacier

    NASA Astrophysics Data System (ADS)

    Eilar, C. A.; Mikesell, D.; Malcolm, A. E.; Bradford, J. H.

    2014-12-01

    Regular patterns of fractures in solid materials induce seismic velocity anisotropy. These fracture patterns can also create azimuthally dependent attenuation in seismic amplitudes due to a preferential scattering direction. A parallel set of surface (or bed) crevasses in a glacier is an example of one such fracture pattern. These patterns are caused by the local strains within the glacier. In this study we analyze an active source 3D seismic survey recorded at Bench Glacier, Alaska, USA. We compare the Rayleigh group wave velocity as a function of azimuth and estimate that the mean velocity is 1672 m/s and 1% velocity anisotropy exists. We present an interpretation for the observed anisotropy by comparing our results with satellite imagery of the glacier in the survey area. Finally, we present the results of ongoing analysis of the Rayleigh wave amplitudes and compare with existing studies of glacier attenuation that do not take into account scattering attenuation when estimating the ice temperature from attenuation.

  10. Detailed p- and s-wave velocity models along the LARSE II transect, Southern California

    USGS Publications Warehouse

    Murphy, J.M.; Fuis, G.S.; Ryberg, T.; Lutter, W.J.; Catchings, R.D.; Goldman, M.R.

    2010-01-01

    Structural details of the crust determined from P-wave velocity models can be improved with S-wave velocity models, and S-wave velocities are needed for model-based predictions of strong ground motion in southern California. We picked P- and S-wave travel times for refracted phases from explosive-source shots of the Los Angeles Region Seismic Experiment, Phase II (LARSE II); we developed refraction velocity models from these picks using two different inversion algorithms. For each inversion technique, we calculated ratios of P- to S-wave velocities (VP/VS) where there is coincident P- and S-wave ray coverage.We compare the two VP inverse velocity models to each other and to results from forward modeling, and we compare the VS inverse models. The VS and VP/VS models differ in structural details from the VP models. In particular, dipping, tabular zones of low VS, or high VP/VS, appear to define two fault zones in the central Transverse Ranges that could be parts of a positive flower structure to the San Andreas fault. These two zones are marginally resolved, but their presence in two independent models lends them some credibility. A plot of VS versus VP differs from recently published plots that are based on direct laboratory or down-hole sonic measurements. The difference in plots is most prominent in the range of VP = 3 to 5 km=s (or VS ~ 1:25 to 2:9 km/s), where our refraction VS is lower by a few tenths of a kilometer per second from VS based on direct measurements. Our new VS - VP curve may be useful for modeling the lower limit of VS from a VP model in calculating strong motions from scenario earthquakes.

  11. Electromagnetic wave propagation with negative phase velocity in regular black holes

    SciTech Connect

    Sharif, M., E-mail: msharif.math@pu.edu.pk; Manzoor, R., E-mail: rubabmanzoor9@yahoo.com [University of the Punjab, Department of Mathematics (Pakistan)

    2012-12-15

    We discuss the propagation of electromagnetic plane waves with negative phase velocity in regular black holes. For this purpose, we consider the Bardeen model as a nonlinear magnetic monopole and the Bardeen model coupled to nonlinear electrodynamics with a cosmological constant. It turns out that the region outside the event horizon of each regular black hole does not support negative phase velocity propagation, while its possibility in the region inside the event horizon is discussed.

  12. On the use of rayleigh wave group velocities for the analysis of continental margins

    Microsoft Academic Search

    S. A. P. L. Cloetingh; G. Nolet; R. Wortel

    1979-01-01

    Rayleigh wave group velocities provide a low-cost means for a quick assessment of averaged local properties of the Earth's crust in continental margin regions of the Atlantic type. Sufficiently accurate measurements (with a standard error of 0.3 km\\/s or less) of group velocities in continental shelf areas at periods between 5 and 30 seconds provide important information about structural parameters.

  13. Determination of the elastic constants of anisotropic solids from acoustic-wave group-velocity measurements

    Microsoft Academic Search

    A. G. Every; Wolfgang Sachse

    1990-01-01

    A method is proposed for determining the elastic constants of an anisotropic solid from acoustic-wave group velocities measured in off-symmetry directions in a specimen. The method corresponds to a two-stage optimization procedure in which the elastic constants are varied so as to obtain a least-squares fit of measured to calculated group velocities. At each iterative step a numerical minimization process

  14. High resolution Rayleigh wave phase velocity tomography in northern North China

    NASA Astrophysics Data System (ADS)

    Wang, Weilai; Wu, Jianping; Fang, Lihua

    2012-04-01

    This study presents the Rayleigh wave phase velocity tomographic results in northern North China. The data are from 190 broad-band and 10 very broad-band stations of the North China Seismic Array and 50 permanent stations nearby. All available teleseismic vertical component time-series are used to extract the phase velocity dispersion curves of the fundamental mode Rayleigh wave by interstation method. Tomographic maps are obtained at periods of 10, 15, 25 and 60 s with a grid spacing of 0.25°× 0.25°. The short-period phase velocity maps show good correlation with the geological and tectonic features. To be specific, lower velocities correspond to North China Basin and depression area whereas higher velocities are associated with Taihangshan and Yanshan uplifts. At 25 s, there are obvious low-velocity anomalies in Jizhong depression and Beijing-Tianjin-Tangshan region, indicating that ascendant low velocity channel may be formed beneath these areas and induce the velocity difference in the upper crust. The phase velocity map at 60 s reflects the upper-mantle information in the study area. High-velocity anomalies are observed at Yanshan blocks north to Zhangjiakou-Bohai seismic belt, suggesting that the materials are stable beneath these areas or the asthenosphere is at deeper location. Low-velocity anomalies are mainly south to the seismic belt, implying the asthenosphere is shallower and the materials are transformed by the open stretching rift trending NNE, resulting in many NNE-directed fault belts. These structural differences at depth may be controlled by the fault activity and strong tectonic movements.

  15. Three-dimensional crustal S wave velocity structure in Japan using microseismic data recorded by Hi-net

    E-print Network

    Kawakatsu, Hitoshi

    for obtaining a group velocity map. This method is called ambient noise surface wave tomog- raphy. The ambient for obtaining 3-D S wave velocity structure (0.1° � 0.1° � 1 km grid from the surface to a depth of 50 km) using of the ambient seismic noise at around 0.1 Hz to obtain a group velocity anomaly of Rayleigh waves due

  16. Shift in the longitudinal sound velocity due to sliding charge-density waves

    SciTech Connect

    Coppersmith, S.N.; Varma, C.M.

    1984-09-15

    The nonlinear conductivity observed for moderate electric fields in NbSe/sub 3/, TaS/sub 3/, (TaS/sub 4/) /sub 2/I, and K/sub 0.3/MoO/sub 3/ below the charge-density-wave transition is believed to be due to the sliding of the charge-density waves. The sliding motion leads to a Doppler shift of the x-ray diffraction peaks, but this effect has not yet been resolved. We show here that besides the Doppler shift, a sliding incommensurate charge-density wave causes a change in the longitudinal sound velocity of the crystal that is linear in the charge-density-wave velocity. The resulting anisotropic shift is estimated in a mean-field approximation and found to be experimentally observable.

  17. Uppermost Mantle S-wave Velocity Structure of the East Anatolian-Caucasus Region

    NASA Astrophysics Data System (ADS)

    Skobeltsyn, G.; Mellors, R.; Gok, R.; Turkelli, N.; Forsyth, D. W.; Sandvol, E. A.

    2011-12-01

    The East Anatolian-Caucasus region is a part of the orogenic belt which formed as the result of the closure of the Neo Tethys Ocean and the corresponding continental collision of Arabian and Eurasian plates. Our study region includes the southwestern part of the Caspian basin, the Kura basin, the Lesser and Greater Caucasus mountains, and the East Anatolian and North Iranian plateaus. We used the data from the Eastern Turkey Seismic Experiment network (1999-2001) in addition to the data which was recorded by 26 permanent broadband stations located in eastern Turkey and Azerbaijan during January of 2006 - July of 2008 in order to develop a 3D S-wave velocity model of the regional uppermost mantle. We selected total of 62 teleseismic events with surface wave magnitudes larger than 5.8 and with good signal-to-noise ratio to determine the fundamental mode Rayleigh wave phase velocities at 13 periods between 20 and 143 seconds. The phase velocity maps show a broad low velocity zone beneath East Anatolian and North Iranian plateaus and three high velocity zones located under the eastern part of the Greater Caucasus, the Talesh and Pontides. Furthermore, the regional uppermost mantle appears to be relatively isotropic. We inverted the Rayleigh wave phase velocities to obtain the regional 3D S-wave velocity model (0-350 km). The low velocity zone is observed starting right at the moho down to 150 km, which suggests asthenospheric material underlying a very thin lithosphere of eastern Anatolia where widespread Late Miocene - Quaternary calc-alkaline volcanic products of mantle origin are reported. Eastern Arabia and Black Sea each have lithospheric roots reaching depths of 150 km. The high velocity body beneath the eastern Greater Caucasus and Kura Basin lies at depths below the moho down to 180 km, and apparently represents either a thick lithospheric mantle root or a shallow subducting slab associated with the South Caspian block. The high velocity bodies beneath the Talesh and Pontides are observed below 160 km. We believe that these high velocity bodies represent remnant Neo Tethys slabs that broke off after the initiation of continental collision between Arabia and Eurasia and could serve as an evidence of two subduction zones beneath Pontide and Bitlis arcs during the Neogene.

  18. S-Band space traveling-wave tubes employing velocity resynchronization and collector depression

    Microsoft Academic Search

    M. K. Schreba

    1972-01-01

    Two related traveling-wave tubes, both of which demonstrate in excess of 50 percent efficiency over the design bandwidth, are introduced. Low dielectric and conductive shield loading are combined with suitable velocity resynchronization techniques to provide effective beam-circuit wave interaction. Use is made of multi-stage depressed collectors to sort the electrons according to energy, thus recovering a portion of the spent

  19. Validity, Reproducibility, and Clinical Significance of Noninvasive Brachial-Ankle Pulse Wave Velocity Measurement

    Microsoft Academic Search

    Akira YAMASHINA; Hirofumi TOMIYAMA; Kazuhiro TAKEDA; Hideichi TSUDA; Tomio ARAI; Kenichi HIROSE; Yutaka KOJI; Saburoh HORI; Yoshio YAMAMOTO

    2002-01-01

    The present study was conducted to evaluate the validity and reproducibility of noninvasive brachial-ankle pulse wave velocity (baPWV) measurements and to examine the alteration of baPWV in patients with coro- nary artery disease (CAD). Simultaneous recordings of baPWV by a simple, noninvasive method and aortic pulse wave velosity (PWV) using a catheter tip with pressure manometer were performed in 41

  20. Crustal thickness variation beneath the Romanian seismic network from Rayleigh wave dispersion and receiver function analysis

    NASA Astrophysics Data System (ADS)

    Tataru, Dragos; Grecu, Bogdan; Zaharia, Bogdan

    2014-05-01

    Variations in crustal thickness in Romania where determined by joint inversion of P wave receiver functions (RFs) and Rayleigh wave group velocity dispersion. We present new models of shear wave velocity structure of the crust beneath Romanian broad band stations. The data set consist in more than 500 teleseismic earthquake with epicentral distance between 30° and 95°, magnitude greater than 6 and a signal-to-noise ratio greater than 3 for the P-wave pulse. Most epicenters are situated along the northern Pacific Rim and arrive with backazimuths (BAZs) between 0° and 135° at the Romanian seismic network. We combine receiver functions with fundamental-mode of the Rayleigh wave group velocities to further constrain the shear-wave velocity structure.To extract the group velocities we applied the Multiple Filter Technique analysis to the vertical components of the earthquakes recordings. This technique allowed us to identify the Rayleigh wave fundamental mode and to compute the dispersion curves of the group velocities at periods between 10 and 150 s allowing us to resolve shear wave velocities to a depth of 100 km. The time-domain iterative deconvolution procedure of Ligorr?a and Ammon (1999) was employed to deconvolve the vertical component of the teleseismic P waveforms from the corresponding horizontal components and obtain radial and transverse receiver functions at each broadband station. The data are inverted using a joint, linearized inversion scheme (Hermann, 2002) which accounts for the relative influence of each set of observations, and allows a trade-off between fitting the observations, constructing a smooth model, and matching a priori constraints. The results show a thin crust for stations located inside the Pannonian basin (28-30 km) and a thicker crust for those in the East European Platform (36-40 km). The stations within the Southern and Central Carpathian Orogen are characterized by crustal depths of ~35 km. For stations located in the Northern part of the Eastern Carpathians we found a crustal depth of 32 km. For two station located in the Apuseni Mountains the Moho discontinuity is replace by a transition zone extended between 36 to 40 km depth. For a station located in the Carpathians bent area we identify a double Moho (32 respectively 44 km depth) possible due to the Vrancea subduction process. For the crust of Moesian Platform we get higher values (~35 km) compare to those obtained from seismic refraction profile (VRANCEA'2001). The North Dobrogea crust reaches a thickness of about 44-46 km. For most of the stations the crust-mantle transition zone has a significant gradient, with velocity values varying from 3.8 to 4.7 km/s. Our results are compatible with results from previous studies.

  1. Testing group velocity maps for Eurasia

    Microsoft Academic Search

    Nathalie Cotte; Gabi Laske

    2002-01-01

    SUMMARY Group velocity maps for seismic surface waves play an important role in monitoring the Comprehensive Test Ban Treaty so their accuracy is crucial. Group velocity anomalies can be modelled in terms of lateral variations in crustal and shallow mantle structure, the knowledge of which is important for understanding wave propagation and the blockage of regional phases. Accurate group velocity

  2. Rayleigh-Wave, Group-Velocity Tomography of the Borborema Province, NE Brazil, from Ambient Seismic Noise

    NASA Astrophysics Data System (ADS)

    Dias, Rafaela Carreiro; Julià, Jordi; Schimmel, Martin

    2015-06-01

    Ambient seismic noise has traditionally been regarded as an unwanted perturbation that "contaminates" earthquake data. Over the last decade, however, it has been shown that consistent information about subsurface structure can be extracted from ambient seismic noise. By cross-correlation of noise simultaneously recorded at two seismic stations, the empirical Green's function for the propagating medium between them can be reconstructed. Moreover, for periods less than 30 s the seismic spectrum of ambient noise is dominated by microseismic energy and, because microseismic energy travels mostly as surface-waves, the reconstruction of the empirical Green's function is usually proportional to the surface-wave portion of the seismic wavefield. In this paper, we present 333 empirical Green's functions obtained from stacked cross-correlations of one month of vertical component ambient seismic noise for different pairs of seismic stations in the Borborema Province of NE Brazil. The empirical Green's functions show that the signal obtained is dominated by Rayleigh waves and that dispersion velocities can be measured reliably for periods between 5 and 20 s. The study includes permanent stations from a monitoring seismic network and temporary stations from past passive experiments in the region, resulting in a combined network of 34 stations separated by distances between approximately 40 and 1,287 km. Fundamental-mode group velocities were obtained for all station pairs and then tomographically inverted to produce maps of group velocity variation. For short periods (5-10 s) the tomographic maps correlate well with surface geology, with slow velocities delineating the main rift basins (Potiguar, Tucano, and Recôncavo) and fast velocities delineating the location of the Precambrian São Francisco craton and the Rio Grande do Norte domain. For longer periods (15-20 s) most of the velocity anomalies fade away, and only those associated with the deep Tucano basin and the São Francisco craton remain. The fading of the Rio Grande do Norte domain fast-velocity anomaly suggests this is a supracrustal structure rather than a lithospheric terrain, and places new constraints on the Precambrian evolution of the Borborema Province.

  3. Rayleigh wave group velocity distributions for East Asia using ambient seismic noise

    NASA Astrophysics Data System (ADS)

    Witek, Michael; van der Lee, Suzan; Kang, Tae-Seob

    2014-11-01

    Vertical component data from 206 broadband seismometer stations from Korean networks Korean Institute of Geoscience and Mineral Resources and Korea Meteorological Administration, the Japanese F-net network, and the Chinese New China Digital Seismograph Network and Northeast China Extended Seismic Array network are collected for the year 2011, and the ambient seismic noise is analyzed. Rayleigh wave group velocity distribution maps are created in the period range 10 to 70 s. Our results are largely consistent with previous studies of the area but provide greater detail in the Korean peninsula and the Sea of Japan. Low group velocities are observed in the Ulleung basin, and the Chubu-Kanto and Kyushu regions in Japan. At 10 s period, sediment basins in the Sea of Japan appear as low group velocity regions relative to higher group velocity continental regions. At periods longer than 40 s, a low group velocity region emerges in the Ulleung basin region, and is bounded by the Korean peninsula.

  4. Using second-sound shock waves to probe the intrinsic critical velocity of liquid helium II

    NASA Technical Reports Server (NTRS)

    Turner, T. N.

    1983-01-01

    A critical velocity truly intrinsic to liquid helium II is experimentally sought in the bulk fluid far from the apparatus walls. Termed the 'fundamental critical velocity,' it necessarily is caused by mutual interactions which operate between the two fluid components and which are activated at large relative velocities. It is argued that flow induced by second-sound shock waves provides the ideal means by which to activate and isolate the fundamental critical velocity from other extraneous fluid-wall interactions. Experimentally it is found that large-amplitude second-sound shock waves initiate a breakdown in the superfluidity of helium II, which is dramatically manifested as a limit to the maximum attainable shock strength. This breakdown is shown to be caused by a fundamental critical velocity. Secondary effects include boiling for ambient pressures near the saturated vapor pressure or the formation of helium I boundary layers at higher ambient pressures. When compared to the intrinsic critical velocity discovered in highly restricted geometries, the shock-induced critical velocity displays a similar temperature dependence and is the same order of magnitude.

  5. Shear-wave velocity structure of the western part of the Mediterranean Sea from Rayleigh-wave analysis

    NASA Astrophysics Data System (ADS)

    Corchete, Victor; Chourak, M.

    2010-07-01

    The lithospheric structure of the western part of the Mediterranean Sea is shown by means of S-velocity maps, for depths ranging from 0 to 35 km, determined from Rayleigh-wave analysis. The traces of 55 earthquakes, which occurred from 2001 to 2003 in and around the study area have been used to obtain Rayleigh-wave dispersion. These earthquakes were registered by 10 broadband stations located on Iberia and the Balearic Islands. The dispersion curves were obtained for periods between 1 and 45 s, by digital filtering with a combination of MFT and TVF filtering techniques. After that, all seismic events were grouped in source zones to obtain a dispersion curve for each source-station path. These dispersion curves were regionalized and after inverted according to the generalized inversion theory, to obtain shear-wave velocity models for rectangular blocks with a size of 1° × 1°. The shear velocity structure obtained through this procedure is shown in the S-velocity maps plotted for several depths. These maps show the existence of lateral and vertical heterogeneity. In these maps is possible to distinguish several types of crust with an average S-wave velocity ranging from 2.6 to 3.9 km/s. The South Balearic Basin (SBB) is more characteristic of oceanic crust than the rest of the western Mediterranean region, as it is demonstrated by the crustal thickness. We also find a similar S-wave velocity (ranging from 2.6 km/s at the surface to 3.2 km/s at 10 km depth) for the Iberian Peninsula coast to Ibiza Island, the North Balearic Basin (NBB) and Mallorca Island. In the lower crust, the shear velocity reaches a value of 3.9 km/s. The base of the Moho is estimated from 15 to 20 km under Iberian Peninsula coast to Ibiza Island, continues towards NBB and increases to 20-25 km beneath Mallorca Island. While, the SBB is characterized by a thinner crust that ranges from 10 to 15 km, and a faster velocity. A gradual increase in velocity from the north to the south (especially in the upper 25 km) is obtained for the western part of the Mediterranean Sea. The base of the crust has a shear-wave velocity value around of 3.9 km/s for the western Mediterranean Sea area. This area is characterized by a thin crust in comparison with the crustal thickness of the eastern Mediterranean Sea area. This thin crust is related with the distensive tectonics that exists in this area. The low S-wave velocities obtained in the upper mantle might be an indication of a serpentinized mantle. The obtained results agree well with the geology and other geophysical results previously obtained. The shear velocity generally increases with depth for all paths analyzed in the study area.

  6. Azimuthal anisotropy of the crust and uppermost mantle in northeast North China Craton from inversion of Rayleigh wave phase velocity

    NASA Astrophysics Data System (ADS)

    Chen, Haopeng; Zhu, Liangbao; Ye, Qingdong; Wang, Qingdong; Yang, Yinghang; Zhang, Pan

    2015-07-01

    We imaged the azimuthal anisotropy of Rayleigh wave phase velocity (10-60 s) in northeast North China Craton using the teleseismic data recorded by a dense temporary array, and then inverted for the 3-D azimuthal anisotropy of the crust and uppermost mantle (20-110 km). The results reveal that the azimuthal anisotropy varies both horizontally and vertically. Obvious stratified azimuthal anisotropy is shown in the Central Orogenic Belt, where the fast direction is NE-SW to NNE-SSW in the depth range of 20-40 km and changes to NW-SE to NWW-SEE in the depth range of 60-110 km. In the depth range of 30-40 km, a prominent low velocity belt is shown on the southwest of Zhangjiakou-Penglai fault zone (ZPFZ) and the fast direction is subparallel to the strike of the low velocity belt. Distinct lateral variations of azimuthal anisotropy are clearly shown at 110 km. Our results provide new evidence for the existence of upwelling asthenosphere beneath the Datong volcano and support the assumption that ZPFZ may act as the channel of upwelling asthenosphere. Historical strong earthquakes (M ? 6.0) mainly occurred in the transition zone between low and high velocity anomalies in the upper and middle crust. The upwelling asthenosphere may prompt the generation of large earthquake.

  7. 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).

  8. Correlation of the 410 km Discontinuity Low Velocity Layer with Tomographic Wavespeed Variations

    NASA Astrophysics Data System (ADS)

    Zhang, Z.; Dueker, K. G.

    2010-12-01

    The transition zone water-filter model predicts that a hydrous melt layer at the 410-km discontinuity is only actively produced in upwelling region, and does not exist in downwelling region (Bercovici and Karato, 2003). This prediction has been tested by stacking of P-S receiver functions using the RISTRA linear array which crosses west-Texas, New Mexico and Utah. The receiver functions are binned into the NW, SE, SW azimuthal quadrants and stacked to produce well-resolved images of the 410- and 660-km discontinuities. The three receiver function quadrant stack images find a correlation between the occurrence of negative polarity 410-km low velocity layer arrival and the teleseismic body wave velocity tomogram of Schmandt and Humphreys (2010); the 410 low velocity layer arrival is absent where the velocities about the 410 km discontinuity are relatively high and present where the velocities are low. Our finding is consistent with a simple interpretation of the transition zone water filter model which predicts the production of a hydrous melt layer where upflow of sufficiently hydrated transition zone mantle occurs and destruction of a hydrous melt layer where there is downflow. We test this prediction by analyzing the Colorado Rockies Experiment and Seismic Transects (CREST) seismic data which was collected in 2008-2009. This 15 month deployment of 59 CREST stations in tandem with 31 Transportable Array stations yields a total of 161 Mb>5.5 events at 30°-95° distances. The P-S receiver functions are calculated using a multi-channel deconvolution methodology and filtered with a 30-3 s post-deconvolution filter. The receiver function dataset contains about 1800 SV components after RMS, cross-correlation, and visual data quality culling. Common conversion point images are constructed using Pds timing correction from a 3-D upper mantle tomography model (McCarthy and Aster, pers. com.) to account for lateral P/S velocity heterogeneity.

  9. Effect of CO2 hydrate formation on seismic wave velocities of fine-grained sediments

    NASA Astrophysics Data System (ADS)

    Kim, Hak-Sung; Cho, Gye-Chun; Kwon, Tae-Hyuk

    2013-06-01

    study examines the effect of gas hydrate formation on seismic wave velocities of fine-grained sediments. Synthesis of gas hydrates in fine-grained sediments has proved to be challenging, and how hydrate formation would affect the seismic wave velocities and stiffness of clay-rich sediments has not yet been fully understood. In this study, CO2 hydrate was synthesized in remolded and partially water-saturated clayey silt sediments that were originally cored from a hydrate occurrence region in the Ulleung Basin, East Sea, offshore Korea. After achieving excess water conditions, compressional wave and shear wave velocities were measured for different hydrate saturations and under different vertical effective stresses. The results reveal that the compressional wave velocity VP and shear wave velocity VS increase, and the stress-dependency of VP and VS decreases as the hydrate saturation SH increases from 0% to ~60%. In particular, the VS-SH trend lies between the grain-cementing model and the load-bearing model, suggesting that gas hydrate formation in clayey silt sediments causes weak cementation from a hydrate saturation less than ~28%. The weak cementation in fine-grained sediments can be explained by the breakage of hydrate bonds that are cementing grains during sediment compression and/or the innate weakness in bonding between hydrate crystals and fine mineral grains owing to the presence of unfrozen water films on clay mineral surfaces. In addition, it is found that at low SH, the cementation effect on VP is masked by the high stiffness of pore-filling phases, but it becomes pronounced at SH greater than 47%.

  10. Liquefaction Hazard Assessment of Earth Quake Prone Area: a Study Based on Shear Wave Velocity by Multichannel Analysis of Surface Waves (MASW)

    Microsoft Academic Search

    N. Sundararajan; T. Seshunarayana

    2011-01-01

    The shear wave velocity (VS) profile based on the dispersive characteristics of fundamental mode of Rayleigh type surface waves indicate underground\\u000a stiffness change with depth as well as near surface stiffness. The most important utility of shear wave velocity (VS) is to estimate the liquefaction hazard potential of an area particularly in seismically active region. Rayleigh type surface\\u000a waves were

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

    E-print Network

    Zeng, Chong

    2011-05-18

    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...

  12. Effect of an external magnetic field on the propagation velocities of magnetoacoustic waves in a magnetic fluid

    NASA Astrophysics Data System (ADS)

    Ovchinnikov, I. E.; Sokolov, V. V.

    2009-05-01

    Theoretical results on the propagation of magnetoacoustic waves in an ideal magnetic fluid with frozen magnetization are generalized. Expressions for the propagation velocity of fast and slow magnetoacoustic waves and Alfven waves are derived. Agreement between the theoretical and experimental results is demonstrated for the fast magnetoacoustic waves propagating in a water-based magnetic fluid.

  13. Seismic velocity variations at TCDP are controlled by MJO driven precipitation pattern and high fluid discharge properties

    NASA Astrophysics Data System (ADS)

    Hillers, G.; Campillo, M.; Ma, K.-F.

    2014-04-01

    Using seismic noise based monitoring techniques we find that seismic velocity variations (dv/v) observed with the borehole array of the Taiwan Chelungpu-fault Drilling Project (TCDP) are controlled by strong precipitation events associated with the Madden-Julian Oscillation (MJO), a dynamic intraseasonal atmospheric pattern in the tropical atmosphere. High-frequency noise (>1 Hz) excited by steady anthropogenic activity in the vicinity of the TCDP allows daily resolution of dv/v time series. Relatively large fluid discharge properties control the equilibration of the ground water table and hence seismic velocities on time scales smaller than the average precipitation recurrence interval. This leads to the observed synchronous 50-80 day periodicity in dv/v and rainfall records in addition to the dominant annual component. Further evidence for the governing role of hydraulic properties is inferred from the similarity of observed dv/v timing, amplitude, and recovery properties with dv/v synthetics generated by a combined model of ground water table changes and diffusive propagation of seismic energy. The lapse time (?) dependent increase of dv/v amplitudes is controlled by the sensitivity of the diffuse wave field sampled at 1100 m depth to shallower water level fluctuations. The significant vertical offset between stations and water level explains the direct ? dependence which is opposite to the trend previously inferred from measurements at the surface.

  14. 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 of February 2014 involving about 5000 m³ of materials. Analyzing the data collected inside the landslide's body, I observed an increase of Vs over time, due to the decrease of landslide velocity and, probability, to the remedial works carried out after the reactivation; • The Mozuno (BO) rotational landslide. This landslide was reactivated around the first day of March 2014. The data collected show a decrease of Vs variability, due to an increase of fractures near the main scarp; • The Borgo Val di Taro (PR) complex landslide. This landslide was reactivated during the night between the 9th and the 10th of February 2014 with a maximum velocity around 40m/d. The data collected show an increase of Vs, due to the slowing of the movements and the consolidation of landslide material; • The Camugnano (BO) transitional landslide. The reactivation of this landslide was around the 15th of March 2014. Analyzing the data collected inside the landslide's body, I noted an increase of Vs over time, due to the slowing of the movements; • The Zattaglia-Poggio Zampiroli (BO) transitional landslide. The reactivation of the landslide occurred on the 9th of February 2014. The data show really different values of Vs in relation to the landslide's portion investigated and show an increase of Vs over time. In all these cases, the measures taken outside the landslide's body do not show a significant Vs variability, because the material are not involved in the landslide's movements. Preliminary results from field data clearly show that the variation of the shear wave velocity with time is related to the movements of the landslides and to the different consistence of the materials.

