Science.gov

Sample records for wave velocity variation

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

    SciTech Connect

    Ravindran, S.; Reddy, C.A.

    1993-12-01

    The authors report the use of VHF coherent backscatter radar to detect the phase velocity variations of type I and type II plasma waves coming from the equatorial electrojet in conjunction with substorm and magnetic storm events. These plasma waves are generated by two-stream type instabilities. The authors observe a correlation between the phase velocity of the type I plasma waves and the electron drift velocity, which is consistent with present models which explain the generation of such 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. Variation of Fundamental Mode Surface Wave Group Velocity Dispersion in Iran and the Surrounding Region

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

    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 from IRIS and Geofone. 1D path- averaged dispersion measurements have been made for ~5500 source-receiver paths using multiple filter analysis. We combine these observations in a tomographic inversion to produce group velocity images between 10 and 60 s period. Because of the dense path coverage, these images have substantially higher lateral resolution for this region than is currently available from global and regional group velocity studies. We observe variations in short-period wave group velocity which is consistent with the surface geology. Low group velocities (2.00-2.55 km/s) at short periods (10-20 s), for both Rayleigh and Love waves are observed beneath thick sedimentary deposits; The south Caspian Basin, Black Sea, the eastern Mediterranean, the Persian Gulf, the Makran, the southern Turan shield, and the Indus and Gangetic basins. Somewhat higher group velocity (2.80-3.15 km/s for Rayleigh, and 3.00-3.40 km/s for Love) at these periods occur in sediment poor regions, such as; the Turkish-Iranian plateau, the Arabian shield, and Kazakhstan. At intermediate periods (30-40 s) group velocities over most of the region are low (2.65-3.20 km/s for Rayleigh, and 2.80-3.45 km/s for love) compared to Arabia (3.40-3.70 km/s Rayleigh, 3.50-4.0 km/s Love). At longer periods (50-60 s) Love wave group velocities remain low (3.25-3.70 km/s) over most of Iran, but there are even lower velocities (2.80-3.00 km/s) still associated with the thick sediments of the south Caspian basin, the surrounding shield areas have much higher group velocities (3.90-4.45 km/s) at these periods. A similar pattern is seen for longer period Rayleigh waves, with low velocities (2.85-3.60 km/s) beneath the Alpine-Himalaya belt, compared to the velocities (3.80-4.10 km/s) of the Turan and Arabian shields, to the north and south respectively, no large anomaly beneath the south Caspian is observed for these longer period Rayleigh waves.

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

    E-print Network

    Al-Shaibani, Abdulaziz Muhareb

    1994-01-01

    Seismic-wave velocities in cracked rocks increase with stress. It is believed that, within less than half the rupture pressure, this velocity increase occurs due to the closure of cracks. Previous studies have shown that, if a cracked rock...

  5. Variation of P-wave velocity before the Bear Valley, California, earthquake of 24 February 1972

    USGS Publications Warehouse

    Robinson, R.; Wesson, R.L.; Ellsworth, W.L.

    1974-01-01

    Residuals for P-wave traveltimes at a seismograph station near Bear Valley, California, for small, precisely located local earthquakes at distances of 20 to 70 kilometers show a sharp increase of nearly 0.3 second about 2 months before a magnitude 5.0 earthquake that occurred within a few kilometers of the station. This indicates that velocity changes observed elsewhere premonitory to earthquakes, possibly related to dilatancy, occur along the central section of the San Andreas fault system.

  6. Variation of P-Wave Velocity before the Bear Valley, California, Earthquake of 24 February 1972.

    PubMed

    Robinson, R; Wesson, R L; Ellsworth, W L

    1974-06-21

    Residuals for P-wave traveltimes at a seismnograph station near Bear Valley, California, for small, precisely located local earthquakes at distances of 20 to 70 kilometers show a sharp increase of nearly 0.3 second about 2 months before a magnitude 5.0 earthquake that occurred within a few kilometers of the station. This indicates that velocity changes observed elsewhere premonitory to earthquakes, possibly related to dilatancy, occur along the central section of the San Andreas fault system. PMID:17784227

  7. 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.

  8. CHINESE JOURNAL OF GEOPHYSICS Vol.50, No.1, 2007, pp: 183191 FINE STRUCTURE OF P-WAVE VELOCITY VARIATIONS UNDERNEATH

    E-print Network

    Song, Xiaodong

    effective methods to study the deep structure of the Earth. In recent years, researches on the core mantle of the crust and upper mantle but are sensitive to the structure in the lowermost mantle. Our results show. There are three branches of PKP waves: the branch traversing the inner core (DF), the branch turning at the bottom

  9. Wave Tank Studies of Phase Velocities of Short Wind Waves

    NASA Astrophysics Data System (ADS)

    Ermakov, S.; Sergievskaya, I.; Shchegolkov, Yu.

    Wave tank studies of phase velocities of short wind waves have been carried out using Ka-band radar and an Optical Spectrum Analyser. The phase velocities were retrieved from measured radar and optical Doppler shifts, taking into account measurements of surface drift velocities. The dispersion relationship was studied in centimetre (cm)- and millimetre(mm)-scale wavelength ranges at different fetches and wind speeds, both for a clean water surface and for water covered with surfactant films. It is ob- tained that the phase velocities do not follow the dispersion relation of linear capillary- gravity waves, increasing with fetch and, therefore, depending on phase velocities of dominant decimetre (dm)-centimetre-scale wind waves. One thus can conclude that nonlinear cm-mm-scale harmonics bound to the dominant wind waves and propagat- ing with the phase velocities of the decimetric waves are present in the wind wave spectrum. The resulting phase velocities of short wind waves are determined by re- lation between free and bound waves. The relative intensity of the bound waves in the spectrum of short wind waves is estimated. It is shown that this relation depends strongly on the surfactant concentration, because the damping effect due to films is different for free and bound waves; this results to changes of phase velocities of wind waves in the presence of surfactant films. This work was supported by MOD, UK via DERA Winfrith (Project ISTC 1774P) and by RFBR (Project 02-05-65102).

  10. Elastic wave velocities of Apollo 14, 15, and 16 rocks

    NASA Technical Reports Server (NTRS)

    Mizutani, H.; Newbigging, D. F.

    1973-01-01

    Elastic wave velocities of two Apollo 14 rocks, 14053 and 14321, three Apollo 15 rocks, 15058, 15415, and 15545, and one Apollo 16 rock 60315 have been determined at pressures up to 10 kb. For sample 14321, the variation of the compressional wave velocities with temperature has been measured over the temperature range from 27 to 200 C. Overall elastic properties of these samples except sample 15415 are very similar to those of Apollo 11, 12, and 14 rocks and are concordant with Toksoz et al.'s (1972) interpretation that lunar upper crust is of basaltic composition. Temperature derivative of the P wave velocity for sample 14321 is a half to one order of magnitude larger than that for single crystalline minerals. This suggests that the seismic velocity in the lunar crust may be affected significantly by the temperature distribution.

  11. Lateral variations in lower mantle seismic velocity

    NASA Technical Reports Server (NTRS)

    Duffy, Thomas S.; Ahrens, Thomas J.

    1992-01-01

    To obtain a theoretical model which provides a rationale for the observed high values of velocity variations, the effect of a 0.1 to 0.2 percent partially molten volatile-rich material in various geometries which are heterogeneously dispersed in the lower mantle is examined. Data obtained indicate that, depending on aspect ratio and geometry, 0.1-0.2 percent partial melting in conjunction with about 100 K thermal anomalies can explain the seismic variations provided the compressibility of the melt differs by less than about 20 percent from the surrounding solid.

  12. Inter-laboratory comparison of wave velocity measures.

    USGS Publications Warehouse

    Waite, William F.; Santamarina, J.C.; Rydzy, M.; Chong, S.H.; Grozic, J.L.H.; Hester, K.; Howard, J.; Kneafsey, T.J.; Lee, J.Y.; Nakagawa, S.; Priest, J.; Reese, E.; Koh, H.; Sloan, E.D.; Sultaniya, A.

    2011-01-01

     This paper presents an eight-laboratory comparison of compressional and shear wave velocities measured in F110 Ottawa sand. The study was run to quantify the physical property variations one should expect in heterogeneous, multiphase porous materials by separately quantifying the variability inherent in the measurement techniques themselves. Comparative tests were run in which the sand was dry, water-saturated, partially water-saturated, partially ice-saturated and partially hydrate-saturated. Each test illustrates a collection of effects that can be classified as inducing either specimen-based or measurement-based variability. The most significant variability is due to void ratio variations between samples. Heterogeneous pore-fill distributions and differences in measurement techniques also contribute to the observed variability, underscoring the need to provide detailed sample preparation and system calibration information when reporting wave velocities in porous media. 

  13. Variational Principles for Water Waves

    E-print Network

    Boris Kolev; David H. Sattinger

    2007-12-01

    We describe the Hamiltonian structures, including the Poisson brackets and Hamiltonians, for free boundary problems for incompressible fluid flows with vorticity. The Hamiltonian structure is used to obtain variational principles for stationary gravity waves both for irrotational flows as well as flows with vorticity.

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  15. Measurements of the Gravity Waves Velocity

    NASA Astrophysics Data System (ADS)

    Dubrovskiy, Vladimir A.

    We suppose the gravity waves excite microseismic background. Peaks of the background spectrum can be observed if the wave length l is comparable with distance L between Earth and some cosmic gravity object. Such resonance peaks where observed using laser interferometer and spectranalyser SK4-72 that enlarges periodical signal component relative chaotic one. They are around 2.3 1.0 0.9 0.6 0.4 0.2 Hz. And there exist massive gravity objects at 1.3 2.7 3.5 5.0 8.0 and 11.0 parsecs distances (nearest and brightest stars). This all distances correspond to all peaks in accordance with f=C/l (l/2~L due to resonance) only if the gravity velocity C should be nearly nine order more then light velocity. If this conclusion is not casual it is possible to observe resonance peaks corresponding to the gravity waves exchange of the Earth with Moon (~240MHz) Sun (~0.6MHz) Venus (0.3-2.2MHz) Jupiter (100-150kHz) Saturn (58-72kHz). Moreover peak corresponding to Venus Jupiter or Saturn should change its frequency position during orbital motion. Such correlation will support decisively the presented result elastic model of the physical vacuum and Laplace's result concerning to the lower limit of the gravity velocity.

  16. Shear velocity structure of the Mariana mantle wedge from Rayleigh wave phase velocities

    E-print Network

    Shear velocity structure of the Mariana mantle wedge from Rayleigh wave phase velocities Moira L velocities and invert these results for the shear velocity structure and azimuthal anisotropy in the region. In the backarc region low phase velocities indicate shear velocities as low as 3.9 ± 0.1 km/s at depths of about

  17. 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.

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

    NASA Technical Reports Server (NTRS)

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

    1973-01-01

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

  19. Shear-wave velocity structure of Africa from Rayleigh-wave analysis

    NASA Astrophysics Data System (ADS)

    Corchete, V.

    2013-04-01

    The 3D S-velocity structure beneath Africa is shown by means of a 2D S-velocity mapping for depths raging from zero to 500 km, determined by the regionalization and inversion of Rayleigh-wave dispersion. The traces of 94 earthquakes, occurred from 1990 to 2009 in the study area, have been used to obtain the Rayleigh-wave dispersion. These earthquakes were registered by 61 seismic stations located on Africa and the surrounding area. The dispersion curves were obtained for periods between 5 and 300 s, by digital filtering with a combination of MFT and TVF filtering techniques. After that, all seismic events (and some stations) were grouped to obtain a dispersion curve for each source-station path. These dispersion curves were regionalized and after inverted according to generalized inversion theory, to obtain shear-wave velocity models for rectangular blocks with a size of 5° × 5°. The 3D S-velocity structure obtained through this procedure is shown in the 2D S-velocity maps plotted for several depths. These results agree well with the geology and other geophysical results previously obtained. The obtained S-velocity models suggest the existence of lateral and vertical heterogeneity. The zones with consolidated and old structures (as cratons) present greater S-velocity values than the other younger zones. Nevertheless, in the depth range from 20 to 40 km, the different Moho depths present in the study area generate the principal variation of S-velocity. A similar behaviour is found for the depth range from 60 to 230 km, in which the lithosphere-asthenosphere boundary generates the principal variations of S-velocity. Finally, it should be highlighted a new and interesting feature obtained in this study: the definition of the base of the asthenosphere, for depths ranging from 160 to 280 km, in the whole African continent.

  20. Anisotropic Rayleigh-wave phase velocities beneath northern Vietnam

    NASA Astrophysics Data System (ADS)

    Legendre, Cédric P.; Zhao, Li; Huang, Win-Gee; Huang, Bor-Shouh

    2015-12-01

    We explore the Rayleigh-wave phase-velocity structure beneath northern Vietnam over a broad period range of 5 to 250 s. We use the two-stations technique to derive the dispersion curves from the waveforms of 798 teleseismic events recoded by a set of 23 broadband seismic stations deployed in northern Vietnam. These dispersion curves are then inverted for both isotropic and azimuthally anisotropic Rayleigh-wave phase-velocity maps in the frequency range of 10 to 50 s. Main findings include a crustal expression of the Red River Shear Zone and the Song Ma Fault. Northern Vietnam displays a northeast/southwest dichotomy in the lithosphere with fast velocities beneath the South China Block and slow velocities beneath the Simao Block and between the Red River Fault and the Song Da Fault. The anisotropy in the region is relatively simple, with a high amplitude and fast directions parallel to the Red River Shear Zone in the western part. In the eastern part, the amplitudes are generally smaller and the fast axis displays more variations with periods.

  1. 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.

  2. 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.

  3. Joint inversion of Rayleigh wave phase velocity and ellipticity using USArray: Constraining velocity and density structure

    E-print Network

    Johnson, Cari

    Joint inversion of Rayleigh wave phase velocity and ellipticity using USArray: Constraining structure. In this study, we jointly invert measurements of Rayleigh wave H/V ratio and phase velocity, is better constrained by the joint inversion compared to inversions based on phase velocities alone

  4. Measurements of mantle wave velocities and inversion for lateral heterogeneity and anisotropy. I - Analysis of great circle phase velocities

    NASA Technical Reports Server (NTRS)

    Nakanishi, I.; Anderson, D. L.

    1983-01-01

    The global lateral heterogeneity of the upper mantle is investigated using the classical Fourier-transform method of Sato(1958) and IDA/GDSN data from 25 1980 earthquakes. The great-circle phase velocities of 200 Love and 250 Rayleigh 100-330-sec-period fundamental-mode wave paths are determined and interpreted in terms of regional phase-velocity variation, using additional data on surface tectonics to extrapolate odd-harmonic information from the even-harmonic data. The results are presented in extensive tables, maps, and graphs. Regionalized inversion using the seven-region model of Okal (1977) is found to give maximum variance reductions of 65 percent for Love waves and 85 percent for Rayleigh waves, compared to 60 and 90 percent for l(max) = 2 inversion. Significant interregion differences are found in the regionalized Love-wave phase velocities.

  5. Radial velocity variations in 69 Orionis

    NASA Astrophysics Data System (ADS)

    Bossi, M.; Guerrero, G.; Mantegazza, L.

    1982-04-01

    Red and blue spectrograms and B and V photoelectric observations of the Be star 69 Ori are considered. Separate analyses of the blue and red radial velocities by means of a least squares periodogram method exclude any significant variability within a period of 1.28 days, although alternative periods of 0.56 and 5.0 days remain as possibilities. The photometric data also excludes the possibility of binary star eclipses as the source of variability.

  6. 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.

  7. A simple method of predicting S-wave velocity

    USGS Publications Warehouse

    Lee, M.W.

    2006-01-01

    Prediction of shear-wave velocity plays an important role in seismic modeling, amplitude analysis with offset, and other exploration applications. This paper presents a method for predicting S-wave velocity from the P-wave velocity on the basis of the moduli of dry rock. Elastic velocities of water-saturated sediments at low frequencies can be predicted from the moduli of dry rock by using Gassmann's equation; hence, if the moduli of dry rock can be estimated from P-wave velocities, then S-wave velocities easily can be predicted from the moduli. Dry rock bulk modulus can be related to the shear modulus through a compaction constant. The numerical results indicate that the predicted S-wave velocities for consolidated and unconsolidated sediments agree well with measured velocities if differential pressure is greater than approximately 5 MPa. An advantage of this method is that there are no adjustable parameters to be chosen, such as the pore-aspect ratios required in some other methods. The predicted S-wave velocity depends only on the measured P-wave velocity and porosity. ?? 2006 Society of Exploration Geophysicists.

  8. P/n/ velocity and cooling of the continental lithosphere. [upper mantle compression waves in North America

    NASA Technical Reports Server (NTRS)

    Black, P. R.; Braile, L. W.

    1982-01-01

    The average upper mantle compressional wave velocity and heat flow figures presently computed for continental physiographic provinces in North America exhibit an inverse relationship, and possess a statistically significant correlation coefficient. A correlation is also demonstrated between compressional wave velocity and material temperature by estimating crust-mantle boundary temperatures from heat flow values. The dependency of compressional wave velocity on temperature implies that the observed geographical distribution in upper mantle seismic velocity may be due to the temperature effect character of upper mantle compressional wave velocity variation.

  9. Theoretical relationship between elastic wave velocity and electrical resistivity

    NASA Astrophysics Data System (ADS)

    Lee, Jong-Sub; Yoon, Hyung-Koo

    2015-05-01

    Elastic wave velocity and electrical resistivity have been commonly applied to estimate stratum structures and obtain subsurface soil design parameters. Both elastic wave velocity and electrical resistivity are related to the void ratio; the objective of this study is therefore to suggest a theoretical relationship between the two physical parameters. Gassmann theory and Archie's equation are applied to propose a new theoretical equation, which relates the compressional wave velocity to shear wave velocity and electrical resistivity. The piezo disk element (PDE) and bender element (BE) are used to measure the compressional and shear wave velocities, respectively. In addition, the electrical resistivity is obtained by using the electrical resistivity probe (ERP). The elastic wave velocity and electrical resistivity are recorded in several types of soils including sand, silty sand, silty clay, silt, and clay-sand mixture. The appropriate input parameters are determined based on the error norm in order to increase the reliability of the proposed relationship. The predicted compressional wave velocities from the shear wave velocity and electrical resistivity are similar to the measured compressional velocities. This study demonstrates that the new theoretical relationship may be effectively used to predict the unknown geophysical property from the measured values.

  10. Pulse Wave Velocity in Postmenopausal Women

    PubMed Central

    Suzuki, Hiromichi; Kondo, Kazuoki

    2013-01-01

    Cardiovascular disease (CVD) and osteoporosis are major causes of morbidity and mortality in postmenopausal women. The relationship between atherosclerosis and osteoporosis has been established by studies of the underlying pathophysiological mechanisms and biochemical pathways that seem to overlap in many places. Pulse wave velocity (PWV) is one of the known predictors of cardiovascular and all-cause mortality. Studies indicate that PWV in hypertensive postmenopausal women is increased, and hormone replacement therapy (HRT) attenuates this increase. In addition, recently, many studies have suggested a role for arterial stiffness in the association between CVD and osteoporosis. From these findings, it appears that estrogen deficiency combined with production of inflammatory cytokines plays a role in increased PWV closely associated with CVD and osteoporosis, although the mechanisms of arterial stiffness in postmenopausal women may be more complex. Accordingly, a possible role for PWV as a surrogate marker of CVD as well as osteoporosis in postmenopausal women is discussed in this review. First, menopause leads to increased arterial stiffness with aging in females. Further, epidemiological data evaluating arterial stiffness assessed by PWV provided evidence that most of the established CVD risk factors are determinants of PWV, and these risk factors are increased in patients with CVD. In turn, contrary to expectation, HRT did not always contribute to a lower incidence of CVD in postmenopausal women. By reviewing the current data available, it becomes clear that, at present, the effects of menopause including HRT on PWV remain controversial, and further studies are needed to clarify these associations.

  11. 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.

  12. Measurement of velocity distribution for longitudinal acoustic waves in welds by a laser optoacoustic technique

    NASA Astrophysics Data System (ADS)

    Ivochkin, A. Yu.; Karabutov, A. A.; Lyamshev, M. L.; Pelivanov, I. M.; Rohatgi, U.; Subudhi, M.

    2007-07-01

    An optoacoustic technique for diagnostics of residual stress in metals is proposed. The theoretical part of the technique employs acoustoelastic relations establishing a linear relationship between the biaxial residual stress and the relative variation of the velocity of longitudinal ultrasonic waves. The experimental technique is based on laser excitation of nanosecond ultrasonic pulses at the surface of samples under investigation and their detection with a high time resolution. Distributions of the relative variation of longitudinal wave velocities due to the presence of residual stress in the samples are obtained.

  13. Local variations of seismic velocity in the Imperial Valley, California

    SciTech Connect

    Jackson, D.D.; Lee, W.B.

    1981-12-01

    The authors inverted local earthquake arrival times to estimate spatial variations of seismic velocity. Their model consisted of near-surface station corrections and local perturbations to a standard crustal velocity model. The authors found a zone of relatively high-velocity trending southeast from the Salton Sea. This zone corresponds to the region of thickest sediments. The authors compared results with those of teleseismic studies by Savino et al (1977). The agreement was excellent, suggesting that the teleseismic delays are caused primarily by crustal velocity variations. Residual delays between the teleseismic observations and predicted crustal delays imply crustal thinning of 3 or 4 km along the axis of the valley. Known geothermal resource areas at Salton Sea (or Obsidian Buttes), Brawley, and East Mesa, lie on the axis of a zone of thin crust, and they may be intimately related to the Brawley fault. Neither local earthquake nor teleseismic arrival times can discriminate between these hypotheses, but the issue might be resolved by combining both types of data. Known geothermal resource areas at Heber, Dunes, and Glamis, lie away from the projected trace of the Brawley fault. These areas are nearly aseismic, and overlie crust with apparent seismic velocities only mildly higher than the regional average. These apparent velocity anomalies could be related to crustal thinning, but because of the very mild Bouguer gravity anomalies in these areas, it seems more likely that the velocity anomalies occur entirely within the crust. 7 references, 6 figures, 3 tables.