  15. Explosion Waves and Shock Waves. VII. The Velocity of Detonation in Cast T.N.T

    Microsoft Academic Search

    W. B. Cybulski; W. Payman; D. W. Woodhead

    1949-01-01

    The Buxton rotating-mirror camera has been used for the precise determination of velocities of detonation in cylinders of cast T.N.T. The method has an advantage over the indirect Dautriche method in that it affords a direct measure of the velocity. The effects on the velocity of detonation of the following variables have been studied in so far as each can

  16. Laboratory measurements of wave height variations and currents along a steep-sided channel 

    E-print Network

    Way, Francis

    2000-01-01

    for numerical model predictions of wave transformation. A frequently applied model, REFDIF1, was used to compare with the measurements. Orbital velocities and mean currents were also measured to document any wave and bathymetry induced changes in particle...

  17. P-wave velocity structure of the uppermost mantle beneath Hawaii from traveltime tomography

    USGS Publications Warehouse

    Tilmann, F.J.; Benz, H.M.; Priestley, K.F.; Okubo, P.G.

    2001-01-01

    We examine the P-wave velocity structure beneath the island of Hawaii using P-wave residuals from teleseismic earthquakes recorded by the Hawaiian Volcano Observatory seismic network. The station geometry and distribution of events makes it possible to image the velocity structure between ~ 40 and 100 km depth with a lateral resolution of ~ 15 km and a vertical resolution of ~ 30 km. For depths between 40 and 80 km, P-wave velocities are up to 5 per cent slower in a broad elongated region trending SE-NW that underlies the island between the two lines defined by the volcanic loci. No direct correlation between the magnitude of the lithospheric anomaly and the current level of volcanic activity is apparent, but the slow region is broadened at ~ 19.8??N and narrow beneath Kilauea. In the case of the occanic lithosphere beneath Hawaii, slow seismic velocities are likely to be related to magma transport from the top of the melting zone at the base of the lithosphere to the surface. Thermal modelling shows that the broad elongated low-velocity zone cannot be explained in terms of conductive heating by one primary conduit per volcano but that more complicated melt pathways must exist.

  18. Measurements of acoustic wave velocities at P-T conditions of the Earth's mantle

    NASA Astrophysics Data System (ADS)

    Knoche, Ruth; Webb, Sharon L.; Rubie, David C.

    A method is being developed to determine acoustic wave velocities in polycrystalline samples at pressures and temperatures of the Earth's mantle using an MA-8 multianvil apparatus. Ultrasonic sound waves, generated by a LiNbO3 transducer, are transmitted through one of the eight tungsten carbide anvils and a platinum buffer rod to the sample which is situated at the center of the multianvil high P-T assembly. Travel times are determined by interferometry using the phase comparison method. Currently, the main uncertainty in determining velocities arises from estimating the changes in sample length at high pressure and temperature. Potentially, however, both compressional and shear wave velocities can be measured simultaneously using this technique. This leads to the possibility of determining the compressibility and resulting changes in sample length with pressure in a self consistent manner on the same sample, thus greatly improving the accuracy of the determined velocities. The technique has the potential for improving our knowledge of acoustic velocities in single phase and polyphase aggregates relevant to the Earth's mantle without the need for large extrapolations of experimental data.

  19. Experimental verification of stress-wave bands and negative phase velocity in layered media

    E-print Network

    Nemat-Nasser, Sia

    and coworkers analysis [5, 6] and the following experimental and numerical work by Smith and coworkers [7, 8, and consequently, the reversal of Snell's law. The first experimental demonstration of such behavior was performedExperimental verification of stress-wave bands and negative phase velocity in layered media Alireza

  20. Effects of desiccation on the elastic wave velocities of clay-rocks

    Microsoft Academic Search

    Ahmad Ghorbani; Maria Zamora; Philippe Cosenza

    2009-01-01

    Compressional (P) and shear (S) wave velocities were measured in a set of clay-rock samples subjected to a desaturation phase during which the samples were dried at ambient temperature conditions, with a median relative humidity equal to 37%, followed by a heating phase during which the same samples were heated to five different temperature levels, ranging from 65 to 105°C.

  1. Measurement of Local Pulse Wave Velocity: Effects of Signal Processing on Precision

    Microsoft Academic Search

    Evelien Hermeling; Koen D. Reesink; Robert S. Reneman; Arnold P. G. Hoeks

    2007-01-01

    Pulse wave velocity (PWV) provides information about the mechanical properties of the vessel: the stiffer the artery is, the higher the PWV will be. PWV measured over a short arterial segment facilitates direct characterization of local wall properties corrected for prevailing pressure without the necessity of measuring pulse pressure locally. Current methods for local PWV assessment have a poor precision,

  2. The Velocity of Compressional Waves in Rocks to 10 Kilobars, Part 2

    Microsoft Academic Search

    Francis Birch

    1961-01-01

    The measurements of the velocity of compressional waves up to 10 kilobars for some 250 specimens of rock, reported in part 1, are discussed with respect to the effects of porosity, alteration, anisotropy, and composition. The relations of isotropic elasticity are shown to be approximately valid for a number of examples. Reasonable agreement with theoretical values for quasi-isotropic aggregates is

  3. A New Global Rayleigh and Love Wave Group Velocity Dataset For Constraining Lithosphere Properties

    E-print Network

    Laske, Gabi

    A New Global Rayleigh and Love Wave Group Velocity Dataset For Constraining Lithosphere Properties features and fit our data very well. This dataset will be used to constrain lithospheric structure globally the global datasets used in Ritzwoller et al. (2002) already consist of more than 100,000 paths, the nature

  4. Pulse Wave Velocity as a Marker of Arteriosclerosis and Its Comorbidities in Chinese Patients

    Microsoft Academic Search

    Xiao-Ning Liu; Hai-Qing Gao; Bao-Ying Li; Mei Cheng; Ya-Bing Ma; Zhi-Mian Zhang; Xi-Mei Gao; Yuan-Ping Liu; Min Wang

    2007-01-01

    To obtain reliable data on the epidemiology of arteriosclerosis and the comorbidities in patients with hypertension (HP), coronary heart disease (CHD), type 2 diabetes mellitus (T2DM) and stroke, we evaluated the clinical significance of pulse wave velocity (PWV) as an indicator of arteriosclerosis and its comorbidities in Chinese patients. A total of 910 subjects, including 748 Chinese patients with one

  5. 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.

  6. perovskite phase suggests slow longitudinal elastic-wave velocities propagating along the

    E-print Network

    Hansell, Dennis

    perovskite phase suggests slow longitudinal elastic-wave velocities propagating along the [010] direction. In addition, it is also inferred that the post-perovskite phase forms a platy crystal habit) observed in the D region (1, 2) is possibly caused by the preferred orientation of the post-perovskite

  7. Pulse wave velocity—a useful tool for cardiovascular surveillance in pre-dialysis patients

    Microsoft Academic Search

    Marcelo M. Lemos; Alessandra D. B. Jancikic; Fabiana M. R. Sanches; Dejaldo M. Christofalo; Sergio A. Ajzen; M arcio H. Miname; Raul D. Santos; Fernando C. Fachini; Aluizio B. Carvalho; A. Draibe; Maria Eugenia; F. Canziani

    2007-01-01

    Background. Cardiovascular mortality is high among patients with chronic kidney disease. Pulse wave velocity (PWV) is a simple method used for arterial distensibility evaluation. Few data are available con- cerning PWV in pre-dialysis patients. The aim of this study was to evaluate the association between PWV and cardiovascular disease in pre-dialysis. Methods. One hundred and four patients were sub- mitted

  8. RESEARCH NOTE : Shear-wave velocity in marine sediments on young oceanic crust: constraints from dispersion analysis of Scholte waves

    NASA Astrophysics Data System (ADS)

    Heinz-Essen, H.; Grevemeyer, Ingo; Herber, Rolf; Weigel, Wilfried

    1998-01-01

    An experiment with a newly developed implosive source, located about 1 m above the seafloor at 3665 m depth, revealed a slow interface wave. This wave is attributed to S waves in a soft sediment layer covering the hard rock sub-bottom. Dispersion analysis by means of the multiple-filter technique yields the group velocity as a function of frequency. Model calculations showed that the observed dispersion curve can be reproduced by considering a steep gradient of S velocity within the sediment layer. Nearly perfect agreement of experimental and model data could be achieved with a sediment layer thickness of 21.5 m, an S speed of 225 m s- 1 at the water-sediment interface and an increase by 23 s- 1 within the layer. These values are relatively high compared to data from the literature. However, previous estimates of in situ S-wave velocity have been obtained on old oceanic crust in the vicinity of continents or islands, while our experiment was carried out on young Pacific crust. Therefore, we suggest two mechanisms which could support a relatively high S speed in sediments: (1) the input of hydrothermally generated metalliferous sediments from the adjacent spreading axis; and (2) post-depositional diagenesis which has accelerated the induration of sediments.

  9. 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.

  10. Analysis of coordinate variation and stability of velocities by GPS observations in Tien Shan

    NASA Astrophysics Data System (ADS)

    Barkalova, T.; Kuzikov, S.

    2009-04-01

    The velocity vectors got from highly accurate GPS measurements are one of the main sources of information in contemporary geodynamics. Thus, GPS technologies are used for the study of boundaries and movement of plates (Abdrakhmatov et al., 1996; Steblov et al., 2003; etc.), seismic deformations (Segall, Davis, 1997; etc.) and other geophysical researches. However, the velocity calculated by straight-line approximation of time variation of coordinates for GPS site, may provoke doubts of its stability and correctness. It is important to know about the time series, on basis of which the linear velocities of points of the Earth's surface are calculated. Coordinate deviation from the approximating linear trend can be caused both by geodynamic factors and accuracy of GPS technology. This paper covers the analysis of coordinate time variation and the assessment of velocities estimation. For 15 years, the Research Station of the Russian Academy of Sciences in Bishkek has taken regularly observations (from one to several times a year) in the territory of Central Asian GPS network. It contains more then 500 sites, including 10 sites of permanent observation. Detail and duration of the measurements in Kyrgyz Tien Shan allows us to analyze the time variations of the GPS data. Basically, the linear velocities of the Central Asian GPS network have been stable for the observations 1995-2005; deviations do not exceed 1/6 from the average effective horizontal vector of velocity (Kuzikov, 2007). The coordinates after deduction of straight-line trend are coordinates' remainders. Some GPS sites have general tendency of coordinates' remainders for twelve years (1995-2006) annual measurements. The GPS sites form different groups as to northern and eastern components of coordinates' remainders. Remainders of coordinates' daily variations of unmoved relative to each other GPS sites have considerable positive correlation. A real geodynamic factor can be the source that appropriately influences the synchronous behavior of coordinates' remainders. But meanwhile the influence of the features of cameral treatment of GPS materials is not excepted, for example options' choice of velocities calculation via Gamit/Globk (Herring et al., 2006a, 2006b). In so doing, the accuracy of daily GPS measurements (ITRF2005) at the average is about 0.8 mm for northern component and about 1.8 mm for southern one. The comparison of the accuracy of the daily GPS measurements according to in various reference frames is present. References Abdrakhmatov K.Ye., Aldazhanov S.A., Hager B.H. et al., 1996. Relatively construction of the Tien Shan inferred from GPS measurements of present-day crustal deformation rates. Nature. Vol. 384. P. 450-453. Segall P., Davis J., 1997. GPS applications and earthquake studies. Annu. Rev. Earth Planet. Sci. Vol. 25. No. 2. P. 301-336. Steblov G.M., Kogan M.G., King R.W. et al., 2003. Imprint of the North American plate in Siberia revealed by GPS. Geophys. Res. Lett. Vol. 30. No. 18, 1924, doi: 10.1029/2003GL017805. Kuzikov S.I., 2007. The structural analysis of horizontal velocities of GPS data and feature of modern deformation crust of Central Asia: Ph.D. thesis. (Russ.) Moscow, Institute of Physics of the Earth, RAS. 167 p. Herring T., King B., McClusky S., 2006a. Documentation for the GAMIT GPS analysis software. Release 10.3 EAPS, MIT. 105 p. Herring T., King B., McClusky S., 2006b. GLOBK. Reference manual. Global Kalman filter VLBI and GPS analysis program. Release 10.3. EAPS, MIT. 87 p.

  11. 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 ?) 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.

  12. Rayleigh Wave Dispersion and A 1d S-velocity Model of The Fennoscandian Mantle

    NASA Astrophysics Data System (ADS)

    Funke, S.; Friederich, W.; Sstwg, The

    We derive a Rayleigh wave dispersion curve from surface wave data recorded at the SVEKALAPKO tomographic array deployed in Southern Finland from September 1998 to March 1999. After a suite of processing steps, complex spectral amplitudes of the Rayleigh wave train are determined for each available seismogram. The process- ing includes low-pass filtering, instrument correction, deconvolution using a standard earth model to compress the Rayleigh wave train, computation of Gabor matrices (sonograms) to pick group travel times, and finally estimation of complex spectral amplitudes in a Gaussian time window of frequency-dependent width centered on the group travel time. Spectral amplitude values are only accepted if the signal-to-noise ratio in the considered frequency interval is above a pre-chosen threshold and if the picked group travel time does not deviate too strongly from that predicted by a stan- dard earth model. The final dataset contains spectral amplitude values at 34 selected periods from 52 earthquakes observed at on average 25 stations. For each selected frequency, we determine a phase velocity by fitting plane waves propagating across the array with this velocity to the complex spectral amplitudes of all earthquakes and stations. Errors are estimated with a bootstrap method. We obtain reliable phase velocities in the frequency band from 8 mHz to 50 mHz. Phase veloci- ties for lower frequencies exhibit large errors due to the lack of big earthquakes during the time of deployment. The phase velocities are substantially higher than predicted by standard earth model ak135 below 20 mHz and slightly lower above 25 mHz. We have inverted the dispersion curve for a 1D shear wave velocity model down to about 400 km depth and obtain a 50 km thick crust and a fast upper mantle with a sub- Moho velocity of 4.7 km/s. Our data do not require a low-velocity zone in the upper mantle. Indeed, the dispersion curve can be explained by a nearly straight velocity profile from the Moho to the 410 km discontinuity.

  13. Subduction zones beneath Indonesia imaged by Rayleigh wave phase velocity tomography

    NASA Astrophysics Data System (ADS)

    Liu, F.; Yang, T.; Harmon, N.

    2013-12-01

    Situated at the junction of several tectonic plates including Indian-Australia, Eurasia, and Philippine Sea, the Indonesian archipelago is one of the most tectonically complex regions on earth with subductions, collisions and accretions occurring along and within its boundaries. A high-resolution lithospheric and upper mantle model, therefore, is needed to understand these complex processes beneath this region. We present a phase velocity model derived from teleseismic Rayleigh waves recorded at seismic stations in this region. We use the modified version of the two-plane wave tomography, in which the non-planar effects of surface wave propagation such as multipathing and scattering are accounted for by two plane wave interference and using of finite frequency kernels. We measure the amplitudes and phases at 16 individual periods ranging from 20s to 150s for the fundamental mode of Rayleigh waves at over 30 stations. 254 earthquakes are selected from global events greater than Ms 5.5 in the distance range of 25°- 150°. To account for the wavefield inconsistencies among stations for each earthquake due to the large scale of our study region, we divide the seismic array into 4 groups of stations in the two-plane wave parameter inversion. The phase velocity maps from our preliminary results show coherent features between adjacent periods. The most dominant structure in phase velocity maps for all periods is the strong fast-velocity belts beneath Sunda Trench, Java Trench, Timor Trough and the trenches around Celebes Sea, which shift gradually toward the subduction directions. The strength of the high velocity anomaly varies among trenches, likely suggesting the different age of subducting slabs. In addition, a velocity contrast in the middle of Borneo appears to mark the Lupar Line, a boundary between the stable Sundaland continental core and fragments of ophiolitic and Asian continental material accreted to Borneo during the Cretaceous. The 3-D shear wave structure derived from these 2-D phase velocity maps at different periods, which is in progress, certainly will sharpen the images of the complex subduction system, unraveling more geodynamic processes in this region.

  14. Developing regionalized models of lithospheric thickness and velocity structure across Eurasia and the Middle East from jointly inverting P-wave and S-wave receiver functions with Rayleigh wave group and phase velocities

    SciTech Connect

    Julia, J; Nyblade, A; Hansen, S; Rodgers, A; Matzel, E

    2009-07-06

    In this project, we are developing models of lithospheric structure for a wide variety of tectonic regions throughout Eurasia and the Middle East by regionalizing 1D velocity models obtained by jointly inverting P-wave and S-wave receiver functions with Rayleigh wave group and phase velocities. We expect the regionalized velocity models will improve our ability to predict travel-times for local and regional phases, such as Pg, Pn, Sn and Lg, as well as travel-times for body-waves at upper mantle triplication distances in both seismic and aseismic regions of Eurasia and the Middle East. We anticipate the models will help inform and strengthen ongoing and future efforts within the NNSA labs to develop 3D velocity models for Eurasia and the Middle East, and will assist in obtaining model-based predictions where no empirical data are available and for improving locations from sparse networks using kriging. The codes needed to conduct the joint inversion of P-wave receiver functions (PRFs), S-wave receiver functions (SRFs), and dispersion velocities have already been assembled as part of ongoing research on lithospheric structure in Africa. The methodology has been tested with synthetic 'data' and case studies have been investigated with data collected at an open broadband stations in South Africa. PRFs constrain the size and S-P travel-time of seismic discontinuities in the crust and uppermost mantle, SRFs constrain the size and P-S travel-time of the lithosphere-asthenosphere boundary, and dispersion velocities constrain average S-wave velocity within frequency-dependent depth-ranges. Preliminary results show that the combination yields integrated 1D velocity models local to the recording station, where the discontinuities constrained by the receiver functions are superimposed to a background velocity model constrained by the dispersion velocities. In our first year of this project we will (i) generate 1D velocity models for open broadband seismic stations in the western half of the study area (Eurasia and the Middle East) and (ii) identify well located seismic events with event-station paths isolated to individual tectonic provinces within the study area and collect broadband waveforms and source parameters for the selected events. The 1D models obtained from the joint inversion will then be combined with published geologic terrain maps to produce regionalized models for distinctive tectonic areas within the study area, and the models will be validated through full waveform modeling of well-located seismic events recorded at local and regional distances.

  15. Regional variations in upper mantle compressional velocities beneath southern California 1. Post-shock temperatures: Their experimental determination, calculation, and implications, 2.. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Raikes, S. A.

    1978-01-01

    The compressional velocity within the upper mantle beneath Southern California is investigated through observations of the dependence of teleseismic P-delays at all stations of the array on the distance and azimuth to the event. The variation of residuals with azimuth was found to be as large as 1.3 sec at a single station; the delays were stable as a function of time, and no evidence was found for temporal velocity variations related to seismic activity in the area. These delays were used in the construction of models for the upper mantle P-velocity structure to depths of 150 km, both by ray tracing and inversion techniques. The models exhibit considerable lateral heterogeneity including a region of low velocity beneath the Imperial Valley, and regions of increased velocity beneath the Sierra Nevada and much of the Transverse Ranges. The development is described of a technique for the experimental determination of post-shock temperatures, and its application to several metals and silicates shocked to pressures in the range 5 to 30 GPa. The technique utilizes an infra-red radiation detector to determine the brightness temperature of the free surface of the sample after the shock wave has passed through it.

  16. The effects of velocity shear on the resonance absorption of MHD surface waves: Cold plasma

    SciTech Connect

    Yang, Guang; Hollweg, J.V. (Univ. of New Hampshire, Durham (United States))

    1991-08-01

    Magnetohydrodymnamic (MHD) surface waves may decay via a process called resonance absorption, which is a candidate for solar coronal heating. Recently, Hollweg, Yang, Cadez and Gakovic studied the effects of velocity shear on the rate of resonance absorption of incompressible MHD surface waves. The authors extend the theory to a compressible but cold plasma, which is the case more applicable to the solar corona. They find that the rate of resonance absorption can be either increased or decreased significantly by velocity shear. They also find that there can exist resonances which lead to instability of the surface mode at values of the velocity shear below the Kelvin-Helmholtz threshold. However, the resonance instability usually occurs when the density ratio across the surface is less than about 0.1. The resonant instability may therefore not be important in the solar corona, though resonance absorption remains an atractive possibility for coronal heating.

  17. Inverse method for determining the depth of nonhomogeneous surface layers in elastic solids from the measurements of the dispersion curves of group velocity of surface SH Waves

    Microsoft Academic Search

    P. Kielczynski; W. Pajewski

    1989-01-01

    In this paper, the variational inverse method for determining the depth of nonhomogeneous surface layers in elastic materials, from the measurements of the group velocity of surface shear horizontal (SH) waves, is developed. The direct problem for a given a priori type of profile of the coefficientc44in(x) (e.g. linear, Gaussian, etc.) is solved. The dispersion curves of phase and group

  18. A reappraisal of surface wave group velocity tomography in the Subantarctic Scotia Sea and surrounding ridges

    NASA Astrophysics Data System (ADS)

    Vuan, A.; Sugan, M.; Plasencia Linares, M. P.

    2014-12-01

    A reappraisal of surface wave tomography in the remote Scotia Sea region and surrounding ridges is presented. New group velocity dispersion curves were obtained from local and regional earthquakes recorded at permanent Antarctic stations from 2001 to 2013 and used to update the measurements reported by Vuan et al. (2000). Rayleigh and Love group velocity maps for periods ranging from 15 to 50 s were retrieved using a tomographic inversion. The group velocity anomalies are clearly associated with the major crustal and upper mantle features of the Antarctic, Scotia and South American plates. The updated dataset allows for considerable decrease of the correlation length of the crustal heterogeneities that can be resolved, especially in the west Scotia Sea, central Scotia Sea and Bransfield Basin. Surface wave tomography results were compared with CRUST 1.0 group velocity maps and revealed specific areas where more detailed information is made available by our regional study. In particular, low group velocity anomalies of the Bransfield Strait rifting and continental fragments that are detached from the Antarctic Peninsula and spreading along the South Scotia ridge are not shown by the reference CRUST 1.0 model. A comparison between the average seismic velocities beneath the west and central Scotia Sea shows that both have an oceanic-type structure; however, the crust of the central sea is thicker (12-14 km) and slower than that of the 20 Ma old western sea.

  19. Variations in the electrical short-circuit current decay for recombination lifetime and velocity measurements

    NASA Technical Reports Server (NTRS)

    Jung, Tae-Won; Lindholm, Fredrik A.; Neugroschel, Arnost

    1987-01-01

    An improved measurement system for electrical short-circuit current decay is presented that extends applicability of the method to silicon solar cells having an effective lifetime as low as 1 microsec. The system uses metal/oxide/semiconductor transistors as voltage-controlled switches. Advances in theory developed here increase precision and sensitivity in the determination of the minority-carrier recombination lifetime and recombination velocity. A variation of the method, which exploits measurements made on related back-surface field and back-ohmic contact devices, further improves precision and sensitivity. The improvements are illustrated by application to 15 different silicon solar cells.

  20. Radial velocity variations in EX Lup: hints for a low-mass close companion

    NASA Astrophysics Data System (ADS)

    Kóspál, Ágnes; Mohler-Fischer, Maren; Sicilia-Aguilar, Aurora; Ábrahám, Péter; Curé, Michel; Henning, Thomas; Kiss, Csaba; Launhardt, Ralf; Moór, Attila; Müller, André

    2013-07-01

    EXors are low-mass pre-main sequence objects producing repetitive optical outbursts attributed to highly enhanced accretion from the circumstellar disk onto the star. One type of outburst theories requires a close stellar or sub-stellar companion that perturbs the inner part of the disk and triggers the onset of the enhanced accretion. Here, we look for a possible companion to EX Lup, the prototype of the EXor class, using radial velocity (RV) observations. The RVs show large periodic variations that can be explained by the presence of a close companion in the brown dwarf mass range. Chromospheric activity or starspots are less likely to explain the observed RV curve.

  1. Surface-wave attenuation and its lateral variation in the crust of the southwestern United States

    NASA Astrophysics Data System (ADS)

    Sholy, Beshara Ibrahim

    Shear wave Q (Qmu) models are obtained for a broad region of the southwestern United States. A single station method that compares observed amplitude spectra of fundamental and higher-mode Rayleigh waves to theoretically predicted spectra for assumed Qmu models is used to determine Q mu as a function of depth. Velocity structure and initial Qmu models are assumed for event-station pairs in which the events have known source depths and focal mechanisms. 164 event-station paths obtained from 33 earthquakes and 32 stations provide good path coverage for the region. The coverage is adequate to map lateral variations of Qmu at various depths in the continental crust of the southwestern United States. Two Qmu earth models of the crust are presented. Both models have three horizontal crustal layers of varying thickness overlying a uniform half-space. The analyses reveal that the Qmu variations correlate with changes in surface tectonics of the region. Average Qmu values for the upper crust for the whole region are found to vary between 55 and 75. These low values are expected for the seismically active and highly fractured crust of California and for the rifted Basin and Range province. Higher average Qmu values (103--116) are found at mid-crustal and lower-crustal depths. Qmu variations patterns are compared to geological and geophysical parameters of the southwestern United States, and found to partially correlate with heat flow patterns of the region.

  2. Diurnal variations of mesospheric ozone using millimeter-wave measurements

    NASA Technical Reports Server (NTRS)

    Wilson, W. J.; Schwartz, P. R.

    1981-01-01

    In March 1979, millimeter-wave observations of the ozone emission line at 101737 MHz were made to measure the diurnal variations in mesospheric ozone. Changes in mesospheric ozone were measured diurnally for a 10-day period. The ozone column above approximately 76 km rapidly decreased after sunrise to half value within 1 hour and was then followed by a slower (approximately 8 hours) decrease to an absolute minimum at 1600 hours. At sunset, the ozone column above approximately 76 km increased rapidly to its maximum value within 2 hours. In the 48-68 km altitude range, the ozone changes were gradual with a minimum near local noon (1200 hours).

  3. Estimation of the wave height from the sea surface velocity measured by Along-Track interferometry SAR

    NASA Astrophysics Data System (ADS)

    Kojima, S.

    2014-12-01

    NICT developed the along-track interferometry SAR (AT-InSAR) system to detect the cars and ships and measure its speed in 2011. The preliminary experiments for the running truck and ship were performed to check its function and capability of the moving targets detection. As a result, it was confirmed that the system performance was satisfactory to its specifications. In this paper, to estimate the distribution of the wave height from SAR images observed by the AT-InSAR precisely, the relationship between the wave height and the sea surface velocity measured by the AT-InSAR was clarified and a method to estimate the wave height from the measured sea surface velocity was developed. In addition, to check the capability of the ocean waves observation by the AT-InSAR, the preliminary observation for the ocean waves was performed. To estimate the wave height from the sea surface velocity, the relationship between the velocity in the sight direction and the wave height was formulated. From this formulation, it was clarified that the phase of the velocity in the sight direction is shifted to -1/2?for the phase of the wave height. To estimate the distribution of the wave height, the wave surface velocity was estimated by subtracting the average velocity from the estimated sea surface velocity. The spectra of the wave surface velocity were calculated by 2D FFT and the spectra of the wave height were estimated from the spectra of the wave surface velocity. The distribution of the wave height was calculated from the spectra of the wave height by 2D inverse FFT. To check the capability of this wave height estimation method, I observed the sea surface by the AT-InSAR. The observation area is the sea surface at 3 km off the coast of Ooarai, north-east to Tokyo, JAPAN. The analysis area is about 2 km square. The incident angle at the center of the SAR image was 55 degrees. The sea state condition was a calm during the observation. The observation was performed in 2 directions and the accuracy of the estimation results were checked. The significant wave height and period measured by the AT-InSAR agreed with it measured by the wave gage located close to this observation area. In addition, there were no irregular wave heights in the distribution of the estimated wave height. As a result, it was confirmed that the AT-InSAR could observe the wave height in a calm sea.

  4. Pulse wave velocity testing in the Baltimore longitudinal study of aging.

    PubMed

    David, Melissa; Malti, Omar; AlGhatrif, Majd; al Ghatrif, Majd; Wright, Jeanette; Canepa, Marco; Strait, James B

    2014-01-01

    Carotid-femoral pulse wave velocity is considered the gold standard for measurements of central arterial stiffness obtained through noninvasive methods(1). Subjects are placed in the supine position and allowed to rest quietly for at least 10 min prior to the start of the exam. The proper cuff size is selected and a blood pressure is obtained using an oscillometric device. Once a resting blood pressure has been obtained, pressure waveforms are acquired from the right femoral and right common carotid arteries. The system then automatically calculates the pulse transit time between these two sites (using the carotid artery as a surrogate for the descending aorta). Body surface measurements are used to determine the distance traveled by the pulse wave between the two sampling sites. This distance is then divided by the pulse transit time resulting in the pulse wave velocity. The measurements are performed in triplicate and the average is used for analysis. PMID:24561745

  5. Variation of the extended s-wave superconducting order parameter: from s-wave to g-wave

    NASA Astrophysics Data System (ADS)

    Kim, Heesang; Chung, H.; Kim, Nammee

    2014-03-01

    It has been reported that the existence of fermi surface nesting may lead to strong anisotropy of order parameter even in phonon-mediated superconductors such as YNi2B2CandLuNi2B2C. The strong k& circ;-dependence may result in nodes as well, and yet the order parameter keeps the full rotational symmetry of the host metal in this case unlike the d-wave in the cuprates. This anisotropic order parameter transforms according to the totally symmetric representation in the group theoretical point of view, and can be classified as an s-wave. It is often called ``an extended s-wave.'' s + g -wave order parameter, studied in connection with the non-magnetic borocarbides, is a good example of the extended s-wave. Here, the effect of variation of the gap anisotropy on superconducting properties of the s + g -wave superconductor is presenteded as a concrete example of the extended s-wave order parameter. Starting from an s-wave, and adding the g-wave component, we investigate the changing shape of the order parameter, evolution of the maximum and minimum of the gap, temperature dependence of the gap amplitude, the density of states, and the specific heat. This work was supported by Basic Science Research program through NRF (grant 2012R1A1A2006303 & 2010-0021328) funded by MEST.

  6. 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.

  7. Crust and upper-mantle velocity structure beneath the northern and central Indian Ocean from the phase and group velocity of Rayleigh and Love waves

    Microsoft Academic Search

    D. D. Singh

    1988-01-01

    Fundamental-mode Rayleigh and Love waves generated by nine earthquakes, which occurred in the central Indian Ocean (with epicentres extending to 40° S) and recorded at seven WWSSN stations of central Asia, have been used to determine the phase and group velocity along various paths across the northern and central Indian Ocean. The dispersion characteristics of Rayleigh and Love waves show

  8. Effects of exciting frequencies, grain sizes, and damage upon P-wave velocity for ultrasonic NDT of concrete

    Microsoft Academic Search

    Jiann W. Ju; Lisheng Weng

    2000-01-01

    This paper focuses on the experimental study of the effects of exciting frequencies, grain (aggregate) sizes, and damage upon the ultrasonic P-wave velocity when performing the ultrasonic nondestructive testing (NDT) for concrete specimens. Two batches of concrete and mortar specimens were prepared in the laboratory for the investigation of the effects from the stated factors upon the P-wave velocity. Damage

  9. Identification of composite materials elastic moduli from Lamb wave velocities measured with single sided, contactless ultrasonic method

    Microsoft Academic Search

    Bernard Hosten; Michel Castaings; Hervé Tretout; Hubert Voillaume

    2001-01-01

    The identification of the elastic properties of composite materials is done from measured phase velocities of Lamb waves. In the purpose to set up an industrial, contactless and single-sided access device for in service inspection of aircrafts, air-coupled, capacitive transducers are used to generate and receive Lamb waves which are sensitive to material properties. The set of phase velocities corresponding

  10. P-wave velocity structure of the crust and uppermost mantle beneath Iceland from local earthquake tomography

    E-print Network

    Shen, Yang

    P-wave velocity structure of the crust and uppermost mantle beneath Iceland from local earthquake tomography Ting Yang*, Yang Shen Graduate School of Oceanography, University of Rhode Island, South Ferry develop a three-dimensional P-wave velocity model of the Icelandic crust and uppermost mantle from

  11. 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 Da?lari) 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), indicating higher than usual temperatures consistent with the influx of asthenosphere to shallow depths as a result of the segmentation and break-up of the subducting African lithosphere.

  12. Determination of elastic anisotropy of rocks from P- and S-wave velocities: numerical modelling and lab measurements

    NASA Astrophysics Data System (ADS)

    Svitek, Tomáš; Vavry?uk, Václav; Lokají?ek, Tomáš; Petružálek, Mat?j

    2014-12-01

    The most common type of waves used for probing anisotropy of rocks in laboratory is the direct P wave. Information potential of the measured P-wave velocity, however, is limited. In rocks displaying weak triclinic anisotropy, the P-wave velocity depends just on 15 linear combinations of 21 elastic parameters, called the weak-anisotropy parameters. In strong triclinic anisotropy, the P-wave velocity depends on the whole set of 21 elastic parameters, but inversion for six of them is ill-conditioned and these parameters are retrieved with a low accuracy. Therefore, in order to retrieve the complete elastic tensor accurately, velocities of S waves must also be measured and inverted. For this purpose, we developed a lab facility which allows the P- and S-wave ultrasonic sounding of spherical rock samples in 132 directions distributed regularly over the sphere. The velocities are measured using a pair of P-wave sensors with the transmitter and receiver polarized along the radial direction and using two pairs of S-wave sensors with the transmitter and receiver polarized tangentially to the spherical sample in mutually perpendicular directions. We present inversion methods of phase and ray velocities for elastic parameters describing general triclinic anisotropy. We demonstrate on synthetic tests that the inversion becomes more robust and stable if the S-wave velocities are included. This applies even to the case when the velocity of the S waves is measured in a limited number of directions and with a significantly lower accuracy than that of the P wave. Finally, we analyse velocities measured on a rock sample from the Outokumpu deep drill hole, Finland. We present complete sets of elastic parameters of the sample including the error analysis for several levels of confining pressure ranging from 0.1 to 70 MPa.

  13. Possible detection of failure wave velocity in SiC using hypervelocity penetration experiments

    NASA Astrophysics Data System (ADS)

    Orphal, D. L.; Kozhushko, A. A.; Sinani, A. B.

    2000-04-01

    Data for projectile penetration of silicon carbide (SiC) from two types of experiments are combined. For impact velocities, v, in the range 1.5-4.6 km/s the data are from reverse ballistic two-stage light-gas gun experiments with long tungsten rods. For impact velocities of about 5-7 km/s copper shaped charge jets are the projectile. The data exhibit an apparent inflection in the penetration velocity, u, versus impact velocity curve at u?3 km/s, corresponding to v?4.5 km/s. The apparent decrease in the slope of u versus v for u>3 km/s, and the consequent rapid increase in the Alekseevskii and Tate target resistance term Rt with v is tentatively interpreted in terms of a failure wave in SiC. With this interpretation the propagation speed of the failure wave in SiC is about 3 km/s or 1/3 of the compressional wave speed.

  14. Elastic wave velocity measurement in multi-anvil apparatus to 10 GPa using ultrasonic interferometry

    NASA Astrophysics Data System (ADS)

    Li, Baosheng; Jackson, Ian; Gasparik, Tibor; Liebermann, Robert C.

    1996-11-01

    Elastic wave velocities of dense fine-grained polycrystalline Al 2O 3 were measured to 10 GPa at room temperature by ultrasonic interferometry within a multi-anvil apparatus. This technique features the use of a WC cube as the acoustic buffer rod allowing the location of 40 MHz LiNbO 3 transducers in a stress-free environment, an in-situ pressure indicator (Bi and/or ZnTe), and a wide frequency range (20 to 70 MHz) for precise (10 -3) measurement of travel times. The specimens recovered from the high-pressure experiments are undamaged and re-usable; and the travel times measured during successive pressure cycles are reproducible within 0.4%. Room pressure velocity measurements for Lucalox alumina yield VP = 10.92 ± 0.05 km s -1 and VS = 6.39 ± 0.03 km s -1. The average pressure derivatives of P and S wave velocities are dV P/dP = 5.4 × 10 -2km s -1 GPa -1 and dV S/dP = 2.2 × 10 -2km s -1 GPa -1 in the pressure range of 3-9.6 GPa, which are consistent with previous results from single-crystal and polycrystal specimens at much lower pressures. This study demonstrates the feasibility of measuring the acoustic wave velocity of mantle minerals at the pressures corresponding to the Earth's transition zone using ultrasonic interferometry in multi-anvil apparatus.

  15. On measuring surface-wave phase velocity from station-station1 cross-correlation of ambient signal2

    E-print Network

    Paris-Sud XI, Université de

    On measuring surface-wave phase velocity from station-station1 cross-correlation of ambient signal2, ambient-noise cross-correlation, and phase and group velocities.22 1 Introduction23 The ability to observe at various depths between the two stations.39 Most authors either extract group velocity vg from its envelope

  16. Longitudinal and seasonal variations of the equatorial ionospheric density and drift velocities during solar minimum

    NASA Astrophysics Data System (ADS)

    Mohapatra, S.; Earle, G. D.

    2010-12-01

    The C/NOFS satellite sensors measure the ion density, electric and magnetic fields, ion drift, ion and electron temperatures, neutral wind, total electron content and ionsopheric scintillation. The extended solar minimum prevailing during C/NOFS mission allow us to establish a baseline model of the seasonal variations of the topside equatorial ionosphere. The 13-degree inclination of the C/NOFS orbit causes the perigee to advances through all local times in about 66 days. This allows seasonal sampling of the ionsopheric density and drift velocity as a function of local time, magnetic latitude, altitude, and longitude. Measurements taken near the spacecraft's perigee at about 420 km altitude indicate an unusually cold low-density ionosphere with an O+ to H+ ratio of approximately 4 during nighttime conditions. Our analysis focuses on the behavior of the longitudinal structure of the equatorial ionospheric density and velocity at all the local times during the equinox months (August 21 to October 21st, February 21 to April 21st), northern summer months (April 21 to August 21st) and northern winter (October 21 to February 21) months for the year 2008 and 2009 near the perigee. The systematic study of the ion velocity and ion density with longitude will reveal new characteristics of the low latitude ionosphere during extreme solar minimum conditions.

  17. Scattering of acoustic waves into Tollmien-Schlichting waves by small streamwise variations in surface geometry

    NASA Technical Reports Server (NTRS)

    Goldstein, M. E.

    1985-01-01

    By using the triple-deck scaling of Stewartson (1969) and Messiter (1970) it is shown that small but relatively sudden surface geometry variations that produce only very weak static pressure variations can nevertheless produce strong, i.e. O(1), coupling between an externally imposed acoustic disturbance and a spatially growing Tollmien-Schlichting wave. The analysis provides a qualitative explanation of the Leehey and Shapiro (1979) boundary-layer receptivity measurements and is in good quantitative agreement with the Aizin and Poliakov (1979) experiment. It may also explain why small 'trip wires' can promote early transition.

  18. [Estimates of velocity of the travelling wave in the high-range cochlea of the dolphin].

    PubMed

    Popov, V V; Supin, A Ia

    2014-07-01

    Auditory brainstem responses (ABR) to sound pulses of precisely defined spectrum band of 0.5 oct (from 11.2-16 to 90-128 kHz) were recorded in bottlenose dolphins Tursiops truncatus. At equal stimulus levels, ABR amplitude depended on the stimulus spectrum band: the higher the frequency, the higher the amplitude. ABR waveform little depended on the stimulus spectrum band, however ABR latency did depend: the higher the frequency, the shorter the latency. The latency difference between responses to the lowest-frequency (11.2-16 kHz) and the highest-frequency (90-129 kHz) stimuli was up to 0.3 ms. This latency difference was attributed to the time of the wave travelling along the basilar membrane. Therefore, the data were used to compute the travelling-wave velocity. The obtained estimates were: 38.2 oct/ms at the proximal (high-frequ- ency) end of the basilar membrane to 2.8 oct/ms at the distal (low-frequency) end. Comparison of the travelling-wave velocities in humans and dolphins shows that the travelling-wave velocity is linked to the characteristic frequency, not to the place in the cochlea. PMID:25669111

  19. Rayleigh Wave Phase Velocity Structure of the Cameroon Volcanic Line Region

    NASA Astrophysics Data System (ADS)

    Shore, P.; Euler, G. G.; Tibi, R.; Wiens, D. A.; Larson, A. M.; Nyblade, A.; Tokam, A. P.; Tabod, C.; Nnange, J. M.; Ateba, B.

    2007-12-01

    The Cameroon Volcanic Line (CVL) is an 1800 km lineament of Cenozoic volcanism that extends from the Gulf of Guinea into Central Africa. With most of the line having experienced recent holocene volcanism, the CVL is one of the more prominent volcanic tracks exhibiting little to no discernible age progression. Previous interpretations of the CVL have been diverse and included volcanic activity associated with laterally transported material from a plume, multiple plumes, rift-flank processes, plate-driven Richter rolls, plume-fed small-scale convection cells, or propagating lithosphere cracks in order to reconcile the lack of age progression with the strong linearity and position of the CVL. Discriminating between these models can be significantly aided by the determination of the extent and depth of the source of the volcanism. In early 2005, a dense broadband seismometer array located over the continental section of the CVL was deployed to image the underlying mantle structure and resolve the source of the volcanism. This two-year PASSCAL deployment consisted of 8 trial stations for the first year and the following year was upgraded to 32 stations with a station spacing of 50 to 200 km. We present preliminary results of surface wave phase velocity maps from this new dataset that successfully image a low-velocity anomaly beneath the CVL as well as high velocities associated with the lithosphere of the Congo Craton. Phase velocity maps were determined by an inversion of teleseismic Rayleigh waves with Forsyth and Lee's two-plane wave method to reduce bias from multipathing. The low-velocity anomaly is observed over a period range of 20 to 140 s suggesting that the CVL anomaly extends across a substantial depth range of the lithosphere and asthenosphere. Furthermore, the lowest velocities of the anomaly are centered at the junction of the 'Y' in the volcanic track, 400 km northeast (inland) of the CVL's largest active volcano Mt. Cameroon.

  20. Planetary Wave Influence on Wintertime OH Meinel Longitudinal Variation?

    NASA Astrophysics Data System (ADS)

    Winick, J. R.; Picard, R. H.; Wintersteiner, P. P.; Mlynczak, M. G.; Russell, J. M.; Gordley, L.

    2009-05-01

    We report on very unusual conditions in the upper mesosphere during the boreal winters of 2004 and 2006. Unusually bright OH volume emissions, as measured by TIMED/SABER, occurred in the region north of 60N. These emissions also occurred at unusually low altitudes, while at the same time very high temperatures characterized the upper mesosphere. These large perturbations allowed us to see more clearly longitudinal spatial and temporal variations that were present in the emissions. The affected areas varied in size and location on time scales of a few days and had a distinct planetary-wave wave-1 structure. We present data demonstrating the variability in the emissions and temperatures throughout the polar region and the correlations among them, and we contrast their behavior with that in normal years. The underlying cause of the correlations and longitudinal structure appears to be greatly enhanced downwelling in the upper mesosphere, which in turn was produced by unusual dynamical conditions in the lower atmosphere, consisting of stratospheric warmings and perturbations of wave structures within the polar vortex.

  1. Magnetic Activity–related Radial Velocity Variations in Cool Stars: First Results from the Lick Extrasolar Planet Survey

    Microsoft Academic Search

    Steven H. Saar; R. Paul Butler; Geoffrey W. Marcy

    1998-01-01

    The discovery of the radial velocity ( ) signatures of planets around several solar-like stars highlights the v rimportance of exploring the sources of variations intrinsic to the stars themselves. We study the stars in the v rLick planetary survey for variations related to stellar activity: the rotation of starspots and convective inhomv rogeneities and their temporal evolution. We study

  2. Generation of dispersive acoustic waves by the phase velocity scanning of a laser beam

    NASA Astrophysics Data System (ADS)

    Yamanaka, Kazushi; Nagata, Yoshihiko; Koda, Toshio

    The laser beam phase velocity scanning (PVS) method can selectively generate single-mode surface acoustic waves (SAWs) in multirole media for noncontacting NDT. The laser's rapid scanning causes a heat pulse, and the SAW generated by this pulse is coherently amplified when the dispersion is small. MHz-range SAWs are thus obtainable with greater-than-1 nm amplitude; the temperature increase of the tested object can be suppressed to less than 1 K. Dispersion curves are easily obtained by changing the scanning velocity.

  3. Higher Brachial-Ankle Pulse Wave Velocity Is Associated with More Advanced Carotid Atherosclerosis in End-Stage Renal Disease

    Microsoft Academic Search

    Masanori Munakata; Junko Sakuraba; Jun Tayama; Takashi Furuta; Akira Yusa; Tohru Nunokawa; Kaoru Yoshinaga; Takayoshi Toyota

    2005-01-01

    Brachial-ankle pulse wave velocity is a new measure of arterial stiffness. We examined whether higher brachial-ankle pulse wave velocity is associated with more advanced carotid atherosclerosis and left ventricular hypertrophy in patients with end-stage renal disease, and whether this effect would be mediated by the influence of wave reflection on central arterial pressure. In 68 patients with end stage renal

  4. Imaging Near-Surface Buried Structure with High-Resolution Surface-Wave Group-Velocity Tomography

    Microsoft Academic Search

    Jeffrey T. Martin; Toshiro Kubota; L. Timothy Long

    2000-01-01

    Often costs or hazardous conditions prohibit geophysical measurements within the survey area. Surface-wave tomography can be a practical method of imaging the near surface shear-wave velocity structure. We demonstrate that this method can resolve meter-size objects. Surface-wave group-velocity travel times along ray-paths through the survey area are determined as a function of frequency by using the \\

  5. Measurements of the changing wave velocities of sand during the formation and dissociation of disseminated methane hydrate

    NASA Astrophysics Data System (ADS)

    Sultaniya, A. K.; Priest, J. A.; Clayton, C. R. I.

    2015-02-01

    The formation and dissociation of methane hydrate within sediment can lead to large changes in wave velocities, which provide valuable insights into the processes involved in hydrate formation. These are of practical importance in geophysical characterization, as well as developing strategies for the future exploitation of methane hydrates. This paper presents changes in wave velocity, measured during hydrate formation, and subsequent dissociation, using the resonant column apparatus. Hydrate was formed under "drained" and "undrained" conditions. Drained specimens had free access to methane during formation, while for undrained specimens, methane content was fixed. Hydrate formation and dissociation were induced by changing the specimen temperature under constant effective stress. In excess of 20 determinations of shear wave and flexural wave velocity were carried out over a 9 h period, both during hydrate formation and dissociation. This time was sufficient to record almost all of the changes in wave velocity within a specimen. The exothermic nature of hydrate formation was clearly seen in the form of spikes in temperature measured at the base of the specimens. For all specimens, the relationship between wave velocity and degree of hydrate saturation was nonlinear and significantly different during formation and dissociation. The patterns observed suggest that hydrate morphology not only is important in controlling the ultimate wave velocities, at the end of formation, but has a significant impact on the rates of change of wave velocities during formation and dissociation. A conceptual model is presented to explain differences in observed behavior during formation and dissociation.

  6. wave velocity group velocity

    E-print Network

    Walker, D. Greg

    thermalized boundary · · · · Partitioning of phonon energy to electronic energy is comparable Localized phonon) equilibrium strike distribution is averaged over entire domain at 25 picoseconds The distribution of phonons. - Seitz and Koehler (1956) solve Boltzmann transport equations Monte Carlo approach is used to· 90 100 3e

  7. Lateral variations in SH velocity structure of the transition zone beneath Korea and adjacent regions

    NASA Astrophysics Data System (ADS)

    Zhang, Ruiqing; Wu, Qingju; Li, Yonghua; Romanowicz, Barbara

    2012-09-01

    Using seismic profiles of triplicated waveforms, we show significant lateral variations in the SH velocity (Vs) structure of the transition zone (TZ) beneath Korea and adjacent regions. Beneath Sakhalin, we detected a high Vsanomaly (˜2%) limited to middle regions of the TZ (mid-TZ), and a largeVsjump across the 660-km discontinuity. A similar jump inVs also occurs beneath the northern portion of the North China Craton (NCC). Beneath Korea, a high Vs anomaly (˜2%) in the lower TZ is inferred, accompanied by a relatively small Vsjump across the 660-km discontinuity, which is depressed by about ˜15-20 km. The deep structure under the eastern part of northeast China (NEC) also includes a slightVsanomaly (˜1%) in the lower TZ but does not exhibit significant depression of the 660-km discontinuity. Compared with previous study, our observations reveal strong regional variations of the TZ structure on a relatively short scale. These variations most likely reflect the geometrical distribution of the subducting northwest Pacific plate. Our results suggest that the subducting slab dips across the mid-TZ under Sakhalin, and becomes flattened atop of the 660-km discontinuity beneath Korea, while only the tip of the slab reaches the lower TZ beneath the NEC. The TZ beneath the NCC does not show evidence of the slab stagnation.

  8. Extensional wave attenuation and velocity in partially saturated sand in the sonic frequency range

    SciTech Connect

    Liu, Z.; Rector, J.W.; Nihei, K.T.; Tomutsa, L.; Myer, L.R.; Nakagawa, S.

    2001-08-10

    Extensional wave attenuation and velocity measurements on a high permeability Monterey sand were performed over a range of gas saturations for imbibition and degassing conditions. These measurements were conducted using extensional wave pulse propagation and resonance over a 1-9 kHz frequency range for a hydrostatic confining pressure of 8.3 MPa. Analysis of the extensional wave data and the corresponding X-ray CT images of the gas saturation show strong attenuation resulting from the presence of the gas (Q{sub E} dropped from 300 for the dry sand to 30 for the partially-saturated sand), with larger attenuation at a given saturation resulting from heterogeneous gas distributions. The extensional wave velocities are in agreement with Gassmann theory for the test with near-homogeneous gas saturation and with a patchy saturation model for the test with heterogeneous gas saturation. These results show that partially-saturated sands under moderate confining pressure can produce strong intrinsic attenuation for extensional waves.

  9. Rarefaction wave propagation and longitudinal sound velocities in shock compressed tantalum

    NASA Astrophysics Data System (ADS)

    Scharff, Robert

    2013-06-01

    The purpose of this work is to investigate the bcc to hexagonal structural phase transition recently reported for shock compressed tantalum. Longitudinal sound velocities were obtained using a velocimetry diagnostic to record the shock and rarefaction wave arrival times at the sample/anvil interface in the reverse-ballistic plate impact geometry. This approach allows for the determination of the sound speed as a function of pressure and is sensitive to volume changes associated with phase transition behavior. The authors demonstrate that if elastic - plastic wave interactions are correctly determined, then the high pressure structural phase transition that has been previously reported is notably absent.

  10. Rarefaction wave propagation and longitudinal sound velocities in shock compressed tantalum to 105 GPa

    NASA Astrophysics Data System (ADS)

    Scharff, Robert; Rigg, Paulo; Hixson, Robert

    2013-03-01

    The purpose of this work is to investigate the bcc to hexagonal structural phase transition recently reported for shock compressed tantalum. Longitudinal sound velocities were obtained using a velocimetry diagnostic to record the shock and rarefaction wave arrival times at the sample/anvil interface in the reverse-ballistic plate impact geometry. This approach allows for the determination of the sound speed as a function of pressure and is sensitive to volume changes associated with phase transition behavior. The authors demonstrate that if elastic - plastic wave interactions are correctly determined, then the high pressure structural phase transition that has been previously reported is notably absent.

  11. Transitional continental-oceanic structure beneath the Norwegian Sea from inversion of surface wave group velocity data

    Microsoft Academic Search

    V. Midzi; D. D. Singh; K. Atakan; J. Havskov

    1999-01-01

    We have analysed the fundamental mode of Love and Rayleigh waves generated by 12 earthquakes located in the mid-Atlantic ridge and Jan Mayen fracture zone. Using the multiple filter analysis technique, we isolated the Rayleigh and Love wave group velocities for periods between 10 and 50 s. The surface wave propagation paths were divided into five groups, and average group

  12. Vertical velocities associated with gravity waves measured in the mesosphere and lower thermosphere with the EISCAT VHF radar

    E-print Network

    Paris-Sud XI, Université de

    Vertical velocities associated with gravity waves measured in the mesosphere and lower thermosphere. The data reveal a motion ®eld dominated by quasi-monochromatic gravity waves with represen- tative apparent advanced to explain gravity-wave spectra. The spectral slopes evaluated for individual days have a range

  13. 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 lithological sequence gives rise to a ubiquitous peak between 1 and 2 Hz which is observed in all the studied sites and is in agreement with studies previously done on the islands. The H/V curve and the Rayleigh wave dispersion curve were then jointly inverted using a genetic algorithm, considering higher modes, so that the Vs profiles are obtained. All the curves were well fitted and the 10 final profiles extracted in each process show a good agreement especially in the velocity and thickness of the BC layer, emphasizing the sensitivity of the curves to this layer. Regional differences were observed for the velocities in the UCL and BC, e.g. highly fractured UCL demonstrates a lower Vs. The Vs in the clay also varied according to the depth of burial of the clay, clearly increasing from a surface outcrop of BC to a deeply buried layer. This could essentially be linked to the effective pressure caused by the UCL overburden which makes the BC more compact and having a higher Vs. Comparisons are also done with one particular site in Malta where the BC layer is not present in the geological sequence.

  14. Three-dimensional P and S wave velocity structures of southern Peru and their tectonic implications

    NASA Technical Reports Server (NTRS)

    Cunningham, Paul S.; Roecker, Steven W.; Hatzfeld, Denis

    1986-01-01

    Arrival times of compressional and shear (S) waves from microearthquakes recorded in 1981 by an 18-station regional array are used to study the three-dimensional velocity structure of the crust and upper mantle of the central Andes. The data suggest a crustal thickness of about 40 km beneath the coast, increasing to about 70 km beneath the Cordillera Occidental. The inverse correlation between the dip in the Moho and the dip of the slab may indicate a broad-scale causal relation between the two. S wave velocities in the mantle between 70 and 130 km depth above the 30-degree dipping slab are low, possibly indicating the presence of a partially melted asthenosphere that may be responsible for the magmatic activity recorded in southern Peru.

  15. The velocity structure of the Carpathian zone from the ambient noise surface wave tomography

    NASA Astrophysics Data System (ADS)

    Yanovskaya, T. B.; Lyskova, E. L.; Koroleva, T. Yu.

    2014-09-01

    The dispersion curves of the Rayleigh wave group velocities are constructed along 60 interstation seismic paths in Central Europe based on the cross-correlation function of seismic noise. Together with the previous data (Yanovskaya and Lyskova, 2013), this information was used for reconstructing the three-dimensional distribution of S-wave velocities in the upper mantle of the Carpathian region. In the present work, the previous results are refined by expanding the data set by the additional seismic paths that intersect the Carpathian region and by modifying the procedure for constructing the locally averaged dispersion curves so as to obtain a more compact resolution. The results of the study suggest the complex, multidirectional character of the plate motion in the region.

  16. Influence of pressure on permeability and elastic wave velocities in macro- and micro-fractured rock

    NASA Astrophysics Data System (ADS)

    Meredith, Philip; Nara, Yoshitaka; Yoneda, Tetsuro; Kaneko, Katsuhiko

    2010-05-01

    Long-term integrity is required for many sub-surface structures excavated in the rock mass; such as repositories for radioactive wastes and caverns for the storage of liquid petroleum gas and natural gas. An essential requirement for long-term integrity is to retard the migration of fluids into and through these structures. In crustal rocks, fracture and pore networks provide the principal pathways for fluid flow. However, if fractures and pores are closed or sealed, the migration of fluids can be retarded. Thus it is important to study the process of fracture and pore closure. Here, we report changes in the fluid permeability and P- and S-wave velocities of intact, macro-fractured, and micro-fractured rock sample subjected to elevated effective pressures. In order to investigate the influence of pressure on the closure of macro-fractures and micro-fractures, we used a rock sample with no visible pre-existing cracks and very low initial permeability. For this reason, Seljadur basalt (SB) from Iceland was chosen as the sample material. SB is a fresh, columnar-jointed, intrusive basalt with a porosity of 4 % and no visible microcracks. Permeability was measured in a servo-controlled permeameter using the steady-state flow method. The permeameter is equipped with transducers that allow the simultaneous measurement of P- and S-wave velocities. The wave velocities were measured by the ultrasonic transmission method. Measurements of permeability and elastic wave velocities were first made on intact samples. The Brazil test technique was then used to split the samples in half to provide macro-fractured sample for further testing. Measurments of permeability and elastic wave velocities were then made on the macro-fractured sample in order to investigate the effect of fracture closure. Then, we heated the macro-fractured sample at 800 degree Celsius in order to produce micro-fractures in the sample and conducted further measurements of permeability and wave velocities. It was shown that the permeability of intact SB was low and remains essentially constant over the whole effective pressure range. By contrast, the permeability of the macro-fractured SB was initially much higher, but decreased clearly as effective pressure was increased and the fracture became closed. The permeability of the macro- and micro-fractured SB also decreased with increasing the pressure. The permeability of the macro- and micro-fractured SB was similar to that of the macro-fractured SB under low pressure. This result indicates that the open macro-fractures dominate the permeability under low pressure. On the other hand, the permeability of the macro-and micro-fractured SB was higher than that of the macro-fractured SB under high pressure. This indicates that the macro-fractures with low aspect ratio close easily and open micro-fractures with high aspect ratio become dominant to the permeability with increasing the pressure. The difference in the wave velocities between intact, macro-fractured, and macro- and micro-fractured samples decreased with increasing effective pressure, tracking the closure of the fractures. Specifically, the increase of S-wave velocity vibrating nornal to the macro-fractures was clear with increasing the pressure, which indicates the closure of fracture. Overall, results in this study demonstrate the importance of the closure of fractures to increase the shielding ability of rock and to retard the migration of fluids into and through structres in a rock mass.