  14. Coupled cavity traveling wave tube with velocity tapering

    NASA Technical Reports Server (NTRS)

    Connolly, D. J. (inventor)

    1982-01-01

    A coupled cavity traveling wave tube with a velocity taper, which affords beam wave resynchronization and thereby enhances is described. The wave velocity reduction is achieved by reducing the resonant frequencies of the individual resonant cavities as a function of the distance from the electron gun, through changes in internal cavity dimensions. The required changes in cavity dimensions can be accomplished by gradually increasing the cavity radius decreasing the gap length from cavity to cavity. The velocity reduction is carried out without an increase in circuit resistive losses and the upper and lower cut off frequencies are reduced in approximately the same manner.

  15. 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.

  16. Distinct Velocity variations around the Base of the Upper Mantle beneath Northeastern Asia

    NASA Astrophysics Data System (ADS)

    Wang, T.; Chen, L.

    2007-12-01

    Both the global and regional P wave tomographic studies have revealed low-velocity anomalies beneath the high velocity descending slabs in the mantle transition zone and uppermost lower mantle under a number of subduction zones. The limited resolution at large depths and possible trade-off between the high and low velocities, however, makes it difficult to substantiate this feature and evaluate accurately the vertical extent of the low-velocity structure. Using broadband waveform modeling on the triplicated phases near the 660-km discontinuity for three deep events, we constrained both the P and SH wave velocity structures around the base of the upper mantle in northeastern Asia. For the two events beneath the south Kurile, the rays traveled through the lowermost transition zone and uppermost lower mantle under the descending Pacific slab. Our preferred models consistently suggest normal-to-lower P and significantly low SH wave velocities above and below the 660-km discontinuity extending to about 760-km depth compared with the global IASP91 model, corroborating previous observations for a slow structure underneath the slab. In contrast, both high P and SH wave velocity anomalies are shown in our preferred model for the region beneath the Japan back arc, likely reflecting the structural feature of a slab stagnant above the 660-km discontinuity. The velocity jumps across the 660-km discontinuity were found to be on average 4.5% and 7% for P and S waves under the south Kurile, and 3% and 6% under the Japan back arc. The relatively small velocity contrasts in the latter are also consistent with the stagnant slab scenario in which the amplitude of the discontinuity is reduced by the high velocity of the slab. In addition, our synthetic modeling indicates that an apparent uplift or depression of the discontinuity (>10 km) could not expain the data reasonably well, suggesting that temperature variations might be small in both regions. While the limited temperature effect may be sufficient to induce the high velocities of the slab beneath the Japan back arc, the low velocity anomalies, especially the apparently different P and SH velocity gradients around the 660-km discontinuity beneath the south Kurile are likely indicative of lateral chemical heterogeneities existing at the upper and lower mantle boundary. Given the complex morphology of the subducting Pacific slab in this region, we speculate that the distinct velocity structure retrieved here may represent mantle materials that are trapped at around the base of the upper mantle between the surrounding subducting Pacific slabs, and are probably different from the slabs and ordinary mantle both thermally and chemically.

  17. Anisotropic parameter estimation using velocity variation with offset analysis

    SciTech Connect

    Herawati, I.; Saladin, M.; Pranowo, W.; Winardhie, S.; Priyono, A.

    2013-09-09

    Seismic anisotropy is defined as velocity dependent upon angle or offset. Knowledge about anisotropy effect on seismic data is important in amplitude analysis, stacking process and time to depth conversion. Due to this anisotropic effect, reflector can not be flattened using single velocity based on hyperbolic moveout equation. Therefore, after normal moveout correction, there will still be residual moveout that relates to velocity information. This research aims to obtain anisotropic parameters, ? and ?, using two proposed methods. The first method is called velocity variation with offset (VVO) which is based on simplification of weak anisotropy equation. In VVO method, velocity at each offset is calculated and plotted to obtain vertical velocity and parameter ?. The second method is inversion method using linear approach where vertical velocity, ?, and ? is estimated simultaneously. Both methods are tested on synthetic models using ray-tracing forward modelling. Results show that ? value can be estimated appropriately using both methods. Meanwhile, inversion based method give better estimation for obtaining ? value. This study shows that estimation on anisotropic parameters rely on the accuracy of normal moveout velocity, residual moveout and offset to angle transformation.

  18. 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).

  19. 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.

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

    NASA Astrophysics Data System (ADS)

    Wiberg, Patricia L.; Sherwood, Christopher R.

    2008-10-01

    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.

  1. 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.

  2. Common Genetic Variation in the 3-BCL11B Gene Desert Is Associated With Carotid-Femoral Pulse Wave Velocity and Excess Cardiovascular Disease Risk The AortaGen Consortium

    PubMed Central

    Mitchell, Gary F.; Verwoert, Germaine C.; Tarasov, Kirill V.; Isaacs, Aaron; Smith, Albert V.; Yasmin; Rietzschel, Ernst R.; Tanaka, Toshiko; Liu, Yongmei; Parsa, Afshin; Najjar, Samer S.; O’Shaughnessy, Kevin M.; Sigurdsson, Sigurdur; De Buyzere, Marc L.; Larson, Martin G.; Sie, Mark P.S.; Andrews, Jeanette S.; Post, Wendy S.; Mattace-Raso, Francesco U.S.; McEniery, Carmel M.; Eiriksdottir, Gudny; Segers, Patrick; Vasan, Ramachandran S.; van Rijn, Marie Josee E.; Howard, Timothy D.; McArdle, Patrick F.; Dehghan, Abbas; Jewell, Elizabeth; Newhouse, Stephen J.; Bekaert, Sofie; Hamburg, Naomi M.; Newman, Anne B.; Hofman, Albert; Scuteri, Angelo; De Bacquer, Dirk; Ikram, Mohammad Arfan; Psaty, Bruce; Fuchsberger, Christian; Olden, Matthias; Wain, Louise V.; Elliott, Paul; Smith, Nicholas L.; Felix, Janine F.; Erdmann, Jeanette; Vita, Joseph A.; Sutton-Tyrrell, Kim; Sijbrands, Eric J.G.; Sanna, Serena; Launer, Lenore J.; De Meyer, Tim; Johnson, Andrew D.; Schut, Anna F.C.; Herrington, David M.; Rivadeneira, Fernando; Uda, Manuela; Wilkinson, Ian B.; Aspelund, Thor; Gillebert, Thierry C.; Van Bortel, Luc; Benjamin, Emelia J.; Oostra, Ben A.; Ding, Jingzhong; Gibson, Quince; Uitterlinden, André G.; Abecasis, Gonçalo R.; Cockcroft, John R.; Gudnason, Vilmundur; De Backer, Guy G.; Ferrucci, Luigi; Harris, Tamara B.; Shuldiner, Alan R.; van Duijn, Cornelia M.; Levy, Daniel; Lakatta, Edward G.; Witteman, Jacqueline C.M.

    2012-01-01

    Background Carotid-femoral pulse wave velocity (CFPWV) is a heritable measure of aortic stiffness that is strongly associated with increased risk for major cardiovascular disease events. Methods and Results We conducted a meta-analysis of genome-wide association data in 9 community-based European ancestry cohorts consisting of 20,634 participants. Results were replicated in 2 additional European ancestry cohorts involving 5,306 participants. Based on a preliminary analysis of 6 cohorts, we identified a locus on chromosome 14 in the 3?-BCL11B gene desert that is associated with CFPWV (rs7152623, minor allele frequency = 0.42, beta=?0.075±0.012 SD/allele, P = 2.8 x 10?10; replication beta=?0.086±0.020 SD/allele, P = 1.4 x 10?6). Combined results for rs7152623 from 11 cohorts gave beta=?0.076±0.010 SD/allele, P=3.1x10?15. The association persisted when adjusted for mean arterial pressure (beta=?0.060±0.009 SD/allele, P = 1.0 x 10?11). Results were consistent in younger (<55 years, 6 cohorts, N=13,914, beta=?0.081±0.014 SD/allele, P = 2.3 x 10?9) and older (9 cohorts, N=12,026, beta=?0.061±0.014 SD/allele, P=9.4x10?6) participants. In separate meta-analyses, the locus was associated with increased risk for coronary artery disease (hazard ratio [HR]=1.05, confidence interval [CI]=1.02 to 1.08, P=0.0013) and heart failure (HR=1.10, CI=1.03 to 1.16, P=0.004). Conclusions Common genetic variation in a locus in the BCL11B gene desert that is thought to harbor one or more gene enhancers is associated with higher CFPWV and increased risk for cardiovascular disease. Elucidation of the role this novel locus plays in aortic stiffness may facilitate development of therapeutic interventions that limit aortic stiffening and related cardiovascular disease events. PMID:22068335

  3. 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.

  4. Estimating propagation velocity through a surface acoustic wave sensor

    DOEpatents

    Xu, Wenyuan (Oakdale, MN); Huizinga, John S. (Dellwood, MN)

    2010-03-16

    Techniques are described for estimating the propagation velocity through a surface acoustic wave sensor. In particular, techniques which measure and exploit a proper segment of phase frequency response of the surface acoustic wave sensor are described for use as a basis of bacterial detection by the sensor. As described, use of velocity estimation based on a proper segment of phase frequency response has advantages over conventional techniques that use phase shift as the basis for detection.

  5. 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.

  6. Group velocity of gravitational waves in an expanding universe

    E-print Network

    Vladimír Balek; Vratko Polák

    2008-05-09

    The group velocity of gravitational waves in a flat Friedman-Robertson-Walker universe is investigated. For plane waves with wavelength well inside the horizon, and a universe filled with an ideal fluid with the pressure to density ratio less than 1/3, the group velocity is greater than the velocity of light. As a result, a planar pulse of gravitational waves propagating through the universe during the matter/dark energy dominated era arrives to the observer with the peak shifted towards the forefront. For gravitational waves emitted by inspiralling supermassive black holes at the edge of the observable universe, the typical shift that remains after the effects of nonplanarity are suppressed is of order of ten picoseconds.

  7. A Local Concept of Wave Velocities

    E-print Network

    I. V. Drozdov; A. A. Stahlhofen

    2007-04-11

    The classical characterization of \\wp, as a typical concept for far field phenomena, has been successfully applied to many \\w phenomena in past decades. The recent reports of superluminal tunnelling times and negative group velocities challenged this concept. A new local approach for the definition of \\wvs avoiding these difficulties while including the classical definitions as particular cases is proposed here. This generalisation of the conventional non-local approach can be applied to arbitrary \\w forms and propagation media. Some applications of the formalism are presented and basic properties of the concept are summarized.

  8. Uppermost mantle P wave velocities beneath Turkey and Iran

    SciTech Connect

    Chen, C.; Chen, W.; Molnar, P.

    1980-01-01

    The uppermost mantle P wave velocities beneath Turkey and Iran were estimated by applying the conventional travel time-distance relation method to arrival times of well located earthquakes recorded at a few stations. The average uppermost mantle P wave velocity under Turkey is estimated from two stations of the World Wide Standardized Seismograph Network (WWSSN), Istanbul and Tabriz. The data are consistent with a crust of uniform, but poorly determined, thickness and an uppermost mantle P wave velocity of 7.73 +- 0.08 km/s. This velocity is very similar to that for the Aegean Sea and suggests that its structure could be closely related to that beneath Turkey. For Iran, the results calculated from travel times to three WWSSN stations, Meshed, Shiraz, and Tabriz, can be explained by a crust dipping toward the south-southeast at about 1/sup 0/ with an uppermost mantle P wave velocity of 8.0 +- 0.1 km/s. If the crustal thickness were 34 km in the north it would reach about 49 km in the south. Based on these uppermost mantle velocities, the temperature at Moho beneath Turkey is probably close to the melting temperature of peridotite but that beneath Iran is probably lower.

  9. Thermally induced velocity variations of ferropericlase in Earth's lower mantle

    NASA Astrophysics Data System (ADS)

    Wentzcovitch, Renata

    2014-03-01

    Understanding the origin of lateral velocity heterogeneities in the mantle is crucial to understand the constitution of and internal processes at work in the Earth. The spin crossover in iron in ferropericlase (Fp) and the unusual and well documented elastic anomalies introduce unfamiliar effects on seismic velocities. In this work we investigate by first principles calculations potential velocity anomalies caused by lateral temperature variations in the presence of a spin crossover in Fp under mantle conditions. Anti-correlation between shear velocity (VS) and bulk sound velocity (V?) in the mantle has long been viewed as an indicator of compositional or mineralogical heterogeneity. This view is not entirely justified in the presence of spin crossover in ferropericlase. We also identify new effects that exist in the presence of a spin crossover. Signatures of these effects appear to exist in the lower mantle. Research supported by China-NSF (41274087), NSF (EAR-1341862 and EAR-1047629) and CAS International Partnership Program for Creative Research Teams.

  10. Inversion of Rayleigh wave phase velocities between RSNT and RSON

    SciTech Connect

    Randall, G.E.; Taylor, S.R.

    1985-07-01

    Rayleigh wave phase velocities in the Canadian Shield are estimated for the path between RSNT and RSON in the period range of 10 to 100 sec. Frequency dependent stacking techniques are employed to form an estimate of phase velocity from a limited data set of marginal quality. Inversion of the phase velocities for shear velocity structure indicates an average crustal thickness of 40 km which is consistent with results from previous studies. The lower crustal velocities from our study appear to be slightly greater than those from other studies and Sn velocities along the path are about 4.7 km/s. The effectiveness of the frequency dependent stacking techniques confirms the assumption of signal-independent background noise dominating the records for periods less than about 30 sec and signal-dependent multipathing noise dominating for periods longer than about 40 sec. 14 refs., 5 figs., 2 tabs.

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    - Rayleigh wave group velocity dispersion measurements from 10s to 160s periods have been made for paths traversing Northern Africa. Data were accumulated from the IRIS DMC, GEOSCOPE, and MEDNET seismic networks covering the years 1991-1997. The group velocity measurements are made including the effects of debiasing for instantaneous period and a single-iteration, mode-isolation (phase match) filter. The curves are grouped by tectonic province and compared to tomographic model-based curves in an effort to test and validate the tomographic models. Within each tectonic category (rift, orogenic zone, or craton) group velocity curves from various provinces are similar. Between tectonic categories, however, there are marked differences. The rift related paths exhibit the lowest group velocities observed, and cratonic paths the fastest. One-dimensional shear velocity inversions are performed, and while highly nonunique, the ranges of models show significant differences in upper mantle velocities between the tectonic provinces.This work is part of a larger project to determine group velocity maps for North Africa and the Middle East. The work presented here provides important tools for the validation of tomographic group velocity models. This is accomplished by comparing group velocity curves calculated from the tomographic models with carefully selected high-quality group velocity measurements. The final group velocity models will be used in Ms measurements, which will contribute to the mb:Ms discriminant important to the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The improved shear wave velocity models provided by this study also contribute to the detection, location, and identification of seismic sources.

  13. Seismic waves velocity dispersion: An indicator of hydrocarbons

    SciTech Connect

    Rapoport, M.B.; Ryjkov, V.I.

    1994-12-31

    VSP data recorded in eleven wells located in different geological conditions were analyzed for studying the phase velocity dispersion of seismic waves. Strong positive dispersion (velocity increases with rising frequency) with the intensity of between 1.7 and 5.0% was obtained in all productive wells in depths of oil and gas pools. The close correlation between local increasing of velocity dispersion and absorption occurred in most cases. Background level of velocity dispersion with both signs (less then {+-}1.0%) which the authors consider as a level of mistakes was observed outside productive intervals and in ``dry`` wells. Modeling has shown that pseudodispersion caused by layered media may attain {+-}0.5% and, besides, curves of pseudodispersion and pseudoabsorption exhibit no correlation. Analysis of seismic waves dispersion together with the absorption may provide with reliable indicators of hydrocarbon pools.

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

    USGS Publications Warehouse

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

  15. Impact of Phase Transitions on P Wave Velocities

    SciTech Connect

    D Weidner; L Li

    2011-12-31

    In regions where a high pressure phase is in equilibrium with a low pressure phase, the bulk modulus defined by the P-V relationship is greatly reduced. Here we evaluate the effect of such transitions on the P wave velocity. A model, where cation diffusion is the rate limiting factor, is used to project laboratory data to the conditions of a seismic wave propagating in the two-phase region. We demonstrate that for the minimum expected effect there is a significant reduction of the seismic velocity, as large as 10% over a narrow depth range.

  16. 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.

  17. Impact of Phase Transitions on P Wave Velocities

    SciTech Connect

    Weidner, D.; Li, L

    2010-01-01

    In regions where a high pressure phase is in equilibrium with a low pressure phase, the bulk modulus defined by the P-V relationship is greatly reduced. Here we evaluate the effect of such transitions on the P wave velocity. A model, where cation diffusion is the rate limiting factor, is used to project laboratory data to the conditions of a seismic wave propagating in the two-phase region. We demonstrate that for the minimum expected effect there is a significant reduction of the seismic velocity, as large as 10% over a narrow depth range.

  18. 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.

  19. Shear-wave velocity structure of the crust and uppermost mantle in the Shanxi rift zone

    NASA Astrophysics Data System (ADS)

    Song, Meiqing; Zheng, Yong; Liu, Chun; Li, Li; Wang, Xia

    2015-04-01

    The Shanxi rift zone is one of the largest and active Cenozoic grabens in the world, studying the velocity structure of the crust and upper mantle in this region may help us to understand the mechanisms of rift processes and the seismogenic environment of active seismicity in continental rifts. In this work, using the broadband seismic data of Shanxi, Hebei, Henan, Shaanxi provinces, and the Inner Mongolia Autonomous Region from February 2009 to November 2011, we have picked out 350 high-quality phase velocity dispersion curves of fundamental mode Rayleigh waves at periods from 8 to 75 s, and Rayleigh wave phase velocity maps have been constructed from 8 to 75 s period with horizontal resolution ranging from 40 to 50 km by two-station surface-wave tomography. Then, using a genetic algorithm, a 3D shear-wave speed model of the crust and uppermost mantle have been derived from these maps with a spatial resolution of 0.4° × 0.4°. Four characteristics can be outlined from the results: (1) Except in the Datong volcanic zone, in the depth range of 11-30 km, the location of a transition zone between the high- and low-velocity regions is in agreement with the seismicity pattern in the study region, and the earthquakes are mostly concentrated near this transition zone; (2) In the depth range of 31-40 km, shear-wave velocities are higher to the south of the Taiyuan Basin and lower to the north, which is similar to the distribution pattern of Moho depth variations in the Shanxi region; (3) The shear-wave velocity pattern of higher velocities to the south of 38°N and lower velocities to the north is found to be consistent with that from the upper crustal levels to depth of 70 km. At the deeper depths, the spatial scale of the low-velocity anomalies zone in the north is gradually shrinking with depth increasing, the low-velocity anomalies are gradually disappearing beneath the Datong volcanic zone at the depth of 151-200 km. We proposed that the root of the Datong volcano may reach to a depth around 150 km; (4) Along the N-S vertical profile at 112.8°E, the 38°N latitude is the boundary between high and low velocities, arguing the tectonic difference between the Shanxi rift zone and its flanks, in the rift zone the seismic velocity is dominated by low-velocity anomalies while in the flanks it is high.

  20. Estimation of shear velocity contrast from transmitted Ps amplitude variation with ray-parameter

    NASA Astrophysics Data System (ADS)

    Kumar, Prakash; Sen, Mrinal K.; Haldar, Chinmay

    2014-09-01

    Amplitude versus offset of P to P reflection is commonly used by the exploration seismology community for hydrocarbon exploration. In this paper, we investigate the feasibility to estimate crustal velocity structure from transmitted P- to S-wave amplitude variation with ray-parameter. First the transmission coefficient for the plane P wave converting to S wave (P- to -S) is approximated and expressed as a function of slowness. The resulting linear relation involves two coefficients (intercept, X and gradient, Y), which are functions of velocities and densities. Due to the stable nature of X and the fact that P- to -S amplitudes are weakly dependent on the density contrast, we use this parameter next to estimate the shear wave velocity contrast across an interface using the forward scattered P- to -S amplitude versus slowness data. We report on the effectiveness of the approach using various synthetics data sets. The present methodology is also tested on real data sets from two broad-band seismic stations from HYB and COR.

  1. 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.

  2. P wave velocity tomography of the Venezuelan region from local arrival times

    NASA Astrophysics Data System (ADS)

    Bosch, Miguel

    1997-03-01

    Arrival times from the local seismological network of Venezuela were used to estimate a three-dimensional P wave velocity model for the region between longitude 60°-74° W and latitude 6°-14° N to a depth of more than 80 km. The inversion was carried out by damped least squares, describing the media by homogeneous velocity blocks. The resolved lateral velocity variations in the first layer (0-30 km depth) showed a correlation with the main stratigraphic features of the area, while second layer (30-50 km depth) showed the influence of Moho depth variations through the region, generating a pattern well correlated to the Bouguer Anomaly Map. Lithospheric seismic velocities below the Moho appear to be influenced by the major crustal fault systems. An important low-velocity zone is present below the triple junction of the fault systems of Oca, Boconó, and Morón in northwestern Venezuela. Farther south, a similar low-velocity zone is present below the junction of the Boconó and the Santa Marta fault systems. Those are the two continental corners of the triangular Maracaibo Block. Below 80 km depth (the fourth layer) the low velocity zones show a connected pattern that follows or is adjacent to the crustal fault zones. The presence of subducted Atlantic lithosphere below the Eastern Venezuelan Basin could explain the high-velocity zone at this location. A similar interpretation emerges from the tectonic wedging model, previously proposed to explain the pronounced minimum of the gravity anomaly.