  17. Collisional and wave-particle interactions in critical-velocity ionization

    Microsoft Academic Search

    W. J. McNeil; S. T. Lai; E. Murad

    1989-01-01

    Alfven's critical ionization velocity (CIV) process involves collective and collisional interactions of a magnetoplasma streaming through a neutral gas. Numerical simulations of CIV are reported using particle-in-cell plasma codes including various collisional interactions. Fast electron heating is observed. The interplay between collisional and collective interactions renders the hot electron tail shorter than in non-CIV situations with collisionless wave-particle interactions without

  18. A simple method for evaluating liquefaction potential from shear wave velocity

    Microsoft Academic Search

    Lianyang Zhang

    2010-01-01

    The simplified procedure using shear wave velocity measurements is increasingly used to evaluate the seismic liquefaction\\u000a potential of soils. This procedure is based on finding the boundary separating the liquefaction and non-liquefaction cases\\u000a through the analysis of liquefaction case histories, following the general format of the Seed-Idriss simplified procedure\\u000a based on standard penetration test (SPT) data. It is noted that

  19. Elastic-wave velocity in marine sediments with gas hydrates: Effective medium modeling

    Microsoft Academic Search

    M. B. Helgerud; J. Dvorkin; A. Nur; A. Sakai; T. Collett

    1999-01-01

    We offer a first-principle-based effective medium model for elastic-wave velocity in unconsolidated, high porosity, ocean bottom sediments containing gas hydrate. The dry sediment frame elastic constants depend on porosity, elastic moduli of the solid phase, and effective pressure. Elastic moduli of saturated sediment are calculated from those of the dry frame using Gassmann's equation. To model the effect of gas

  20. Rayleigh-wave Group Velocity Tomography in the Vicinity of the Hawaiian Hotspot

    Microsoft Academic Search

    A. E. Strader; G. Laske; J. A. Orcutt; C. J. Wolfe; J. A. Collins; S. C. Solomon; R. S. Detrick; D. Bercovici; E. H. Hauri

    2009-01-01

    We present maps of long-period Rayleigh wave group velocity maps for the area spanned by the Hawaiian PLUME (Plume-Lithosphere Undersea Mantle Experiment) project. Specifically, we used observations from the second deployment of ocean-bottom and land broadband instruments that operated from April 2006 through May 2007. The recording network consisted of13 land stations with ten temporary and three observatory instruments and

  1. Distribution characteristics of Rayleigh wave group velocity in China mainland and its adjacent sea areas

    Microsoft Academic Search

    Zhong-He Song; Guo-Ying Chen; Chang-Qiang An; Li-Hua Chen; Zhen Zhuang; Zhu-Wu Fu; Zi-Ling Lü; Jia-Fu Hu

    1993-01-01

    Making use of 75 earthquake data of China mainland and adjacent areas recorded by long period seismometers of 27 stations\\u000a of China and 3 stations of WWSSN and processed by match-filtering frequency-time analysis technique and grid dispersion inversion,\\u000a the authors obtain pure-path dispersion curves of Rayleigh surface wave in 147 grids in this paper.\\u000a \\u000a The distribution characteristics of group velocity

  2. Elastic wave velocity measurement in multi-anvil apparatus to 10 GPa using ultrasonic interferometry

    Microsoft Academic Search

    L. Baosheng; Ian Jackson; Tibor Gasparik; Robert C. Liebermann

    1996-01-01

    Elastic wave velocities of dense fine-grained polycrystalline Al2O3 were measured to 10 GPa at room temperature by ultrasonic interferometry within a multi-anvil apparatus. This technique features the use of a WC cube as the acoustic buffer rod allowing the location of 40 MHz LiNbO3 transducers in a stress-free environment, an in-situ pressure indicator (Bi and\\/or ZnTe), and a wide frequency

  3. A wind tunnel study of air flow in waving wheat: Single-point velocity statistics

    Microsoft Academic Search

    Y. Brunet; J. J. Finnigan; M. R. Raupach

    1994-01-01

    We analyse single-point velocity statistics obtained in a wind tunnel within and above a model of a waving wheat crop, consisting of nylon stalks 47 mm high and 0.25 mm wide in a square array with frontal area index 0.47. The variability of turbulence measurements in the wind tunnel is illustrated by using a set of 71 vertical traverses made

  4. Effect of cracks on the pressure dependence of P wave velocities in crystalline rocks

    Microsoft Academic Search

    Richard L. Carlson; Anthony F. Gangi

    1985-01-01

    To test the ``bed of nails'' model, we have made detailed measurements of P wave velocities in five low-porosity, crystalline rocks at effective pressures to 500 MPa and fit two equations based on the model to the laboratory data. The first equation, V(P) =V0(1+P\\/Pi)(1-m)\\/2, applies at relatively low pressures because it assumes that the grain modulus is very much larger

  5. Permeability and P-wave velocity change in granitic rocks under freeze–thaw cycles

    Microsoft Academic Search

    M. Takarli; W. Prince

    2007-01-01

    An extensive experimental investigation of microstructural changes in granites under freeze–thaw cycles using permeability and P-wave velocity measurements is described. Two types of natural granite rocks are considered and tested under dry and saturated conditions. The specimens were subjected to 200 heating–cooling cycles (??20°C\\/?+?20°C); each cycle had a duration of 24 h. The results indicate that the ageing process decreases the

  6. Structure of the Crust beneath Cameroon, West Africa, from the Joint Inversion of Rayleigh Wave Group Velocities and Receiver Functions

    SciTech Connect

    Tokam, A K; Tabod, C T; Nyblade, A A; Julia, J; Wiens, D A; Pasyanos, M E

    2010-02-18

    The Cameroon Volcanic Line (CVL) is a major geologic feature that cuts across Cameroon from the south west to the north east. It is a unique volcanic lineament which has both an oceanic and a continental sector and consists of a chain of Tertiary to Recent, generally alkaline volcanoes stretching from the Atlantic island of Pagalu to the interior of the African continent. The oceanic sector includes the islands of Bioko (formerly Fernando Po) and Sao Tome and Principe while the continental sector includes the Etinde, Cameroon, Manengouba, Bamboutos, Oku and Mandara mountains, as well as the Adamawa and Biu Plateaus. In addition to the CVL, three other major tectonic features characterize the region: the Benue Trough located northwest of the CVL, the Central African Shear Zone (CASZ), trending N70 degrees E, roughly parallel to the CVL, and the Congo Craton in southern Cameroon. The origin of the CVL is still the subject of considerable debate, with both plume and non-plume models invoked by many authors (e.g., Deruelle et al., 2007; Ngako et al, 2006; Ritsema and Allen, 2003; Burke, 2001; Ebinger and Sleep, 1998; Lee et al, 1994; Dorbath et al., 1986; Fairhead and Binks, 1991; King and Ritsema, 2000; Reusch et al., 2010). Crustal structure beneath Cameroon has been investigated previously using active (Stuart et al, 1985) and passive (Dorbath et al., 1986; Tabod, 1991; Tabod et al, 1992; Plomerova et al, 1993) source seismic data, revealing a crust about 33 km thick at the south-western end of the continental portion of the CVL (Tabod, 1991) and the Adamawa Plateau, and thinner crust (23 km thick) beneath the Garoua Rift in the north (Stuart et al, 1985) (Figure 1). Estimates of crustal thickness obtained using gravity data show similar variations between the Garoua rift, Adamawa Plateau, and southern part of the CVL (Poudjom et al., 1995; Nnange et al., 2000). In this study, we investigate further crustal structure beneath the CVL and the adjacent regions in Cameroon using 1-D shear wave velocity models obtained from the joint inversion of Rayleigh wave group velocities and P-receiver functions for 32 broadband seismic stations. From the 1-D shear wave velocity models, we obtain new insights into the composition and structure of the crust and upper mantle across Cameroon. After briefly reviewing the geological framework of Cameroon, we describe the data and the joint inversion method, and then interpret variations in crustal structure found beneath Cameroon in terms of the tectonic history of the region.

  7. Wave Velocity Attenuation and Sediment Retention among Different Vegetation Types in a Pacific Northwest Estuary

    NASA Astrophysics Data System (ADS)

    Lemein, T.; Cox, D. T.; Albert, D.; Blackmar, P.

    2012-12-01

    Feedbacks between vegetation, wave climate, and sedimentation create stable ecosystem states within estuaries that provide ecosystem services such as wildlife habitat, erosion control, and pollution filtration. Flume and field studies conducted with cordgrass (Spartina spp.) and sea grasses (Zostera spp., Halodule spp.) have demonstrated that the presence of vegetation reduces wave energy and increases sediment retention. Since the spatial distribution of plant species and the presence of unique plant species differ between estuaries, there is a need to understand how individual plant species, or groups of species with similar morphology, influence wave characteristics and sedimentation. Within Tillamook Bay, Oregon, three species of emergent vascular vegetation species (Carex lyngbyei, Eleocharis sp., Schoenoplectus pungens) and one species of submergent vascular vegetation species (Zostera marina) are present in the high wave energy portion of the estuary at the border of open water and the start of vegetation. These species represent three distinct growth forms (emergent reeds, emergent grasses, submergent grasses) and occur at varying densities relative to each other, as well as within the estuary. Using paired acoustic Doppler velocimeters (ADVs), we quantify the relative attenuation of wave velocity between vegetation types and densities within the estuary and compare these results with published attenuation rates from flume and field studies in different environments. The effect of decreased wave velocity on sediment retention is measured using permanent sediment markers within and outside of vegetation stands and paired with ADV data. Sediment retention is predicted to vary seasonally with seasonal vegetation composition changes and remain constant in unvegetated areas. From this experiment we expect to identify like groups of plant species whose attenuation characteristics are the same, allowing for models of wave-vegetation-sediment interaction to be created with multiple vegetation types.

  8. P-wave velocity anomalies of the plume beneath the French Polynesia

    NASA Astrophysics Data System (ADS)

    Obayashi, Masayuki; Yoshimitsu, Junko; Sugioka, Hiroko; Ito, Aki; Isse, Takehi; Shiobara, Hajime; Suetsugu, Daisuke

    2015-04-01

    The French Polynesian region is characterized by positive topographic anomalies of 700 m, a concentration of hotspot chains. Many seismic tomography results show a broad low-velocity anomaly in the lower mantle continued from the base of the mantle. These observations suggest that a large-scale mantle flow rises from the bottom of the mantle beneath the region. Joint Japanese-French broadband seismological observations were performed from 2001 to 2005 with 10 island stations from the Polynesian PLUME project (Barruol et al. 2002) and 10 broadband ocean bottom seismometers (BBOBSs) from the Polynesian BBOBS project (Suetsugu et al. 2005). A P-wave tomography using the data from these projects revealed that large-scale low-velocity anomalies (on the order of 1000 km in diameter) from the bottom of the mantle become smaller-scale low-velocity anomalies (on the order of 100 km in diameter) at the depth of about 1000 km. However the connection of the small-scale low-velocity anomalies to the surface hotspots was not unrevealed because of the poor resolution in the upper mantle. A new P-wave tomography with better resolution in the upper mantle was obtained by adding data from BBOSBSs around Society Islands deployed along the TIARES project during 2009 - 2010 (Suetsugu et al. 2012) and by taking the finite frequency effect into account for the frequency-depended differential travel times. The frequency-depended differential travel times were measured by multi-band cross correlating P waveforms. The new P-wave tomography shows strong low-velocity anomalies beneath the Society Islands and Pitcairn in the upper mantle although they do not extend to the 660-km discontinuity. This model also shows that small-scale low-velocity anomalies in the uppermost lower mantle. The low-velocity anomalies in the depth range about 550 - 900 km are smaller both in lateral area and amplitude than those in most of the upper mantle and the lower mantle. The velocity patterns are well correlated each other in the depth range but are not correlated with the patterns above and below, indicating the mantle beneath the French polynesia can be divided into 3 layers in terns of radial correlation.

  9. Effect of compositional variation on the shock wave response of bulk amorphous alloys

    NASA Astrophysics Data System (ADS)

    Jaglinski, T.; Turneaure, Stefan J.; Gupta, Y. M.

    2012-09-01

    The objective of this work was to determine how variations in composition influence the shock wave response of bulk amorphous alloys (BAAs). Toward this end, (Hf,Zr)-based bulk amorphous alloy specimens (nominal composition of (Hf0.5Zr0.5)56.7Cu15.3Ni12.5Nb5.0Al10.0Y0.5) were subjected to peak stresses of 4-16 GPa in plate impact experiments and their response was compared to a previously studied Zr-based BAA (nominal composition of Zr56.7Cu15.3Ni12.5Nb5.0Al10.0Y0.5). The (Hf,Zr)-based BAA displayed a Hugoniot elastic limit (HEL) of ˜7.4 GPa corresponding to an elastic strain of 4.3%. (Hf,Zr)-based BAAs shock compressed above the HEL exhibited distinct two wave structures, small elastic precursor relaxation, non-steady plastic waves, and strength loss. All of these features are qualitatively similar to previous observations in various Zr-based BAAs. One dimensional wave propagation simulations incorporating a strain-softening strength model, developed previously for a Zr-based BAA, showed excellent agreement between measured and simulated particle velocity histories for the (Hf,Zr)-based BAA. The only significant differences in the shock wave responses of the (Hf,Zr)-based alloy and the Zr-based alloy are elastic shock velocity and plastic shock velocity differences which are due to the different ambient densities and different elastic moduli for the two alloy compositions. These findings demonstrate that, apart from differences related to ambient density and elastic stiffness, the substitution of Hf for 50% of the Zr did not significantly alter the shock compression response of the (Hf,Zr)-based BAA as compared to the previously examined Zr-based BAA. Based on the results of this study and other relevant data in the literature, it is expected that monolithic BAAs displaying brittle quasi-static compression behavior will likely display shock compression response that is comparable to Zr-based and (Hf,Zr)-based BAAs.

  10. Non-Doppler shift related experimental shock wave measurements using velocity interferometer systems for any reflector

    SciTech Connect

    Forsman, A. C.; Kyrala, G. A.

    2001-05-01

    Velocity interferometer system for any reflectors (VISARs), are becoming increasingly popular in the measurement of shock waves in solids and liquids. VISAR techniques are used in measurements of transit time, speed of shock waves in flight in transparent media [L. C. Chhabildas and J. L. Wise, in Proceedings of the 4th APS Topical Conference on Shock Waves in Condensed Matter, Spokane, Washington, 1985, edited by Y. M. Gupta (Plenum, New York, 1986); P. M. Celliers , Appl. Phys. Lett. 73, 1320 (1998)], and in measurements of particle velocity. However, in cases where shock compression or release may change the index of refraction n+ik of the material being studied, the VISAR technique must be applied with care. Changes in n and k introduce phase shifts into the VISAR results that are not associated with changes in velocity. This paper presents a derivation of the theoretical output of a line VISAR that includes the effects of changing n and k and an experimental observation of a non-Doppler shift related effect.

  11. Non-Doppler shift related experimental shock wave measurements using velocity interferometer systems for any reflector

    NASA Astrophysics Data System (ADS)

    Forsman, A. C.; Kyrala, G. A.

    2001-05-01

    Velocity interferometer system for any reflectors (VISARs), are becoming increasingly popular in the measurement of shock waves in solids and liquids. VISAR techniques are used in measurements of transit time, speed of shock waves in flight in transparent media [L. C. Chhabildas and J. L. Wise, in Proceedings of the 4th APS Topical Conference on Shock Waves in Condensed Matter, Spokane, Washington, 1985, edited by Y. M. Gupta (Plenum, New York, 1986); P. M. Celliers et al., Appl. Phys. Lett. 73, 1320 (1998)], and in measurements of particle velocity. However, in cases where shock compression or release may change the index of refraction n+ik of the material being studied, the VISAR technique must be applied with care. Changes in n and k introduce phase shifts into the VISAR results that are not associated with changes in velocity. This paper presents a derivation of the theoretical output of a line VISAR that includes the effects of changing n and k and an experimental observation of a non-Doppler shift related effect.

  12. Time-dependent three dimensional P-wave velocity models derived for the Geysers geothermal field

    NASA Astrophysics Data System (ADS)

    Friberg, P. A.; Roecker, S. W.; Dricker, I. G.; Lisowski, S.; Hellman, S. B.

    2011-12-01

    The Geysers geothermal field is a source of significant small earthquake (M< 2.0) seismicity in northern California. The region has been actively monitored for seismicity, both natural and induced, since the geothermal field has been put into production. A modern digital seismic monitoring network in the area consists of 34 LBNL/Calpine (BG) borehole short-period and 12 Northern California Seismic Network (NCSN) network surface short-period seismic stations. The USGS has auto-located approximately 25,033 earthquakes (NCEDC catalog) for the years 2009 and 2010 combined from the composite seismic network. Using the auto-located solutions and a Geysers specific one-dimensional velocity model (Eberhart-Philips and Oppenheimer, 1984) as a starting point, we have simultaneously inverted for three dimensional P-wave velocities for each year's data set. Before beginning the inversion we established that the automatic S-phase picks were too unstable and thus focused only on the P-wave velocities. After culling events with initial RMS uncertainty greater than 0.06 seconds, we start with 7,403 earthquakes in 2009 and 11,199 earthquakes in 2010. The technique we use is a finite-difference travel time technique that Roecker et al. (Tectonophysics, 2006) used for the Parkfield SAFOD site. We will present the results of the simultaneous inversion for each of the 2009 and 2010 years along with plots of the seismicity relocated using these new velocity models.

  13. Attenuation and velocity structure from diffuse coda waves: Constraints from underground array data

    NASA Astrophysics Data System (ADS)

    Galluzzo, Danilo; La Rocca, Mario; Margerin, Ludovic; Del Pezzo, Edoardo; Scarpa, Roberto

    2015-03-01

    An analysis of coda waves excited in the 0.2-20 Hz frequency band and recorded by the underground array Underseis (central Italy) has been performed to constrain both seismic attenuation at regional scale and velocity structure in the Mount Gran Sasso area. Attenuation was estimated with the MLTWA method, and shows a predominance of scattering phenomena over intrinsic absorption. The values of Qi and Qs are compatible with other estimates obtained in similar tectonic environments. Array methods allowed for a detailed study of the propagation characteristics, demonstrating that earthquake coda at frequencies greater than about 6 Hz is composed of only body waves. Coherence and spectral characteristics of seismic waves measured along the coda of local and regional earthquakes indicate that the wavefield becomes fully diffuse only in the late coda. The frequency-dependent energy partitioning between horizontal and vertical components has been also estimated and compared with synthetic values computed in a layered half-space under the diffuse field assumption. This comparison confirms that, for frequencies higher than 6 Hz, the coda appears as a sum of body waves coming from all directions while, in the low frequency range (0.2-2 Hz), the observations can be well explained by a coda wavefield composed of an equipartition mixture of surface and body waves traveling in a multiple-layered medium. A Monte-Carlo inversion has been performed to obtain a set of acceptable velocity models of the upper crust. The present results show that a broadband coda wavefield recorded in an underground environment is useful to constrain both the regional attenuation and the velocity structure of the target area, thereby complementing the results of classical array analysis of the wavefield.

  14. Dust-acoustic solitary waves and double layers in a magnetized dusty plasma with nonthermal ions and dust charge variation

    SciTech Connect

    El-Taibany, W.F.; Sabry, R. [Department of Physics, Faculty of Science-Damietta, Mansoura University, Damietta El-Gedida, P.O. 34517 (Egypt)

    2005-08-15

    The effect of nonthermal ions and variable dust charge on small-amplitude nonlinear dust-acoustic (DA) waves is investigated. It is found that both compressive and rarefactive solitons exist and depend on the nonthermal parameter a. Using a reductive perturbation theory, a Zakharov-Kuznetsov (ZK) equation is derived. At critical value of a, a{sub c}, a modified ZK equation with third- and fourth-order nonlinearities, is obtained. Depending on a, the solution of the evolution equation reveals whether there is coexistence of both compressive and rarefactive solitary waves or double layers (DLs) with the possibility of their two kinds. In addition, for certain plasma parameters, the solitary wave disappears and a DL is expected. The variation of dust charge number, wave velocity, and soliton amplitude and its width against system parameters is investigated for the DA solitary waves. It is shown that the incorporation of both the adiabatic dust-charge variation and the nonthermal distributed ions modifies significantly the nature of DA solitary waves and DA DLs. The findings of this investigation may be useful in understanding the ion acceleration mechanisms close to the Moon and also enhances our knowledge on pickup ions around unmagnetized bodies, such as comets, Mars, and Venus.

  15. Ultrasonic wave velocity measurement in small polymeric and cortical bone specimens

    NASA Technical Reports Server (NTRS)

    Kohles, S. S.; Bowers, J. R.; Vailas, A. C.; Vanderby, R. Jr

    1997-01-01

    A system was refined for the determination of the bulk ultrasonic wave propagation velocity in small cortical bone specimens. Longitudinal and shear wave propagations were measured using ceramic, piezoelectric 20 and 5 MHz transducers, respectively. Results of the pulse transmission technique were refined via the measurement of the system delay time. The precision and accuracy of the system were quantified using small specimens of polyoxymethylene, polystyrene-butadiene, and high-density polyethylene. These polymeric materials had known acoustic properties, similarity of propagation velocities to cortical bone, and minimal sample inhomogeneity. Dependence of longitudinal and transverse specimen dimensions upon propagation times was quantified. To confirm the consistency of longitudinal wave propagation in small cortical bone specimens (< 1.0 mm), cut-down specimens were prepared from a normal rat femur. Finally, cortical samples were prepared from each of ten normal rat femora, and Young's moduli (Eii), shear moduli (Gij), and Poisson ratios (Vij) were measured. For all specimens (bone, polyoxymethylene, polystyrene-butadiene, and high-density polyethylene), strong linear correlations (R2 > 0.997) were maintained between propagation time and distance throughout the size ranges down to less than 0.4 mm. Results for polyoxymethylene, polystyrene-butadiene, and high-density polyethylene were accurate to within 5 percent of reported literature values. Measurement repeatability (precision) improved with an increase in the wave transmission distance (propagating dimension). No statistically significant effect due to the transverse dimension was detected.

  16. Wavefront velocity oscillations of carbon-nanotube-guided thermopower waves: nanoscale alternating current sources.

    PubMed

    Abrahamson, Joel T; Choi, Wonjoon; Schonenbach, Nicole S; Park, Jungsik; Han, Jae-Hee; Walsh, Michael P; Kalantar-Zadeh, Kourosh; Strano, Michael S

    2011-01-25

    The nonlinear coupling between exothermic chemical reactions and a nanowire or nanotube with large axial heat conduction results in a self-propagating thermal wave guided along the nanoconduit. The resulting reaction wave induces a concomitant thermopower wave of high power density (>7 kW/kg), resulting in an electrical current along the same direction. We develop the theory of such waves and analyze them experimentally, showing that for certain values of the chemical reaction kinetics and thermal parameters, oscillating wavefront velocities are possible. We demonstrate such oscillations experimentally using a cyclotrimethylene-trinitramine/multiwalled carbon nanotube system, which produces frequencies in the range of 400 to 5000 Hz. The propagation velocity oscillations and the frequency dispersion are well-described by Fourier's law with an Arrhenius source term accounting for reaction and a linear heat exchange with the nanotube scaffold. The frequencies are in agreement with oscillations in the voltage generated by the reaction. These thermopower oscillations may enable new types of nanoscale power and signal processing sources. PMID:21182252

  17. Near-surface wave velocity structure of Faial (Azores - Portugal) Island for site effect studies

    NASA Astrophysics Data System (ADS)

    Borges, José; Neves, Samuel; Caldeira, Bento; Bezzeghoud, Mourad; Carvalho, João; Carvalho, Alexandra

    2015-04-01

    Throughout history, the life of the Azorean people has been marked by earthquakes that have had different effects depending on their proximity and magnitude. This seismic activity, which may have volcanic or tectonic origins, has affected the population of these islands by destroying infrastructure and claiming lives. The social and economic impacts of these phenomena are enormous. The last significant event affecting the Azores (Portugal) was the July 1998 Mw=6.2 earthquake causing major destruction affecting more than 5000 people, causing 8 deaths, 150 persons injured and 1500 homeless. Ground motion simulations are mainly based on source characteristics and are heavily dependent on the medium, which is still poorly understood. Subsurface soil condition can amplify the seismic waves, so, for seismic response analysis, it is necessary to know the shallow soil properties and its spatial variability. For this purpose, we applied P and S-wave refraction, Multichannel Analysis of Surface Waves (MASW) to characterize shear wave velocity at different sites in the Faial Island, in particular, in sites where already occurred amplification. Ambient vibrations can also be used to estimate physical properties of the shallower geological formations. With this goal, the obtained velocity models were confirmed by comparison between real H/V curves with synthetic ones. We concluded that the anomalous intensities observed in some sites are strongly related to thick layers of soft sediments of pyroclastic deposits produced by old volcanic eruptions occurred in the Faial Island.

  18. Modeling Biot's Coefficient for High Porosity Sediments From P Wave Velocity and Density Data.

    NASA Astrophysics Data System (ADS)

    Fabricius, I. L.

    2006-12-01

    The effective stress coefficient predicts to which extent the fluid pressure in a given sediment counteracts the load of overlying sediments. When monitoring changes in fluid pressure and fluid composition from seismic data, the effective stress coefficient may be approximated by Biot's coefficient, ?. ? is under assumption of hydrostatic stress and linear elasticity defined as: ? = 1 - Kdry/Kmin where Kdry is bulk modulus of the dry sediment and Kmin is the mineral bulk modulus. In heavily cemented sedimentary rocks ? is close to porosity. In lightly cemented sediments Biot's coefficient is close to one and the effective stress, ?' is then predicted from Terzaghi's law: ?' = ? - U where ? is the stress due to the total load of the overburden and U is pore pressure. When ? is taken into account we get the equivalent expression: ?' = ? - ? U For calculation of ? we need information on Kdry. It may be calculated from density, ?dry, P wave velocity vP-dry and shear velocity vS-dry for the dry sediment: Kdry = ?dry (vP-dry2 - 4/3 vS-dry2) In many cases only wet density and P wave velocity are known, and then a possibility is to use Castagna's relations for predicting wet shear wave velocity and then using Gassmann's equations to predict the sonic velocities of the dry sediment. An alternative, which also works outside the range of Castagna's relations is to calculate the isoframe value from wet density and wet P-wave velocity and then use the isoframe value to model Kdry. The isoframe value, IF, is derived from a Hashin-Shtrikman model: K = ((? + (1-IF)(1-?))/(Ksus + 4/3Gmin) + (IF(1-?))/(Kmin + 4/3Gmin))-1 - 4/3Gmin G = ((? + (1-IF)(1-?))/? + (IF(1-?))/(Gmin + ?))-1 - ? ? = Gmin/6 ((9Kmin + 8 Gmin)/(Kmin + 2Gmin)) M = K + 4/3G = ? vP2 Where: K is bulk modulus, G is shear modulus, ? is porosity, Gmin is mineral shear modulus, Kfluid is bulk modulus of pore fluid, Kair is bulk modulus of air, and where for wet sediments: Ksus = (?/Kfluid + ((1-?)(1-IF))/ Kmin)-1 and for dry sediments: Ksus = Kair

  19. On-chip laser Doppler vibrometer for arterial pulse wave velocity measurement.

    PubMed

    Li, Yanlu; Segers, Patrick; Dirckx, Joris; Baets, Roel

    2013-07-01

    Pulse wave velocity (PWV) is an important marker for cardiovascular risk. The Laser Doppler vibrometry has been suggested as a potential technique to measure the local carotid PWV by measuring the transit time of the pulse wave between two locations along the common carotid artery (CCA) from skin surface vibrations. However, the present LDV setups are still bulky and difficult to handle. We present in this paper a more compact LDV system integrated on a CMOS-compatible silicon-on-insulator substrate. In this system, a chip with two homodyne LDVs is utilized to simultaneously measure the pulse wave at two different locations along the CCA. Measurement results show that the dual-LDV chip can successfully conduct the PWV measurement. PMID:23847745

  20. On-chip laser Doppler vibrometer for arterial pulse wave velocity measurement

    PubMed Central

    Li, Yanlu; Segers, Patrick; Dirckx, Joris; Baets, Roel

    2013-01-01

    Pulse wave velocity (PWV) is an important marker for cardiovascular risk. The Laser Doppler vibrometry has been suggested as a potential technique to measure the local carotid PWV by measuring the transit time of the pulse wave between two locations along the common carotid artery (CCA) from skin surface vibrations. However, the present LDV setups are still bulky and difficult to handle. We present in this paper a more compact LDV system integrated on a CMOS-compatible silicon-on-insulator substrate. In this system, a chip with two homodyne LDVs is utilized to simultaneously measure the pulse wave at two different locations along the CCA. Measurement results show that the dual-LDV chip can successfully conduct the PWV measurement. PMID:23847745

  1. Shear Wave Velocity Imaging over Quick Clays Using Multiple Seismic Methods

    NASA Astrophysics Data System (ADS)

    Comina, C.; Krawczyk, C. M.; Polom, U.; Socco, L. V.

    2014-12-01

    Quick-clays are characterized by an highly unstable particle structure. This structure is usually caused by freshwater leaching of the original high salinity pore water generated by the former marine deposition environment. Given this instability, the clay structure can easily collapse leading to landslides of varying destructiveness. It is, therefore, of major importance to detect the presence of quick-clays. While resistivity based methodologies are commonly used to detect them (lower conductivity of the leached interstitial fluid in respect to the original one) there are also some evidences that leaching can result in a reduction of the undisturbed shear strength of these clays. Multiple integrated shear wave velocity based seismic methods (mainly SH seismic reflection and Love wave dispersion data) have been therefore applied in a case study to evaluate the potential of shear wave velocity imaging for detecting quick clays. An area near the Göta River in southwest Sweden, which was the scene of a quick clay landslide about 40 years ago, was chosen as experimental site. High-resolution SH reflection data were acquired in the area, as part of a joint project studying clay-related landslides. Seismic reflection processing has evidenced several geologically interesting interfaces related to the presence of quick clays (locally confirmed by boreholes), and sand-gravelly layers strongly contributing to water circulation within them. Dispersion data have been extracted along one of the reflection arrays with a Gaussian windowing approach, and data have been inverted with a Laterally Constrained Inversion using a priori information coming from the seismic reflection imaging. The inversion of dispersion curves has evidenced, in some portion of the seismic line, the presence of a low velocity layer most probably correlatable with quick clays. Even given the limited dispersion information extracted from the dataset, and the not yet completely understood shear wave velocity properties of quick clays, our work has evidenced the potential of the proposed approach for a more comprehensive imaging of the shear wave velocity distribution. This could be a valuable approach in quick clay identification in general.

  2. Changes in elastic wave velocity and rock microstructure due to basalt-CO2-water reactions

    NASA Astrophysics Data System (ADS)

    Adam, Ludmila; Wijk, Kasper; Otheim, Thomas; Batzle, Michael

    2013-08-01

    The chemical interaction between carbon dioxide, water, and basalt is a common process in the earth, which results in the dissolution of primary minerals that later precipitate as alteration minerals. This occurs naturally in volcanic settings, but more recently basalts have been suggested as reservoirs for sequestration of anthropogenic CO2. In both the natural and man-made cases, rock-fluid reactions lead to the precipitation of carbonates. Here, we quantify changes in ultrasonic wave speeds, associated with changes in the frame of whole-rock basalts, as CO2 and basalt react. After 30weeks of reactions and carbonate precipitation, the ultrasonic wave speed in dry basalt samples increases between 4% and 20% and permeability is reduced by up to an order of magnitude. However, porosity decreases only by 2% to 3%. The correlation between significant changes in wave speed and permeability indicates that a precipitate is developing in fractures and compliant pores. Thin sections, XRF-loss on ignition, and water chemistry confirm this observation. This means time-lapse seismic monitoring of a CO2-water-basalt system cannot assume invariance of the rock frame, as typically done in fluid substitution models. We conclude that secondary mineral precipitation causes a measurable change in the velocities of elastic waves in basalt-water-CO2 systems, suggesting that seismic waves could be used to remotely monitor future CO2 injection sites. Although monitoring these reactions in the field with seismic waves might be complicated due to the heterogeneous nature of basalt, quantifying the elastic velocity changes associated with rock alteration in a controlled laboratory experiment forms an important step toward field-scale seismic monitoring.

  3. Changes in Elastic Wave Velocity and Rock Microstructure due to Basalt-CO2-Water Reactions

    NASA Astrophysics Data System (ADS)

    Adam, L.; van Wijk, K.; Otheim, L. T.; Batzle, M. L.

    2013-12-01

    The chemical interaction between carbon dioxide, water and basalt is a common process in the earth, which results in the dissolution of primary minerals that later precipitate as alteration minerals. This occurs naturally in volcanic settings, but more recently basalts have been suggested as reservoirs for sequestration of anthropogenic CO2. In both the natural and man-made case, rock-fluid reactions lead to the precipitation of carbonates. Here, we quantify changes in ultrasonic wave speeds, associated with changes in the frame of whole-rock basalt samples, as CO2 and basalt react. After 30 weeks of reactions and carbonate precipitation, the ultrasonic wave speed in dry basalt samples increases between 4% and 20% and permeability is reduced by up to an order of magnitude. However, porosity decreases only by 2% to 3%. The correlation between significant changes in wave speed and permeability indicates that precipitate is developing in fractures and compliant pores. Thin sections, XRF-Loss On Ignition and water chemistry confirm this. Our findings show that time-lapse seismic monitoring of a CO2-water-basalt system cannot assume invariance of the rock frame, as typically done in fluid substitution models. We conclude that secondary mineral precipitation causes a measurable change in the velocities of elastic waves in basalt-water-CO2 systems, suggesting that seismic waves could be used to remotely monitor future CO2 injection sites. Although monitoring these reactions in the field with seismic waves might be complicated due to the heterogeneous nature of basalt, quantifying the elastic velocity changes associated with rock alteration in a controlled laboratory experiment forms an important step toward field-scale seismic monitoring.

  4. Monitoring seismic wave velocity changes associated with the Mw 7.9 Wenchuan earthquake: increasing the temporal resolution using curvelet filters

    NASA Astrophysics Data System (ADS)

    Stehly, Laurent; Froment, Bérénice; Campillo, Michel; Liu, Qi Yuan; Chen, Jiu Hui

    2015-06-01

    The aim of this study is to improve the temporal resolution of seismic wave velocity variations measured using ambient noise correlations. We first reproduce the result obtained by Chen et al. using a network of 21 broad-band stations ideally located around the fault system activated during the Wenchuan earthquake.We measure a velocity drop of 0.07 per cent that was associated with the main shock, with a temporal resolution of 30 days. To determine whether this velocity drop is co-seismic or post-seismic, we attempt to increase the temporal resolution of our observations. By taking advantage of the properties of the curvelet transform, we increase the signal-to-noise ratio of the daily correlations computed between each station pair. It is then possible to measure the velocity drop associated with the Wenchuan earthquake with a temporal resolution of 1 day. This shows that the velocity drop started on 2008 May 12, which was the day of the earthquake, and the velocity reached its lowest value 2 days after the main shock. Moreover, there was a second velocity drop on 2008 May 27, which might relate to strong aftershocks.

  5. Increased heat transfer to a cylindrical leading edge due to spanwise variations in the freestream velocity

    NASA Technical Reports Server (NTRS)

    Rigby, D. L.; Vanfossen, G. J.

    1991-01-01

    The present study numerically demonstrates how small spanwise variations in velocity upstream of a body can cause relatively large increases in the spanwise-averaged heat transfer to the leading edge. Vorticity introduced by spanwise variations, first decays as it drifts downstream, then amplifies in the stagnation region as a result of vortex stretching. This amplification can cause a periodic array of 3 D structures, similar to horseshoe vortices, to form. The numerical results indicate that, for the given wavelength, there is an amplitude threshold below which a structure does not form. A one-dimensional analysis, to predict the decay of vorticity in the absence of the body, in conjunction with the full numerical results indicated that the threshold is more accurately stated as minimum level of vorticity required in the leading edge region for a structure to form. It is possible, using the one-dimensional analysis, to compute an optimum wavelength in terms of the maximum vorticity reaching the leading edge region for given amplitude. A discussion is presented which relates experimentally observed trends to the trends of the present phenomena.

  6. Surface Wave/Dispersion Curves For A Velocity Model Of The Sacramento/San Joaquin Delta

    NASA Astrophysics Data System (ADS)

    Fletcher, J. B.; Seats, K.; Lawrence, J. F.; Teel, A.

    2012-12-01

    Using ambient noise tomography we have obtained Rayleigh wave dispersion curves to determine the velocity structure of the Sacramento/San Joaquin Delta. The velocity structure is a first step in using simulations to better estimate of seismic hazard for the Delta. We have combined ray paths for stations from the Earthscope/Transportable array, Berkeley Digital Seismic Network, and the USGS portable network in the Delta to determine dispersion curves for ray paths that travel through the western Central Valley near the Delta. Ground motion from broad band velocity sensors, originally sampled at 100 Hz, was decimated to 20 Hz and filtered to provide data between about 3 and 20s. Coherence was determined between stations from the three networks using hour-long records and then stacked over two or three months. We recovered 134 paths over a maximum dimension of about 250 km, but most paths are concentrated near the Delta. For travel paths that travel through the Delta north of the Lower Jones tract, the group velocities are usually lower than 1 km/s at periods of 3 to 8s. At longer periods (or deeper depths) the velocities are still low, but usually reach 2 km/s at a period of 18s. This compared with travel paths in the Sierra foothills that are more scattered, but have velocities exceeding 3 km/s at periods of 10 to 18s. Preliminary images show basin-like patches of slow velocities near the Delta, that when strung together, are roughly shaped like an L with one arm pointing back into the Central Valley and one arm pointing south southeast along the western margin of the Central Valley. The basins in these images have dimensions of about 20 to 40 km. More stations are being deployed to increase the resolution and stability of these images.

  7. S-wave velocity self-adaptive prediction based on a variable dry rock frame equivalent model

    NASA Astrophysics Data System (ADS)

    Feng-Ying, Yang; Xing-Yao, Yin; Bo, Liu

    2014-08-01

    Seismic velocities are important reservoir parameters in seismic exploration. The Gassmann theory has been widely used to predict velocities of fluid-saturated isotropic reservoirs at low frequency. According to Gassmann theory, dry rock frame moduli are essential input parameters for estimating reservoir velocities. A variable dry rock frame equivalent model called VDEM based on the differential effective medium (DEM) theory is constructed in this paper to obtain the dry rock frame moduli. We decouple the DEM equations by introducing variable parameters, then simplify these decoupled equations to get the equivalent dry rock fame model. The predicted dry rock frame moduli by the VDEM are in good agreement with the laboratory data. The VDEM is also utilized to predict S-wave velocity combined with Gassmann theory. A self-adaptive inversion method is applied to fit the variable parameters with the constraint of P-wave velocity from well logging data. The S-wave velocity is estimated from these inversed parameters. A comparison between the self-adaptive method and the Xu-White model on S-wave velocity estimation is made. The results corroborate that the self-adaptive method is flexible and effective for S-wave velocity prediction.

  8. Compressional wave velocity and attenuation at ultrasonic and sonic frequencies in near-surface sedimentary rocks

    SciTech Connect

    Best, A.I. [Univ. of Reading (United Kingdom). Postgraduate Research Inst. for Sedimentology] [Univ. of Reading (United Kingdom). Postgraduate Research Inst. for Sedimentology; Sams, M.S. [Imperial College of Science, Technology and Medicine, London (United Kingdom). Dept. of Geology] [Imperial College of Science, Technology and Medicine, London (United Kingdom). Dept. of Geology

    1997-03-01

    Laboratory ultrasonic measurements of compressional wave velocity and attenuation were made as a function of effective pressure on samples of limestone, sandstone and siltstone taken from a shallow borehole test site. The results indicate that the sandstones are pervaded by grain contact microcracks which dramatically affect their compressional wave attenuations. Clean sandstone shows a compressional wave quality factor (Q{sub p}) of 24 {+-} 2 at 5 MPa effective pressure (close to the estimated in situ burial pressure) and a Q{sub p} of 83 {+-} 29 at 60 MPa. The Q{sub p} of limestones and siltstones at the site show negligible and small increases with pressure in the laboratory, respectively. The strong pressure dependence of Q{sub p} in clean sandstone was used to infer the presence of in situ microcracks. Sediment velocities measured in the laboratory at about 1 MHz were compared with those from the full waveform sonic log at about 10 kHz implies that they must also be highly attenuating over a significant part of the frequency range 10 kHz to 1 MHz, to account for the magnitude of the observed velocity dispersion. Assuming the laboratory Q{sub p} values measured at 5 MPa remain constant down to 10 kHz predicts the observed dispersion quite well. Furthermore, the sonic log velocities of sandstones, limestones and siltstones (after normalizing each lithology for porosity and clay content) were found to reflect the same pressure (depth) trends observed in the laboratory. The results provide evidence for the existence of in situ microcracks in near-surface sediments.

  9. Spatial variations of waves propagating over a submerged rectangular obstacle

    Microsoft Academic Search

    C. L. Ting; M. C. Lin; C. M. Hsu

    2005-01-01

    Experiments are performed in a wave flume to examine the generation of harmonics by non-breaking surface waves travelling over a submerged obstacle. Spatial wave profiles are recorded using an optical measurement system, similar to the approach used by Perlin [Perlin, M., Lin, H., Ting, C.L., 1993. On parasitic capillary waves generated by steep gravity waves: an experimental investigation with spatial

  10. Bulletinof the SeismologicalSocietyof America,Vol. 87, No. 1, pp. 183-199, February 1997 Shear-Wave Velocity Structurein the Northern Basin and Range Province

    E-print Network

    Sheehan, Anne F.

    Abstract A new method based on the joint inversion of receiver functions and surface-wave phase velocities takes advantage of average-velocity information present in the surface-wave method and differential a group of final-velocity models with differing average velocities to be found that fit the observed

  11. Shallow three-dimensional P-wave velocity structure revealed by seismic experiment Sakurajima volcano, Japan

    NASA Astrophysics Data System (ADS)

    Tameguri, T.; Iguchi, M.

    2009-12-01

    Sakurajima is a post-caldera cone situated on the southern rim of Aira caldera, south Kyushu, Japan. It consists of two adjoining stratovolcanoes, Kitadake (-13,000 yrs BP) and Minamidake (-5,000 yrs BP). Explosive eruptions have frequently occurred at the summit crater Minamidake since 1955. Main magma reservoir is estimated at a depth of 10 km near the center of the Aira caldera and a minor reservoir is located at shallow (5 km) beneath the Minamidake (Eto, 1991). The two reservoirs are possibly connected by a tensile fault of strike NE-SW as inferred from hypocenter distributions and source mechanisms of VT earthquakes and geodetic data (Hidayati et al., 2007). Seismic experiment was carried in November, 2008 in order to investigate seismic velocity structure, location of magma storage and magma path from the chamber beneath the Aira caldera to the crater of Sakurajima volcano. In the seismic experiment, we used 15 shot points of dynamite and installed about 640 temporary seismic stations. Three-dimensional P-wave velocity structure beneath the Sakurajima volcano is estimated using 3400 arrival times of the first motions from large 8 shots. A high velocity anomaly (+10 % from initial structure) at sea level is detected at north part of the active crater and velocity around mountain body is lower than 2.1 km/s. This high velocity may correspond to old mountain body of the Kitadake. A high velocity anomaly (+15 %) and a low velocity anomaly (-10 %) are found in SSE and NE parts of the crater at the depth of 2 km, respectively. Gravity survey showed that high and low gravity anomalies at SE and NE parts of Sakurajima, respectively (Komazawa et al., 2008). The seismic velocity structure is consistent with the anomalies of the gravity research. The low velocity anomaly at NE part at the depth of 2 km may be related to magma path from the reservoir beneath the Aira caldera to the Minamidake crater, because tensile fault across the volcano from magma reservoir beneath the Aira caldera (Hidayati et al., 2007) is located beneath the low velocity anomaly.

  12. 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.

  13. The Sensitivity of Stationary Waves to Variations in the Basic State Zonal Flow

    Microsoft Academic Search

    Sumant Nigam; Richard S. Lindzen

    1989-01-01

    A linear, primitive equation stationary wave model having high vertical and meridional resolution is used to examine the sensitivity of orographically forced (primarily by Himalayas) stationary waves at middle and high latitudes to variations in the basic state zonal wind distribution. We find relatively little sensitivity to the winds in high latitude but remarkable sensitivity to small variations in the

  14. AN EXPERIMENTAL STUDY OF SHOCK WAVES RESULTING FROM THE IMPACT OF HIGH VELOCITY MISSILES ON ANIMAL TISSUES

    PubMed Central

    Harvey, E. Newton; McMillen, J. Howard

    1947-01-01

    The spark shadowgram method of studying shock waves is described. It has been used to investigate the properties of such waves produced by the impact of a high velocity missile on the surface of water. The method can be adapted for study of behavior of shock waves in tissue by placing the tissue on a water surface or immersing it in water. Spark shadowgrams then reveal waves passing from tissue to water or reflected from tissue surfaces. Reflection and transmission of shock waves from muscle, liver, stomach, and intestinal wall are compared with reflection from non-living surfaces such as gelatin gel, steel, plexiglas, cork, and air. Because of its heterogeneous structure, waves transmitted by tissue are dispersed and appear as a series of wavelets. When the accoustical impedance (density x wave velocity) of a medium is less than that in which the wave is moving, reflection will occur with inversion of the wave; i.e., a high pressure wave will become a low pressure wave. This inversion occurs at an air surface and is illustrated by shadowgrams of reflection from stomach wall, from a segment of colon filled with gas, and from air-filled rubber balloons. Bone (human skull and beef ribs) shows good reflection and some transmission of shock waves. When steel is directly hit by a missile, clearly visible elastic waves pass from metal to water, but a similar direct hit on bone does not result in elastic waves strong enough to be detected by a spark shadowgram. PMID:19871617

  15. An explicit relation for the apparent phase velocity of Rayleigh waves in a vertically heterogeneous elastic half-space

    NASA Astrophysics Data System (ADS)

    Lai, Carlo G.; Mangriotis, Maria-Daphne; Rix, Glenn J.

    2014-11-01

    This paper presents the mathematical derivation of an explicit relation for the apparent (or effective) phase velocity of Rayleigh waves in a vertically heterogeneous, isotropic elastic half-space for harmonic excitation. As a kinematical feature, the apparent phase velocity captures the superposition, in a spatial Fourier series, of the individual modes of propagation of Rayleigh waves and describes the speed of propagation of a composite waveform generated by a vertically oscillating point load. The relation, which is a function of the distance from the source, frequency and depth, depends explicitly on the modal phase and group velocities of Rayleigh waves, and their corresponding wavenumbers and eigenfunctions, which can be computed directly from the solution of the Rayleigh-wave eigenproblem. A practical scenario for the application of the notion of apparent Rayleigh-wave phase velocity is the modelling of the dispersion curve in the well-known surface wave measurement methods `spectral analysis of surface waves' (SASW) and `multichannel analysis of surface waves' (MASW). Apart from a theoretical motivation, the availability in surface wave testing of an explicit formula for the calculation of the apparent Rayleigh-wave phase velocity may lead to the development of a new class of inversion algorithms capable of taking into account the influence of all the modes of surface wave propagation. To demonstrate the exactness of the explicit relation, the predicted values of apparent phase velocity are compared to those computed synthetically from a numerical simulation of SASW and MASW testing for three case studies, which show both single as well as multiple mode dominance effects.

  16. Fast simulated annealing inversion of surface waves on pavement using phase-velocity spectra

    USGS Publications Warehouse

    Ryden, N.; Park, C.B.

    2006-01-01

    The conventional inversion of surface waves depends on modal identification of measured dispersion curves, which can be ambiguous. It is possible to avoid mode-number identification and extraction by inverting the complete phase-velocity spectrum obtained from a multichannel record. We use the fast simulated annealing (FSA) global search algorithm to minimize the difference between the measured phase-velocity spectrum and that calculated from a theoretical layer model, including the field setup geometry. Results show that this algorithm can help one avoid getting trapped in local minima while searching for the best-matching layer model. The entire procedure is demonstrated on synthetic and field data for asphalt pavement. The viscoelastic properties of the top asphalt layer are taken into account, and the inverted asphalt stiffness as a function of frequency compares well with laboratory tests on core samples. The thickness and shear-wave velocity of the deeper embedded layers are resolved within 10% deviation from those values measured separately during pavement construction. The proposed method may be equally applicable to normal soil site investigation and in the field of ultrasonic testing of materials. ?? 2006 Society of Exploration Geophysicists.

  17. Redetermination of Galactic Spiral Density Wave Parameters Based on Spectral Analysis of Maser Radial Velocities

    E-print Network

    Bajkova, A T; 10.1134/S1063773712080014

    2012-01-01

    To redetermine the Galactic spiral density wave parameters, we have performed a spectral (Fourier) analysis of the radial velocities for 44 masers with known trigonometric parallaxes, proper motions, and line-of-sight velocities. The masers are distributed in a wide range of Galactocentric distances $(3.5wave with the following parameters from the maser radial velocities: the perturbation amplitude $f_R = 7.7^{+1.7}_{-1.5}$ km s$^{-1}$, the...

  18. Velocity sensitivity of seismic body waves to the anisotropic parameters of a TTI-medium

    NASA Astrophysics Data System (ADS)

    Zhou, Bing; Greenhalgh, Stewart

    2008-09-01

    We formulate the derivatives of the phase and group velocities for each of the anisotropic parameters in a tilted transversely isotropic medium (TTI-medium). This is a common geological model in seismic exploration and has five elastic moduli or related Thomsen parameters and two orientation angles defining the axis of symmetry of the rock. We present two independent methods to compute the derivatives and examine the formulae with real anisotropic rocks. The formulations and numerical computations do not encounter any singularity problem when applied to the two quasi shear waves, which is a problem with other approaches. The two methods yield the same results, which show in a quantitative way the sensitivity behaviour of the phase and the group velocities to all of the elastic moduli or Thomsen's anisotropic parameters as well as the orientation angles in the 2D and 3D cases. One can recognize the dominant (strong effect) and weak (or 'dummy') parameters for the three seismic body-wave modes (qP, qSV, qSH) and their effective domains over the whole range of phase-slowness directions. These sensitivity patterns indicate the possibility of nonlinear kinematic inversion with the three wave modes for determining the anisotropic parameters and imaging an anisotropic medium.

  19. Estimating the influence of stress on elastic wave velocities from measurements made at different scales on sandstone facies

    NASA Astrophysics Data System (ADS)

    Wandler, Aaron Vallejo

    Knowing how stress influences velocity is crucial for seismic reservoir monitoring because seismic reflection signatures are sensitive to the dynamic processes related to production or injection. In this thesis, I address this issue by conducting research to quantify the influence of stress on elastic wave velocities at different measurement scales. I compare the influence of stress on elastic wave velocities measured from borehole sonic data, time-lapse multicomponent surface seismic data, and laboratory core experiments. To make this comparison, I develop a methodology by combining a series of existing techniques to estimate the influence of stress on shear-wave velocity acquired from crossed-dipole borehole sonic data. By combining the crossed-dipole radial profile of shear wave velocity with the redistribution of stress caused by the presence of a borehole, I establish a relationship between velocity and stress from borehole measurements made within the reservoir. Previously, information about the influence of stress on elastic wave velocity has been primarily obtained through laboratory measurements. To estimate the magnitude of far-field principal stresses at the reservoir level in the subsurface I first integrate the formation bulk density well log to approximate the stress exerted by the overburden. Then, I use radial profiles of shear-wave slowness obtained from borehole sonic data to estimate the far-field principal horizontal stresses. Estimates of the far-field principal stresses are needed to model the stress redistribution caused by the drillout of a borehole. To study the influence that borehole stress redistribution has on shear-wave velocity, I combine the borehole stresses that influence a vertically propagating fast shear wave and the radial profile of the fast shear wave velocity. I use an excess compliance rock physics model to extrapolate the borehole shear wave velocity/stress relationship to predict the influence stress has on compressional wave velocity. Time-lapse multicomponent surface seismic data were recorded to monitor a water alternating gas (CO2) injection scheme for enhanced oil recovery. Interpretations of the time-lapse seismic data, in conjunction with a reservoir simulation model, indicate regions of increased reservoir pore pressure. To simulate the reservoir conditions during a water alternating gas injection scheme, I conducted laboratory core experiments in which I measured compressional and shear-wave velocities as a function of confining pressure, pore pressure, fluid type (which included CO2 in the gas and supercritical phase), and lithology. The shear wave velocity from the borehole sonic data and the time-lapse multicomponent surface seismic data show a very similar response to changes in stress. The laboratory experiments indicate the core velocity measurements are less sensitive to a change in stress than both the borehole and seismic data. Borehole sonic data provide an alternative and, in this case, a more accurate method than laboratory core measurements for estimating stress-induced changes in shear-wave velocity within a reservoir. An accurate rock-physics relationship between shear-wave velocity and effective stress is required for a quantitative interpretation of pore pressure changes from multicomponent time-lapse seismic data.

  20. Teleseismic tomography of the compressional wave velocity structure beneath the Long Valley region, California

    SciTech Connect

    Dawson, P.B.; Evans, J.R.; Iyer, H.M. (Geological Survey, Menlo Park, CA (USA))

    1990-07-10

    In 1982 and 1984 the U.S. Geological Survey used several seismic networks, totaling over 90 stations, to record teleseismic P waves and measure travel time residuals in an area centered on the Long Valley caldera. The authors inverted the travel time residuals to obtain a three-dimensional image of the velocity structure with resolution of 5-6 km to depths of 70 km beneath the array. Direct inversion of these data indicates that the 2- to 4-km-thick low-velocity caldera fill contaminates the signal from any midcrustal velocity anomalies beneath the caldera. Thus two methods were used to strip the effects of the upper crust from the travel time residuals: (1) ray tracing through upper crustal velocity models provided by seismic refraction experiments and gravity surveys, and (2) an iterative stripping scheme using the inversion itself. The methods produce essentially identical results and adequately remove the effects of the shallowest crustal structures, including the caldera fill and hydrothermal alteration effects. The resulting stripped models show two well-resolved midcrustal low-velocity bodies in the Long Valley region. The first body is centered between 7 and 20 km depth beneath the resurgent dome of the Long Valley caldera and has a volume of 150-600 km{sup 3}. The second, with a similar volume, is centered between 10 and 20 km depth beneath the Mono Craters, about 10 km north of Long Valley. Velocity contrasts in both of these bodies are about 6-10%, and the features are interpreted as silicic magma chambers. This experiment does not preclude the presence of additional pockets of magma smaller than 5 km across in the upper crust, particularly beneath the resurgent dome of the caldera (which would be removed with the stripping methods). The high eruptive rate of the Mono Craters and these upper mantle structures suggest that the focus of volcanism is shifting north from Long Valley to the Mono Craters

  1. RESEARCH PAPERS : Wave-theoretical inversion of teleseismic surface waves in a regional network: phase-velocity maps and a three-dimensional upper-mantle shear-wave-velocity model for southern Germany

    NASA Astrophysics Data System (ADS)

    Friederich, Wolfgang

    1998-01-01

    Using teleseimic surface-wave data from 110 selected earthquakes recorded at 10broad-band stations in southern Germany we construct phase-velocity maps of Rayleigh waves for southern Germany. In a further step these maps are inverted for a three-dimensional model of the SV velocity of the upper 200 km of the mantle. We attempt to take into account the effect of heterogeneous structure outside the study region by jointly inverting the data for heterogeneous phase velocity inside the study region and the distortion of the incoming wavefields by the surrounding structure. The total wavefield in the study region is computed with a scattering formalism which includes multiple forward scattering and single backscattering. Since, in principle, the data can be perfectly fit by the incoming wavefields without any heterogeneous structure inside the study area, we impose additional constraints on the incoming wavefields to reduce the non-uniqueness. The most important constraint is an energy criterion which states that the energy of the modelled wavefield in the study area, averaged over many events, should be equal to the energy sampled by the stations. We demonstrate that enforcing this criterion generates phase-velocity maps with heterogeneous structure. Nevertheless, we are able to satisfy the energy criterion without any heterogeneous structure at the price of an only slightly increased data misfit. Hence, it must be concluded that a seismic network of size and station density such as the one used in this study is still insufficient to demonstrate convincingly the existence of heterogeneities in the network area using teleseismic surface waves. Any reasonable structure combined with the appropriate incoming wavefields would allow an acceptable fit of our data. This frustrating conclusion, of course, applies to all other comparable studies which use teleseismic surface waves. Although we cannot convincingly show that any phase-velocity map we find should be preferred over others, we are able to obtain good reconstructions of test structures from realistic synthetic data with the same station and event distribution as the real data. Moreover, we find that the geometric pattern of the phase-velocity maps obtained from real data depends only weakly on the constraints applied in the inversion, while the amplitude of the phase-velocity perturbations is almost completely determined by the constraints. For all periods considered the fit to the data is extremely good. The reduction of the quadratic misfit relative to the case of plane incoming waves and no structure is dramatic for the shorter periods. The 3-D model of vertical shear-wave velocity down to a depth of 200 km exhibits a basic division into four quadrants separated by a vertical plane intersecting the surface along a nearly west-east line and a horizontal plane at about 130 km depth. The northern rants show high velocities in the top 120 km and low velocities below 140 km. The opposite is the case for the southern quadrants. An exception to this general feature is a pronounced low-velocity zone in the northwestern corner of the region.