  3. Quasi-periodic variations in Doppler velocities of H ? spicules

    NASA Astrophysics Data System (ADS)

    Khutsishvili, E.; Kulidzanishvili, V.; Kvernadze, T.; Zaqarashvili, T. V.; Kakhiani, V.; Khutsishvili, D.; Sikharulidze, M.

    2014-12-01

    New series of CCD spectral observations of spicules were obtained using 53-cm Lyot coronagraph of Abastumani Astrophysical Observatory (Georgia) at 5500 km height above the solar limb on October 17, 2012 in H ? spectral line. The line-of-sight Doppler velocities of 34 spicules were measured with the cadence of 4.5 s and standard error equal to ±0.3 km/s. Life times of almost all measured spicules were 5-6 min (and longer), therefore they resemble the type I spicules. No short lived structures (similar to type II spicules) were identified during the time series neither inside nor outside the observed spicules. The Doppler velocity time series were processed using Lomb Periodogram Algorithm revealing 4 types of dominating period intervals centered around: 254 s, 136 s, 94 s and 65 s having confidence levels over 95 %. The oscillations with periods around 254 s can be caused by quasi-periodic rebound shocks after the propagation of photospheric pulses. The oscillations with periods around 136 s can be caused by the oscillation of spicules axis at the kink cut-off frequency in gravitationally stratified magnetic tubes. In this case, seismological estimations give the density scale height as 380-540 km for the kink wave speed of 70-100 km/s in spicules. Shorter period oscillations are probably caused by propagating kink waves in spicules.

  4. Detonation wave velocity and curvature of brass encased PBXN-111

    SciTech Connect

    Forbes, J.W.; Lemar, E.R.

    1996-05-01

    Detonation velocities and wave front curvatures were measured for PBXN-111 charges encased in 5 mm thick brass tubes. In all the experiments (charge diameters from 19 to 47 mm) the brass case affected the detonation properties of PBXN-111. Steady detonation waves propagated in brass encased charges with diameters as small as 19 mm, which is about half of the unconfined failure diameter. The radii of curvature of the detonation waves at the center of the wave fronts ranged from 52 to 141 mm for charge diameters of 25 to 47 mm. The angles between the detonation wave fronts and the brass/charge interfaces were between 72 and 74 degrees. {copyright} {ital 1996 American Institute of Physics.}

  5. Recording of Dispersion of Elastic Wave Velocity in Natural Uranium

    NASA Astrophysics Data System (ADS)

    Fedorov, Alexey

    2005-07-01

    Under shock-wave loading of planar samples of natural uranium, difference in time of elastic wave arrival to free surface was recorded by Fabry-Perot laser interferometer. This difference reached 100-250ns at sample thicknesses of 3-10 mm. In tests, the recorded value of longitudinal sound velocity is in the range from 3.26 to 3.6 km/s. Value of dispersion of longitudinal sound velocity was ˜350 m/s (˜ 10%). In tests, dispersion of particle velocity was recorded at elastic precursor. It implies that different profiles and different amplitudes of elastic wave are recorded at different interferometric lines. Front of elastic wave in heterogeneous medium has complicated structure, which can be explained by shift and turning of structural elements of deformed medium at mesoscale. According to interferometric measurements, period of shear bands at elastic wave is 4-25 mm, and it is in good agreement with period of sliding lines recorded during microstructural analysis of recovered samples. At heterogeneous deformation of material, it is shown that plastic shears occur already at elastic precursor.

  6. Traveling waves in an optimal velocity model of freeway traffic

    NASA Astrophysics Data System (ADS)

    Berg, Peter; Woods, Andrew

    2001-03-01

    Car-following models provide both a tool to describe traffic flow and algorithms for autonomous cruise control systems. Recently developed optimal velocity models contain a relaxation term that assigns a desirable speed to each headway and a response time over which drivers adjust to optimal velocity conditions. These models predict traffic breakdown phenomena analogous to real traffic instabilities. In order to deepen our understanding of these models, in this paper, we examine the transition from a linear stable stream of cars of one headway into a linear stable stream of a second headway. Numerical results of the governing equations identify a range of transition phenomena, including monotonic and oscillating travelling waves and a time- dependent dispersive adjustment wave. However, for certain conditions, we find that the adjustment takes the form of a nonlinear traveling wave from the upstream headway to a third, intermediate headway, followed by either another traveling wave or a dispersive wave further downstream matching the downstream headway. This intermediate value of the headway is selected such that the nonlinear traveling wave is the fastest stable traveling wave which is observed to develop in the numerical calculations. The development of these nonlinear waves, connecting linear stable flows of two different headways, is somewhat reminiscent of stop-start waves in congested flow on freeways. The different types of adjustments are classified in a phase diagram depending on the upstream and downstream headway and the response time of the model. The results have profound consequences for autonomous cruise control systems. For an autocade of both identical and different vehicles, the control system itself may trigger formations of nonlinear, steep wave transitions. Further information is available [Y. Sugiyama, Traffic and Granular Flow (World Scientific, Singapore, 1995), p. 137].

  7. Traveling waves in an optimal velocity model of freeway traffic.

    PubMed

    Berg, P; Woods, A

    2001-03-01

    Car-following models provide both a tool to describe traffic flow and algorithms for autonomous cruise control systems. Recently developed optimal velocity models contain a relaxation term that assigns a desirable speed to each headway and a response time over which drivers adjust to optimal velocity conditions. These models predict traffic breakdown phenomena analogous to real traffic instabilities. In order to deepen our understanding of these models, in this paper, we examine the transition from a linear stable stream of cars of one headway into a linear stable stream of a second headway. Numerical results of the governing equations identify a range of transition phenomena, including monotonic and oscillating travelling waves and a time- dependent dispersive adjustment wave. However, for certain conditions, we find that the adjustment takes the form of a nonlinear traveling wave from the upstream headway to a third, intermediate headway, followed by either another traveling wave or a dispersive wave further downstream matching the downstream headway. This intermediate value of the headway is selected such that the nonlinear traveling wave is the fastest stable traveling wave which is observed to develop in the numerical calculations. The development of these nonlinear waves, connecting linear stable flows of two different headways, is somewhat reminiscent of stop-start waves in congested flow on freeways. The different types of adjustments are classified in a phase diagram depending on the upstream and downstream headway and the response time of the model. The results have profound consequences for autonomous cruise control systems. For an autocade of both identical and different vehicles, the control system itself may trigger formations of nonlinear, steep wave transitions. Further information is available [Y. Sugiyama, Traffic and Granular Flow (World Scientific, Singapore, 1995), p. 137]. PMID:11308709

  8. 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.

  9. THEMIS Observations of the Wavy Variations in the Plasma Velocity at the inner edge of the Low-Latitude Boundary Layer

    NASA Astrophysics Data System (ADS)

    Nowada, M.; Shue, J.; Lin, C.; Sakurai, T.; Sibeck, D. G.; Lyu, L.; Angelopoulos, V.; McFadden, J. P.; Carlson, C. W.; Auster, H.

    2008-12-01

    The THEMIS spacecraft provides opportunities to make unique simultaneous observations in the magnetosheath, the magnetospheric boundary layers and the magnetosphere by a string-of-pearls configuration. We have examined how the variations caused by the surface waves on the dayside magnetopause can propagate into the magnetosphere. On July 31, 2007, THEMIS-C and -D observed the wavy variations in the plasma velocity at the inner edge of Low-Latitude Boundary Layer (LLBL) under the northward Interplanetary Magnetic Field (IMF) and quiet solar wind conditions. These wavy velocity variations appeared in the Vx and Vy components. The associated magnetic field had microscopic wavy fluctuations, but no periodic variations were found in simultaneous plasma density and temperature. The hodograms of the velocities perpendicular to the magnetic field line had clear vortex-like structures. From these results, observed plasma velocity variations are Alfvén waves. On the other hand, THEMIS-E also observed the wavy velocity variations at the same region as well as THEMIS-C and -D, but the velocity hodogram did not present the vortex-like structures. Therefore, these wavy velocity variations are local phenomena. THEMIS-B simultaneously observed the diamagnetic-like waves due to the magnetopause undulations in the magnetosheath. This is because the correlation between the magnetic and plasma pressures was clearly out-of-phase. During the interval of these waves, the periodicities of these pressure variations were between 0.5 minute and 1 minute, and consistent with those of the wavy velocity variations. From these results, the fast-mode waves are induced by the magnetopause diamagnetic-like waves, and can propagate into the magnetosphere.

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

    PubMed

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

    2013-07-01

    This paper estimates seabed shear-wave velocity profiles and their uncertainties using interface-wave dispersion curves extracted from data generated by a shear-wave source. The shear-wave source generated a seismic signature over a frequency range between 2 and 60 Hz and was polarized in both in-line and cross-line orientations. Low-frequency Scholte- and Love-waves were recorded. Dispersion curves of the Scholte- and Love-waves for the fundamental mode and higher-order modes are extracted by three time-frequency analysis methods. Both the vertically and horizontally polarized shear-wave velocity profiles in the sediment are estimated by the Scholte- and Love-wave dispersion curves, respectively. A Bayesian approach is utilized for the inversion. Differential evolution, a global search algorithm is applied to estimate the most-probable shear-velocity models. Marginal posterior probability profiles are computed by Metropolis-Hastings sampling. The estimated vertically and horizontally polarized shear-wave velocity profiles fit well with the core and in situ measurements. PMID:23862796

  11. Measurements of parallel electron velocity distributions using whistler wave absorption.

    PubMed

    Thuecks, D J; Skiff, F; Kletzing, C A

    2012-08-01

    We describe a diagnostic to measure the parallel electron velocity distribution in a magnetized plasma that is overdense (?(pe) > ?(ce)). This technique utilizes resonant absorption of whistler waves by electrons with velocities parallel to a background magnetic field. The whistler waves were launched and received by a pair of dipole antennas immersed in a cylindrical discharge plasma at two positions along an axial background magnetic field. The whistler wave frequency was swept from somewhat below and up to the electron cyclotron frequency ?(ce). As the frequency was swept, the wave was resonantly absorbed by the part of the electron phase space density which was Doppler shifted into resonance according to the relation ? - k([parallel])v([parallel]) = ?(ce). The measured absorption is directly related to the reduced parallel electron distribution function integrated along the wave trajectory. The background theory and initial results from this diagnostic are presented here. Though this diagnostic is best suited to detect tail populations of the parallel electron distribution function, these first results show that this diagnostic is also rather successful in measuring the bulk plasma density and temperature both during the plasma discharge and into the afterglow. PMID:22938290

  12. Measurements of parallel electron velocity distributions using whistler wave absorption

    SciTech Connect

    Thuecks, D. J.; Skiff, F.; Kletzing, C. A.

    2012-08-15

    We describe a diagnostic to measure the parallel electron velocity distribution in a magnetized plasma that is overdense ({omega}{sub pe} > {omega}{sub ce}). This technique utilizes resonant absorption of whistler waves by electrons with velocities parallel to a background magnetic field. The whistler waves were launched and received by a pair of dipole antennas immersed in a cylindrical discharge plasma at two positions along an axial background magnetic field. The whistler wave frequency was swept from somewhat below and up to the electron cyclotron frequency {omega}{sub ce}. As the frequency was swept, the wave was resonantly absorbed by the part of the electron phase space density which was Doppler shifted into resonance according to the relation {omega}-k{sub ||v||} = {omega}{sub ce}. The measured absorption is directly related to the reduced parallel electron distribution function integrated along the wave trajectory. The background theory and initial results from this diagnostic are presented here. Though this diagnostic is best suited to detect tail populations of the parallel electron distribution function, these first results show that this diagnostic is also rather successful in measuring the bulk plasma density and temperature both during the plasma discharge and into the afterglow.

  13. 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

  14. Seasonal variations of seismic velocities in the San Jacinto fault area observed with ambient seismic noise

    NASA Astrophysics Data System (ADS)

    Hillers, G.; Ben-Zion, Y.; Campillo, M.; Zigone, D.

    2015-08-01

    We observe seasonal seismic wave speed changes (dv/v) in the San Jacinto fault area and investigate several likely source mechanisms. Velocity variations are obtained from analysis of 6 yr data of vertical component seismic noise recorded by 10 surface and six borehole stations. We study the interrelation between dv/v records, frequency-dependent seismic noise properties, and nearby environmental data of wind speed, rain, ground water level, barometric pressure and atmospheric temperature. The results indicate peak-to-peak seasonal velocity variations of ˜0.2 per cent in the 0.5-2 Hz frequency range, likely associated with genuine changes of rock properties rather than changes in the noise field. Phase measurements between dv/v and the various environmental data imply that the dominant source mechanism in the arid study area is thermoelastic strain induced by atmospheric temperature variations. The other considered environmental effects produce secondary variations that are superimposed on the thermal-based changes. More detailed work with longer data on the response of rocks to various known external loadings can help tracking the evolving stress and effective rheology at depth.

  15. 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

  16. A 1D P wave velocity model under the pacific region using multiply reflected P waves

    NASA Astrophysics Data System (ADS)

    Foundotos, M.; Nolet, G.

    2012-12-01

    In order to constrain the shallow structure of the Earth in global tomography, Love and Rayleigh waves are often used. However these waves are mostly sensitive to the S wave velocity structure. P-wave energy is either evanescent, or leaking away at every surface reflection that generates an S wave which travels much deeper into the mantle. For that reason, to study the shallow P velocity structure of the Earth, we need to study P-waves at regional distances if a good seismic station coverage is available. Otherwise we can use multiply reflected P waves at teleseismic distance when regional data are not available (as in the oceans for instance). We used 203 events of magnitude Mw > 6.0 recorded from the dense network of US ARRAY, which allows us to make a very large number of group arrival and slowness measurements of multiply reflected P waves . Our study shows that two times reflected PPP and three times reflected PPPP waves are very well observed despite the ray- theoretical prediction that at certain distances almost all of their compressional energy is converted to shear waves. We also observed Four times reflected 5P and five times reflected 6P which show a strong interference for epicentral distances larger than 80 degree. These observations of multiply reflected P waves allow us to inferred a 1D P wave model for the shallow structure under the pacific region.

  17. Flow velocity measurement with the nonlinear acoustic wave scattering

    NASA Astrophysics Data System (ADS)

    Didenkulov, Igor; Pronchatov-Rubtsov, Nikolay

    2015-10-01

    A problem of noninvasive measurement of liquid flow velocity arises in many practical applications. To this end the most often approach is the use of the linear Doppler technique. The Doppler frequency shift of signal scattered from the inhomogeneities distributed in a liquid relatively to the emitted frequency is proportional to the sound frequency and velocities of inhomogeneities. In the case of very slow flow one needs to use very high frequency sound. This approach fails in media with strong sound attenuation because acoustic wave attenuation increases with frequency and there is limit in increasing sound intensity, i.e. the cavitation threshold. Another approach which is considered in this paper is based on the method using the difference frequency Doppler Effect for flows with bubbles. This method is based on simultaneous action of two high-frequency primary acoustic waves with closed frequencies on bubbles and registration of the scattered by bubbles acoustic field at the difference frequency. The use of this method is interesting since the scattered difference frequency wave has much lower attenuation in a liquid. The theoretical consideration of the method is given in the paper. The experimental examples confirming the theoretical equations, as well as the ability of the method to be applied in medical diagnostics and in technical applications on measurement of flow velocities in liquids with strong sound attenuation is described. It is shown that the Doppler spectrum form depends on bubble concentration velocity distribution in the primary acoustic beams crossing zone that allows one to measure the flow velocity distribution.

  18. Variational water wave model -with accurate dispersion and vertical vorticity

    E-print Network

    Al Hanbali, Ahmad

    travel with different speeds velocity irrotational u = (e) Offshore oil platform "Thunder Horse" tilted for offshore and marine engineering problems: acurate dispersion: (deep-water) waves of different wave length

  19. 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.

  20. Lanczos steps to improve variational wave functions

    NASA Astrophysics Data System (ADS)

    Becca, Federico; Hu, Wen-Jun; Iqbal, Yasir; Parola, Alberto; Poilblanc, Didier; Sorella, Sandro

    2015-09-01

    Gutzwiller-projected fermionic states can be efficiently implemented within quantum Monte Carlo calculations to define extremely accurate variational wave functions for Heisenberg models on frustrated two-dimensional lattices, not only for the ground state but also for low-energy excitations. The application of few Lanczos steps on top of these states further improves their accuracy, allowing calculations on large clusters. In addition, by computing both the energy and its variance, it is possible to obtain reliable estimations of exact results. Here, we report the cases of the frustrated Heisenberg models on square and Kagome lattices.

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

    SciTech Connect

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

    2014-06-15

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

  2. Azimuthal anisotropy of Rayleigh-wave phase velocities in the east-central United States

    NASA Astrophysics Data System (ADS)

    Deschamps, Frédéric; Lebedev, Sergei; Meier, Thomas; Trampert, Jeannot

    2008-06-01

    We explore the Rayleigh-wave phase velocity structure of the east-central US in a broad period range (10-200 s). Using a recent implementation of the two-stations method, we first measure interstation dispersion curves of Rayleigh-wave phase velocities along 60 paths. We then invert our collection of dispersion curves for isotropic and azimuthally anisotropic (2? and 4?) phase-velocity maps. The inversion is performed by a damped, smoothed LSQR, and the output model is parametrized on a triangular grid of knots with a 140 km grid spacing. Using the isotropic component of the phase velocity maps to constrain regional variations in shear velocity and Moho-depth, we observe that over the upper-middle crust depth range (z < 30 km) shear wave velocities are lower beneath the Grenville and Appalachian orogenic provinces than beneath the Central Plains to the west. The amplitude of (2?) anisotropy and the azimuth of the fast-propagation direction at periods between 20 and 34 s vary laterally. Beneath the Grenville and Appalachian provinces, the amplitude of anisotropy reaches 1 per cent of the average phase velocity, and the azimuth of the fast-propagation direction is uniform and equal to 32°. West of the Grenville front, the average amplitude falls to 0.5 per cent, and the azimuth of the fast-propagation direction is less uniform. In the period range 45-60 s, anisotropy is smaller in amplitude (~0.5 per cent) and with a regionally uniform azimuth of the fast-propagation direction of around 165°. Around 140 s, the amplitude of 2? anisotropy is larger again (>1 per cent), and the azimuth of the fast-propagation direction is uniform over the entire region and equal to 54°. Our results suggest that azimuthal anisotropy beneath the east-central US is vertically distributed in three distinct layers, with a different geodynamic origin for each of them.

  3. Potential Misidentification of Love-Wave Phase Velocity Based on Three-Component Ambient Seismic Noise

    NASA Astrophysics Data System (ADS)

    Xu, Zongbo; Xia, Jianghai; Luo, Yinhe; Cheng, Feng; Pan, Yudi

    2015-08-01

    People have calculated Rayleigh-wave phase velocities from vertical component of ambient seismic noise for several years. Recently, researchers started to extract Love waves from transverse component recordings of ambient noise, where "transverse" is defined as the direction perpendicular to a great-circle path or a line in small scale through observation sensors. Most researches assumed Rayleigh waves could be negligible, but Rayleigh waves can exist in the transverse component when Rayleigh waves propagate in other directions besides radial direction. In study of data acquired in western Junggar Basin near Karamay city, China, after processing the transverse component recordings of ambient noise, we obtain two energy trends, which are distinguished with Rayleigh-wave and Love-wave phase velocities, in the frequency-velocity domain using multichannel analysis of surface waves (MASW). Rayleigh waves could be also extracted from the transverse component data. Because Rayleigh-wave and Love-wave phase velocities are close in high frequencies (>0.1 Hz), two kinds of surface waves might be merged in the frequency-velocity domain. Rayleigh-wave phase velocities may be misidentified as Love-wave phase velocities. To get accurate surface-wave phase velocities from the transverse component data using seismic interferometry in investigating the shallow geology, our results suggest using MASW to calculate real Love-wave phase velocities.

  4. 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

  5. On the group-velocity property for wave-activity conservation laws

    E-print Network

    Wirosoetisno, Djoko

    On the group-velocity property for wave- activity conservation laws Article Published Version Vanneste, J. and Shepherd, T. G. (1998) On the group-velocity property for wave-activity conservation laws-Velocity Property for Wave-Activity Conservation Laws J. VANNESTE AND T. G. SHEPHERD Department of Physics

  6. The Study on S-Wave Velocity Structure of Upper Crust in Three Gorges Region of Yangtze River

    NASA Astrophysics Data System (ADS)

    Li, X.; Zhu, P.; Zhou, Q.

    2014-12-01

    The profile of S-wave velocity structure along Badong-Maoping-Tumen is presented using the ambient noise data observed at 10 stations from mobile broadband seismic array which is located at Three Gorges Region. All of available vertical component time series during April and May?2011 have been cross-correlated to estimate the empirical Green functions. Group velocity dispersion curves were measured by applying multiple filtering technique. Using these dispersion curves?we obtain high resolution pure-path dispersions at 0.5-10 second periods. The S-wave velocity structure?which was reconstructed by inverting the pure-path dispersions?reveals the velocity variations of upper crust at Three Gorges Region. Main conclusions are as follows?(1)The velocity variations in the study region have a close relationship with the geological structure and the velocity profile suggests a anticline unit which core area is Huangling block?(2)The relative fast velocity variations beneath Jiuwanxi and its surrounding areas may correspond to the geological structure and earthquake activity there?(3) The high velocity of the upper crustal in Sandouping indicates that the Reservoir Dam of Three Gorges is located at a tectonic stable region.

  7. 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.

  8. 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.

  9. New Hybridized Surface Wave Approach for Geotechnical Modeling of Shear Wave Velocity at Strong Motion Recording Stations

    NASA Astrophysics Data System (ADS)

    Kayen, R.; Carkin, B.; Minasian, D.