  2. Monitoring of crustal seismic velocity variations in the L'Aquila fault zone inferred from noise cross-correlation

    NASA Astrophysics Data System (ADS)

    Soldati, Gaia; Zaccarelli, Lucia; Faenza, Licia; Michelini, Alberto

    2015-07-01

    The relative seismic velocity variations possibly associated to large earthquakes can be readily monitored via cross-correlation of seismic noise. In a recently published study, more than 2 yr of continuous seismic records have been analysed from three stations surrounding the epicentre of the 2009 April 6, Mw 6.1 L'Aquila earthquake, observing a clear decrease of seismic velocities likely corresponding to the co-seismic shaking. Here, we extend the analysis in space, including seismic stations within a radius of 60 km from the main shock epicentre, and in time, collecting 5 yr of data for the six stations within 40 km of it. Our aim is to investigate how far the crustal damage is visible through this technique, and to detect a potential post-seismic recovery of velocity variations. We find that the co-seismic drop in velocity variations extends up to 40 km from the epicentre, with spatial distribution (maximum around the fault and in the north-east direction from it) in agreement with the horizontal co-seismic displacement detected by global positioning system (GPS). In the first few months after L'Aquila earthquake, the crust's perturbation in terms of velocity variations displays a very unstable behaviour, followed by a slow linear recovery towards pre-earthquake conditions; by almost 4 yr after the event, the co-seismic drop of seismic velocity is not yet fully recovered. The strong oscillations of the velocity changes in the first months after the earthquake prevent to detect the fast exponential recovery seen by GPS data. A test of differently parametrized fitting curves demonstrate that the post-seismic recovery is best explained by a sum of a logarithmic and a linear term, suggesting that processes like viscoelastic relaxation, frictional afterlip and poroelastic rebound may be acting concurrently.

  3. Characteristics of Mitral and Tricuspid Annular Velocities Determined by Pulsed Wave Doppler Tissue Imaging in Healthy Subjects

    Microsoft Academic Search

    Mahbubul Alam; Johan Wardell; Eva Andersson; Bassem A Samad; Rolf Nordlander

    1999-01-01

    Assessment of myocardial velocities by Doppler tissue imaging is gaining in importance. However, generally accepted reference values are still missing. In this study we examined 62 consecutive healthy subjects (mean age 46, range 22-82 years) by pulsed wave Doppler tissue imaging to characterize the systolic and diastolic velocity profiles of the left and right ventricles. The subjects were divided into

  4. P and S wave velocity and VP///VS in the wake of the Yellowstone hot spot

    E-print Network

    Humphreys, Eugene

    P and S wave velocity and VP///VS in the wake of the Yellowstone hot spot Derek L. Schutt1, and VP/VS structure is imaged across the Yellowstone hot spot swell, including the hot spot track where molten up to 1.0%, and the high-velocity Yellowstone swell mantle away from the Snake River Plain is $80

  5. Elastic-wave velocity in marine sediments with gas hydrates: Effective medium modeling

    NASA Astrophysics Data System (ADS)

    Helgerud, M. B.; Dvorkin, J.; Nur, A.; Sakai, A.; Collett, T.

    1999-07-01

    We offer a first-principle-based effective medium model for elastic-wave velocity in unconsolidated, high porosity, ocean bottom sediments containing gas hydrate. The dry sediment frame elastic constants depend on porosity, elastic moduli of the solid phase, and effective pressure. Elastic moduli of saturated sediment are calculated from those of the dry frame using Gassmann's equation. To model the effect of gas hydrate on sediment elastic moduli we use two separate assumptions: (a) hydrate modifies the pore fluid elastic properties without affecting the frame; (b) hydrate becomes a component of the solid phase, modifying the elasticity of the frame. The goal of the modeling is to predict the amount of hydrate in sediments from sonic or seismic velocity data. We apply the model to sonic and VSP data from ODP Hole 995 and obtain hydrate concentration estimates from assumption (b) consistent with estimates obtained from resistivity, chlorinity and evolved gas data.

  6. Characteristics of light reflected from a dense ionization wave with a tunable velocity.

    PubMed

    Zhidkov, A; Esirkepov, T; Fujii, T; Nemoto, K; Koga, J; Bulanov, S V

    2009-11-20

    An optically dense ionization wave (IW) produced by two femtosecond (approximately 10/30 fs) laser pulses focused cylindrically and crossing each other may become an efficient coherent x-ray converter in accordance with the Semenova-Lampe theory. The resulting velocity of a quasiplane IW in the vicinity of pulse intersection changes with the angle between the pulses from the group velocity of ionizing pulses to infinity allowing a tuning of the wavelength of x rays and their bunching. The x-ray spectra after scattering of a lower frequency and long coherent light pulse change from the monochromatic to high order harmoniclike with the duration of the ionizing pulses. PMID:20366045

  7. Elastic-wave velocity in marine sediments with gas hydrates: Effective medium modeling

    USGS Publications Warehouse

    Helgerud, M.B.; Dvorkin, J.; Nur, A.; Sakai, A.; Collett, T.

    1999-01-01

    We offer a first-principle-based effective medium model for elastic-wave velocity in unconsolidated, high porosity, ocean bottom sediments containing gas hydrate. The dry sediment frame elastic constants depend on porosity, elastic moduli of the solid phase, and effective pressure. Elastic moduli of saturated sediment are calculated from those of the dry frame using Gassmann's equation. To model the effect of gas hydrate on sediment elastic moduli we use two separate assumptions: (a) hydrate modifies the pore fluid elastic properties without affecting the frame; (b) hydrate becomes a component of the solid phase, modifying the elasticity of the frame. The goal of the modeling is to predict the amount of hydrate in sediments from sonic or seismic velocity data. We apply the model to sonic and VSP data from ODP Hole 995 and obtain hydrate concentration estimates from assumption (b) consistent with estimates obtained from resistivity, chlorinity and evolved gas data. Copyright 1999 by the American Geophysical Union.

  8. Combined ultrasonic elastic wave velocity and microtomography measurements at high pressures

    NASA Astrophysics Data System (ADS)

    Kono, Yoshio; Yamada, Akihiro; Wang, Yanbin; Yu, Tony; Inoue, Toru

    2011-02-01

    Combined ultrasonic and microtomographic measurements were conducted for simultaneous determination of elastic property and density of noncrystalline materials at high pressures. A Paris-Edinburgh anvil cell was placed in a rotation apparatus, which enabled us to take a series of x-ray radiography images under pressure over a 180° angle range and construct accurately the three-dimensional sample volume using microtomography. In addition, ultrasonic elastic wave velocity measurements were carried out simultaneously using the pulse reflection method with a 10° Y-cut LiNbO3 transducer attached to the end of the lower anvil. Combined ultrasonic and microtomographic measurements were carried out for SiO2 glass up to 2.6 GPa and room temperature. A decrease in elastic wave velocities of the SiO2 glass was observed with increasing pressure, in agreement with previous studies. The simultaneous measurements on elastic wave velocities and density allowed us to derive bulk (Ks) and shear (G) moduli as a function of pressure. Ks and G of the SiO2 glass also decreased with increasing pressure. The negative pressure dependence of Ks is stronger than that of G, and as a result the value of Ks became similar to G at 2.0-2.6 GPa. There is no reason why we cannot apply this new technique to high temperatures as well. Hence the results demonstrate that the combined ultrasonic and microtomography technique is a powerful tool to derive advanced (accurate) P-V-Ks-G-(T) equations of state for noncrystalline materials.

  9. Shear-wave structure of the lithosphere above the Hawaiian hot spot from two-station Rayleigh wave phase velocity measurements

    Microsoft Academic Search

    Keith Priestley; Frederik Tilmann

    1999-01-01

    We have measured fundamental mode Rayleigh wave phase velocity dispersion from seismograms of five earthquakes recorded at stations on the islands of Hawaii and Oahu and inverted these data for upper mantle velocity structure. The seismic lithosphere of the velocity model is 88+\\/-7km thick, which is similar to that of 80-90 Myr oceanic lithosphere, indicating that no significant lithospheric thinning

  10. Acoustic Fields of Bulk Acoustic Waves Excited by Phase Velocity Scanning of Laser Interference Fringes

    NASA Astrophysics Data System (ADS)

    Nishino, Hideo; Tsukahara, Yusuke; Takemoto, Mikio; Yamanaka, Kazushi

    2002-04-01

    Directivity and generation efficiency of transverse and longitudinal bulk acoustic waves (BAWs) excited by phase velocity scanning (PVS) of laser interference fringes were theoretically investigated. Formulas were derived for the BAW generation based on scanning interference fringes (SIF) which were produced by intersecting two coherent laser beams with different frequencies on an opaque specimen. It was deduced that the amplitude of the BAW was proportional to the product of the scanning length of the SIF and the directivity pattern due to the thermoelastic line source. Unidirectionality of the BAW generated by the SIF was theoretically verified in an ideal state.

  11. Dual-beam interferometer for the accurate determination of surface-wave velocity

    NASA Astrophysics Data System (ADS)

    McKie, Andrew D. W.; Wagner, James W.; Spicer, James B.; Deaton, John B., Jr.

    1991-10-01

    A novel dual-beam interferometer has been designed and constructed that enables two beams from an He-Ne laser to probe remotely the surface of a material. The separation of the two He-Ne beams is adjustable in the 15-40-mm range with a spatial resolution of 2 microns. SAW measurements have been performed with two different probe separations so that the travel time for the surface waves over a known distance can be determined accurately. With the aid of autocorrelation algorithms, the Rayleigh pulse velocity on 7075-T651 aluminum has been measured to be 2888 +/-4 m/s.

  12. Optical pin apparatus for measuring the arrival time and velocity of shock waves and particles

    DOEpatents

    Benjamin, R.F.

    1987-03-10

    An apparatus is disclosed for the detection of the arrival and for the determination of the velocity of disturbances such as shock-wave fronts and/or projectiles. Optical pins using fluid-filled microballoons as the light source and an optical fiber as a link to a photodetector have been used to investigate shock-waves and projectiles. A microballoon filled with a noble gas is affixed to one end of a fiber-optic cable, and the other end of the cable is attached to a high-speed streak camera. As the shock-front or projectile compresses the microballoon, the gas inside is heated and compressed producing a bright flash of light. The flash of light is transmitted via the optic cable to the streak camera where it is recorded. One image-converter streak camera is capable of recording information from more than 100 microballoon-cable combinations simultaneously. 3 figs.

  13. Optical pin apparatus for measuring the arrival time and velocity of shock waves and particles

    DOEpatents

    Benjamin, Robert F. (315 Rover Blvd., Los Alamos, NM 87544)

    1987-01-01

    An apparatus for the detection of the arrival and for the determination of the velocity of disturbances such as shock-wave fronts and/or projectiles. Optical pins using fluid-filled microballoons as the light source and an optical fiber as a link to a photodetector have been used to investigate shock-waves and projectiles. A microballoon filled with a noble gas is affixed to one end of a fiber-optic cable, and the other end of the cable is attached to a high-speed streak camera. As the shock-front or projectile compresses the microballoon, the gas inside is heated and compressed producing a bright flash of light. The flash of light is transmitted via the optic cable to the streak camera where it is recorded. One image-converter streak camera is capable of recording information from more than 100 microballoon-cable combinations simultaneously.

  14. Optical pin apparatus for measuring the arrival time and velocity of shock waves and particles

    DOEpatents

    Benjamin, R.F.

    1983-10-18

    An apparatus for the detection of the arrival and for the determination of the velocity of disturbances such as shock-wave fronts and/or projectiles. Optical pins using fluid-filled microballoons as the light source and an optical fiber as a link to a photodetector have been used to investigate shock-waves and projectiles. A microballoon filled with a noble gas is affixed to one end of a fiber-optic cable, and the other end of the cable is attached to a high-speed streak camera. As the shock-front or projectile compresses the microballoon, the gas inside is heated and compressed producing a bright flash of light. The flash of light is transmitted via the optic cable to the streak camera where it is recorded. One image-converter streak camera is capable of recording information from more than 100 microballoon-cable combinations simultaneously.

  15. Solar Wind Driving of Magnetospheric ULF Waves: Pulsations Driven by Velocity Shear at the Magnetopause

    E-print Network

    Claudepierre, S G; Wiltberger, M; 10.1029/2007JA012890

    2010-01-01

    We present results from global, three-dimensional magnetohydrodynamic (MHD) simulations of the solar wind/magnetosphere interaction. These MHD simulations are used to study ultra low frequency (ULF) pulsations in the Earth's magnetosphere driven by shear instabilities at the flanks of the magnetopause. We drive the simulations with idealized, constant solar wind input parameters, ensuring that any discrete ULF pulsations generated in the simulation magnetosphere are not due to fluctuations in the solar wind. The simulations presented in this study are driven by purely southward interplanetary magnetic field (IMF) conditions, changing only the solar wind driving velocity while holding all of the other solar wind input parameters constant. We find surface waves near the dawn and dusk flank magnetopause and show that these waves are generated by the Kelvin-Helmholtz (KH) instability. We also find that two KH modes are generated near the magnetopause boundary. One mode, the magnetopause KH mode, propagates tailwa...

  16. 3D P-Wave Velocity Structure of the Crust and Relocation of Earthquakes in 21 the Lushan Source Area

    NASA Astrophysics Data System (ADS)

    Yu, X.; Wang, X.; Zhang, W.

    2014-12-01

    The double difference seismic tomography method is applied to the absolute first arrival P wave arrival times and high quality relative P arrival times of the Lushan seismic sequence to determine the detailed crustal 3D P wave velocity structure and the hypocenter parameters in the Lushan seismic area. The results show that the Lushan mainshock locates at 30.28 N, 103.98 E, with the depth of 16.38 km. The leading edge of aftershock in the northeast of mainshock present a spade with a steep dip angle, the aftershocks' extended length is about 12 km. In the southwest of the Lushan mainshock, the leading edge of aftershock in low velocity zone slope gently, the aftershocks' extended length is about 23 km. The P wave velocity structure of the Lushan seismic area shows obviously lateral heterogeneity. The P wave velocity anomalies represent close relationship with topographic relief and geological structure. In Baoxing area the complex rocks correspond obvious high-velocity anomalies extending down to 15 km depth?while the Cenozoic rocks are correlated with low-velocity anomalies. Our high-resolution tomographic model not only displays the general features contained in the previous models, but also reveals some new features. An obvious high-velocity anomaly is visible in Daxing area. The high-velocity anomalies beneath Baoxing and Daxing connect each other in 10 km depth, which makes the contrast between high and low velocity anomalies more sharp. Above 20 km depth the velocity structure in southwest and northeast segment of the mainshock shows a big difference: low-velocity anomalies are dominated the southwest segment, while high-velocity anomalies rule the northeast segment. The Lushan mainshock locates at the leading edge of a low-velocity anomaly surrounded by the Baoxing and Daxing high-velocity anomalies. The Lushan aftershocks in southwest are distributed in low-velocity anomalies or the transition belt: the footwall represents low-velocity anomalies, while the hanging wall shows high-velocity anomalies. The northeastern aftershocks are distributed at the boundary between high-velocity anomalies in Baoxing and Daxing area. The main seismogenic layer dips to northwest.

  17. Letter to the Editor Inter-ear variations in the eardrum impedance and stapes velocity in the

    E-print Network

    Allen, Jont

    Letter to the Editor Inter-ear variations in the eardrum impedance and stapes velocity in the human middle ear Douglas H. Keefe * Boys Town National Research Hospital, 555 N. 30th Street, Omaha, NE 68131, USA Received 11 May 2001; accepted 5 June 2001 In a study elucidating many aspects of middle-ear

  18. The thin section rock physics: Modeling and measurement of seismic wave velocity on the slice of carbonates

    SciTech Connect

    Wardaya, P. D., E-mail: pongga.wardaya@utp.edu.my; Noh, K. A. B. M., E-mail: pongga.wardaya@utp.edu.my; Yusoff, W. I. B. W., E-mail: pongga.wardaya@utp.edu.my [Petroleum Geosciences Department, Universiti Teknologi PETRONAS, Tronoh, Perak, 31750 (Malaysia); Ridha, S. [Petroleum Engineering Department, Universiti Teknologi PETRONAS, Tronoh, Perak, 31750 (Malaysia); Nurhandoko, B. E. B. [Wave Inversion and Subsurface Fluid Imaging Research Laboratory (WISFIR), Dept. of Physics, Institute of Technology Bandung, Bandung, Indonesia and Rock Fluid Imaging Lab, Bandung (Indonesia)

    2014-09-25

    This paper discusses a new approach for investigating the seismic wave velocity of rock, specifically carbonates, as affected by their pore structures. While the conventional routine of seismic velocity measurement highly depends on the extensive laboratory experiment, the proposed approach utilizes the digital rock physics view which lies on the numerical experiment. Thus, instead of using core sample, we use the thin section image of carbonate rock to measure the effective seismic wave velocity when travelling on it. In the numerical experiment, thin section images act as the medium on which wave propagation will be simulated. For the modeling, an advanced technique based on artificial neural network was employed for building the velocity and density profile, replacing image's RGB pixel value with the seismic velocity and density of each rock constituent. Then, ultrasonic wave was simulated to propagate in the thin section image by using finite difference time domain method, based on assumption of an acoustic-isotropic medium. Effective velocities were drawn from the recorded signal and being compared to the velocity modeling from Wyllie time average model and Kuster-Toksoz rock physics model. To perform the modeling, image analysis routines were undertaken for quantifying the pore aspect ratio that is assumed to represent the rocks pore structure. In addition, porosity and mineral fraction required for velocity modeling were also quantified by using integrated neural network and image analysis technique. It was found that the Kuster-Toksoz gives the closer prediction to the measured velocity as compared to the Wyllie time average model. We also conclude that Wyllie time average that does not incorporate the pore structure parameter deviates significantly for samples having more than 40% porosity. Utilizing this approach we found a good agreement between numerical experiment and theoretically derived rock physics model for estimating the effective seismic wave velocity of rock.

  19. The thin section rock physics: Modeling and measurement of seismic wave velocity on the slice of carbonates

    NASA Astrophysics Data System (ADS)

    Wardaya, P. D.; Noh, K. A. B. M.; Yusoff, W. I. B. W.; Ridha, S.; Nurhandoko, B. E. B.

    2014-09-01

    This paper discusses a new approach for investigating the seismic wave velocity of rock, specifically carbonates, as affected by their pore structures. While the conventional routine of seismic velocity measurement highly depends on the extensive laboratory experiment, the proposed approach utilizes the digital rock physics view which lies on the numerical experiment. Thus, instead of using core sample, we use the thin section image of carbonate rock to measure the effective seismic wave velocity when travelling on it. In the numerical experiment, thin section images act as the medium on which wave propagation will be simulated. For the modeling, an advanced technique based on artificial neural network was employed for building the velocity and density profile, replacing image's RGB pixel value with the seismic velocity and density of each rock constituent. Then, ultrasonic wave was simulated to propagate in the thin section image by using finite difference time domain method, based on assumption of an acoustic-isotropic medium. Effective velocities were drawn from the recorded signal and being compared to the velocity modeling from Wyllie time average model and Kuster-Toksoz rock physics model. To perform the modeling, image analysis routines were undertaken for quantifying the pore aspect ratio that is assumed to represent the rocks pore structure. In addition, porosity and mineral fraction required for velocity modeling were also quantified by using integrated neural network and image analysis technique. It was found that the Kuster-Toksoz gives the closer prediction to the measured velocity as compared to the Wyllie time average model. We also conclude that Wyllie time average that does not incorporate the pore structure parameter deviates significantly for samples having more than 40% porosity. Utilizing this approach we found a good agreement between numerical experiment and theoretically derived rock physics model for estimating the effective seismic wave velocity of rock.

  20. Velocity contrast along the Calaveras fault from analysis of fault zone head waves generated by repeating earthquakes

    E-print Network

    Black, Robert X.

    Velocity contrast along the Calaveras fault from analysis of fault zone head waves generated fault from analysis of fault zone head waves generated by repeating earthquakes, Geophys. Res. Lett., 35 contrast along the Calaveras fault that ruptured during the 1984 Morgan Hill earthquake using fault zone

  1. Computation of the Drift Velocity of Spiral Waves using Response Functions I.V. Biktasheva and A.J. Foulkes

    E-print Network

    Biktashev, Vadim N.

    wave rotation frequency, and spatial drift, that is slow movement of the spiral's rotation centre'' drift caused by (approx­ imately) periodic modulation of medium properties through external forcing [20Computation of the Drift Velocity of Spiral Waves using Response Functions I.V. Biktasheva and A

  2. Computation of the Drift Velocity of Spiral Waves using Response Functions I.V. Biktasheva and A.J. Foulkes

    E-print Network

    Biktashev, Vadim N.

    wave rotation frequency, and spatial drift, that is slow movement of the spiral's rotation centre" drift caused by (approx- imately) periodic modulation of medium properties through external forcing [20Computation of the Drift Velocity of Spiral Waves using Response Functions I.V. Biktasheva and A

  3. Shear Wave Velocity Structure and Evolution of Old Oceanic Lithosphere: Constraints from Rayleigh Wave Dispersion Across a Local Array of Ocean-Bottom Seismometers

    NASA Astrophysics Data System (ADS)

    Black, L.; Sotirov, T. A.; Weeraratne, D. S.; Forsyth, D. W.

    2014-12-01

    The growth process of old ocean lithosphere has long been debated. Thermal models have included half-space conductive cooling, constant thickness cooling plate models with heat supplied to the base of the lithosphere by small-scale convection, and half-space cooling disrupted by impinging plumes. Seafloor subsidence and heat flux values for seafloor ages above 80 Ma are satisfied by the plate model, but previous Rayleigh wave studies have shown that thickening of the plate extends deeper than expected for those models. However, there is a lack of data from sufficiently old seafloor to describe end-member upper mantle structure in areas that have not been reheated by hotspot activity. We analyze Rayleigh wave data obtained from the PLATE project (Pacific Lithosphere Anisotropy and Thickness Experiment), where the seafloor is 150-160 Ma and has not been resurfaced by subsequent volcanism. Rayleigh wave phase velocities for periods from 18 to 125 s are inverted for shear wave velocities to study upper mantle structure. Shear velocities in the western region of our study area reach approximately 5.0 km/s in the top 20 km of the lithosphere and slightly higher in the eastern region. These velocities are higher than any reported in regional or global studies of the oceanic lithosphere that have poorer lateral resolution. These velocities are consistent with those predicted for conductive cooling of old, dehydrated oceanic lithosphere in previous petrologic studies. Shear wave velocities show a negative velocity gradient from 30 to 150 km depth, reaching a minimum velocity of ~4.3 km/s in the asthenospheric low velocity zone. Overall, the velocity structure for our study area beneath old oceanic seafloor is very similar to that predicted for a cooling half-space.

  4. Three-dimensional P wave velocity model for the San Francisco Bay region, California

    USGS Publications Warehouse

    Thurber, C.H.; Brocher, T.M.; Zhang, H.; Langenheim, V.E.

    2007-01-01

    A new three-dimensional P wave velocity model for the greater San Francisco Bay region has been derived using the double-difference seismic tomography method, using data from about 5,500 chemical explosions or air gun blasts and approximately 6,000 earthquakes. The model region covers 140 km NE-SW by 240 km NW-SE, extending from 20 km south of Monterey to Santa Rosa and reaching from the Pacific coast to the edge of the Great Valley. Our model provides the first regional view of a number of basement highs that are imaged in the uppermost few kilometers of the model, and images a number of velocity anomaly lows associated with known Mesozoic and Cenozoic basins in the study area. High velocity (Vp > 6.5 km/s) features at ???15-km depth beneath part of the edge of the Great Valley and along the San Francisco peninsula are interpreted as ophiolite bodies. The relocated earthquakes provide a clear picture of the geometry of the major faults in the region, illuminating fault dips that are generally consistent with previous studies. Ninety-five percent of the earthquakes have depths between 2.3 and 15.2 km, and the corresponding seismic velocities at the hypocenters range from 4.8 km/s (presumably corresponding to Franciscan basement or Mesozoic sedimentary rocks of the Great Valley Sequence) to 6.8 km/s. The top of the seismogenic zone is thus largely controlled by basement depth, but the base of the seismogenic zone is not restricted to seismic velocities of ???6.3 km/s in this region, as had been previously proposed. Copyright 2007 by the American Geophysical Union.

  5. Lithospheric structure beneath Indochina block from Rayleigh wave phase velocity tomography

    NASA Astrophysics Data System (ADS)

    Yang, Ting; Liu, Fang; Harmon, Nicholas; Le, Khanh Phon; Gu, Shenyi; Xue, Mei

    2015-03-01

    The Indochina block is important to our understanding of the extrusion model as a consequence of the Indo-Eurasia collision. The lithospheric structure of this block, however, remains obscured due to a lack of sufficient instrumentation for high resolution seismic imaging. We present a shear velocity model derived from Rayleigh wave phase velocity tomography using data from recently deployed seismic networks in this region. Our inversion results for lithospheric structure show strong correlations with tectonic history in this block. A prominent slow-velocity anomaly (5 per cent) is observed in northern Indochina along the Ailao Shan-Red River (ASRR) shear zone including Chuxiong basin, Lanping-Simao fold belt and Thailand rift basin, which has seen extensive deformation events since Eocene. The Khorat Plateau basin is characterized by thick continental keel type lithosphere, consistent with palaeomagnetic and geological observations indicating this basin has experienced much less deformation than the surrounding regions. Additionally, our inversion imaged a sharp, lithospheric-scale velocity contrast across the southeastern segment of ASRR, indicative of a thin and thus relatively weak lithosphere southwest of Red River Fault. The thin lithosphere, low asthenospheric seismic velocities we observe and the average crustal thicknesses in the region suggest that the topography high is dynamically supported by upwelling asthenosphere rather than thickening of the crust/lithosphere. Based on the occurrence of Palaeogene volcanism and its timing, we prefer an explanation of thinning of the lithosphere and allowing a throughgoing fault rather than emplacement of a thin terrane to explain the thin lithosphere. Therefore, the anomalously thin lithosphere between Khorat Plateau and the ASRR in conjunction with other geological observations is generally consistent with the extrusion model for Indochina, which requires localization of lithospheric deformation around tectonic blocks.

  6. Crust and Upper Mantle Shear Velocity Structure and Azimuthal Anisotropy of Northeastern Tibet from Rayleigh-wave Two-station Analysis

    NASA Astrophysics Data System (ADS)

    Yang, Y.; Yao, H.

    2014-12-01

    Surface wave tomography is an important tool to study crust and upper mantle structure as well as seismic anisotropy, therefore providing insights into patterns of deformation in tectonically active regions. As we known, depth sensitivity of surface waves to shear wave speeds varies with period; therefore, we can probe seismic anisotropy at different depths from the inversion of surface wave dispersion data. In this study we use the earthquake surface-wave two-station method to determine the inter-station Rayleigh wave phase velocity dispersion curves in NE Tibet. We use 107 stations in NE Tibet, which are mainly from the INDEPTH-IV project and some regional networks. Rayleigh waves from 628 teleseismic events are analyzed to obtain 16771 dispersion curves in the period band 20-150 s, which are finally used to produce 2619 average inter-station dispersion curves. Then we perform surface wave tomography at various periods to simultaneously obtain phase speed variations and azimuthal anisotropy. The fast directions at different periods and the magnitudes of anisotropy are not alike in different regions. In some region the variation of fast axes with periods is small, possibly implying a vertically coherent deformation pattern there. There are regions with large changes of fast directions with periods, indicating complex deformation patterns in NE Tibet. We observe clear fault-parallel fast axes at intermediate periods, implying that the lithospheric deformation may be controlled by big strike-slip faults regionally in NE Tibet, for instance, the Kunlun fault. In the next step, we are planning to invert for 3-D depth-dependent shear wavespeeds and azimuthal anisotropy from the azimuthally anisotropic dispersion curve at each grid point using a Neighborhood Algorithm. This will provide more direct constraints on depth-dependent deformation patterns in the crust and upper mantle in NE Tibet.

  7. Bayesian Inversion of Broadband Surface Waves Dispersion Curves for Shear Velocity Structure and Anisotropy of the Crust and Upper Mantle

    NASA Astrophysics Data System (ADS)

    Ravenna, M.; Lebedev, S.

    2014-12-01

    The increasing amount of broadband phase velocity dispersion measurements around the world is leading to significant improvements in shear velocity models on both regional and global scales. As the relation between surface-wave dispersion and the seismic velocity structure of the earth is nonlinear, a reliable way to perform the inversion is Monte Carlo sampling in a Bayesian framework. Considering the high sensitivity of surface waves to Vs in broad depth intervals and their low sensitivity to Vs in thin layers, there are strong trade-offs between shear speeds at neighboring depths. MC sampling provides a way to quantify non-uniqueness of the inverted shear velocity models.We develop a Markov Chain Monte Carlo method for joint inversion of Rayleigh- and Love-wave dispersion curves that is able to yield robust radially and azimuthally anisotropic shear velocity profiles, with resolution to depths down to the transition zone. The inversion is a one step process that doesn't involve any linearization procedure or a priori bounds around a reference model. In a fixed dimensional Bayesian formulation, we chose to set the number of parameters relatively high, with a more dense parametrization in the uppermost mantle, therefore we used a Gaussian a priori distribution of the parameters in order to avoid overfitting.We apply the MCMC algorithm to the inversion of surface-wave phase velocities accurately determined in broad period ranges in a few test regions, and present the resulting radially and azimuthally anisotropic shear velocity models.