    2006-12-01

    Strong motion recording (SMR) networks often have little or no shear wave velocity measurements at stations where characterization of site amplification and site period effects is needed. Using the active Spectral Analysis of Surface Waves (SASW) method, and passive H/V microtremor method we have investigated nearly two hundred SMR sites in California, Alaska, Japan, Australia, China and Taiwan. We are conducting these studies, in part, to develop a new hybridized method of site characterization that utilizes a parallel array of harmonic-wave sources for active-source SASW, and a single long period seismometer for passive-source microtremor measurement. Surface wave methods excel in their ability to non-invasively and rapidly characterize the variation of ground stiffness properties with depth below the surface. These methods are lightweight, inexpensive to deploy, and time-efficient. They have been shown to produce accurate and deep soil stiffness profiles. By placing and wiring shakers in a large parallel circuit, either side-by-side on the ground or in a trailer-mounted array, a strong in-phase harmonic wave can be produced. The effect of arraying many sources in parallel is to increase the amplitude of waves received at far-away spaced seismometers at low frequencies so as to extend the longest wavelengths of the captured dispersion curve. The USGS system for profiling uses this concept by arraying between two and eight electro-mechanical harmonic-wave shakers. With large parallel arrays of vibrators, a dynamic force in excess of 1000 lb can be produced to vibrate the ground and produce surface waves. We adjust the harmonic wave through a swept-sine procedure to profile surface wave dispersion down to a frequency of 1 Hz and out to surface wave-wavelengths of 200-1000 meters, depending on the site stiffness. The parallel-array SASW procedure is augmented using H/V microtremor data collected with the active source turned off. Passive array microtremor data reveal the natural and resonance characteristics of the ground by capturing persistent natural vibrations. These microtremors are the result of the interaction of surface waves arriving from distant sources and the stiffness structure of the site under investigation. As such, these resonance effects are effective in constraining the layer thicknesses of the SASW shear wave velocity structure and aid in determining the depth of the deepest layer. Together, the hybridized SASW and H/V procedure provides a complete data set for modeling the geotechnical aspects of ground amplification of earthquake motions. Data from these investigations are available at http://walrus.wr.usgs.gov/geotech.

  10. Love wave group velocities in Czech Republic L. Valentova1,2

    E-print Network

    Cerveny, Vlastislav

    Love wave group velocities in Czech Republic L. Valentova1,2 , F. Gallovic2 , B. Ruzek3 and J. de of Geophysics AS CR Prague, CR 4) CASE BSC Barcelona, Spain Group velocities of 20s Love waves Resulting modelSol and assuming that the membrane wave approximation is valid, we performed inversion of traveltimes of Love waves

  11. 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.

  12. Determination of in situ shear wave velocities from spectral analysis of surface waves

    NASA Astrophysics Data System (ADS)

    Hensley, J. S.; Stokoe, K. H.; Hudson, W. R.; Meyer, A. H.

    1982-12-01

    A method for determining elastic moduli at soil and pavement sites was proposed and tested. Surface receivers were utilized to evaluate the Rayleigh wave motion created by a vertical, impulsive source that could excite a wide range of frequencies with a single impact. Analysis was facilitated by using a portable spectral analyzer to study the magnitude and phase of the frequency content of the recorded wave pulse. Results from field testing at two flexible pavement sites and two soil sites indicate that the spectral analysis of surface waves provides an accurate estimation of the velocity (and hence modulus) profile at a site. Moduli calculated from wave propagation velocities were generally comparable to moduli calculated by deflection measurements from Dynaflect testing.

  13. 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.

  14. 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)

  15. Variational wave functions for homogenous Bose systems

    SciTech Connect

    Sueto, Andras; Szepfalusy, Peter

    2008-02-15

    We study variational wave functions of the product form, factorizing according to the wave vectors k, for the ground state of a system of bosons interacting via positive pair interactions with a positive Fourier transform. Our trial functions are members of different orthonormal bases in Fock space. Each basis contains a quasiparticle vacuum state and states with an arbitrary finite number of quasiparticles. One of the bases is that of Valatin and Butler (VB), introduced fifty years ago and parametrized by an infinite set of variables determining Bogoliubov's canonical transformation for each k. In another case, inspired by Nozieres and Saint James the canonical transformation for k=0 is replaced by a shift in the creation/annihilation operators. For the VB basis we prove that the lowest energy is obtained in a state with {approx}{radical}(volume) quasiparticles in the zero mode. The number of k=0 physical particles is of the order of the volume and its fluctuation is anomalously large, resulting in an excess energy. The same fluctuation is normal in the second type of optimized bases, the minimum energy is smaller and is attained in a vacuum state. Associated quasiparticle theories and questions about the gap in their spectrum are also discussed.

  16. 3-D Wave Velocity Structure for the Ultrahigh-Pressure Metamorphosed Terrace in the Dabie- Sulu region,Chind

    NASA Astrophysics Data System (ADS)

    Zhao, Z.; Xu, J.; Yang, W.; Xu, Z.

    2004-12-01

    3-D Wave Velocity Structure for the Ultrahigh-Pressure Metamorphosed Terrace in the Dabie- Sulu region,Chind Zhixin ZHAO 1 (+86-010-68999734; zhaozhixin@ccsd.org.cn) Jiren XU 1 (+86-10-68992879; xujiren@ccsd.org.cn) Wencai YANG 1 (yangwencai@ccsd.org.cn) Zhiqing XU 1 (xuzhiqing@ccsd.org.cn) 1 Institute of Geology, CAGS£¬Baiwanzhuang Road 26, Beijing 100037, China 3-D wave velocity structure image in the crust and upper mantle in the east continent of China were analyzed in the present study. The velocity beneath the North China block is generally higher than that beneath the Yangtze block at 150 km depth. A velocity variation boundary appears beneath the Dabie-Sulu orogeny belt. Velocity values beneath Sulu region and the Shandong peninsula are in the identical contour line with that beneath the Dabie orogeny belt. In velocity profile crossing the Dabie mountain along near N-S direction, at the region shallower than 100 km depth, velocities beneath the North China and Yangtze blocks are lightly less than the average value. Velocity beneath the Yangtze block at the region deeper than 100 km£¬ however, is slower than that beneath North China block. A anomalous velocity zone lightly less than zero at the south side of velocity variation boundary beneath Dabie mountain thrusts downward greater than 300 km depth beneath the North China block from south to north, at the dip angle of about 30 degrees. A near zero velocity zone north of the velocity boundary seems to thrust upward the surface of the Yangtze block from 100 km depth along the N-S direction beneath the North China block. Such geometries of the velocity structure images beneath the region crossing the Dabie orogeny belt imply that the zones thrusting down and upward might be related to the evidences of the ¡°traces¡± for the subduction and exhumation process of ultrahigh-pressure metamorphosed terrace beneath the Dabie mountain.

  17. 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.

  18. Magnetospheric electron-velocity-distribution function information from wave observations

    NASA Astrophysics Data System (ADS)

    Benson, Robert F.; ViñAs, Adolfo F.; Osherovich, Vladimir A.; Fainberg, Joseph; Purser, Carola M.; Adrian, Mark L.; Galkin, Ivan A.; Reinisch, Bodo W.

    2013-08-01

    The electron-velocity-distribution function was determined to be highly non-Maxwellian and more appropriate to a kappa distribution, with ? ? 2.0, near magnetic midnight in the low-latitude magnetosphere just outside a stable plasmasphere during extremely quiet geomagnetic conditions. The kappa results were based on sounder-stimulated Qn plasma resonances using the Radio Plasma Imager (RPI) on the IMAGE satellite; the state of the plasmasphere was determined from IMAGE/EUV observations. The Qn resonances correspond to the maximum frequencies of Bernstein-mode waves that are observed between the harmonics of the electron cyclotron frequency in the frequency domain above the upper-hybrid frequency. Here we present the results of a parametric investigation that included suprathermal electrons in the electron-velocity-distribution function used in the plasma-wave dispersion equation to calculate the Qn frequencies for a range of kappa and fpe/fce values for Qn resonances from Q1 to Q9. The Qn frequencies were also calculated using a Maxwellian distribution, and they were found to be greater than those calculated using a kappa distribution with the frequency differences increasing with increasing n for a fixed ? and with decreasing ? for a fixed n. The calculated fQn values have been incorporated into the RPI BinBrowser software providing a powerful tool for rapidly obtaining information on the nature of the magnetospheric electron-velocity-distribution function and the electron number density Ne. This capability enabled accurate (within a few percent) in situ Ne determinations to be made along the outbound orbital track as IMAGE moved away from the plasmapause. The extremely quiet geomagnetic conditions allowed IMAGE/EUV-extracted counts to be compared with the RPI-determined orbital-track Ne profile. The comparisons revealed remarkably similar Ne structures.

  19. Shear wave velocity structure in North America from large-scale waveform inversions of surface waves

    NASA Astrophysics Data System (ADS)

    Alsina, D.; Woodward, R. L.; Snieder, R. K.

    1996-07-01

    A two-step nonlinear and linear inversion is carried out to map the lateral heterogeneity beneath North America using surface wave data. The lateral resolution for most areas of the model is of the order of several hundred kilometers. The most obvious feature in the tomographic images is the rapid transition between low velocities in the tectonically active region west of the Rocky Mountains and high velocities in the stable central and eastern shield of North America. The model also reveals smaller-scale heterogeneous velocity structures. A high-velocity anomaly is imaged beneath the state of Washington that could be explained as the subducting Juan de Fuca plate beneath the Cascades. A large low-velocity structure extends along the coast from the Mendocino to the Rivera triple junction and to the continental interior across the southwestern United States and northwestern Mexico. Its shape changes notably with depth. This anomaly largely coincides with the part of the margin where no lithosphere is consumed since the subduction has been replaced by a transform fault. Evidence for a discontinuous subduction of the Cocos plate along the Middle American Trench is found. In central Mexico a transition is visible from low velocities across the Trans-Mexican Volcanic Belt (TMVB) to high velocities beneath the Yucatan Peninsula. Two elongated low-velocity anomalies beneath the Yellowstone Plateau and the eastern Snake River Plain volcanic system and beneath central Mexico and the TMVB seem to be associated with magmatism and partial melting. Another low-velocity feature is seen at depths of approximately 200 km beneath Florida and the Atlantic Coastal Plain. The inversion technique used is based on a linear surface wave scattering theory, which gives tomographic images of the relative phase velocity perturbations in four period bands ranging from 40 to 150 s. In order to find a smooth reference model a nonlinear inversion based on ray theory is first performed. After 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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  2. 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.

  3. Diffractive Nonlinear Geometrical Optics for Variational Wave Equations

    E-print Network

    Hunter, John K.

    Diffractive Nonlinear Geometrical Optics for Variational Wave Equations and the Einstein Equations of strongly nonlinear geometrical optics for the Einstein equations with nonlinear geometri- cal optics theories for variational wave equations. c 2000 Wiley Periodicals, Inc. 1 Introduction Geometrical optics1

  4. Thermal structure of continental upper mantle inferred from S-wave velocity and surface heat ow

    E-print Network

    Snieder, Roel

    Thermal structure of continental upper mantle inferred from S-wave velocity and surface heat £ow. This is borne out by the good agreement between tectonic age, surface heat flow and a tomographic S-wave upper crustal radiogenic heat production. The S-wave velocity in the continental upper mantle appears

  5. 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.

  6. Brachial-Ankle Pulse Wave Velocity: Myths, Misconceptions, and Realities

    PubMed Central

    Sugawara, Jun; Tanaka, Hirofumi

    2015-01-01

    A variety of techniques to evaluate central arterial stiffness have been developed and introduced. None of these techniques, however, have been implemented widely in regular clinical settings, except for brachial-ankle pulse wave velocity (baPWV). The most prominent procedural advantage of baPWV is its ease of use, since it only requires the wrapping of blood pressure cuffs on the 4 extremities. There is mounting evidence indicating the ability of baPWV to predict the risk of future cardiovascular events and total mortality. Additionally, the guidelines for the management of hypertension in Japan recommended the measurement of baPWV be included in the assessment of subclinical target organ damage. However, baPWV has not been fully accepted worldwide due to perceived theoretical and methodological issues. In this review, we address the most frequently mentioned questions and concerns regarding baPWV to shed some light on this simple and easy arterial stiffness measurement.

  7. Warm wave breaking of nonlinear plasma waves with arbitrary phase velocities C. B. Schroeder, E. Esarey, and B. A. Shadwick

    E-print Network

    Geddes, Cameron Guy Robinson

    Warm wave breaking of nonlinear plasma waves with arbitrary phase velocities C. B. Schroeder, E, collisionless plasma is developed to analyze nonlinear plasma waves excited by intense drive beams. The maximum amplitude and wavelength are calculated for nonrelativistic plasma temperatures and arbitrary plasma wave

  8. The influence of temperature variations on ultrasonic guided waves in anisotropic CFRP plates.

    PubMed

    Putkis, O; Dalton, R P; Croxford, A J

    2015-07-01

    Carbon Fibre Reinforced Polymer (CFRP) materials are lightweight and corrosion-resistant and therefore are increasingly used in aerospace, automotive and construction industries. In Structural Health Monitoring (SHM) applications of CFRP materials, ultrasonic guided waves potentially offer large area inspection or inspection from a remote location. This paper addresses the effect of temperature variation on guided wave propagation in highly anisotropic CFRP materials. Temperature variations cause changes in guided wave velocity that can in turn compromise the baseline subtraction procedures employed by many SHM systems for damage detection. A simple model that describes the dependence of elastic properties of the CFRP plates on temperature is presented in this paper. The model can be used to predict anisotropic velocity changes and baseline subtraction performance under varying thermal conditions. The results produced by the model for unidirectional and 0/90 CFRP plates are compared with experimental measurements. PMID:25812468

  9. Surface wave tomography with USArray: Rayleigh wave phase velocity, ellipticity, and local amplification

    NASA Astrophysics Data System (ADS)

    Lin, F.; Schmandt, B.; Tsai, V. C.

    2012-12-01

    The deployment of the EarthScope/USArray Transportable Array allows detailed empirical study of the surface-wave wavefield on a large scale. In this presentation, we show that three local properties of Rayleigh waves, i.e. phase velocity, ellipticity (or H/V ratio), and local amplification, can be determined across the array in the western US between 24 and 100 sec period based on teleseismic measurements. More than 900 earthquakes are analyzed where phase velocity and local amplification are determined based on empirical phase travel time and amplitude mapping. The three Rayleigh wave properties, which are all sensitive to the 1D structure beneath each location, have very distinct depth sensitivity to Vs, Vp/Vs ratio, and density. Joint inversion of these quantities therefore reduces the trade-off between the three different parameters at different depths. Including the H/V ratio, in particular, allows the uppermost (0-3 km) crustal velocity and density structure to be constrained, and our new results are in excellent agreement with known surface features. Pronounced low Vs, low density, and high Vp/Vs anomalies are imaged in the locations of several major sedimentary basins including the Williston, Powder River, Green River, Denver, and San Juan basins. Preliminary results on the inverted 3D Vs, Vp/Vs ratio, and density structure in the crust and upper mantle will also be discussed. (a)-(c) 30-sec Rayleigh-wave phase velocity, local amplification, and H/V ratio observed across USArray in the western US. The red lines denote the tectonic boundaries and the triangles in (b)-(c) shown the stations used. The thick black lines indicate 3-km sediment contours for several major sedimentary basins (WB: Williston Basin; PR: Powder River Basin; GR: Green River Basin; DB: Denver Basin). (d)-(f) The Vs, density, and Vp/Vs ratio in the uppermost crust (0-3 km) inverted by phase velocity and H/V ratio measurements.

  10. Seismic velocity variations along the rupture zone of the 1989 Loma Prieta earthquake, California

    NASA Astrophysics Data System (ADS)

    Lin, G.; Thurber, C. H.

    2012-09-01

    We revisit the rupture zone of the 1989 Mw6.9 Loma Prieta earthquake, central California, by developing high-resolution three-dimensional (3-D)Vp and Vp/Vs models. We apply the simul2000 inversion method and algorithm to a set of "composite" events, which have greater number of picks per event and reduced random picking errors compared with traditional master events. Our final P-wave velocity model generally agrees with previous studies, showing a high velocity body of above 6.7 km/s in the southeast rupture zone of the main shock. The 3-DVp/Vs model, however, has different features, with low Vp/Vs in the upper crust and high Vp/Vs anomalies in deeper layers of the rupture zone. We interpret the low Vp/Vs at shallow depths to be granitic rocks, whereas at greater depths the areas of higher Vp/Vs(around 1.725-1.75) presumably are mafic rocks. The resulting 3-D velocity model was used to improve absolute locations for all local events between 1984 and 2010 in our study area. We then applied a similar event cluster analysis, waveform cross-correlation, and differential time relocation methods to improve relative event location accuracy. Over 88% of the seismicity falls into similar event clusters. A dramatic sharpening of seismicity patterns is obtained after using these methods. The medians of the relative location uncertainties calculated by using the bootstrap approach are 5 m for horizontal and 8 m for vertical. Differential times from cross-correlation are used to estimatein situnear-sourceVp/Vsratio within each event cluster. The high-resolutionVp/Vs method confirms the trend of the velocity variations from the tomographic results, although absolute values are slightly different.

  11. 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

  12. 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.

  13. 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

  14. 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.

  15. 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.

    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.

  16. 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.

  17. Acoustic wave velocity behavior for some Jurassic carbonate samples, north Sinai, Egypt

    NASA Astrophysics Data System (ADS)

    El Sayed, Nahla A.; Abuseda, Hesham; Kassab, Mohamed A.

    2015-11-01

    Seismic data of reservoir rocks use for understand of risk reduction. Acoustic laboratory measurements have been carried out for 75 carbonate rock samples for both dry and fully saturated collected from Jurassic deposits exposed in the north Sinai at Gebel El-Maghara. This study has been carried out to know more about the behavior of compression wave velocity and shear wave velocity in carbonate rock samples for both dry and fully saturated conditions and to investigate the effect of porosity, permeability and density on both dry and fully saturated acoustic velocities. The compressional wave velocities at dry and fully saturated carbonate rock samples increased with increasing the bulk density and decreasing the porosity, while the porosity decreasing with increasing bulk density, the relationships between the porosity as well as shear wave velocity in dry and fully saturated are in cloud points, with no clear relationships. The relationships between the permeability and both the compressional wave and the shear wave velocities at dry and fully saturated cases could not be identified. The statistical analyses indicate that the compressional wave in the fully saturated is higher than the compressional wave in dry case. The compressional wave velocity of the fully saturated carbonate rock samples were strongly correlated with the compressional wave velocity of the dry rock samples and the derived equation can be used for prediction of the compressional wave velocity of fully saturated rock from the compressional wave velocity of dry rock. The shear wave of the fully saturated carbonate rock samples is a fair correlated with the shear wave of the dry rock samples.

  18. Comparision between crustal density and velocity variations in Southern California

    USGS Publications Warehouse

    Langenheim, V.E.; Hauksson, E.

    2001-01-01

    We predict gravity from a three-dimensional Vp model of the upper crust and compare it to the observed isostatic residual gravity field. In general this comparison shows that the isostatic residual gravity field reflects the density variations in the upper to middle crust. Both data sets show similar density variations for the upper crust in areas such as the Peninsular Ranges and the Los Angeles basin. Both show similar variations across major faults, such as the San Andreas and Garlock faults in the Mojave Desert. The difference between the two data sets in regions such as the Salton Trough, the Eastern California Shear Zone, and the eastern Ventura basin (where depth to Moho is <30 km), however, suggests high-density middle to lower crust beneath these regions. Hence the joint interpretation of these data sets improves the depth constraints of crustal density variations.

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

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

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

  20. Feasibility of waveform inversion of Rayleigh waves for shallow shear-wave velocity using a genetic algorithm

    USGS Publications Warehouse

    Zeng, C.; Xia, J.; Miller, R.D.; Tsoflias, G.P.

    2011-01-01

    Conventional surface wave inversion for shallow shear (S)-wave velocity relies on the generation of dispersion curves of Rayleigh waves. This constrains the method to only laterally homogeneous (or very smooth laterally heterogeneous) earth models. Waveform inversion directly fits waveforms on seismograms, hence, does not have such a limitation. Waveforms of Rayleigh waves are highly related to S-wave velocities. By inverting the waveforms of Rayleigh waves on a near-surface seismogram, shallow S-wave velocities can be estimated for earth models with strong lateral heterogeneity. We employ genetic algorithm (GA) to perform waveform inversion of Rayleigh waves for S-wave velocities. The forward problem is solved by finite-difference modeling in the time domain. The model space is updated by generating offspring models using GA. Final solutions can be found through an iterative waveform-fitting scheme. Inversions based on synthetic records show that the S-wave velocities can be recovered successfully with errors no more than 10% for several typical near-surface earth models. For layered earth models, the proposed method can generate one-dimensional S-wave velocity profiles without the knowledge of initial models. For earth models containing lateral heterogeneity in which case conventional dispersion-curve-based inversion methods are challenging, it is feasible to produce high-resolution S-wave velocity sections by GA waveform inversion with appropriate priori information. The synthetic tests indicate that the GA waveform inversion of Rayleigh waves has the great potential for shallow S-wave velocity imaging with the existence of strong lateral heterogeneity. ?? 2011 Elsevier B.V.

  1. Use Your Own Computer Timer: Velocity of Stress Waves in a Solid Rod.

    ERIC Educational Resources Information Center

    Russell, David

    1997-01-01

    Describes how to measure the penultimate laboratory speed, a stress wave velocity in a solid rod. Also includes background information on stress waves, apparatus, and procedures. Employs a homemade interface for the IBM platform. (DDR)

  2. 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.

  3. 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.

  4. 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

  5. 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...

  6. Creep of porous rocks and measurements of elastic wave velocities under different hydrous conditions

    NASA Astrophysics Data System (ADS)

    Eslami, J.; Grgic, D.; Hoxha, D.