  8. Effects of exciting frequencies, grain sizes, and damage upon P-wave velocity for ultrasonic NDT of concrete

    NASA Astrophysics Data System (ADS)

    Ju, Jiann W.; Weng, Lisheng

    2000-05-01

    This paper focuses on the experimental study of the effects of exciting frequencies, grain (aggregate) sizes, and damage upon the ultrasonic P-wave velocity when performing the ultrasonic nondestructive testing (NDT) for concrete specimens. Two batches of concrete and mortar specimens were prepared in the laboratory for the investigation of the effects from the stated factors upon the P-wave velocity. Damage here mostly refers to microcracks and microvoids in concrete. Five different aggregate sizes, 0' (mortar), 3/8', 1/2', 3/4', and 1', were selected to demonstrate the grain (aggregate) size effect. Exciting frequencies of the ultrasonic wave were set to range from 100 kHz to 1,000 kHz, with increment of 50 kHz, to demonstrate the frequency effect. Styrofoam particles were mixed into the comparison concrete and mortar specimens to simulate the distributed microvoids (damage). Different volume fractions of styrofoam particles were mixed into the mortar specimens in order to study the effect of different porosities (damage) upon the P-wave velocity. The experimental observations show that, for mortar and concrete specimens with aggregate sizes from 0 to 1 inch, the P-wave velocity would not be affected significantly within the tested frequency range (100 - 1000 kHz). The normalized P-wave velocity exhibits almost identical pattern upon the exciting frequencies for all specimens.

  9. Measuring the variations of the apparent settling velocity for fine particles

    Microsoft Academic Search

    Torben Larsen

    2000-01-01

    This note establishes the fact that the settling velocity for fine flocculent particles in flowing aquatic systems vary considerably and the settling velocity should therefore be understood as a variable which varies temporally and spatially in the flow field. In the mathematical formulation the settling velocity of a suspension appears in the actual and local mass conservation equation as an

  10. Anisotropic Rayleigh-wave Phase-velocity Maps in Northern Vietnam

    NASA Astrophysics Data System (ADS)

    Zhao, L.; Legendre, C. P.; Huang, W.; Huang, B.

    2013-12-01

    Northern Vietnam is the location of both the Song Ma Complex, the suture between the Indochina and South China Blocks, and the southern end of the giant Red River Shear Zone. Lithospheric structure provides important clues to the evolutions of the tectonic boundary zone and the interaction between the Indochina and South China Blocks. During 2006-2008, an array of 24 broadband stations were deployed in northern Vietnam in a collaborative project between the Institute of Geophysics of the Vietnam Academy of Science and Technology and the Institute of Earth Sciences of Academic Sinica in Taiwan. In this study, we use Rayleigh waveforms recorded at those stations from globally distributed earthquakes to construct the regional isotropic and azimuthally anisotropic phase velocity maps. Rayleigh-wave dispersion curves in the period range of 10-200 sec are obtained manually by the two-station method using vertical-component broadband waveforms. The dispersion curves along the densely distributed crossing paths are inverted via the LSQR algorithm for the isotropic and azimuthally anisotropic phase-velocity maps at a number of periods. Results will be compared with previous studies in this region based on body-wave traveltimes, SKS splitting observations and receiver functions, and with the tectonic features observed in the region.

  11. Elastic constants measured from acoustic wave velocities in barium titanate piezoelectric ceramics

    NASA Astrophysics Data System (ADS)

    Ogawa, Toshio; Ikegaya, Taiki

    2015-01-01

    The longitudinal and transverse wave velocities in barium titanate (BT) ceramics sintered at different firing temperatures were measured using an ultrasonic precision thickness gauge with high-frequency pulse generation to evaluate elastic constants, such as Young’s modulus and Poisson’s ratio. With increasing firing temperature, the longitudinal and transverse wave velocities increased; as a result, Young’s modulus increased because of BT ceramics being mechanically hard. Poisson’s ratio after DC poling, however, was almost independent of the firing temperature. It was confirmed that there was an important factor for generating piezoelectricity regarding changes in Young’s modulus and Poisson’s ratio after DC poling compared with those before DC poling, that is, lowering Young’s modulus and increasing Poisson’s ratio. Furthermore, the modulus of rigidity and bulk modulus increased with the firing temperature because of the increase in ceramic bulk density. The modulus of rigidity decreased and the bulk modulus increased during DC poling because of domain alignment.

  12. Crosswell seismic studies in gas hydrate-bearing sediments: P wave velocity and attenuation tomography

    NASA Astrophysics Data System (ADS)

    Bauer, K.; Haberland, Ch.; Pratt, R. G.; Ryberg, T.; Weber, M. H.; Mallik Working Group

    2003-04-01

    We present crosswell seismic data from the Mallik 2002 Production Research Well Program, an international research project on Gas Hydrates in the Northwest Territories of Canada. The program participants include 8 partners; The Geological Survey of Canada (GSC), The Japan National Oil Corporation (JNOC), GeoForschungsZentrum Potsdam (GFZ), United States Geological Survey (USGS), United States Department of the Energy (USDOE), India Ministry of Petroleum and Natural Gas (MOPNG)/Gas Authority of India (GAIL) and the Chevron-BP-Burlington joint venture group. The crosswell seismic measurements were carried out by making use of two 1160 m deep observation wells (Mallik 3L-38 and 4L-38) both 45 m from and co-planar with the 1188 m deep production research well (5L-38). A high power piezo-ceramic source was used to generate sweeped signals with frequencies between 100 and 2000 Hz recorded with arrays of 8 hydrophones per depth level. A depth range between 800 and 1150 m was covered, with shot and receiver spacings of 0.75 m. High quality data could be collected during the survey which allow for application of a wide range of crosswell seismic methods. The initial data analysis included suppression of tube wave energy and picking of first arrivals. A damped least-squares algorithm was used to derive P-wave velocities from the travel time data. Next, t* values were derived from the decay of the amplitude spectra, which served as input parameters for a damped least-squares attenuation tomography. The initial results of the P-wave velocity and attenuation tomography reveal significant features reflecting the stratigraphic environment and allow for detection and eventually quantification of gas hydrate bearing sediments. A prominent correlation between P velocity and attenuation was found for the gas hydrate layers. This contradicts to the apparently more meaningful inverse correlation as it was determined for the gas hydrates at the Blake Ridge but supports the results from the Mallik 2L-38 sonic log data. The P velocities and attenuation values, if combined with other information can be important for the quantitative evaluation of the gas hydrate saturation, and may further constrain petrophysical models of the hydrate bearing sediment formation.

  13. Shear-wave Velocity Structure of Surabaya, Indonesia, Inferred from Microtremor Observation

    NASA Astrophysics Data System (ADS)

    Deng, X.; Megawati, K.; Yamanaka, H.

    2010-12-01

    Surabaya, the second-largest city of Indonesia, is located on the northern shore of eastern Java at the mouth of the Mas River and along the edge of the Madura Strait. Though there are not many occurrences of large earthquakes, the region has been exposed to moderate earthquakes frequently. Moreover, Surabaya lies over the alluvium deposit that can be critical for the amplification of seismic waves. Towards the southwestern part of the study area, there is the exposure of sedimentary rocks. Shear wave velocity (Vs) is an important parameter for evaluating the dynamic soil behavior of subsurface structures. Small array measurements of microtremor at 36 sites in the city of Surabaya were carried to estimate the shallow Vs profiles for site effect analysis. The spatial autocorrelation coefficient (SPAC) method was used to determine the phase velocity in the period ranging from 0.1 s to 0.5 s and the iterative inversion technique was subsequently applied to determine the Vs profiles at each site. Large array measurements of microtremor at 11 sites were also carried out to estimate deep Vs profiles. Based on the previous shallow Vs profiles from SPAC, the frequency wavenumber (FK) method was subsequently used to determine the phase velocity in the period from 0.5 s to 3 s and depth of soil profiles down to 800 m. Vs30, the average shear wave velocity in the top 30 m of soil profiles, is a representative value to classify the site condition. It was calculated at each site according to definition in the International Building Code (IBC 2006). The maps of site classification are proposed with Kriging interpolations. Site class D is assigned in southwest corner part while site class E is assigned to the rest of Surabaya. The low Vs values confirms well with the loose soil deposit of the area. Additionally, the regression analysis between topographic elevation and Vs in the logarithm shows a linear relationship. However, it is difficult to conclude the relationship between Vs and slope, since most area of the test region are flat lying (slope gradient range from 0 to 2 degree).

  14. Lithospheric Structure of Arabia from the Joint Inversion of P- and S-wave Receiver Functions and Dispersion Velocities

    NASA Astrophysics Data System (ADS)

    Julia, Jordi; Al-Amri, Abdullah; Pasyanos, Michael; Rodgers, Arthur; Matzel, Eric; Nyblade, Andrew

    2013-04-01

    Seismic imaging of the lithosphere under the Arabian shield and platform is critical to help answer important geologic questions of regional and global interest. The Arabian Shield can be regarded as an amalgamation of several arcs and microplates of Proterozoic age that culminated in the accretion of the Arabian portion of Gondwana during the Pan-African event at ~550 Ma and the role of important geologic features observed on the surface - such as the lineaments and shear zones separating the Proterozoic terrains in the shield - is not completely understood. Also, current models of Precambrian crustal evolution predict that Proterozoic terranes are underlain by fertile (FeO-rich) cratonic roots that should promote the production of mafic magmas and underplating of the Arabian shield terranes, and the shield contains Tertiary and Quaternary volcanic rocks related to the early stages of the Red Sea formation that might also be related to plume-related lithospheric "erosion". In order to better understand these relationships, we are developing new velocity models of litospheric structure for the Arabian shield and platform from the joint inversion of up to four seismic data sets: P-wave receiver functions, S-wave receiver functions, dispersion velocities from surface-waves, and dispersion velocities from ambient-noise cross-correlations. The joint inversion combines constraints on crustal thickness from P-wave receiver functions, constraints on lithospheric thickness from S-wave receiver functions and constraints on S-velocity and S-velocity gradients from dispersion velocities to produce detailed S-velocity profiles under single recording stations. We will present S-velocity profiles for a number of permanent stations operated by the Saudi Geological Survey and the King ing Abdulaziz Center for Science and Technology as well as stations from past temporary deployments and discuss the implications of the velocity models regarding composition and tectonics of the Arabian shield and platform.

  15. Interseasonal Variations in the Middle Atmosphere Forced by Gravity Waves

    NASA Technical Reports Server (NTRS)

    Mayr, H. G.; Mengel, J. G.; Drob, D. P.; Porter, H. S.; Chan, K. L.; Bhartia, P. K. (Technical Monitor)

    2002-01-01

    In our Numerical Spectral Model (NSM), which incorporates Hines' Doppler Spread Parameterization, gravity waves (GW) propagating in the east/west direction can generate the essential features of the observed equatorial oscillations in the zonal circulation and in particular the QBO (quasi-biennial oscillation) extending from the stratosphere into the upper mesosphere. We report here that the NSM also produces inter-seasonal variations in the zonally symmetric (m = 0) meridional circulation. A distinct but variable meridional wind oscillation (MWO) is generated, which appears to be the counterpart to the QBO. With a vertical grid-point resolution of about 0.5 km, the NSM produces the MWO through momentum deposition of GWs propagating in the north/south direction. The resulting momentum source represents a third (generally odd) order non-linear function of the meridional winds, and this enables the oscillation, as in the case of the QBO for the zonal winds. Since the meridional winds are relatively small compared to the zonal winds, however, the vertical wavelength that maintains the MWO is much smaller, i.e., only about 10 km instead of 40 km for the QBO. Consistent with the associated increase of the viscous stress, the period of the MWO is then short compared with that of the QBO, i.e., only about two to four months. Depending on the strength of the GW forcing, the computed amplitudes of the MWO are typically 4 m/s in the upper stratosphere and mesosphere, and the associated temperature amplitudes are between about 2 and 3 K. These amplitudes may be observable with the instruments on the TIMED spacecraft. Extended computer simulations with the NSM in 2D (two-dimensional) and 3D (three-dimensional) reveal that the MWO is modulated by and in turn influences the QBO.

  16. Nonlinear low frequency wave propagation in electronegative dusty plasma: Effects of adiabatic and nonadiabatic charge variations

    SciTech Connect

    Sarkar, Subrata; Khan, Manoranjan; Gupta, M. R. [Department of Instrumentation Science, Jadavpur University, Kolkata-700 032 (India); Ghosh, Samiran [Department of Applied Mathematics, University of Calcutta 92, Acharya Prafulla Chandra Road, Kolkata-700 009 (India)

    2011-09-15

    The effects of both adiabatic and nonadiabatic charge variations on small but finite amplitude nonlinear dust acoustic wave (DAW) have been investigated in an electronegative dusty plasma in presence of a static magnetic field. It is found that in case of adiabatic charge variations, the nonlinear wave is governed by the Zakharov-Kuznetsov (ZK) equation which yields the usual solitary wave solution. On the other hand, in case of nonadiabatic charge variations, the dynamics is governed by the Zakharov-Kuznetsov-Burgers' (ZKB) equation which exhibits shock like structures. The results are discussed in the context of cometary plasma.

  17. P and S wave velocity measurements of water-rich sediments from the Nankai Trough, Japan

    NASA Astrophysics Data System (ADS)

    Schumann, Kai; Stipp, Michael; Behrmann, Jan H.; Klaeschen, Dirk; Schulte-Kortnack, Detlef

    2014-02-01

    Acoustic velocities were measured during triaxial deformation tests of silty clay and clayey silt core samples from the Nankai subduction zone (Integrated Ocean Drilling Program Expeditions 315, 316, and 333). We provide a new data set, continuously measured during pressure increase and subsequent axial deformation. A new data processing method was developed using seismic time series analysis. Compressional wave velocities (Vp) range between about 1450 and 2200 m/s, and shear wave velocities (Vs) range between about 150 and 800 m/s. Vp slightly increases with rising effective confining pressure and effective axial stress. Samples from the accretionary prism toe show the highest Vp, while fore-arc slope sediments show lower Vp. Samples from the incoming plate, slightly richer in clay minerals, have the lowest values for Vp. Vs increases with higher effective confining pressures and effective axial stress, irrespective of composition and tectonic setting. Shear and bulk moduli are between 0.2 and 1.3 GPa, and 3.85 and 8.41 GPa, respectively. Elastic moduli of samples from the accretionary prism toe and the footwall of the megasplay fault (1.50 and 3.98 GPa) are higher than those from the hanging wall and incoming plate (0.59 and 0.88 GPa). This allows differentiation between normal and overconsolidated sediments. The data show that in a tectonosedimentary environment of only subtle compositional differences, acoustic properties can be used to differentiate between stronger (accretionary prism toe) and weaker (fore-arc slope, incoming plate) sediments. Especially Vp/Vs ratios may be instrumental in detecting zones of low effective stress and thus high pore fluid pressure.

  18. Robust segmentation methods with an application to aortic pulse wave velocity calculation.

    PubMed

    Babin, Danilo; Devos, Daniel; Pižurica, Aleksandra; Westenberg, Jos; Vansteenkiste, Ewout; Philips, Wilfried

    2014-04-01

    Aortic stiffness has proven to be an important diagnostic and prognostic factor of many cardiovascular diseases, as well as an estimate of overall cardiovascular health. Pulse wave velocity (PWV) represents a good measure of the aortic stiffness, while the aortic distensibility is used as an aortic elasticity index. Obtaining the PWV and the aortic distensibility from magnetic resonance imaging (MRI) data requires diverse segmentation tasks, namely the extraction of the aortic center line and the segmentation of aortic regions, combined with signal processing methods for the analysis of the pulse wave. In our study non-contrasted MRI images of abdomen were used in healthy volunteers (22 data sets) for the sake of non-invasive analysis and contrasted magnetic resonance (MR) images were used for the aortic examination of Marfan syndrome patients (8 data sets). In this research we present a novel robust segmentation technique for the PWV and aortic distensibility calculation as a complete image processing toolbox. We introduce a novel graph-based method for the centerline extraction of a thoraco-abdominal aorta for the length calculation from 3-D MRI data, robust to artifacts and noise. Moreover, we design a new projection-based segmentation method for transverse aortic region delineation in cardiac magnetic resonance (CMR) images which is robust to high presence of artifacts. Finally, we propose a novel method for analysis of velocity curves in order to obtain pulse wave propagation times. In order to validate the proposed method we compare the obtained results with manually determined aortic centerlines and a region segmentation by an expert, while the results of the PWV measurement were compared to a validated software (LUMC, Leiden, the Netherlands). The obtained results show high correctness and effectiveness of our method for the aortic PWV and distensibility calculation. PMID:24405817

  19. Search for radial velocity variations in eight M-dwarfs with NIRSPEC/Keck II

    NASA Astrophysics Data System (ADS)

    Rodler, F.; Deshpande, R.; Zapatero Osorio, M. R.; Martín, E. L.; Montgomery, M. M.; Del Burgo, C.; Creevey, O. L.

    2012-02-01

    Context. Radial velocity (RV) measurements from near-infrared spectra have become a potentially powerful tool to search for planets around cool stars and sub-stellar objects. As part of a large survey to characterize M-dwarfs using NIRSPEC at Keck II, we obtained spectra of eight late M-dwarfs (spectral types M5.0-M8.0) during two or more observing epochs per target. These spectra were taken with intermediate spectral resolving powers (R ~ 20 000) in the J-band. Aims: We search for relative RV variability in these late M-dwarfs and test the NIRSPEC capability of detecting short-period brown dwarf and massive planetary companions around low-mass stars in the J-band (?1.25 ?m). Additionally, we reanalyzed the data of the M8-type star vB10 (one of our targets), which had been presented in another article. Methods: To achieve a precise RV measurement stability, the NIRSPEC spectra were self-calibrated by making use of the telluric absorption lines, which are present in the observed spectra and were used as a long-term stable reference. In the modeling process a multi-parameter ?2-optimization was employed to generate an accurate description of the observation. The telluric lines allowed us to model the instrumental profile of the spectrograph and the determination of the Doppler shift of the stellar absorption lines. Results: For the entire M-dwarf sample, we found no evidence of relative RV variations induced by a short-period brown dwarf or massive planetary companion. The typical RV precision of the measurements is between 180 and 300 m s-1, which is sufficient to detect hot Neptunes around M-dwarfs. Moreover, we found that the spurious RV shift detected previously of the star VB10 was caused by asymmetries in the instrumental profile between different observing epochs, which were not taken into account in the previous analysis.

  20. Ultrasonic P and S Wave Velocities in Carbonates From the Arab Formation, Saudi Arabia, and the Western Canada Sedimentary Basin, Canada

    NASA Astrophysics Data System (ADS)

    Bakhorji, A.; Schmitt, D.

    2008-12-01

    The fact that many of the giant hydrocarbon reservoirs, such as Ghawar field in Saudi Arabia and the Grosmont formation in Alberta, are carbonates make such rocks an important research topic. This is particularly true the bulk of laboratory investigations have focused on siliclatic reservoir materials; more work on carbonates is necessary. Anselmetti and Eberli (1993) have shown that the influence of mineral compositions in carbonates is minimal, and cannot be a reason for large changes in velocities. They found that the velocity variation in carbonates is mainly controlled by porosity and pore type. Assefa et al. (2003) showed that the velocities of rocks with high aspect ratio pores are greater than those with low aspect ratio. In this study, we are investigating the effect of pressure, porosity, permeability and saturation in carbonate rock. To date, we have measured the ultrasonic compressional and shear wave velocities for forty carbonate rocks, thirty eight of them are from Arab formation in Saudi Arabia and two from the Western Canad Sedimentary Basin (WCSB). The samples were measured both in dry and water saturated conditions under different confining pressures that varied from 2.5 MPa to 25 MPa for Arab-D samples and from 5 MPa to 70 MPa for WCSB samples. In order to study the effect of microcrack closure, one Arab and one WCSB samples were measured at confining pressure of 40 MPa and 90 MPa respectively. Higher confining pressures were avoided in order to lower the risk of damaging the samples. Some preliminary results from P and S wave velocity measurements on several samples under dry and water saturation conditions are presented. These measured results and the calculated water saturated velocities from Gassmann's equation are compared

  1. A method to measure a relative transverse velocity of source-lens-observer system using gravitational lensing of gravitational waves

    E-print Network

    Yousuke Itoh; Toshifumi Futamase; Makoto Hattori

    2009-08-03

    Gravitational waves propagate along null geodesics like light rays in the geometrical optics approximation, and they may have a chance to suffer from gravitational lensing by intervening objects, as is the case for electromagnetic waves. Long wavelength of gravitational waves and compactness of possible sources may enable us to extract information in the interference among the lensed images. We point out that the interference term contains information of relative transverse velocity of the source-lens-observer system, which may be obtained by possible future space-borne gravitational wave detectors such as BBO/DECIGO.

  2. Short-scale variations of shear-wave splitting across the Dead Sea basin: Evidence for the effects of sedimentary fill

    NASA Astrophysics Data System (ADS)

    Kaviani, Ayoub; Rümpker, Georg; Weber, Michael; Asch, Günter

    2011-02-01

    We examine shear-wave splitting of SKS waveforms collected by a temporary array of 68 stations in the region of the Dead Sea basin. The observed splitting parameters exhibit systematic variations along a dense, EW-trending 60 km profile across the basin. The delay times vary significantly between 1.0 and 2.8 seconds with smaller values in the very center of the profile. The fast polarizations are oriented more-or-less parallel to the strike of the Dead Sea transform fault and vary between -10 and 20 degrees with respect to North. Finite-frequency waveform modeling reveals that the source-region of the small-scale lateral variations is likely located within the crust. The modeling further shows that purely isotropic velocity variations affect shear-wave splitting: To a large degree, the observed variations of splitting parameters can be explained by the sedimentary fill of the basin and its low isotropic seismic velocities, whereas the mantle is uniformly anisotropic. Our study indicates that precaution must be taken when interpreting short-scale lateral variations of shear wave splitting in terms of anisotropic structures in the crust or upper mantle.

  3. Low-velocity zones along the San Jacinto Fault, Southern California, from body waves recorded in dense linear arrays

    NASA Astrophysics Data System (ADS)

    Yang, Hongfeng; Li, Zefeng; Peng, Zhigang; Ben-Zion, Yehuda; Vernon, Frank

    2014-12-01

    We derive high-resolution information on low-velocity fault zone (FZ) structures along the San Jacinto Fault Zone (SJFZ), Southern California, using waveforms of local earthquakes that are recorded at multiple linear cross-fault arrays. We observe clear across-fault delays of direct P and S waves, indicating damage zones at different segments of the SJFZ. We then compute synthetic traveltimes and waveforms using generalized ray theory and perform forward modeling to constrain the FZ parameters. At the southern section near the trifurcation area, the low-velocity zone (LVZ) of the Clark branch has a width of ~200 m, 30-45% reduction in Vp, and ~50% reduction in Vs. From array data across the Anza seismic gap, we find a LVZ with ~200 m width and ~50% reduction in both Vp and Vs, nearly as prominent as that on the southern section. We only find prominent LVZs beneath three out of the five arrays, indicating along-strike variations of the fault damage. FZ-reflected phases are considerably less clear than those observed above the rupture zone of the 1992 Landers earthquake shortly after the event. This may reflect partially healed LVZs with less sharp boundaries at the SJFZ, given the relatively long lapse time from the last large surface-rupturing event. Alternatively, the lack of observed FZ-reflected phases could be partially due to the relatively small aperture of the arrays. Nevertheless, the clear signatures of damage zones at Anza and other locations indicate very slow healing process, at least in the top few kilometers of the crust.

  4. The Effect of Pressure on the In Situ Variation of Velocity with Depth in IODP Hole U1309D

    NASA Astrophysics Data System (ADS)

    Carlson, R. L.; Blackman, D. K.; Harris, A. C.; Collins, J. A.

    2008-12-01

    It has long been known that cracks have a profound effect on seismic velocities in the uppermost oceanic crust. It is also well known that seismic velocities in cracked media are sensitive to pressure, but this effect has not been confirmed where the velocity structure is not masked by lithologic changes - e.g., in the gabbro section at Hole 735B on Atlantis Bank. The downhole log from the upper 800 m of the altered gabbro section penetrated by IODP Hole U1309D exhibits the characteristic power-law increase of velocity with depth: velocities increase rapidly from 4 - 5 km/s near 60 mbsf, to 5 - 6 km/s at 250 m, then less rapidly to 6 - 6.5 km/s at 800 mbsf. We fit the power law "bed-of-nails" model that describes the dependence of velocity on effective pressure in laboratory data to the sonic log. Excellent agreement of traveltimes computed from the power law model with observed traveltimes from a VSP ("checkshot") survey indicates good internal consistency between the model, the sonic log, and the VSP. Systematic (±0.5 km/s) variations of the sonic log about the best-fit model curve may reflect downhole changes in relative crack density ranging from ~0.6 to 1.4.

  5. VARIATIONAL DISCRETIZATION OF LINEAR WAVE EQUATIONS ON EVOLVING SURFACES

    E-print Network

    Tübingen, Universität

    of the classical acoustic wave equation on a fixed spatial domain. We have no specific application in mind analysis of the linear wave equation on a fixed domain has provided much insight into the numerical is a stability analysis of full discretizations with time-dependent mass and stiffness matrices in the natural

  6. Guided Wave Damage Detection in Composite Plates under Temperature Variations

    Microsoft Academic Search

    Chan Yik Park; Seung Moon Jun

    2010-01-01

    One of the main challenges of guided wave structural damage detection is to find an effective way of compensating temperature changes and to apply it to existing damage detection methods. This article describes a simple method for applying guided waves to the problem of detecting damage in the presence of temperature changes. In order to examine the effectiveness of the

  7. Effect of Finite Velocity of Thermal Wave on Stress Focusing Phenomena

    NASA Astrophysics Data System (ADS)

    Furukawa, Toshio; Sueyoshi, Toshiyasu

    When an isotropic and homogeneous solid sphere and/or infinitely long solid cylinder are suddenly subjected to an instantaneous uniform heating, a stress wave occurs at the moment thermal impact is applied. The stress wave proceeds radially inward to the center of a sphere and/or cylinder. The wave may accumulate at the center and give rise to very large stress magnitudes, even though the initial thermal stress is relatively small. This phenomenon is called the stress-focusing effect. In this study, the stress focusing effect in a solid sphere and solid cylinder under instantaneous uniform heating at the free surface is studied on the basis of the generalized thermoelastic theories, that is, the Lord-Shulman (L-S) and the Green-Lindsay (G-L) theories. The combined governing equations of both theories are solved by the numerical inversion of Laplace transform. Calculations have been performed to exhibit the radial distributions and time variations of the radial and hoop thermal stresses on the basis of the L-S theory. The effects of the thermomechanical coupling and the relaxation time on the stress focusing phenomena as well as the singularity of stresses are discussed.

  8. Moho depth variation beneath southwestern Japan revealed from the velocity structure based on receiver function inversion

    Microsoft Academic Search

    Katsuhiko Shiomi; Kazushige Obara; Haruo Sato

    2006-01-01

    The Philippine Sea plate is subducting under the Eurasian plate beneath the Chugoku-Shikoku region, southwestern Japan. We have constructed depth contours for the continental and oceanic Mohos derived from the velocity structure based on receiver function inversion. Receiver functions were calculated using teleseismic waveforms recorded by the high-density seismograph network in southwestern Japan. In order to determine crustal velocity structure,

  9. 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.

  10. Lunar near-surface shear wave velocities at the Apollo landing sites as inferred from spectral amplitude ratios

    NASA Technical Reports Server (NTRS)

    Horvath, P.; Latham, G. V.; Nakamura, Y.; Dorman, H. J.

    1980-01-01

    The horizontal-to-vertical amplitude ratios of the long-period seismograms are reexamined to determine the shear wave velocity distributions at the Apollo 12, 14, 15, and 16 lunar landing sites. Average spectral ratios, computed from a number of impact signals, were compared with spectral ratios calculated for the fundamental mode Rayleigh waves in media consisting of homogeneous, isotropic, horizontal layers. The shear velocities of the best fitting models at the different sites resemble each other and differ from the average for all sites by not more than 20% except for the bottom layer at station 14. The shear velocities increase from 40 m/s at the surface to about 400 m/s at depths between 95 and 160 m at the various sites. Within this depth range the velocity-depth functions are well represented by two piecewise linear segments, although the presence of first-order discontinuities cannot be ruled out.

  11. The relationship between gas hydrate saturation and P-wave velocity of pressure cores obtained in the Eastern Nankai Trough

    NASA Astrophysics Data System (ADS)

    Konno, Y.; Yoneda, J.; Jin, Y.; Kida, M.; Suzuki, K.; Nakatsuka, Y.; Fujii, T.; Nagao, J.