    2009-04-01

    The long-term mechanical behavior of rocks is of prime importance for many geological hazards (e.g., landslides, rock falls, and volcanoes) as well as for the stability of man-made structures (underground mines, road cuts, and open pits). In some shallow environments, rocks exist in partially saturated conditions which can evolve with time according to variations in the relative humidity hr of the atmosphere (e.g., natural slopes, open cut excavations). In underground mines, rocks are also partially saturated because of artificial ventilation. These variations in liquid saturation may have a large impact on mechanical behavior since they imply variations in capillary pressure and, depending on the porosity and on the shape of the porous network, variations in the effective stresses. Therefore, knowledge of static fatigue under saturated and partially saturated conditions is important for estimating the long-term stability of such rock structures. Many studies have already shown that time-dependent weakening is much more important for a saturated rock than for a dry one and that the time to failure may decrease by several orders of magnitude for saturated rocks as compared to dry rocks. In addition, the weakening effect of water is more significant in long-term experiments than in short-term ones (instantaneous loading). A physical explanation for these results may be the enhancement of subcritical crack growth by stress corrosion at crack tips which is often considered to be the main cause of time-dependent behavior of rocks. The failure of brittle rocks during compression tests is preceded by the formation, growth, and coalescence of microcracks. Elastic wave velocities are reduced due to the presence of open microcraks and fractures and may be used to monitor the progressive damage of rocks. The specific experimental setup available in our lab allows the simultaneous measurement of five velocities (with different polarizations and directions) and two directions of strains on a same sample, under uniaxial compression. Different hydrous conditions (saturated or partially saturated) are tested in all creep tests. In this paper, we focus on the time-dependent behavior and short-term mechanical behavior of iron ore and limestone in saturated and partially saturated domains. The main outcomes of these experiments are: (i) identification of the apparent dynamic stiffness tensor from elastic wave velocity measurements; (ii) assessment of velocity anisotropy, and its evolution under uniaxial loading. This last step allows for the quantification of the intrinsic and stress-induced anisotropies, leading eventually to an estimation of the microcracks density and distribution evolutions in the rock sample under loading.

  7. Tidally induced velocity variations of the Beardmore Glacier, Antarctica, and their representation in satellite measurements of ice velocity

    NASA Astrophysics Data System (ADS)

    Marsh, O. J.; Rack, W.; Floricioiu, D.; Golledge, N. R.; Lawson, W.

    2013-09-01

    Ocean tides close to the grounding line of outlet glaciers around Antarctica have been shown to directly influence ice velocity, both linearly and non-linearly. These fluctuations can be significant and have the potential to affect satellite measurements of ice discharge, which assume displacement between satellite passes to be consistent and representative of annual means. Satellite observations of horizontal velocity variation in the grounding zone are also contaminated by vertical tidal effects, the importance of which is highlighted here in speckle tracking measurements. Eight TerraSAR-X scenes from the grounding zone of the Beardmore Glacier are analysed in conjunction with GPS measurements to determine short-term and decadal trends in ice velocity. Diurnal tides produce horizontal velocity fluctuations of >50% on the ice shelf, recorded in the GPS data 4 km downstream of the grounding line. This variability decreases rapidly to <5% only 15 km upstream of the grounding line. Daily fluctuations are smoothed to <1% in the 11-day repeat pass TerraSAR-X imagery, but fortnightly variations over this period are still visible and show that satellite-velocity measurements can be affected by tides over longer periods. The measured tidal displacement observed in radar look direction over floating ice also allows the grounding line to be identified, using differential speckle tracking where phase information cannot be easily unwrapped.

  8. The interaction between intra-cyclic variation of the velocity and mean swimming velocity in young competitive swimmers.

    PubMed

    Barbosa, T M; Morouço, P G F; Jesus, S; Feitosa, W G; Costa, M J; Marinho, D A; Silva, A J; Garrido, N D

    2013-02-01

    The aim of this study was to assess the relationship between the intra-cyclic variation of the horizontal velocity (dv) and the velocity of the 4 competitive swimming techniques in young swimmers. 45 young swimmers performed a set of maximal 4 × 25 m (freestyle, backstroke, breaststroke and butterfly stroke) swims with in water start. A speed-meter cable was attached to the swimmer's hip. The dv and the swimming velocity were analyzed. Within-subject tests presented significant variations in the dv based on the swimming technique. Post-hoc test revealed significant differences across all pair-wised swimming techniques (P<0.001), except for the comparison between freestyle and backstroke (P=0.98). The dv was higher in the breaststroke, followed by the butterfly, the backstroke and the freestyle. The quadratic models had the best goodness-of-fit and the lower error of estimation for the relationship between the dv and the swimming velocity in all swimming techniques (0.24 ? R(2) ? 0.51). As a conclusion, there is a non-linear relationship where the increase of swimming velocity leads to a decrease of dv in young competitive swimmers. PMID:22972251

  9. 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.

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

    USGS Publications Warehouse

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

    2000-01-01

    Shear-wave velocities (VS) are widely used for earthquake ground-motion site characterization. VS data are now largely obtained using borehole methods. Drilling holes, however, is expensive. Nonintrusive surface methods are inexpensive for obtaining VS information, but not many comparisons with direct borehole measurements have been published. Because different assumptions are used in data interpretation of each surface method and public safety is involved in site characterization for engineering structures, it is important to validate the surface methods by additional comparisons with borehole measurements. We compare results obtained from a particular surface method (array measurement of surface waves associated with microtremor) with results obtained from borehole methods. Using a 10-element nested-triangular array of 100-m aperture, we measured surface-wave phase velocities at two California sites, Garner Valley near Hemet and Hollister Municipal Airport. The Garner Valley site is located at an ancient lake bed where water-saturated sediment overlies decomposed granite on top of granite bedrock. Our array was deployed at a location where seismic velocities had been determined to a depth of 500 m by borehole methods. At Hollister, where the near-surface sediment consists of clay, sand, and gravel, we determined phase velocities using an array located close to a 60-m deep borehole where downhole velocity logs already exist. Because we want to assess the measurements uncomplicated by uncertainties introduced by the inversion process, we compare our phase-velocity results with the borehole VS depth profile by calculating fundamental-mode Rayleigh-wave phase velocities from an earth model constructed from the borehole data. For wavelengths less than ~2 times of the array aperture at Garner Valley, phase-velocity results from array measurements agree with the calculated Rayleigh-wave velocities to better than 11%. Measurement errors become larger for wavelengths 2 times greater than the array aperture. At Hollister, the measured phase velocity at 3.9 Hz (near the upper edge of the microtremor frequency band) is within 20% of the calculated Rayleigh-wave velocity. Because shear-wave velocity is the predominant factor controlling Rayleigh-wave phase velocities, the comparisons suggest that this nonintrusive method can provide VS information adequate for ground-motion estimation.

  11. 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…

  12. 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 not change seasonally. The relationship be- tween conduction velocity and temperature remained con- stant

  13. Temporal changes of surface wave velocity associated with major Sumatra earthquakes from ambient noise correlation

    PubMed Central

    Xu, Zhen J.; Song, Xiaodong

    2009-01-01

    Detecting temporal changes of the medium associated with major earthquakes has implications for understanding earthquake genesis. Here we report temporal changes of surface wave velocity over a large area associated with 3 major Sumatra earthquakes in 2004, 2005, and 2007. We use ambient noise correlation to retrieve empirical Green's function (EGF) of surface waves between stations. Because the process is completely repeatable, the technique is powerful in detecting possible temporal change of medium. We find that 1 excellent station pair (PSI in Indonesia and CHTO in Thailand) shows significant time shifts (up to 1.44 s) after the 2004 and 2005 events in the Rayleigh waves at 10–20 s but not in the Love waves, suggesting that the Rayleigh time shifts are not from clock error. The time shifts are frequency dependent with the largest shifts at the period band of 11–16 s. We also observe an unusual excursion ?1 month before the 2004 event. We obtain a total of 17 pairs for June, 2007 to June, 2008, which allow us to examine the temporal and spatial variation of the time shifts. We observed strong anomalies (up to 0.68 s) near the epicenter after the 2007 event, but not in the region further away from the source or before the event or 3 months after the event. The observations are interpreted as stress changes and subsequent relaxation in upper-mid crust in the immediate vicinity of the rupture and the broad area near the fault zone. PMID:19667205

  14. A linear radio wave velocity model on polythermal glaciers

    NASA Astrophysics Data System (ADS)

    Ai, Songtao; Wang, Zemin; Geng, Hong

    2015-04-01

    The glaciers in Svalbard are mostly polythermal type. On these polythermal glaciers, the radio wave velocity (RWV) of ground penetrating radar (GPR) is variable, and the RWV is an important parameter for the ice volume estimation. But the ice volume estimation usually uses a single RWV for one whole glacier in order to simplify the calculation. How about the difference between the actual volume and the estimated result? We used a linear RWV model, derived from common mid-point (CMP) profiles of GPR measurement, to simulate the RWV for each GPR trace on Pedersenbreen in Svalbard. Then a relative accurate volume of glacier Pedersenbreen was acquired. From which we found the difference among those volumes calculated from a single RWV, three RWVs and our RWV model. Our RWV model for polythermal glaciers refined the volume estimation and enhanced the precision in mass change study. And the difference between different models could raise an error up to 10% of the volume results. Moreover, the fixed RWV usually used was probably larger than the actual one in those polythermal glaciers. Acknowledgements: This work was supported by the National Natural Science Foundation of China(41476162) and the Chinese Polar Environment Comprehensive Investigation & Assessment Programmes.

  15. Intima media thickness, pulse wave velocity, and flow mediated dilation

    PubMed Central

    2014-01-01

    The identification of vascular alterations at the sub-clinical, asymptomatic stages are potentially useful for screening, prevention and improvement of cardiovascular risk stratification beyond classical risk factors. Increased intima-media thickness of the common carotid artery is a well-known marker of early atherosclerosis, which significantly correlates with the development of cardiovascular diseases. More recently, other vascular parameters evaluating both structural and functional arterial proprieties of peripheral arteries have been introduced, for cardiovascular risk stratification and as surrogate endpoints in clinical trials. Increased arterial stiffness, which can be detected by applanation tonometry as carotid-femoral pulse wave velocity, has been shown to predict future cardiovascular events and to significantly improve risk stratification. Finally, earlier vascular abnormalities such as endothelial dysfunction in the peripheral arteries, detected as reduced flow-mediated dilation of the brachial artery, are useful in the research setting and as surrogate endpoints in clinical trials and have also been suggested for their possible clinical use in the future. This manuscript will briefly review clinical evidence supporting the use of these different vascular markers for cardiovascular risk stratification, focusing on the correct methodology, which is a crucial issue to address in order to promote their use in future for routine clinical practice. PMID:25148901

  16. Pulse Wave Velocity and Cognitive Function in Older Adults

    PubMed Central

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

    2013-01-01

    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 (Alam Medical, Vincennes, France). Cognitive function was measured by six tests of executive function, psychomotor speed, memory, and language fluency. A total of 1433 participants were included (mean age 75 years, 43% men). Adjusting for age, sex, education, pulse rate, hemoglobin A1C, HDL cholesterol, hypertension, CVD 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-B (coefficient: 6.30, se: 3.41, p=0.06), CF-PWV was not associated with Trail Making Test-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

  17. Weight Loss, Dietary Intake and Pulse Wave Velocity

    PubMed Central

    Petersen, Kristina; Blanch, Natalie; Keogh, Jennifer; Clifton, Peter

    2015-01-01

    We have recently conducted a meta-analysis to determine the effect of weight loss achieved by an energy-restricted diet with or without exercise, anti-obesity drugs or bariatric surgery on pulse wave velocity (PWV) measured at all arterial segments. Twenty studies, including 1,259 participants, showed that modest weight loss (8% of the initial body weight) caused a reduction in PWV measured at all arterial segments. However, due to the poor methodological design of the included studies, the results of this meta-analysis can only be regarded as hypothesis generating and highlight the need for further research in this area. In the future, well-designed randomised controlled trials are required to determine the effect of diet-induced weight loss on PWV and the mechanisms involved. In addition, there is observational evidence that dietary components such as fruit, vegetables, dairy foods, sodium, potassium and fatty acids may be associated with PWV, although evidence from well-designed intervention trials is lacking. In the future, the effect of concurrently improving dietary quality and achieving weight loss should be assessed in randomised controlled trials. PMID:26587462

  18. Intima media thickness, pulse wave velocity, and flow mediated dilation.

    PubMed

    Bruno, Rosa Maria; Bianchini, Elisabetta; Faita, Francesco; Taddei, Stefano; Ghiadoni, Lorenzo

    2014-01-01

    The identification of vascular alterations at the sub-clinical, asymptomatic stages are potentially useful for screening, prevention and improvement of cardiovascular risk stratification beyond classical risk factors.Increased intima-media thickness of the common carotid artery is a well-known marker of early atherosclerosis, which significantly correlates with the development of cardiovascular diseases. More recently, other vascular parameters evaluating both structural and functional arterial proprieties of peripheral arteries have been introduced, for cardiovascular risk stratification and as surrogate endpoints in clinical trials. Increased arterial stiffness, which can be detected by applanation tonometry as carotid-femoral pulse wave velocity, has been shown to predict future cardiovascular events and to significantly improve risk stratification.Finally, earlier vascular abnormalities such as endothelial dysfunction in the peripheral arteries, detected as reduced flow-mediated dilation of the brachial artery, are useful in the research setting and as surrogate endpoints in clinical trials and have also been suggested for their possible clinical use in the future.This manuscript will briefly review clinical evidence supporting the use of these different vascular markers for cardiovascular risk stratification, focusing on the correct methodology, which is a crucial issue to address in order to promote their use in future for routine clinical practice. PMID:25148901

  19. Assessment of local pulse wave velocity in arteries using 2D distension waveforms.

    PubMed

    Meinders, J M; Kornet, L; Brands, P J; Hoeks, A P

    2001-10-01

    The reciprocal of the arterial pulse wave velocity contains crucial information about the mechanical characteristics of the arterial wall but is difficult to assess noninvasively in vivo. In this paper, a new method to assess local pulse wave velocity (PWV) is presented. To this end, multiple adjacent distension waveforms are determined simultaneously along a short arterial segment, using a single 2D-vessel wall tracking system with a high frame rate (651 Hz). Each B-mode image consists of 16 echo lines spanning a total width of 15.86 mm. Dedicated software has been developed to extract the end-diastolic diameter from the B-mode image and the distension waveforms from the underlying radiofrequency (rf) information for each echo-line. The PWV is obtained by determining the ratio of the temporal and spatial gradient of adjacent distension velocity waveforms. The proposed method is verified in a phantom and in the common carotid artery (CCA) of humans. Phantom experiments show a high concordance between the PWV obtained from 2D distension velocity waveforms (4.21 +/- 0.02 m/s) and the PWV determined using two pressure catheters (4.26 +/- 0.02 m/s). Assuming linear spatial gradients, the PWV can also be obtained in vivo for CCA and averages to 5.5 +/- 1.5 m/s (intersubject variation, n = 23), which compares well to values found in literature. Furthermore, intrasubject PWV compares well with those calculated using the Bramwell-Hill equation. It can be concluded that the PWV can be obtained from the spatial and temporal gradient if the spatial gradient is linear over the observed length of the artery, i.e. the artery should be homogenous in diameter and distension and the influence of reflections must be small. PMID:12051275

  20. Joint Inversion of Crustal Structure with the Rayleigh Wave Phase Velocity Dispersion and the ZH Ratio

    NASA Astrophysics Data System (ADS)

    Chong, Jiajun; Ni, Sidao; Zhao, Li

    2015-10-01

    Surface waves are essential for resolving Earth's structure on both regional and global scales, and surface wave data are mostly exploited with velocity dispersion. However, dispersion is mostly sensitive to the integral feature of velocity structure, resulting in ambiguities of the model interpretation. Recently, it has been demonstrated that the ZH amplitude ratio of a Rayleigh wave is an effective approach for providing extra constraints to reduce ambiguity in surface wave inversion. In this paper, we studied the sensitivities of the Rayleigh wave phase velocity dispersion and the ZH ratio with layered crustal structure via forward modeling. The forward modeling experiments indicate that the Rayleigh wave ZH ratio shows different sensitivity as compared to Rayleigh wave phase velocity dispersion. The ZH ratio is more sensitive to the shallower structure compared to phase velocity dispersion of the same period, and the ZH ratio provides independent constraints on the structure. Thus, the combination of these two datasets should help to better constrain the velocity model. A joint inversion tool is developed to jointly invert for the Rayleigh wave phase velocity and the ZH ratio observations. The inversion is based on a Fast Simulated Annealing algorithm, which generates models randomly and can achieve a global minimum without requiring a sensitivity kernel. Joint inversions based on synthetic datasets confirmed that the ZH ratio together with a phase velocity dispersion curve can reduce the non-uniqueness in crustal structure inversion.

  1. Nationwide Ambient Noise Imaging of New Zealand: Constraining Crustal and Upper Mantle S-Velocities Using Surface Wave Dispersion Curves

    NASA Astrophysics Data System (ADS)

    Behr, Y.; Townend, J.; Savage, M. K.; Bannister, S.

    2008-12-01

    Ambient noise tomography has been shown to yield good results in both continental and oceanic environments. We extend Lin et al.'s pilot study of ambient noise tomography in New Zealand by increasing the number of stations and extending the timespan of the dataset. In particular, we incorporate data acquired during several temporary deployments including CNIPSE (34 stations; 6 months), SAPSE (30 stations; 14 months), NORD (5 stations, 8 months) and Marlborough (7 stations; 6 months) and data from newly operational permanent GeoNet stations (47 vs. 42 used by Lin et al.). We compute Rayleigh and Love wave dispersion curves, and then estimate lateral group velocity variations and S-velocity versus depth profiles. The latter is done by using the neighbourhood algorithm, a direct search method that enables us to estimate posterior uncertainties for model parameters from variations in the dispersion curves. In a test-case study, we have inverted two Rayleigh wave group velocity dispersion curves measured between stations of the NORD deployment in the northernmost North Island. The results are consistent with those of an earlier study by Horspool et al. of the same region using teleseismic receiver functions and Rayleigh wave phase velocities.

  2. Parameterization and simulation of near bed orbital velocities under irregular waves in shallow water

    USGS Publications Warehouse

    Elfrink, B.; Hanes, D.M.; Ruessink, B.G.

    2006-01-01

    A set of empirical formulations is derived that describe important wave properties in shallow water as functions of commonly used parameters such as wave height, wave period, local water depth and local bed slope. These wave properties include time varying near-bed orbital velocities and statistical properties such as the distribution of wave height and wave period. Empirical expressions of characteristic wave parameters are derived on the basis of extensive analysis of field data using recently developed evolutionary algorithms. The field data covered a wide range of wave conditions, though there were few conditions with wave periods greater than 15 s. Comparison with field measurements showed good agreement both on a time scale of a single wave period as well as time averaged velocity moments.

  3. 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.

  4. Estimating near-surface shear wave velocities in Japan by applying seismic interferometry to KiK-net data

    E-print Network

    Cerveny, Vlastislav

    Estimating near-surface shear wave velocities in Japan by applying seismic interferometry to Ki in a borehole. By using seismic interferometry, we extract the shear wave that propagates between these two-surface shear wave velocity all over Japan. Shear wave velocities estimated by seismic interferometry agree well

  5. 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

  6. Improved estimation of P-wave velocity, S-wave velocity, and attenuation factor by iterative structural joint inversion of crosswell seismic data

    NASA Astrophysics Data System (ADS)

    Zhu, Tieyuan; Harris, Jerry M.

    2015-12-01

    We present an iterative joint inversion approach for improving the consistence of estimated P-wave velocity, S-wave velocity and attenuation factor models. This type of inversion scheme links two or more independent inversions using a joint constraint, which is constructed by the cross-gradient function in this paper. The primary advantages of this joint inversion strategy are: avoiding weighting for different datasets in conventional simultaneous joint inversion, flexible for incorporating prior information, and relatively easy to code. We demonstrate the algorithm with two synthetic examples and two field datasets. The inversions for P- and S-wave velocity are based on ray traveltime tomography. The results of the first synthetic example show that the iterative joint inversion take advantages of both P- and S-wave sensitivity to resolve their ambiguities as well as improve structural similarity between P- and S-wave velocity models. In the second synthetic and field examples, joint inversion of P- and S-wave traveltimes results in an improved Vs velocity model that shows better structural correlation with the Vp model. More importantly, the resultant VP/VS ratio map has fewer artifacts and is better correlated for use in geological interpretation than the independent inversions. The second field example illustrates that the flexible joint inversion algorithm using frequency-shift data gives a structurally improved attenuation factor map constrained by a prior VP tomogram.

  7. 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.

  8. 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.

  9. Fracture density estimates in glaciogenic deposits from P-wave velocity reductions

    SciTech Connect

    Karaman, A.; Carpenter, P.J.

    1997-01-01

    Subsidence-induced fracturing of glaciogenic deposits over coal mines in the southern Illinois basis alters hydraulic properties of drift aquifers and exposes these aquifers to surface contaminants. In this study, refraction tomography surveys were used in conjunction with a generalized form of a seismic fracture density model to estimate the vertical and lateral extent of fracturing in a 12-m thick overburden of loess, clay, glacial till, and outwash above a longwall coal mine at 90 m depth. This generalized model accurately predicted fracture trends and densities from azimuthal P-wave velocity variations over unsaturated single- and dual-parallel fractures exposed at the surface. These fractures extended at least 6 m and exhibited 10--15 cm apertures at the surface. The pre- and postsubsidence velocity ratios were converted into fracture densities that exhibited qualitative agreement with the observed surface and inferred subsurface fracture distribution. Velocity reductions as large as 25% were imaged over the static tension zone of the mine where fracturing may extend to depths of 10--15 m. Finally, the seismically derived fracture density estimates were plotted as a function of subsidence-induced drawdown across the panel to estimate the average specific storage of the sand and gravel lower drift aquifer. This value was at least 20 times higher than the presubsidence (unfractured) specific storage for the same aquifer.

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

    USGS Publications Warehouse

    Brocher, T.M.

    2008-01-01

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

  11. Pulse Wave Velocity in Korean American Men and Women

    PubMed Central

    Logan, Jeongok G.; Barksdale, Debra J.

    2013-01-01

    Arterial stiffness is an important clinical marker of cardiovascular diseases. Although many studies have been conducted on different racial groups, less is known about arterial stiffness in Asian Americans. Korean Americans constitute the fifth largest subgroup in the Asian American population and reportedly have a noticeably high prevalence of hypertension. The aims of this study were to assess arterial stiffness and blood pressure and to examine the effect of age and gender on arterial stiffness and blood pressure in 102 Korean American men and women aged 21 to 60 years. The values of arterial stiffness for Korean Americans in this study were compared to published reference values for other racial and ethnic groups. Arterial stiffness was measured by carotid-femoral pulse wave velocity, which is the gold standard for determining arterial stiffness. Findings indicated that aging was an important determinant of arterial stiffness, which increased linearly with age. Although there was no gender difference observed in arterial stiffness, the effect of age on arterial stiffness was greater in women than in men. After adjusting for covariates including age, body mass index, and smoking, multiple regression models showed that arterial stiffness and gender were significant predictors of systolic and diastolic blood pressure. The comparisons of these findings to those from several other studies that used the same method to measure arterial stiffness showed that Korean Americans may have levels of arterial stiffness that are similar to or slightly higher than those of other racial groups. Considering that arterial stiffness is an independent predictor of future development of hypertension, more studies are required to examine cardiovascular risk of this understudied group. PMID:22222176

  12. Inversion of OBC seismic data for P- and S-wave velocities

    E-print Network

    Hall, Guy R

    of processing these two data sets is two seismic time sections: one a P-wave section and the other a converted wave section. By subjectively correlating events in these two sections it is possible to estimate the S-wave velocities. This may lead to further...

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

    USGS Publications Warehouse

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

    2006-01-01

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

  14. 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.

  15. Phase reconstruction from velocity-encoded MRI measurements - A survey of sparsity-promoting variational approaches

    NASA Astrophysics Data System (ADS)

    Benning, Martin; Gladden, Lynn; Holland, Daniel; Schönlieb, Carola-Bibiane; Valkonen, Tuomo

    2014-01-01

    In recent years there has been significant developments in the reconstruction of magnetic resonance velocity images from sub-sampled k-space data. While showing a strong improvement in reconstruction quality compared to classical approaches, the vast number of different methods, and the challenges in setting them up, often leaves the user with the difficult task of choosing the correct approach, or more importantly, not selecting a poor approach. In this paper, we survey variational approaches for the reconstruction of phase-encoded magnetic resonance velocity images from sub-sampled k-space data. We are particularly interested in regularisers that correctly treat both smooth and geometric features of the image. These features are common to velocity imaging, where the flow field will be smooth but interfaces between the fluid and surrounding material will be sharp, but are challenging to represent sparsely. As an example we demonstrate the variational approaches on velocity imaging of water flowing through a packed bed of solid particles. We evaluate Wavelet regularisation against Total Variation and the relatively recent second order Total Generalised Variation regularisation. We combine these regularisation schemes with a contrast enhancement approach called Bregman iteration. We verify for a variety of sampling patterns that Morozov's discrepancy principle provides a good criterion for stopping the iterations. Therefore, given only the noise level, we present a robust guideline for setting up a variational reconstruction scheme for MR velocity imaging.

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

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

    We have conducted a detailed study of the cloud features in the strong southern equatorial wind jet near 7.5 S planetographic latitude. To understand the apparent variations in average zonal wind jet velocity at this latitude [e.g.. 1,2,3], we have searched for variations iIi both feature latitude and velocity with longitude and time. In particular, we focused on the repetitive chevron-shaped dark spots visible on most dates and the more transient large anticyclonic system known as the South Equatorial Disturbance (SED). These small dark spots are interpreted as cloud holes, and are often used as material tracers of the wind field.

  17. 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

  18. Rayleigh wave phase velocity maps from the ambient noise tomography in central Mongolia

    NASA Astrophysics Data System (ADS)

    Pan, J.; Wu, Q.; Gao, M.; Li, Y.; Demberel, S. G.; Munkhuu, U.

    2013-12-01

    The study area (103°E-111°E, 44°N-49°N) located in the Mongolian fold belts and situated at the southeast of Baikal rift zone which is known as one of the most active regions on the Earth due to integrated influence of the India-Asia collision and compression and the subduction of the Pacific Plate. Additionally, it also located in the north of South-North earthquake belts of China. So, it is believed to be an ideal site for understanding intraplate dynamics. Seismic ambient noise tomography has been performed all over the world these years, and it has been proved it's a powerful way to image and study the structure of crust and uppermost mantle due to its exclusive capability to extract estimated Green's functions for short period surface waves. Compared with traditional earthquake tomography methods of surface waves, ambient noise tomography hasn't limitations related to the distribution of earthquakes as well as errors in earthquake locations and source mechanisms. A new scientific project was carried out in 2011 by Institute of Geophysics of China Earthquake Administration (IGP-CEA) and Research center of Astronomy and Geophysics of Mongolian Academy of Science (RCAG-MAS). In the seismic sub-project 60 portable seismic stations were deployed in central Mongolia in August 2011. Continuous time-series of vertical component between August 2011 and July 2012 have been collected and cross-correlated to obtain estimated Green's functions (EGF) of Rayleigh wave. Using the frequency and time analysis technique based on continuous wavelet transformation, 1258 of phase velocity dispersion curves of Rayleigh wave were extracted from EGFs. High resolution phase velocity maps at periods of 5, 10, 20 and 30 s were reconstructed with grid size 0.5°x0.5° by utilizing a generalized 2-D-linear inversion method developed by Ditmar & Yanovskaya. The tomography results reveal lateral heterogeneity of shear wave structure in the crust and upper mantle in the study region. For periods shorter than 10 s, the phase velocity variations are well correlated with the principal geological units, with low-speed anomalies corresponding to the sedimentary basins and high-speed anomalies coinciding with the main mountain ranges. Within the period range from 20 s to 30 s, phase velocity distribution is correlated to the crust thickness. However, the value of phase velocities have little lateral changes with ~0.15km/s on each map for the whole period band ranging from 5 s to 30 s, indicating that it doesn't have big lateral heterogeneity for shear wave structure in the crust and upper mantle in the study region.This study was supported by the international cooperation project of the Ministry of Science and Technology of China (2011DFB20120) and NSFC (41104029)

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  20. Anomalous translational velocity of vortex ring with finite-amplitude Kelvin waves

    SciTech Connect

    Barenghi, C. F.; Haenninen, R.; Tsubota, M.

    2006-10-15

    We consider finite-amplitude Kelvin waves on an inviscid vortex assuming that the vortex core has infinitesimal thickness. By numerically solving the governing Biot-Savart equation of motion, we study how the frequency of the Kelvin waves and the velocity of the perturbed ring depend on the Kelvin wave amplitude. In particular, we show that, if the amplitude of the Kelvin waves is sufficiently large, the perturbed vortex ring moves backwards.

  1. Estimation of S-Wave Velocity Structure at Taichung Area, Taiwan, Using Array Records of Microtremors

    NASA Astrophysics Data System (ADS)

    Huang, H.; Hsu, C.

    2009-12-01

    S-wave velocities have widely been used for earthquake ground-motion site characterization. Thus, here, the S-wave velocity structures of Taichung city, Taiwan are investigated using the array records of microtremors at 21 sites. The dispersion curves at these sites are calculated using the F-K method (Capon, 1969); then, the S-wave velocity structures in Chia-Yi city are estimated by employing the surface wave inversion technique (Herrmann, 1991). At most sites, observed phase velocities are almost flat with the phase velocity of about 1000 m/sec in the frequency range from 0.5 to 2Hz. This suggests that a thickness layer with an S-wave velocity of about 1km/sec was deposited. If the S-wave velocity of bedrock is assumed to be 1500m/sec, the depth of the alluvium at the Taichung area is about 600m~1300m. The depth of the alluvium gradually increases from east to west and from north to south.

  2. 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 develop a three-dimensional P-wave velocity model of the Icelandic crust and uppermost mantle from a broad low-velocity anomaly in the middle and lower crust underlying a high velocity body in the shallow

  3. A BOTTOM VELOCITY COMPUTATION METHOD FOR ESTIMATING BED VARIATION IN A CHANNEL WITH SUBMERGED GROINS E

    NASA Astrophysics Data System (ADS)

    Uchida, Tatsuhiko; Fukuoka, Shoji

    A practical numerical bed variation method is required for evaluating various functions of groins installed in rivers. The conventional depth integrated (2D) computation method, which has been used for practical computations of flood flows and bed variations in rivers, is inadequate for local scouring around hydraulic structures due to 3D flow. However, the use of full 3D turbulence flow computation methods is not common for floods in rivers. Therefore, a refined depth integrated model is required for the practical use. In this paper, the Bottom Velocity Computation (BVC) method is proposed to evaluate velocity acting on sediment particles effectively and compute bed variation in a channel. In the BVC method, depth-integrated horizontal vorticity and water surface velocity equations are computed simultaneously with shallow water equations and a depth averaged turbulence energy transport equation. To compute bed variation around submerged groins, evaluation methods for non-equilibrium bed load and bed tractive force by using bottom velocity is presented. The applicability of the method is discusse d through the comparisons with the laboratory experimental results of flows and bed variations in a channel with submerged groins.

  4. Intracyclic Velocity Variation and Arm Coordination for Different Skilled Swimmers in the Front Crawl

    PubMed Central

    Matsuda, Yuji; Yamada, Yosuke; Ikuta, Yasushi; Nomura, Teruo; Oda, Shingo

    2014-01-01

    The aim of this study was to examine whether the intracyclic velocity variation (IVV) was lower in elite swimmers than in beginner swimmers at various velocities, and whether differences may be related to arm coordination. Seven elite and nine beginner male swimmers swam front crawl at four different swimming velocities (maximal velocity, 75%, 85%, and 95% of maximal swimming velocity). The index of arm coordination (IDC) was calculated as the lag time between the propulsive phases of each arm. IVV was determined from the coefficient of variation of horizontal velocity within one stroke cycle. IVV for elite swimmers was significantly lower (26%) than that for beginner swimmers at all swimming velocities (p<0.01, 7.28 1.25% vs. 9.80 1.70%, respectively). In contrast, the IDC was similar between elite and beginner swimmers. These data suggest that IVV is a strong predictor of the skill level for front crawl, and that elite swimmers have techniques to decrease IVV. However, the IDC does not contribute to IVV differences between elite and beginner swimmers. PMID:25713666

  5. Temporal changes of surface wave velocity associated with major Sumatra earthquakes from ambient noise correlation.

    PubMed

    Xu, Zhen J; Song, Xiaodong

    2009-08-25

    Detecting temporal changes of the medium associated with major earthquakes has implications for understanding earthquake genesis. Here we report temporal changes of surface wave velocity over a large area associated with 3 major Sumatra earthquakes in 2004, 2005, and 2007. We use ambient noise correlation to retrieve empirical Green's function (EGF) of surface waves between stations. Because the process is completely repeatable, the technique is powerful in detecting possible temporal change of medium. We find that 1 excellent station pair (PSI in Indonesia and CHTO in Thailand) shows significant time shifts (up to 1.44 s) after the 2004 and 2005 events in the Rayleigh waves at 10-20 s but not in the Love waves, suggesting that the Rayleigh time shifts are not from clock error. The time shifts are frequency dependent with the largest shifts at the period band of 11-16 s. We also observe an unusual excursion approximately 1 month before the 2004 event. We obtain a total of 17 pairs for June, 2007 to June, 2008, which allow us to examine the temporal and spatial variation of the time shifts. We observed strong anomalies (up to 0.68 s) near the epicenter after the 2007 event, but not in the region further away from the source or before the event or 3 months after the event. The observations are interpreted as stress changes and subsequent relaxation in upper-mid crust in the immediate vicinity of the rupture and the broad area near the fault zone. PMID:19667205

  6. The microscopic state of the solar wind: Links between composition, velocity distributions, waves and turbulence

    NASA Technical Reports Server (NTRS)

    Marsch, E.

    1995-01-01

    An overview is given of the microscopic state of the solar wind with emphasis on recent Ulysses high-latitude observations and previous Helios in-ecliptic observations. The possible links between composition, ionization state. velocity distribution functions of electrons, protons and heavy ions. kinetic plasma waves and MHD-scale turbulence are elaborated. Emphasis is placed on a connection of interplanetary kinetic-scale phenomena with their generating microscopic processes in the corona. The fast streams seem to consist of mesoscale pressure-balanced plasma filaments and magnetic flux tubes, reminiscent of the supergranular-size structures building the open corona, from which copious Alfven waves emanate. The wind from the magnetically structured and active corona shows developed compressive turbulence and considerable abundance and ionization state variations. Some modelling attempts to explain the observed element fractionation are briefly reviewed. The causes of the nonthermal particle features. such as proton-ion differential streaming, ion beams. temperature anisotropies, and skewed distributions associated with collisionless heat conduction, are ultimately to be searched in the fact, that the corona is never quiescent but fundamentally variable in space and time. Consequently, the radial evolution of the internal state of the wind resembles at all latitudes a complicated relaxation process, in the course of which the free (in comparison with LTE conditions) particle kinetic energy is converted into plasma waves and MHD turbulence on a wide range of scales. This leads to intermittent wave-particle interactions and unsteady anomalous transport, mixed with the weak effects of the rare Coulomb collisions. Spherical expansion and large-scale inhomogeneity forces the wind to attain microscopically a complex internal state of dynamic statistical equilibrium.

  7. A comprehensive dispersion model of surface wave phase and group velocity for the globe

    NASA Astrophysics Data System (ADS)

    Ma, Zhitu; Masters, Guy; Laske, Gabi; Pasyanos, Michael

    2014-10-01

    A new method is developed to measure Rayleigh- and Love-wave phase velocities globally using a cluster analysis technique. This method clusters similar waveforms recorded at different stations from a single event and allows users to make measurements on hundreds of waveforms, which are filtered at a series of frequency ranges, at the same time. It also requires minimal amount of user interaction and allows easy assessment of the data quality. This method produces a large amount of phase delay measurements in a manageable time frame. Because there is a strong trade-off between the isotropic part of the Rayleigh-wave phase velocity and azimuthal anisotropy, we include the effect of azimuthal anisotropy in our inversions in order to obtain reliable isotropic phase velocity. We use b-splines to combine these isotropic phase velocity maps with our previous group velocity maps to produce an internally consistent global surface wave dispersion model.

  8. 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

    NASA Astrophysics Data System (ADS)

    Kie?czy?ski, P.; Pajewski, W.

    1989-05-01

    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 coefficient c44in( x) (e.g. linear, Gaussian, etc.) is solved. The dispersion curves of phase and group velocity of surface SH waves in nonhomogeneous solids are calculated. Experimental verification of the inverse method has been performed for step profiles (structure of Cu on steel). It is stated that the inverse method based on the measurements of group velocity (for step profile) gives a smaller error in the unknown depth of the surface layer than that resulting from the inverse method based on the measurements of phase velocity of surface SH waves.

  9. 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.

  10. 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.

  11. In-situ, high-frequency P-Wave velocity measurements within 1 m of the Earth’s surface

    E-print Network

    Baker, Gregory S.; Steeples, Don W.; Schmeissner, Chris M.

    1999-03-01

    Seismic P-wave velocities in near?surface materials can be much slower than the speed of sound waves in air (normally 335 m/s or 1100 ft/s). Difficulties often arise when measuring these low?velocity P-waves because of interference by the air wave...

  12. 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.

  13. Phase and group velocities for Lamb waves in DOP-26 iridium alloy sheet

    SciTech Connect

    Simpson, W.A.; McGuire, D.J.

    1994-07-01

    The relatively coarse grain structure of iridium weldments limits the ultrasonic inspection of these structures to frequencies in the low megahertz range. As the material thickness is nominally 0.635 mm for clad vent set capsules, the low frequencies involved necessarily entail the generation of Lamb waves m the specimen. These waves are, of course, dispersive and detailed knowledge of both the phase and group velocities is required in order to determine accurately the location of flaws detected using Lamb waves. Purpose of this study is to elucidate the behavior of Lamb waves propagating in the capsule alloy and to quantify the velocities so that accurate flaw location is ensured. We describe a numerical technique for computing the phase velocities of Lamb waves (or of any other type of guided wave) and derive the group velocities from this information. A frequency-domain method is described for measuring group velocity when multiple Lamb modes are present and mutually interfering in the time domain, and experimental confirmation of the group velocity is presented for the capsule material.

  14. Temperature variation effects on sparse representation of guided-waves for damage diagnosis in pipelines

    NASA Astrophysics Data System (ADS)

    Eybpoosh, Matineh; Berges, Mario; Noh, Hae Young

    2015-04-01

    Multiple ultrasonic guided-wave modes propagating along a pipe travel with different velocities which are themselves a function of frequency. Reflections from the features of the structure (e.g., boundaries, pipe welding, damage, etc.), and their complex superposition, adds to the complexity of guided-waves. Guided-wave based damage diagnosis of pipelines becomes even more challenging when environmental and operational conditions (EOCs) vary (e.g., temperature, flow rate, inner pressure, etc.). These complexities make guided-wave based damage diagnosis of operating pipelines a challenging task. This paper reviews the approaches to-date addressing these challenges, and highlights the preferred characteristics of a method that simplifies guided-wave signals for damage diagnosis purposes. A method is proposed to extract a sparse subset of guided-wave signals in time-domain, while retaining optimal damage information for detection purpose. In this paper, the general concept of this method is proved through an extensive set of experiments. Effects of temperature variation on detection performance of the proposed method, and on discriminatory power of the extracted damage-sensitive features are investigated. The potential of the proposed method for real-time damage detection is illustrated, for wide range of temperature variation scenarios (i.e., temperature difference between training and test data varying between -2°C and 13°C).

  15. Abnormal acoustic wave velocities in basaltic and (Fe,Al)-bearing silicate glasses

    E-print Network

    Lin, Jung-Fu "Afu"

    Abnormal acoustic wave velocities in basaltic and (Fe,Al)-bearing silicate glasses at high of (Fe,Al)-bearing MgSiO3 silicate glasses and an Icelandic basalt glass up to 25GPa. The velocity profiles of the (Fe,Al)-bearing and basaltic silicate glasses display decreased VP and VS with minima

  16. Shear velocity model for the Kyrgyz Tien Shan from joint inversion of receiver function and surface wave data

    NASA Astrophysics Data System (ADS)

    Gilligan, Amy; Roecker, Steven W.; Priestley, Keith F.; Nunn, Ceri

    2014-10-01

    The Tien Shan is the largest active intracontinental orogenic belt on Earth. To better understand the processes causing mountains to form at great distances from a plate boundary, we analyse passive source seismic data collected on 40 broad-band stations of the MANAS project (2005-2007) and 12 stations of the permanent KRNET seismic network to determine variations in crustal thickness and shear wave speed across the range. We jointly invert P- and S-wave receiver functions with surface wave observations from both earthquakes and ambient noise to reduce the ambiguity inherent in the images obtained from the techniques applied individually. Inclusion of ambient noise data improves constraints on the upper crust by allowing dispersion measurements to be made at shorter periods. Joint inversion can also reduce the ambiguity in interpretation by revealing the extent to which various features in the receiver functions are amplified or eliminated by interference from multiples. The resulting wave speed model shows a variation in crustal thickness across the range. We find that crustal velocities extend to ˜75 km beneath the Kokshaal Range, which we attribute to underthrusting of the Tarim Basin beneath the southern Tien Shan. This result supports the plate model of intracontinental convergence. Crustal thickness elsewhere beneath the range is about 50 km, including beneath the Naryn Valley in the central Tien Shan where previous studies reported a shallow Moho. This difference apparently is the result of wave speed variations in the upper crust that were not previously taken into account. Finally, a high velocity lid appears in the upper mantle of the Central and Northern part of the Tien Shan, which we interpret as a remnant of material that may have delaminated elsewhere under the range.

  17. 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.

  18. VARIATIONAL BOUSSINESQ MODEL FOR SIMULATION OF COASTAL WAVES AND TSUNAMIS

    E-print Network

    Al Hanbali, Ahmad

    1 VARIATIONAL BOUSSINESQ MODEL FOR SIMULATION OF COASTAL WAVES AND TSUNAMIS DIDIT ADYTIA E. VAN different applications in this paper. One application deals with tsunami simulations, for which we show the phenomenon of tsunami waveguiding before the coast of Lampung in Indonesia. Another application deals

  19. Assessment of Model Based (Input) Impedance, Pulse Wave Velocity, and Wave Reflection in the Asklepios Cohort

    PubMed Central

    Parragh, Stephanie; Mayer, Christopher; Weber, Thomas; Van Bortel, Luc; De Buyzere, Marc; Segers, Patrick; Rietzschel, Ernst

    2015-01-01

    Objectives Arterial stiffness and wave reflection parameters assessed from both invasive and non-invasive pressure and flow readings are used as surrogates for ventricular and vascular load. They have been reported to predict adverse cardiovascular events, but clinical assessment is laborious and may limit widespread use. This study aims to investigate measures of arterial stiffness and central hemodynamics provided by arterial tonometry alone and in combination with aortic root flows derived by echocardiography against surrogates derived by a mathematical pressure and flow model in a healthy middle-aged cohort. Methods Measurements of carotid artery tonometry and echocardiography were performed on 2226 ASKLEPIOS study participants and parameters of systemic hemodynamics, arterial stiffness and wave reflection based on pressure and flow were measured. In a second step, the analysis was repeated but echocardiography derived flows were substituted by flows provided by a novel mathematical model. This was followed by a quantitative method comparison. Results All investigated parameters showed a significant association between the methods. Overall agreement was acceptable for all parameters (mean differences: -0.0102 (0.033 SD) mmHg*s/ml for characteristic impedance, 0.36 (4.21 SD) mmHg for forward pressure amplitude, 2.26 (3.51 SD) mmHg for backward pressure amplitude and 0.717 (1.25 SD) m/s for pulse wave velocity). Conclusion The results indicate that the use of model-based surrogates in a healthy middle aged cohort is feasible and deserves further attention. PMID:26513463

  20. Tomographic Imaging of Upper Mantle P- and S-wave Velocity Heterogeneity Beneath the Arabian Peninsula

    NASA Astrophysics Data System (ADS)

    Park, Y.; Nyblade, A. A.; Rodgers, A.; Al-Amri, A.