    2014-12-01

    P-wave velocity is an important parameter to estimate gas hydrate saturation in sediments. In this study, the relationship between gas hydrate saturation and P-wave velocity have been analyzed using natural hydrate-bearing-sediments obtained in the Eastern Nankai Trough, Japan. The sediment samples were collected by the Hybrid Pressure Coring System developed by Japan Agency for Marine-Earth Science and Technology during June-July 2012, aboard the deep sea drilling vessel CHIKYU. P-wave velocity was measured on board by the Pressure Core Analysis and Transfer System developed by Geotek Ltd. The samples were maintained at a near in-situ pressure condition during coring and measurement. After the measurement, the samples were stored core storage chambers and transported to MHRC under pressure. The samples were manipulated and cut by the Pressure-core Non-destructive Analysis Tools or PNATs developed by MHRC. The cutting sections were determined on the basis of P-wave velocity and visual observations through an acrylic window equipped in the PNATs. The cut samples were depressurized to measure gas volume for saturation calculations. It was found that P-wave velocity correlates well with hydrate saturation and can be reproduced by the hydrate frame component model. Using pressure cores and pressure core analysis technology, nondestructive and near in-situ correlation between gas hydrate saturation and P-wave velocity can be obtained. This study was supported by funding from the Research Consortium for Methane Hydrate Resources in Japan (MH21 Research Consortium) planned by the Ministry of Economy, Trade and Industry (METI), Japan.

  12. MEASUREMENT OF COMPRESSIONAL-WAVE SEISMIC VELOCITIES IN 29 WELLS AT THE HANFORD SITE

    SciTech Connect

    PETERSON SW

    2010-10-08

    Check shot seismic velocity surveys were collected in 100 B/C, 200 East, 200-PO-1 Operational Unit (OU), and the Gable Gap areas in order to provide time-depth correlation information to aid the interpretation of existing seismic reflection data acquired at the Hanford Site (Figure 1). This report details results from 5 wells surveyed in fiscal year (FY) 2008, 7 wells in FY 2009, and 17 wells in FY 2010 and provides summary compressional-wave seismic velocity information to help guide future seismic survey design as well as improve current interpretations of the seismic data (SSC 1979/1980; SGW-39675; SGW-43746). Augmenting the check shot database are four surveys acquired in 2007 in support of the Bechtel National, Inc. Waste Treatment Plant construction design (PNNL-16559, PNNL-16652), and check shot surveys in three wells to support seismic testing in the 200 West Area (Waddell et al., 1999). Additional sonic logging was conducted during the late 1970s and early 1980s as part of the Basalt Waste Isolation Program (BWIP) (SSC 1979/1980) and check shot/sonic surveys as part of the safety report for the Skagit/Hanford Nuclear project (RDH/10-AMCP-0164). Check shot surveys are used to obtain an in situ measure of compressional-wave seismic velocity for sediment and rock in the vicinity of the well point, and provide the seismic-wave travel time to geologic horizons of interest. The check shot method deploys a downhole seismic receiver (geophone) to record the arrival of seismic waves generated by a source at the ground surface. The travel time of the first arriving seismic-wave is determined and used to create a time-depth function to correlate encountered geologic intervals with the seismic data. This critical tie with the underlying geology improves the interpretation of seismic reflection profile information. Fieldwork for this investigation was conducted by in house staff during the weeks of September 22, 2008 for 5 wells in the 200 East Area (Figure 2); June 1, 2009 for 7 wells in the 200-PO-1 OU and Gable Gap regions (see Figure 3 and Figure 4); and March 22, 2010 and April 19, 2010 for 17 wells in the 200 East, The initial scope of survey work was planned for Wells 299-EI8-1, 699-2-E14, 699-12-18, 699-16-51, 699-42-30, 699-53-55B, 699-54-18D, and 699-84-34B. Well 299-E18-1 could not be entered due to bent casing (prevented removal of the pump), wells 699-12-18 and 699-42-30 could not be safely reached by the logging truck, Well 699-16-51 was decommissioned prior to survey start, Well 699-53-55B did not have its pump pulled, and Wells 699-2-EI4, 699-54-18D, and 699-84-34B are artesian and capped with an igloo structure. Table 1 provides a list of wells that were surveyed and Figure 1 through Figure 5 show the well locations relative to the Hanford Site.

  13. Estimation of ultrasonic guided wave mode conversion in a plate with thickness variation

    Microsoft Academic Search

    Younho Cho

    2000-01-01

    The hybrid boundary element method aimed at analyzing Lamb wave scattering from defects can provide us with an excellent numerical tool for tackling complicated mode conversion phenomena under waveguide thickness variation. In this paper, utilization of hybrid boundary element modeling for specific Lamb wave mode incidence situations with special energy distributions along the structural cross section is proposed for estimating

  14. Antenna patterns of nonsinusoidal waves with the time variation of a Gaussian pulse. IV

    Microsoft Academic Search

    Malek G. M. Hussain; Maha M. M. Al-Halabi; Amjad A. Omar

    1989-01-01

    An experimental setup of a large-current radiator and a closed-loop sensor has recently been developed for the radiation and reception of nonsinusoidal electromagnetic waves. The time variation of the radiated waves approximately equals that of a Gaussian pulse. Here, oscillograms of antenna current and radiated nonsinusoidal pulses are presented. Magnetic flux lines representing the radiation of Gaussian pulses from a

  15. Red Algae Respond to Waves: Morphological and Mechanical Variation in Mastocarpus papillatus Along

    E-print Network

    Denny, Mark

    Red Algae Respond to Waves: Morphological and Mechanical Variation in Mastocarpus papillatus Along Grove, California, 93950 Abstract. Intertidal algae are exposed to the potentially severe drag forces generated by crashing waves, and several species of brown algae respond, in part, by varying the strength

  16. A Variational Stereo Method for the Three-Dimensional Reconstruction of Ocean Waves

    Microsoft Academic Search

    Guillermo Gallego; Anthony Yezzi; Francesco Fedele; Alvise Benetazzo

    2011-01-01

    We develop a novel remote sensing technique for the observation of waves on the ocean surface. Our method infers the 3-D waveform and radiance of oceanic sea states via a variational stereo imagery formulation. In this setting, the shape and radiance of the wave surface are given by minimizers of a composite energy functional that combines a photometric matching term

  17. Seismic Velocity Structure and Depth-Dependence of Anisotropy in the Red Sea and Arabian Shield from Surface Wave Analysis

    SciTech Connect

    Hansen, S; Gaherty, J; Schwartz, S; Rodgers, A; Al-Amri, A

    2007-07-25

    We investigate the lithospheric and upper mantle structure as well as the depth-dependence of anisotropy along the Red Sea and beneath the Arabian Peninsula using receiver function constraints and phase velocities of surface waves traversing two transects of stations from the Saudi Arabian National Digital Seismic Network. Frequency-dependent phase delays of fundamental-mode Love and Rayleigh waves, measured using a cross-correlation procedure, require very slow shear velocities and the presence of anisotropy throughout the upper mantle. Linearized inversion of these data produce path-averaged 1D radially anisotropic models with about 4% anisotropy in the lithosphere, increasing to about 4.8% anisotropy across the lithosphere-asthenosphere boundary (LAB). Models with reasonable crustal velocities in which the mantle lithosphere is isotropic cannot satisfy the data. The lithospheric lid, which ranges in thickness from about 70 km near the Red Sea coast to about 90 km beneath the Arabian Shield, is underlain by a pronounced low-velocity zone with shear velocities as low as 4.1 km/s. Forward models, which are constructed from previously determined shear-wave splitting estimates, can reconcile surface and body wave observations of anisotropy. The low shear velocity values are similar to many other continental rift and oceanic ridge environments. These low velocities combined with the sharp velocity contrast across the LAB may indicate the presence of partial melt beneath Arabia. The anisotropic signature primarily reflects a combination of plate- and density-driven flow associated with active rifting processes in the Red Sea.

  18. Comparison of P- and S-wave velocity profiles obtained from surface seismic refraction\\/reflection and downhole data

    Microsoft Academic Search

    Robert A. Williams; William J. Stephenson; Jack K. Odum

    2003-01-01

    High-resolution seismic-reflection\\/refraction data were acquired on the ground surface at six locations to compare with near-surface seismic-velocity downhole measurements. Measurement sites were in Seattle, WA, the San Francisco Bay Area, CA, and the San Fernando Valley, CA. We quantitatively compared the data in terms of the average shear-wave velocity to 30-m depth (Vs30), and by the ratio of the relative

  19. Simplified equations for the rotational speed response to inflow velocity variation in fixed-pitch small wind turbines

    NASA Astrophysics Data System (ADS)

    Suzuki, H.; Hasegawa, Y.

    2015-02-01

    We propose simplified equations for the rotational speed response to inflow velocity variation in fixed-pitch small wind turbines. The present formulation is derived by introducing a series expansion for the torque coefficient at the constant tip-speed ratio. By focusing on the first- and second-order differential coefficients of the torque coefficient, we simplify the original differential equation. The governing equation based only on the first-order differential coefficient is found to be linear, whereas the second-order differential coefficient introduces nonlinearity. We compare the numerical solutions of the three governing equations for rotational speed in response to sinusoidal and normal-random variations of inflow velocity. The linear equation gives accurate solutions of amplitude and phase lag. Nonlinearity occurs in the mean value of rotational speed variation. We also simulate the rotational speed in response to a step input of inflow velocity using the conditions of two previous studies, and note that the form of this rotational speed response is a system of first-order time lag. We formulate the gain and time constant for this rotational speed response. The magnitude of the gain is approximately three when the wind turbine is operated at optimal tip-speed ratio. We discuss the physical meaning of the derived time constant.

  20. Variational Approach to Yang--Mills Theory with non-Gaussian Wave Functionals

    E-print Network

    Davide R. Campagnari; Hugo Reinhardt

    2010-11-22

    A general method for treating non-Gaussian wave functionals in quantum field theory is presented and applied to the Hamiltonian approach to Yang-Mills theory in Coulomb gauge in order to include a three-gluon kernel in the exponential of the vacuum wave functional. The three-gluon vertex is calculated using the propagators found in the variational approach with a Gaussian trial wave functional as input.

  1. Identification of composite materials elastic moduli from Lamb wave velocities measured with single sided, contactless ultrasonic method

    NASA Astrophysics Data System (ADS)

    Hosten, Bernard; Castaings, Michel; Tretout, Hervé; Voillaume, Hubert

    2001-04-01

    The identification of the elastic properties of composite materials is done from measured phase velocities of Lamb waves. In the purpose to set up an industrial, contactless and single-sided access device for in service inspection of aircrafts, air-coupled, capacitive transducers are used to generate and receive Lamb waves which are sensitive to material properties. The set of phase velocities corresponding to at least three modes over a large frequency domain, is used as data to recover the elastic moduli through a minimization algorithm. The system is tested for anisotropic composite materials made of epoxy matrix reinforced by glass or carbon fibers.

  2. On the noon asymmetry of the diurnal variation of radio wave absorption

    Microsoft Academic Search

    Jan Laštovi?ka; J. Prokop

    1975-01-01

    Summary The assymetry of the diurnal variation of radio-wave ionospheric absorption, measured by the A3 method on the 2775 kHz Kiel — Panská Ves circuit, is studied. Almost full symmetry of absorption is observed in winter and autumn. It is explained by electron concentration variations. A remarkable diurnal asymmetry of absorption is observed in spring and particularly in summer. The

  3. Surface wave tomography of the western United States from ambient seismic noise: Rayleigh wave group velocity maps

    E-print Network

    Ritzwolle, Mike

    group velocity maps M. P. Moschetti and M. H. Ritzwoller Center for Imaging the Earth's Interior. High-resolution group velocity maps at 8-, 16-, 24-, 30-, and 40-s periods are presented interstation spacing (70 km). Velocity anomalies in the group velocity maps correlate well with the dominant

  4. 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.

  5. Two-dimensional spectroscopy of sunspots. II. Search for propagating waves and drifting velocity filaments in photospheric layers

    NASA Astrophysics Data System (ADS)

    Balthasar, H.; Schleicher, H.

    2008-04-01

    Aims: Running penumbral waves are often reported from observations in chromospheric lines or lines formed in the upper photosphere. In this work we investigate whether they can be detected in a line formed in the mid to lower photosphere. Methods: We used time series of two-dimensional spectra of an iron line that is insensitive to the magnetic field and that is formed in the lower to mid photosphere. Results: No running penumbral waves are detected in this line formed in the lower and mid photosphere. In the moat, outward moving velocity features are detected. They are slightly faster than the plasma motions but much slower than running penumbral waves. Conclusions: Running penumbral waves are a phenomenon occurring in higher layers, i.e. the lower chromosphere and the upper photosphere, but not in the mid photosphere or below. In the moat, we found long-living filamentary velocity features drifting outwards.

  6. Stereoscopy of dust density waves under microgravity: Velocity distributions and phase-resolved single-particle analysis

    SciTech Connect

    Himpel, Michael, E-mail: himpel@physik.uni-greifswald.de; Killer, Carsten; Melzer, André [Institute of Physics, Ernst-Moritz-Arndt-University, 17489 Greifswald (Germany)] [Institute of Physics, Ernst-Moritz-Arndt-University, 17489 Greifswald (Germany); Bockwoldt, Tim; Piel, Alexander [IEAP, Christian-Albrechts-Universität Kiel, D-24098 Kiel (Germany)] [IEAP, Christian-Albrechts-Universität Kiel, D-24098 Kiel (Germany); Ole Menzel, Kristoffer [ABB Switzerland Ltd, Corporate Research Center, 5405 Dättwil (Switzerland)] [ABB Switzerland Ltd, Corporate Research Center, 5405 Dättwil (Switzerland)

    2014-03-15

    Experiments on dust-density waves have been performed in dusty plasmas under the microgravity conditions of parabolic flights. Three-dimensional measurements of a dust density wave on a single particle level are presented. The dust particles have been tracked for many oscillation periods. A Hilbert analysis is applied to obtain trajectory parameters such as oscillation amplitude and three-dimensional velocity amplitude. While the transverse motion is found to be thermal, the velocity distribution in wave propagation direction can be explained by harmonic oscillations with added Gaussian (thermal) noise. Additionally, it is shown that the wave properties can be reconstructed by means of a pseudo-stroboscopic approach. Finally, the energy dissipation mechanism from the kinetic oscillation energy to thermal motion is discussed and presented using phase-resolved analysis.

  7. 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.

  8. Serial changes of sensory nerve conduction velocity and minimal F-wave latency in streptozotocin-induced diabetic rats

    Microsoft Academic Search

    Noriaki Kato; Mitsuhiro Makino; Kuniharu Mizuno; Tsunemasa Suzuki; Masaomi Shindo

    1998-01-01

    We studied the serial changes of sensory nerve conduction velocity (SNCV) in the caudal nerve of streptozotocin (STZ)-induced diabetic rats using a new technical method. Minimal F-wave latency was also studied by stimulating the tibial nerve. The SNCV in the diabetic rats was slower than that in the normal rats 2 weeks after STZ injection, and minimal F-wave latency was

  9. EVALUATION OF INTERMEDIATE-PERIOD (10- TO 30SEC) RAYLEIGH-WAVE GROUP-VELOCITY MAPS FOR CENTRAL ASIA

    Microsoft Academic Search

    Xiaoning Yang; Steven R. Taylor; Howard J. Patton; Monica Maceira; Aaron A. Velasco

    2002-01-01

    We are evaluating the 10- to 30-second Rayleigh-wave group-velocity maps for central Asia constructed from maps developed by Levshin et al. (2001), Ritzwoller and Levshin (1998) and Stevens et al. (2001) for predicting surface- wave arrival times. Currently, we are focusing on the region between 15 and 55 degrees north latitude and 70 and 120 degrees east longitude. A new

  10. Modeling and Performance of a Guided-Wave Optical Angular-Velocity Sensor Based on Raman Effect in SOI

    Microsoft Academic Search

    Francesco De Leonardis; Vittorio M. N. Passaro

    2007-01-01

    In this paper, we report, for the first time to the best of our knowledge, the detailed modeling and design of a guided-wave optical angular-velocity sensor based on Raman amplification in a silicon-on-insulator resonant cavity. Theoretical results for continuous-wave Raman laser emission are compared with experiments in the literature, demonstrating very good agreement. The model includes the influence of a

  11. Low-frequency wave modulations in an electronegative dusty plasma in the presence of charge variations

    NASA Astrophysics Data System (ADS)

    Ghosh, Samiran; Sarkar, Subrata; Khan, Manoranjan; Gupta, M. R.

    2011-12-01

    The effects of dust charge variations on low-frequency wave modulations in an electronegative dusty plasma are investigated. The dynamics of the modulated wave is governed by a nonlinear Schrödinger equation with a dissipative term. The dissipation arises due to the nonsteady (nonadiabatic) dust charge variations. Theoretical and numerical investigations predict the formation of dissipative bright (envelope) and dark solitons. The nonsteady charge-variation-induced dissipation reduces the modulational instability growth rate and introduces a characteristic time scale to observe bright solitons. Results are discussed in the context of electronegative dusty plasma experiments.

  12. Low-frequency wave modulations in an electronegative dusty plasma in the presence of charge variations

    SciTech Connect

    Ghosh, Samiran [Department of Applied Mathematics, University of Calcutta, 92 Acharya Prafulla Chandra Road, Kolkata 700 009 (India); Sarkar, Subrata; Khan, Manoranjan; Gupta, M. R. [Department of Instrumentation Science, Jadavpur University, Kolkata 700 032 (India)

    2011-12-15

    The effects of dust charge variations on low-frequency wave modulations in an electronegative dusty plasma are investigated. The dynamics of the modulated wave is governed by a nonlinear Schroedinger equation with a dissipative term. The dissipation arises due to the nonsteady (nonadiabatic) dust charge variations. Theoretical and numerical investigations predict the formation of dissipative bright (envelope) and dark solitons. The nonsteady charge-variation-induced dissipation reduces the modulational instability growth rate and introduces a characteristic time scale to observe bright solitons. Results are discussed in the context of electronegative dusty plasma experiments.

  13. Low-frequency wave modulations in an electronegative dusty plasma in the presence of charge variations.

    PubMed

    Ghosh, Samiran; Sarkar, Subrata; Khan, Manoranjan; Gupta, M R

    2011-12-01

    The effects of dust charge variations on low-frequency wave modulations in an electronegative dusty plasma are investigated. The dynamics of the modulated wave is governed by a nonlinear Schrödinger equation with a dissipative term. The dissipation arises due to the nonsteady (nonadiabatic) dust charge variations. Theoretical and numerical investigations predict the formation of dissipative bright (envelope) and dark solitons. The nonsteady charge-variation-induced dissipation reduces the modulational instability growth rate and introduces a characteristic time scale to observe bright solitons. Results are discussed in the context of electronegative dusty plasma experiments. PMID:22304202

  14. Analysis of excitation and coherent amplitude enhancement of surface acoustic waves by the phase velocity scanning method

    NASA Astrophysics Data System (ADS)

    Yamanaka, Kazushi; Kolosov, O. V.; Nagata, Yoshihiko; Koda, Toshio; Nishino, Hideo; Tsukahara, Yusuke

    1993-12-01

    We present a general theoretical formulation for the characteristics of surface acoustic waves (SAW) generated by the phase velocity scanning (PVS) method that employs a scanning single laser beam (SSB) or a scanning interference fringes (SIF). In the SSB approach, a broad band SAW pulse is generated and its amplitude is coherently enhanced when the laser scanning velocity V is equal to the phase velocity ?R of the SAW. The amplitude of the SAW follows a resonance curve represented by a sinc function of the scanning velocity V, but different spatial frequency components in the SSB significantly suppress the side lobes of the resonance curve. In the SIF approach, the scanning velocity ?f of the fringes is determined by the intersection angle and the frequency difference ?a of the laser beams. A narrow band tone burst of SAW with frequencies higher than 100 MHz can be excited. The SAW frequency ? depends upon a characteristic time t*, defined as a propagation time of the SAW across the laser beam spot. The SAW frequency ? is identical to the frequency difference ?a when the laser pulse width T is longer than the characteristic time t*. But, the SAW frequency ? is determined as a product kf?R of the wave number of the SIF and the SAW velocity when the laser pulse width is shorter than the characteristic time. Precise frequency measurement provided by the amplitude enhancement effect and the narrow frequency bandwidth in the SIF approach make the PVS method particularly promising for the noncontact SAW velocity measurement.

  15. Comparison of P- and S-wave velocity profiles obtained from surface seismic refraction/reflection and downhole data

    USGS Publications Warehouse

    Williams, R.A.; Stephenson, W.J.; Odum, J.K.

    2003-01-01

    High-resolution seismic-reflection/refraction data were acquired on the ground surface at six locations to compare with near-surface seismic-velocity downhole measurements. Measurement sites were in Seattle, WA, the San Francisco Bay Area, CA, and the San Fernando Valley, CA. We quantitatively compared the data in terms of the average shear-wave velocity to 30-m depth (Vs30), and by the ratio of the relative site amplification produced by the velocity profiles of each data type over a specified set of quarter-wavelength frequencies. In terms of Vs30, similar values were determined from the two methods. There is <15% difference at four of the six sites. The Vs30 values at the other two sites differ by 21% and 48%. The relative site amplification factors differ generally by less than 10% for both P- and S-wave velocities. We also found that S-wave reflections and first-arrival phase delays are essential for identifying velocity inversions. The results suggest that seismic reflection/refraction data are a fast, non-invasive, and less expensive alternative to downhole data for determining Vs30. In addition, we emphasize that some P- and S-wave reflection travel times can directly indicate the frequencies of potentially damaging earthquake site resonances. A strong correlation between the simple S-wave first-arrival travel time/apparent velocity on the ground surface at 100 m offset from the seismic source and the Vs30 value for that site is an additional unique feature of the reflection/refraction data that could greatly simplify Vs30 determinations. ?? 2003 Elsevier Science B.V. All rights reserved.

  16. Near-surface S-wave velocity measured with six-degree-of-freedom seismic sensor Rotaphone

    NASA Astrophysics Data System (ADS)

    Malek, Jiri; Brokesova, Johana

    2015-04-01

    An essential parameter in seismic engineering is the near-surface S-wave velocity. Rotaphone, a six-degree-of-freedom seismic sensor can be used with advantage to retrieve it from collocated rotational and translational measurements. Rotaphone consists of highly sensitive geophones connected to a conjoint datalogger. The geophones are mounted in parallel pairs to a rigid (metal) ground-based frame. The instrument is designed to measure short-period translational ground motion (velocity) and, in addition, differential motion between the paired geophones. The records of those differential motions are used to obtain rotational components. In-situ calibration of individual geophones is performed simultaneously with each measurement, which enables to reach high sensitivity and accuracy of rotational measurements. In our method we utilize seismic waves produced by anthropogenic source - a generator of S waves and rotational ground motions. The generator contains a fixed part (anchored to the ground), a revolving part and a braking mechanism for immediate braking of the rotational part, in which rotational seismic motions are generated by immediately stopping the revolving part, whereby energy is transmitted into the rock massive. The generator produces repeatedly identical source pulses. Due to identity of the source pulses, we can suppress noise by means of stacking data from many generator actions and thus increase the depth range and resolution. The phase velocity retrieval is based on matching relevant acceleration and rotation rate components. Thanks to a near-source distance and high-frequency content of the source pulses, well-known equations for plane-wave approximation must be replaced by more adequate equations relating the individual rotation rate components to the translational ones. These equations are derived under an assumption of spherical wave. The resulting S-wave phase velocity is compared to the value obtained by standard profile measurements. The advantage of our approach in comparison to the profile method is that the resulting velocity is obtained from a single-point measurement.

  17. Periods of the Earth's seismicity activation and their relationship to variations in the Earth's rotation velocity

    NASA Astrophysics Data System (ADS)

    Sasorova, Elena; Levin, Boris

    2015-04-01

    It is known that Earth's seismic activity (SA) demonstrates distinct roughness (nonuniformity) in time. Periods of intensification of the SA followed by periods of its decaying. For strong earthquakes these periods are continued several decades. It was also noted that there is a pronounced periodic amplification and attenuation of the SA with a period of about 30 years, which is manifested mainly in two latitudinal belts 50°N-30°N and 0°-30°S [Levin, Sasorova, 2014, 2015]. This work deals with the hypothesis that it is the properties of rotating non-uniform rate of the planet may be the cause of the periodicity of manifestations SA. The objective of this work is the searching of the spatial-temporal interconnection between the Earth rotation irregularity and the observed cyclic increasing and decreasing of the Earth's SA. This requires preparation a long series of observations of seismic events with representative data sets (EQ selected from 1895 up to date with a magnitude M> = 7.5, based on the catalog NEIC). Two sources of data on the angular velocity of the Earth's rotation of (length of day, LOD) were adapted: the world-known database IERS (Annual Report, International Earth Rotation Service) and the data, which were presented in the work (McCarthy, D.D., and Babcock A.K., 1986). The first one contains daily observations from 1962 to 2013, the second one was identified semi-annual observations from 1720 to 1984. It was prepared concatenated data set (CLOD) for the period from 1720 to 2013. Characteristic periods in the time series CLOD: 62, 32, and 23 years have been isolated by the use of spectral analysis. Next, it were used a band-pass filters for the four frequency bands from 124 to 45 years, from 37 do 25 years, from 25 to 19 years, and in the range of less than 19 years. In the frequency bands 37-25 years and 25-19 years marked clear periodic oscillations close to a sine wave. The amplitude of the oscillations with the 1720 to 1790 gradually increases, then decreases until 1860, after which the oscillation amplitude increases again (and amplitude swinging is much stronger than on the stage, from 1720 to 1790). Then correlation and autocorrelation analysis of the CLOD time series for the four bands CLOD and time series of the Earth's SA (density of events) was carried out. The analysis was performed in the range from 1890 to 2013. Significant correlation of seismic activity with a dedicated part of the time series was shown for the frequency band of 37-25 years. The seismic activity maxima correspond to the end of the braking period of the Earth's rotation, and the minimum of the SA occurs at the end of the acceleration process. Previously marked [Levin, Sasorova, 2015] a significant increase in the density of events at the beginning of the 20th century (1900 to 2015). This amplification corresponds to a sharp decrease in the LOD in the late 19th century for the frequency band 124-45 years. The end of the braking process falls on 1905-1912 years.

  18. A new variational method for erythrocyte velocity estimation in wide-field imaging in vivo.

    PubMed

    Deneux, Thomas; Faugeras, Olivier; Takerkart, Sylvain; Masson, Guillaume S; Vanzetta, Ivo

    2011-08-01

    Measuring erythrocyte velocity in individual microvessels has important applications for biomedical and functional imaging. Recent multiphoton fluorescence microscopy approaches require injecting fluorescent tracers; moreover, only one or few vessels can be imaged at a time. To overcome these shortcomings, we used CCD-based optical imaging of intrinsic absorption changes in macroscopic vascular networks to record erythrocytes' trajectories over several mm (2) of cortical surface. We then demonstrate the feasibility of erythrocyte velocity estimation from such wide-field data, using two robust, independent, algorithms. The first one is a recently published Radon transform-based algorithm that estimates erythrocyte velocity locally. We adapt it to data obtained in wide-field imaging and show, for the first time, its performance on such datasets. The second ("fasttrack") algorithm is novel. It is based on global energy minimization techniques to estimate the full spatiotemporal erythrocytes' trajectories inside vessels. We test the two algorithms on both simulated and biological data, obtained in rat cerebral cortex in a spreading depression experiment. On vessels with medium-slow erythrocyte velocities both algorithms performed well, allowing their usage as benchmark one for another. However, our novel fasttrack algorithm outperformed the other one for higher velocities, as encountered in the arterial network. PMID:21427018

  19. The radial variation of HI velocity dispersions in dwarfs and spirals

    E-print Network

    Ianjamasimanana, R; Walter, Fabian; Heald, George H; Caldu-Primo, Anahi; Jarrett, Thomas H

    2015-01-01

    Gas velocity dispersions provide important diagnostics of the forces counteracting gravity to prevent collapse of the gas. We use the 21 cm line of neutral atomic hydrogen (HI) to study HI velocity dispersion and HI phases as a function of galaxy morphology in 22 galaxies from The HI Nearby Galaxy Survey (THINGS). We stack individual HI velocity profiles and decompose them into broad and narrow Gaussian components. We study the HI velocity dispersion and the HI surface density, as a function of radius. For spirals, the velocity dispersions of the narrow and broad components decline with radius and their radial profiles are well described by an exponential function. For dwarfs, however, the profiles are much flatter. The single Gaussian dispersion profiles are, in general, flatter than those of the narrow and broad components. In most cases, the dispersion profiles in the outer disks do not drop as fast as the star formation profiles, derived in the literature. This indicates the importance of other energy sou...

  20. Inversion of phase velocities of high-frequency fundamental-mode Rayleigh waves using simulated annealing approach

    E-print Network

    , and seismic-resistant design of buildings also benefit from the local shallow S- wave velocity structure for the seismic design of engineered structures and facilities. Recent building codes in the United States (BSSC of a region, comprehensive earthquake preparedness, development of the national seismic hazard map