    2005-12-01

    We have studied the three-dimensional P- and S-wave velocity structure beneath the Arabian Peninsula estimated from teleseismic travel time delay tomography. We have completed travel time measurements and inversion of a data set provided by King Abdulaziz City for Science and Technology (KACST: 21 broadband stations and 4 short-period stations). We augmented the KACST data with delay times measured from permanent Incorporated Research Institutions for Seismology (IRIS) stations in the region (RAYN, EIL and MRNI) and the 1996 Saudi Arabian PASSCAL Experiment (9 broadband stations). We used 401 earthquakes resulting in 3416 ray paths with P- and PKP-wave arrivals for the P-wave tomography, and 1602 ray paths with S- and SKS-wave arrivals came from 201 earthquakes for the S-wave tomography. Although the total number of rays for the S-wave model is a half of the rays for the P-wave model, the event distribution shows better azimuthal coverage. The P and S wave models yield consistent results. The models show strong low velocity regions beneath the southeastern Arabian Shield and the mid-eastern edge of Arabian Shield. The low velocity anomaly in the southeastern part of the Arabian Shield does not extend north of 21°N and dips to south. It likely represents the northeastern edge of the Afar hotspot. The origin of the low velocity region under the eastern edge of the Arabian Shield is uncertain.

  1. Measurements of mantle wave velocities and inversion for lateral heterogeneity and anisotropy. II - Analysis by the single-station method

    NASA Technical Reports Server (NTRS)

    Nakanishi, I.; Anderson, D. L.

    1984-01-01

    In the present investigation, the single-station method reported by Brune et al. (1960) is utilized for an analysis of long-period Love(G) and Rayleigh(R) waves recorded on digital seismic networks. The analysis was conducted to study the lateral heterogeneity of surface wave velocities. The data set is examined, and a description is presented of the single-station method. Attention is given to an error analysis for velocity measurements, the estimation of geographical distribution of surface wave velocities, the global distribution of surface wave velocities, and the correlation between the surface wave velocities and the heat flow on the geoid. The conducted measurements and inversions of surface wave velocities are used as a basis to derive certain conclusions. It is found that the application of the single-station method to long-period surface waves recorded on digital networks makes it possible to reach an accuracy level comparable to great circle velocity measurements.

  2. 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.

  3. Wave Packet for Massless Fermions and its Implication to the Superluminal Velocity Statistics of Neutrino

    E-print Network

    Kelin Wang; Zexian Cao

    2012-01-06

    Non-dispersive wave packet for massless fermions is formulated on the basis of squeezed coherent states that are put in a form of common eigenfunction for the Hamiltonian and the helicity operator, starting from the Dirac equation. The wave packet thus constructed is demonstrated to propagate at a constant velocity as that of light. This explicit expression of wave packet for the massless fermions can facilitate theoretical analysis of problems where a wave packet is of formal significance. Furthermore, extensive wave packet may result in a superluminal velocity statistics if determined from the time-of-flight measurement, as recently done on muon neutrinos, when a threshold particle flux or energy transfer, which is eventually referred to the propagation of wave packet, to invoke a detection event is assumed.

  4. Upper-mantle P- and S-wave velocities across the Northern Tornquist Zone from traveltime tomography

    NASA Astrophysics Data System (ADS)

    Hejrani, Babak; Balling, Niels; Jacobsen, Bo Holm; Tilmann, Frederik

    2015-10-01

    This study presents P- and S-wave velocity variations for the upper mantle in southern Scandinavia and northern Germany based on teleseismic traveltime tomography. Tectonically, this region includes the entire northern part of the prominent Tornquist Zone which follows along the transition from old Precambrian shield units to the east to younger Phanerozoic deep sedimentary basins to the southwest. We combine data from several separate temporary arrays/profiles (276 stations) deployed over a period of about 15 yr and permanent networks (31 stations) covering the areas of Denmark, northern Germany, southern Sweden and southern Norway. By performing an integrated P- and S-traveltime analysis, we obtain the first high-resolution combined 3-D VP and VS models, including variations in the VP/VS ratio, for the whole of this region of study. Relative station mean traveltime residuals vary within ±1 s for P wave and ±2 s for S wave, with early arrivals in shield areas of southern Sweden and later arrivals in the Danish and North German Basins, as well as in most of southern Norway. In good accordance with previous, mainly P-velocity models, a marked upper-mantle velocity boundary (UMVB) is accurately delineated between shield areas (with high seismic mantle velocity) and basins (with lower velocity). It continues northwards into southern Norway near the Oslo Graben area and further north across the Southern Scandes Mountains. This main boundary, extending to a depth of at least 300 km, is even more pronounced in our new S-velocity model, with velocity contrasts of up to ±2-3 per cent. It is also clearly reflected in the VP/VS ratio. Differences in this ratio of up to about ±2 per cent are observed across the boundary, with generally low values in shield areas to the east and relatively higher values in basin areas to the southwest and in most of southern Norway. Differences in the VP/VS ratio are believed to be a rather robust indicator of upper-mantle compositional differences. For the depth interval of about 100-300 km, thick, depleted, relatively cold shield lithosphere is indicated in southern Sweden, contrasting with more fertile, warm mantle asthenosphere beneath most of the basins in Denmark and northern Germany. Both compositional and temperature differences seem to play a significant role in explaining the UMVB between southern Norway and southern Sweden. In addition to the main regional upper-mantle velocity contrasts, a number of more local anomaly features are also outlined and discussed.

  5. Estimation of shear velocity contrast for dipping or anisotropic medium from transmitted Ps amplitude variation with ray-parameter

    NASA Astrophysics Data System (ADS)

    Kumar, Prakash

    2015-12-01

    Amplitude versus offset analysis of P to P reflection is often used in exploration seismology for hydrocarbon exploration. In the present work, the feasibility to estimate crustal velocity structure from transmitted P to S wave amplitude variation with ray-parameter has been investigated separately for dipping layer and anisotropy medium. First, for horizontal and isotropic medium, the approximation of P-to-s conversion is used that is expressed as a linear form in terms of slowness. Next, the intercept of the linear regression has been used to estimate the shear wave velocity contrast (??) across an interface. The formulation holds good for isotropic and horizontal layer medium. Application of such formula to anisotropic medium or dipping layer data may lead to erroneous estimation of ??. In order to overcome this problem, a method has been proposed to compensate the SV-amplitude using shifted version of SH-amplitude, and subsequently transforming SV amplitudes equivalent to that from isotropic or horizontal layer medium as the case may be. Once this transformation has been done, ?? can be estimated using isotropic horizontal layer formula. The shifts required in SH for the compensation are ?/2 and ?/4 for dipping layer and anisotropic medium, respectively. The effectiveness of the approach has been reported using various synthetic data sets. The methodology is also tested on real data from HI-CLIMB network in Himalaya, where the presence of dipping Moho has already been reported. The result reveals that the average shear wave velocity contrast across the Moho is larger towards the Indian side compared to the higher Himalayan and Tibetan regions.

  6. 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.

  7. 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.

  8. Group velocity of extraordinary waves in superdense magnetized quantum plasma with spin-1/2 effects

    SciTech Connect

    Li Chunhua; Ren Haijun; Yang Weihong; Wu Zhengwei; Chu, Paul K.

    2012-12-15

    Based on the one component plasma model, a new dispersion relation and group velocity of elliptically polarized extraordinary electromagnetic waves in a superdense quantum magnetoplasma are derived. The group velocity of the extraordinary wave is modified due to the quantum forces and magnetization effects within a certain range of wave numbers. It means that the quantum spin-1/2 effects can reduce the transport of energy in such quantum plasma systems. Our work should be of relevance for the dense astrophysical environments and the condensed matter physics.

  9. Kinetic Alfvén wave and ion velocity distribution functions in the solar wind

    NASA Astrophysics Data System (ADS)

    Li, X.; Lu, Q.; Chen, Y.; Li, B.; Xia, L.

    2010-12-01

    Using 1D test particle simulations, the effect of a kinetic Alfvén wave on the velocity distribution function of protons in the collisionless solar wind is investigated. We first use linear Vlasov theory to obtain the property of a kinetic Alfvén wave numerically (the wave propagates in the direction almost perpendicular to the background magnetic field). We then numerically simulate how the wave will shape the proton velocity distribution function. It is found that Landau resonance may be able to generate two components in the initially Maxwellian proton velocity distribution function: a tenuous beam component along the direction of the background magnetic field and a core component. The streaming speed of the beam relative to the core proton component is about 1.2 -- 1.3 Alfvén speed. However, no perpendicular ion heating is observed from the simulation. Reference: Li, X., Lu, Q.M., Chen, Y., Li, B., Xia, L.D., ApJ, 719, L190, 2010.

  10. Effect of viscosity on the wave propagation: Experimental determination of compression and expansion pulse wave velocity in fluid-fill elastic tube.

    PubMed

    Stojadinovi?, Bojana; Tenne, Tamar; Zikich, Dragoslav; Rajkovi?, Nemanja; Miloševi?, Nebojša; Lazovi?, Biljana; Žiki?, Dejan

    2015-11-26

    The velocity by which the disturbance travels through the medium is the wave velocity. Pulse wave velocity is one of the main parameters in hemodynamics. The study of wave propagation through the fluid-fill elastic tube is of great importance for the proper biophysical understanding of the nature of blood flow through of cardiovascular system. The effect of viscosity on the pulse wave velocity is generally ignored. In this paper we present the results of experimental measurements of pulse wave velocity (PWV) of compression and expansion waves in elastic tube. The solutions with different density and viscosity were used in the experiment. Biophysical model of the circulatory flow is designed to perform measurements. Experimental results show that the PWV of the expansion waves is higher than the compression waves during the same experimental conditions. It was found that the change in viscosity causes a change of PWV for both waves. We found a relationship between PWV, fluid density and viscosity. PMID:26454712

  11. Apparent pulse wave velocity in the canine superior vena cava.

    PubMed

    Minten, J; Van de Werf, F; Aubert, A E; Kesteloot, H; De Geest, H

    1983-10-01

    In order to evaluate clinically recorded jugular vein pulses it is necessary to understand the transmission process of the right atrial pressure pulse through the caval veins up to the jugular veins. The transmission speed at distinct points of the venous pressure curve was studied in the superior vena cava of 20 anaesthetised dogs. Under control conditions the propagation velocities varied from 1.2 +/- 0.49 to 2.5 +/- 1.36 m . s-1. During increased preload of the heart propagation velocities rose significantly from 2.2 to 4.2 m . s-1 per kPa as a function of mean venous pressure and from 2.3 to 5.8 m . s-1 per kPa as a function of phasic pressures. Right atrial pacing (between 60 and 120 beats . min-1) did not influence the propagation velocity of the studied distinct points. It was found that the summits of the pressure pulse propagate at only a slightly higher speed than the nadirs. PMID:6627270

  12. Shear wave velocities from noise correlation at local scale

    SciTech Connect

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

    2008-07-08

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

  13. 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.

  14. VLT observations of rapid radial velocity variations in roAp stars

    NASA Astrophysics Data System (ADS)

    Elkin, V.; Kurtz, D. W.; Mathys, G.

    2008-04-01

    We have studied 27 out of the 37 known roAp stars with high resolution spectroscopy using UVES on the ESO VLT. All 27 stars show rapid radial velocity variations with periods similar to those obtained by photometry. Highest pulsation amplitudes are seen for lines of rare earth elements and the H? core. For some stars other chemical species also have pulsation, but with smaller amplitudes. There are pulsational phase shifts between lines of different rare earth elements. Stars with stronger magnetic fields tend to have lower radial velocity pulsation amplitudes.

  15. 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.

  16. Time-lapse Measurements of Scholte Wave Velocity Over a Compacting Oil Field

    NASA Astrophysics Data System (ADS)

    Wills, P. B.; Hatchell, P. J.

    2007-12-01

    Acquisition of time-lapse seismic data over producing oil and gas fields is a proven method for optimizing hydrocarbon production. Most current data have been acquired using towed-streamer seismic vessels but new systems incorporating permanent Ocean Bottom Cable (OBC) systems are gaining in popularity, both as a way to achieve better repeatability and also to reduce the cost of acquiring many time-lapse repeats of the baseline survey. Over the last three years, more than seven repeat data sets have been acquired at the permanent OBC system installed (by the operator, BP) over the Valhall oil field located offshore Norway. This system contains ~2400 four-component receiver stations that are recorded using a dense areal shot grid ("carpet" shoot) that provides high fold and has delivered excellent time-lapse signals starting from the first repeat occurring just three months after the baseline. Time-lapse OBC data are conventionally used to measure amplitude and velocity changes of body wave reflections (PP and PS) but other measurements are also possible. In particular, Scholte waves are strongly visible on records acquired everywhere in the field on appropriately processed data and, given the high fold (because of the dense shots), Scholte wave velocity and anisotropy time-lapse changes obtained with both hydrophone and geophone sensors are accurately and robustly estimated. The resulting shallow velocity maps are very sensitive to the seabed strains and show large velocity changes overlying deep production. Also, reconstruction of compressional "head wave" velocity difference measurements and vertically propagating shear wave shallow time-lapse statics produce maps that resemble the Scholte wave maps, with differences that reflect the physics of the propagation modes and effective fold. A reservoir model that includes deep reservoir volume changes together with appropriate geomechanical properties in the overburden and a shallow conversion of strain to velocity is used to successfully predict the measured velocity changes. The strain/velocity conversion requires asymmetry between crack opening and closing as well as velocity hysteresis and, in fact, the measurements provide an excellent laboratory for testing fracture-model/velocity conversion on in-situ rocks. After calibration, the model together with the data can constrain both volume changes in the reservoir, for making drilling decisions as well as the overburden geomechanical rock properties model, which itself is used for well- path selection and facilities decisions. Scholte wave velocity measurements can also be made using an oil platform as a "passive" source, removing the need for a conventional source near the seafloor. Finally, these measurements might be applicable on time- lapse controlled source measurements of greater generality in a wider geophysical context wherever an accurate measurement of a time-varying surface strain is desired.

  17. Seasonal variation in concentration, size, and settling velocity of muddy marine flocs in the benthic boundary layer

    NASA Astrophysics Data System (ADS)

    Fettweis, Michael; Baeye, Matthias

    2015-08-01

    Suspended Particulate Matter (SPM) concentration profiles of the lowest 2 m of the water column and particle size distribution at 2 m above the bed were measured in a coastal turbidity maximum area (southern North Sea) during more than 700 days between 2006 and 2013. The long-term data series of SPM concentration, floc size, and settling velocity have been ensemble averaged according to tidal range, alongshore residual flow direction, and season, in order to investigate the seasonal SPM dynamics and its relation with physical and biological processes. The data show that the SPM is more concentrated in the near-bed layer in summer, whereas in winter, the SPM is better mixed throughout the water column. The decrease of the SPM concentration in the water column during summer is compensated by a higher near-bed concentration indicating that a significant part of the SPM remains in the area during summer rather than being advected out of it. The opposite seasonality between near-bed layer and water column has to our knowledge not yet been presented in literature. Physical effects such as wave heights, wind climate, or storms have a weak correlation with the observed seasonality. The argument to favor microbial activity as main driver of the seasonality lies in the observed variations in floc size and settling velocity. On average, the flocs are larger and thus settling velocities higher in summer than winter.

  18. On Variational Methods in the Physics of Plasma Waves

    SciTech Connect

    I.Y. Dodin

    2013-03-08

    A fi rst-principle variational approach to adiabatic collisionless plasma waves is described. The focus is made on one-dimensional electrostatic oscillations, including phase-mixed electron plasma waves (EPW) with trapped particles, such as Bernstein-Greene-Kruskal modes. The well known Whitham's theory is extended by an explicit calculation of the EPW Lagrangian, which is related to the oscillation-center energies of individual particles in a periodic fi eld, and those are found by a quadrature. Some paradigmatic physics of EPW is discussed for illustration purposes. __________________________________________________

  19. S-Wave Velocity Structure of the Puli Basin, Taiwan, Using the Array Records of Microtremors

    NASA Astrophysics Data System (ADS)

    Wu, C.; Huang, H.

    2009-12-01

    The September 21, 1999 Chi-Chi earthquake induced strong shaking, resulting in severe damage in the Puli area. According to Huang and Tarng (2005), the collapse of many structures during the earthquake was very closely related to the site effects. The Shallow Shear-wave velocities have widely been used for earthquake ground-motion site characterization. Thus, the S-wave velocity structures of the Puli area are investigated using the array records of microtremors at 16 sites. The dispersion curves at these sites are calculated using the F-K method (Capon, 1969); then, the S-wave velocity structures at the Puli area are estimated by employing the surface wave inversion technique (Herrmann, 1991). If the S-wave velocity of bedrock is assumed to be 2000m/sec, the depths of the alluvium at the Puli area are between 360m (ZHO) and 810m (AIL, DAH). Besides, there are 3~4 distinct interfaces in the shallow velocity structure (0~1000m). The depth of the alluvium gradually increases from east to west and the deepest one appears at stations AIL and DAH. The results in this study are similar to those using the seismic exploration method (Wang et al., 2003; Huang, 2008) in the Puli area and the well-logging method at LAC.

  20. 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.; Lutter, William J.; Sessions, Robert

    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

  1. 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

  2. Hurricane Directional Wave Spectrum Spatial Variation in the Open Ocean

    NASA Technical Reports Server (NTRS)

    Wright, C. W.; Walsh, E. J.; Vandemark, D.; Krabill, W. B.; Garcia, A. W.

    1999-01-01

    The sea surface directional wave spectrum was measured for the first time in all quadrants of a hurricane in open water using the NASA airborne scanning radar altimeter (SRA) carried aboard one of the NOAA WP-3D hurricane hunter aircraft at 1.5 km height. The SRA measures the energetic portion of the directional wave spectrum by generating a topographic map of the sea surface. At 8 Hz, the SRA sweeps a radar beam of 1 deg half-power width (two-way) across the aircraft ground track over a swath equal to 0. 8 of the aircraft height, simultaneously measuring the backscattered power at its 36 GHz (8.3 mm) operating frequency and the range to the sea surface at 64 positions. These slant ranges are multiplied by the cosine of the incidence angles to determine the vertical distances from the aircraft to the sea surface. Subtracting these distances from the aircraft height produces the sea surface elevation map. The sea surface topography is interpolated to a uniform grid, transformed by a two-dimensional FFT, and Doppler corrected. The data presented were acquired on 24 August 1998 when hurricane Bonnie was east of the Bahamas and moving slowly to the north. Wave heights up to 18 m were observed and the spatial variation of the wave field was dramatic. The dominant waves generally propagated at significant angles to the downwind direction and at times there were wave fields traveling at right angles to each other. The NOAA aircraft spent over five hours within 180 km of the hurricane Bonnie eye, and made five eye penetrations. A 2-minute animation of the directional wave spectrum spatial variation over this period will be shown.

  3. 3-D Seismic Velocity Structure of the Hawaii Hotspot from Joint Inversion of Body Wave and Surface Wave data

    NASA Astrophysics Data System (ADS)

    Cheng, C.; Allen, R. M.; Porritt, R. W.

    2012-12-01

    The Hawaii hotspot and the associated chain of islands have been long regarded as the case example of a deep-rooted mantle plume. However the efforts to detect a thermal plume seismically have been inconclusive. In this study we combine the complementary sensitivities of body- and surface-waves in order to improve resolution of mantle structure beneath Hawaii. Adding surface-wave constraints to the body wave inversion improves the resolution of the crustal and upper mantle structure. We used data from the deployment of temporary broadband ocean-bottom seismometers (OBS) of the Hawaiian Plume-Lithosphere Undersea Melt Experiment (PLUME) together with data from the on-shore stations in order to make the most complete dataset available. In a first step, we obtained stable and reliable OBS orientations over a range of earthquake back-azimuths using teleseismic P-wave particle motions. Due to the high noise of the OBS data in some frequency bands, we began by filtering in the period band of 0.04-1Hz. Using the proper channel orientations, we measured ~800 S-wave relative arrival times (direct S and SKS phases) on the SV component using muti-channel cross correlation. We applied the two-plane wave tomography method to generate surface wave phase velocity information. We use surface waves from 71 events with magnitude greater than 5.8 to generate phase velocity maps from 25 sec to 100 sec. These maps clearly show the low velocities beneath the islands surrounded by relatively high phase velocity. The pure S wave inversion result shows the 3-D structure beneath the PLUME array to a depth of 1000km and reveals a several-hundred-kilometer-wide region of low velocities beneath Hawaii that dips to the southeast. The low velocities continue downward through the mantle transition zone and extend into the uppermost lower-mantle where our resolution begins to degrade. These images are consistent with the interpretation that the Hawaiian hotspot is the result of an upwelling high-temperature plume from the lower mantle. The broader upper-mantle low-velocity region immediately beneath the Hawaiian Islands likely reflects the horizontal spreading of the plume material beneath the lithosphere. We also obtain result from the joint body-wave and surface-wave inversion. The same shallow low velocity zone is imaged along the island chain and the deeper part is identical to the body-wave inversion image. The low velocity to the southwest of the island is also clear to a depth of 600km. However, this low velocity limb is relatively small compared to the one from the southeast. This suggests this southwest limb is the result of spreading and interaction of the plume with the lithosphere. If the observation here is true, it will provide a hot environment for the 660km discontinuity to the west of the Hawaii and may give a new perspective to the plume origin debate.

  4. Correlations between seismic wave velocities and physical properties of near-surface geologic materials in the southern San Francisco Bay region, California

    USGS Publications Warehouse

    Fumal, Thomas E.

    1978-01-01

    To identify geologic units with distinctly different seismic responses for the purposes of seismic zonation, compressional and shear wave velocities have been measured in boreholes at 59 sites in the San Francisco Bay region in a wide range of near-surface (0-30m) geologic materials. Several physical parameters, which can be readily determined in the field, were found to correlate with the shear wave velocities and were used to define seismically distinct groups. For the unconsolidated to semiconsolidated sediments, texture, standard penetration resistance and depth were used to define eight seismically distinct groups. For the bedrock materials, fracture spacing and hardness were used to differentiate ten distinct categories. The correlation obtained between shear wave velocity and the physical parameters were used to regroup the map units defined for the San Francisco Bay region into seismically distinct units. The map units for the younger unconsolidated sediments can be really differentiated seismically. In contrast, the older semiconsolidated sedimentary deposits and bedrock units, which have experienced significant variations in post-depositial changes, show wider and overlapping velocity ranges. The map units for the sedimentary deposits have been regrouped into eight seismically distinct geotechnical units. The bedrock map units have been broadly regrouped into five distinct categories. Compressional wave velocities were not found to be well correlated with the physical parameters dependent on the soil or rock structure. For materials above the water table, the wide velocity variations found for each geotechnical group can be attributed to differences in degree of saturation. The strong correlations observed between shear wave velocity and other readily determine physical properties suggest that geologic maps which incorporate these parameters are most useful for seismic zonation.

  5. Shear Wave Velocity and Site Amplification Factors for 25 Strong-Motion Instrument Stations Affected by the M5.8 Mineral, Virginia, Earthquake of August 23, 2011

    USGS Publications Warehouse

    Kayen, Robert; Carkin, Bradley; Corbett, Skye; Zangwill, Aliza; Estevez, Ivan; Lai, Lena

    2015-01-01

    Vertical one-dimensional shear wave velocity (Vs) profiles are presented for 25 strong-motion instrument sites along the Mid-Atlantic eastern seaboard, Piedmont region, and Appalachian region, which surround the epicenter of the M5.8 Mineral, Virginia, Earthquake of August 23, 2011. Testing was performed at sites in Pennsylvania, Maryland, West Virginia, Virginia, the District of Columbia, North Carolina, and Tennessee. The purpose of the study is to determine the detailed site velocity profile, the average velocity in the upper 30 meters of the profile (VS,30), the average velocity for the entire profile (VS,Z), and the National Earthquake Hazards Reduction Program (NEHRP) site classification. The Vs profiles are estimated using a non-invasive continuous-sine-wave method for gathering the dispersion characteristics of surface waves. A large trailer-mounted active source was used to shake the ground during the testing and produce the surface waves. Shear wave velocity profiles were inverted from the averaged dispersion curves using three independent methods for comparison, and the root-mean square combined coefficient of variation (COV) of the dispersion and inversion calculations are estimated for each site.

  6. Sample Disturbance in Resonant Column Test Measurement of Small-Strain Shear-Wave Velocity

    NASA Astrophysics Data System (ADS)

    Chiara, Nicola; Stokoe, K. H.

    The accurate assessment of dynamic soil properties is a crucial step in the solution process of geotechnical earthquake engineering problems. The resonant column test is one of the ordinary procedures for dynamic characterization of soil. In this paper, the impact of sample disturbance on the resonant column test measurement of small-strain S-wave velocity is examined. Sample disturbance is shown to be a function of the ratio of the laboratory to field S-wave velocities: Vs, lab/Vs,field. The influence of four parameters - soil stiffness, soil plasticity index, in-situ sample depth and in-situ effective mean confining pressure - on sample disturbance is investigated both qualitatively and quantitatively. The relative importance of each parameter in predicting the small-strain field S-wave velocity from the resonant column test values is illustrated and predictive equations are presented.

  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. Minimal position-velocity uncertainty wave packets in relativistic and non-relativistic quantum mechanics

    SciTech Connect

    Al-Hashimi, M.H. Wiese, U.-J.

    2009-12-15

    We consider wave packets of free particles with a general energy-momentum dispersion relation E(p). The spreading of the wave packet is determined by the velocity v={partial_derivative}{sub p}E. The position-velocity uncertainty relation {delta}x{delta}v{>=}1/2 |<{partial_derivative}{sub p}{sup 2}E>| is saturated by minimal uncertainty wave packets {phi}(p)=Aexp(-{alpha}E(p)+{beta}p). In addition to the standard minimal Gaussian wave packets corresponding to the non-relativistic dispersion relation E(p)=p{sup 2}/2m, analytic calculations are presented for the spreading of wave packets with minimal position-velocity uncertainty product for the lattice dispersion relation E(p)=-cos(pa)/ma{sup 2} as well as for the relativistic dispersion relation E(p)={radical}(p{sup 2}+m{sup 2}). The boost properties of moving relativistic wave packets as well as the propagation of wave packets in an expanding Universe are also discussed.

  9. Unraveling overtone interferences in Love-wave phase velocity measurements by radon transform

    NASA Astrophysics Data System (ADS)

    Luo, Yinhe; Yang, Yingjie; Zhao, Kaifeng; Xu, Yixian; Xia, Jianghai

    2015-10-01

    Surface waves contain fundamental mode and higher modes, which could interfere with each other. If different modes are not properly separated, the inverted Earth structures using surface waves could be biased. In this study, we apply linear radon transform (LRT) to synthetic seismograms and real seismograms from the USArray to demonstrate the effectiveness of LRT in separating fundamental-mode Love waves from higher modes. Analysis on synthetic seismograms shows that two-station measurements on reconstructed data obtained after mode separation can completely retrieve the fundamental-mode Love-wave phase velocities. Results on USArray data show that higher mode contamination effects reach up to ˜10 per cent for two-station measurements of Love waves, while two-station measurements on mode-separated data obtained by LRT are very close to the predicted values from a global dispersion model of GDM52, demonstrating that the contamination of overtones on fundamental-mode Love-wave phase velocity measurements is effectively mitigated by the LRT method and accurate fundamental-mode Love-wave phase velocities can be measured.

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

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

    A kinetic theory in the form of an integral equation is provided to study the electrostatic oscillations in a collisionless plasma immersed in a uniform magnetic field and a nonuniform transverse electric field. In the low temperature limit the dispersion differential equation is recovered for the transverse Kelvin-Helmholtz modes for arbitrary values of K parallel, where K parallel is the component of the wave vector in the direction of the external magnetic field assumed in the z direction. For higher temperatures the ion-cyclotron-like modes described earlier in the literature by Ganguli, Lee and Plamadesso are recovered. In this article, the integral equation is reduced to a second-order differential equation and a study is made of the kinetic Kelvin-Helmholtz and ion-cyclotron-like modes that constitute the two branches of oscillation in a magnetized plasma including a transverse inhomogeneous dc electric field.

  11. A CONVERGENT FINITE DIFFERENCE METHOD FOR A NONLINEAR VARIATIONAL WAVE EQUATION

    E-print Network

    A CONVERGENT FINITE DIFFERENCE METHOD FOR A NONLINEAR VARIATIONAL WAVE EQUATION H. HOLDEN, K. H and phrases. Variational wave equation, convergence of finite difference schemes, liquid crystals for the nonlinear variational wave equation utt - c(u)(c(u)ux)x = 0 with u|t=0 = u0 and ut|t=0 = v0. Introducing

  12. Green water velocity due to breaking wave impingement on a tension leg platform

    NASA Astrophysics Data System (ADS)

    Chuang, Wei-Liang; Chang, Kuang-An; Mercier, Richard

    2015-07-01

    The present study employed the image-based bubble image velocimetry (BIV) technique to investigate the flow kinematics of a plunging breaking wave impinging on a geometry-simplified, unrestrained tension leg platform (TLP). A high-speed camera was used to record images for the BIV velocity determination for both fluid and structure velocities. The plunging breaker was generated using a wave focusing method, and repeated measurements were acquired to calculate the mean flow and turbulence intensity using ensemble averaging. BIV measurements were performed on two perpendicular planes: side view and top view. The flow measurements were compared with those of a similar experiment on a fixed structure by Ryu et al. (Exp Fluids 43(4):555-567, 2007a). The maximum velocity occurred in the run-up stage with a magnitude reaching 2.8 C with C being the phase speed of the breaking wave. The dominant velocities for three distinct phases—impingement, run-up, and overtopping—are very close to those found on the fixed structure. Turbulence intensity was also examined, and the ratio among the three components was quantified. Ryu et al. (Appl Ocean Res 29(3):128-136, 2007b) reported that Ritter's dam-break flow solution agrees surprisingly well with the measured green water velocity on the fixed structure to a certain degree. The present study followed the same approach and confirmed that Ritter's solution is also in excellent agreement with the green water velocity on the unrestrained TLP model. Based on the self-similar behavior, the prediction equation proposed by Ryu et al. (2007a) was used to model the green water velocity distribution. The results show that the prediction equation is applicable to not only a fixed structure, but also the unrestrained TLP for green water velocity caused by extreme waves.

  13. Rayleigh Wave Group Velocity Distributions for East Asia from Ambient Seismic Noise Tomography

    NASA Astrophysics Data System (ADS)

    Witek, M.; van der Lee, S.; Kang, T. S.; Chang, S. J.; Ning, S.; Ning, J.

    2014-12-01

    We have collected continuous vertical-component broadband data from 1109 seismic stations in regional networks across China, Korea, and Japan for the year 2011 to perform the largest surface wave tomography study in the region. Using this data set, we have measured over half a million Rayleigh wave group velocity dispersion curves from 1-year stacks of station-pair ambient seismic noise cross-correlations. Quality control is performed by measuring the coherency of the positive and negative lag time sides of the cross-correlations. If the coherency is below an empirically determined threshold, the dispersion curve is measured on the side of the highest SNR. Otherwise, the positive and negative sides of the cross-correlation are averaged before dispersion curve measurement. Group velocity measurements for which the SNR was less than 10 are discarded. The Rayleigh wave group velocity dispersion curves are regionalized on a tessellated spherical shell grid in the period range 10 to 50 s to produce maps of Rayleigh wave group velocity distributions. Preliminary maps at 10 seconds period match well with geologic features at the surface. In particular, we observe low group velocities in the Songliao, Bohai Bay, Sichuan, Ordos, Tarim, and Junggar Basins in China, and the Ulleung and Yamato Basins in the East Sea (Sea of Japan). Higher group velocities are observed in regions with less sediment cover. At periods around 30 s, we observe group velocity decreases going from east to west in China, representing an overall trend of crustal thickening due to the collision between the Indian and Eurasian plates. The Ordos and Sichuan blocks show higher group velocities relative to the eastern margin of the Tibetan Plateau, possibly reflecting low temperatures in these cratons.

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

    SciTech Connect

    Sharif, M. Manzoor, R.

    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.

  15. Length and activation dependent variations in muscle shear wave speed

    PubMed Central

    DeWall, R J; Lee, K S; Thelen, D G

    2013-01-01

    Muscle stiffness is known to vary as a result of a variety of disease states, yet current clinical methods for quantifying muscle stiffness have limitations including cost and availability. We investigated the capability of shear wave elastography (SWE) to measure variations in gastrocnemius shear wave speed induced via active contraction and passive stretch. Ten healthy young adults were tested. Shear wave speeds were measured using a SWE transducer positioned over the medial gastrocnemius at ankle angles ranging from maximum dorsiflexion to maximum plantarflexion. Shear wave speeds were also measured during voluntary plantarflexor contractions at a fixed ankle angle. Average shear wave speed increased significantly from 2.6 m/s to 5.6 m/s with passive dorsiflexion and the knee in an extended posture, but did not vary with dorsiflexion when the gastrocnemius was shortened in a flexed knee posture. During active contractions, shear wave speed monotonically varied with the net ankle moment generated, reaching 8.3 m/s in the maximally contracted condition. There was a linear correlation between shear wave speed and net ankle moment in both the active and passive conditions; however, the slope of this linear relationship was significantly steeper for the data collected during passive loading conditions. The results show that SWE is a promising approach for quantitatively assessing changes in mechanical muscle loading. However, the differential effect of active and passive loading on shear wave speed makes it important to carefully consider the relevant loading conditions in which to use SWE to characterize in vivo muscle properties. PMID:23719230

  16. Changes in P-wave velocity with different full waveform sonic transmitter centre frequency

    NASA Astrophysics Data System (ADS)

    Almalki, Majed; Harris, Brett; Dupuis, J. Christian

    2015-05-01

    Full waveform sonic logging, with the transmitter set at different centre frequencies, often provides different compressional wave velocities over the same interval. There may be several reasons why these velocity differences are recovered where the source has different frequency content. Examples include: intrinsic dispersion, scattering dispersion, geometric dispersion, processing artefacts and acquisition artefacts. We acquired and analysed multifrequency monopole full waveform sonic logging data from the cored drill hole intersecting a high-permeability sandy aquifer in the Northern Gnangara Mound, Perth Basin, Western Australia. A key interval of the shallow, sand-dominated Yarragadee Formation was selected and logged four times with transmitter centre frequencies set to 1, 3, 5 and 15 kHz. We compute apparent velocity dispersion as the percentage velocity differences in the P-wave velocity recovered from full waveform sonic logs completed at different dominant transmitter centre frequencies. We find that high-permeability sediments could be placed into broad groups: cross-bedded and non-cross-bedded sandstones. We find a distinctly different relationship between apparent P-wave velocity dispersion and permeability for cross-bedded and non-cross-bedded sandstones. Cross plots for the two sediment types show a general trend of increasing apparent dispersion with increasing permeability. Grouping the sandstone layers based on sediment type, as observed from core samples, illustrates different but positive correlation between the apparent P-wave velocity dispersion and permeability in these shallow, weakly-consolidated sandstones. The cross-bedded sandstone, for its part, has a wider range of permeability than the non-cross-bedded sandstone but a smaller range of apparent P-wave velocity dispersion. Given these results, our hypothesis is that while permeability plays a role, other factors such as geometric dispersion or scattering dispersion likely contribute the net value of P-wave dispersion recovered between any two receivers. Finally the results from these experiments have shown that there exists at least a weak empirical relationship between P-wave velocity dispersion and hydraulic permeability at the field site.

  17. 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.

  18. Determination of Longitudinal and Bulk Sound Velocities in Natural Uranium under Shock-wave Loading

    NASA Astrophysics Data System (ADS)

    Finyushin, Stanislav; Fedorov, Alexey; Mikhailov, Anatoliy; Nazarov, Dmitriy; Govorunova, Tatiana; Kalashnikov, Denis; Mikhailov, Evgeniy; Knyazev, Vadim

    2009-06-01

    We carried out the experiments on determination of longitudinal and bulk sound velocities in natural uranium in the range of pressures 40-72 GPa using laser interferometer Fabry-Perot. From the registered particle velocities profiles of contact boundary U-LiF the following parameters of elastic-plastic wave were defined: amplitude of elastic release wave 5.3-6.8 GPa, value of Poisson ratio 0.34-0.40, yield strength 0.96-1.36 GPa. It is shown, that influence of internal material structure is the cause of complex elastic-plastic behavior of natural uranium.

  19. Non-Gaussian properties of second-order wave orbital velocity

    E-print Network

    Alberello, Alberto; Gramstad, Odin; Babanin, Alexander V; Toffoli, Alessandro

    2015-01-01

    A stochastic second-order wave model is applied to assess the statistical properties of wave orbital velocity in random sea states below the water surface. Directional spreading effects as well as the dependency of the water depth are investigated by means of a Monte-Carlo approach. Unlike for the surface elevation, sub-harmonics dominate the second-order contribution to orbital velocity. We show that a notable set-down occurs for the most energetic and steepest groups. This engenders a negative skewness in the temporal evolution of the orbital velocity. A substantial deviation of the upper and lower tails of the probability density function from the Gaussian distribution is noticed, velocities are faster below the wave trough and slower below the wave crest when compared with linear theory predictions. Second-order nonlinearity effects strengthen with reducing the water depth, while weaken with the broadening of the wave spectrum. The results are confirmed by laboratory data. Corresponding experiments have b...

  20. 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.

  1. Site response, shallow shear-wave velocity, and wave propagation at the San Jose, California, dense seismic array

    USGS Publications Warehouse

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

    2003-01-01

    Ground-motion records from a 52-element dense seismic array near San Jose, California, are analyzed to obtain site response, shallow shear-wave velocity, and plane-wave propagation characteristics. The array, located on the eastern side of the Santa Clara Valley south of the San Francisco Bay, is sited over the Evergreen basin, a 7-km-deep depression with Miocene and younger deposits. Site response values below 4 Hz are up to a factor of 2 greater when larger, regional records are included in the analysis, due to strong surface-wave development within the Santa Clara Valley. The pattern of site amplification is the same, however, with local or regional events. Site amplification increases away from the eastern edge of the Santa Clara Valley, reaching a maximum over the western edge of the Evergreen basin, where the pre-Cenozoic basement shallows rapidly. Amplification then decreases further to the west. This pattern may be caused by lower shallow shear-wave velocities and thicker Quaternary deposits further from the edge of the Santa Clara Valley and generation/trapping of surface waves above the shallowing basement of the western Evergreen basin. Shear-wave velocities from the inversion of site response spectra based on smaller, local earthquakes compare well with those obtained independently from our seismic reflection/refraction measurements. Velocities from the inversion of site spectra that include larger, regional records do not compare well with these measurements. A mix of local and regional events, however, is appropriate for determination of site response to be used in seismic hazard evaluation, since large damaging events would excite both body and surface waves with a wide range in ray parameters. Frequency-wavenumber, plane-wave analysis is used to determine the backazimuth and apparent velocity of coherent phases at the array. Conventional, high-resolution, and multiple signal characterization f-k power spectra and stacked slowness power spectra are compared. These spectra show surface waves generated/ scattered at the edges of the Santa Clara Valley and possibly within the valley at the western edge of the Evergreen basin.

  2. Applications of stereoscopic particle image velocimetry: Dust acoustic waves and velocity space distribution functions

    SciTech Connect

    Thomas, Edward Jr.; Williams, Jeremiah

    2006-05-15

    Two-dimensional particle image velocimetry (2D-PIV) techniques have been applied to dusty plasmas for the past 5 years. During that time, 2D-PIV has been used to provide detailed measurements of microparticle transport in dusty plasmas. However, a measurement of the third velocity vector direction is necessary to fully understand the microparticle transport. In this paper, stereoscopic particle image velocimetry (stereo-PIV) is used as a technique for obtaining all three-velocity vector components. This paper discusses the application of stereo-PIV techniques to measurements of dust acoustic waves and velocity space distribution functions in dusty plasmas.

  3. Multipoint Vernier VISAR Interferometer System for Measuring Mass Velocity in Shock Wave Experiments

    NASA Astrophysics Data System (ADS)

    Gubskii, K. L.; Koshkin, D. S.; Mikhaylyuk, A. V.; Korolev, A. M.; Pirog, V. A.; Kuznetsov, A. P.

    The results of development of a laser interferometer designed to measure the mass velocity of condensed substances in shock wave experiments in the field of high energy density physics are presented. The developed laser system allows measurements of the velocity of free surfaces of samples in shockwave experiments with accuracy no worse than 10 m/s for the entire range of velocities attained experimentally. The time resolution of measurements is limited by the response speed of the used PMTs and amounts to 2.5 ns.

  4. Investigation of local rayleigh wave velocity dispersion due to surface residual stress

    SciTech Connect

    Martin, Richard W.; Reibel, Richard S.; Sathish, Shamachary; Blodgett, Mark P.

    2004-02-26

    Residual stress induced in materials by surface modification techniques creates a stress gradient very near the top surface. The modified layer can lead to dispersion of Rayleigh surface wave (RSW) velocity. An analysis of the dispersion of RSW is expected to provide a means for nondestructive evaluation of the stress gradient. Small changes in RSW velocity has been measured using an acoustic interferometer based on a three-element focused transducer. Dispersion results on Ti-6Al-4V material of RSW velocity and dispersion in shot-peened samples are presented.

  5. Note on cylindrical waves which propagate at the velocity of light

    SciTech Connect

    Kroll, N.M.

    1982-01-01

    The continuous linear acceleration of ultra relativistic particles in free space by an electromagnetic field requires the presence of a cylindrical wave component with phase velocity that differs negligibly from c and with non-vanishing electric field component in the direction of propagation. Lawson and Woodward have pointed out the fact that certain geometries proposed for laser driven acceleration fail to satisfy these requirements. On the other hand, complex wave number plane wave fields which do satisfy these requirements have been constructed by Palmer, who also points out that any cylindrical wave with the required properties can be formed from superposition of plane waves of the form which he has obtained. The situation is analogous to that which occurs in standard wave-guide theory. There it is also true that any waveguide mode can be constructed by superposition of plane waves. Nevertheless, the study of the general properties of cylindrical waves has proved to be a very powerful tool for the analysis of waveguides and similar structures. Because this may also prove to be the case for fields with propagation velocity c we present a brief study of their properties below.

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

    NASA Astrophysics Data System (ADS)

    Frost, Daniel A.; Rost, Sebastian

    2014-10-01

    The Large Low Shear Velocity Provinces (LLSVPs) in the lower mantle represent volumetrically significant thermal or chemical or thermo-chemical heterogeneities. Their structure and boundaries have been widely studied, mainly using S-waves, but much less is known about their signature in the P-wavefield. We use an extensive dataset recorded at USArray to create, for the first time, a high-resolution map of the location, shape, sharpness, and extent of the boundary of the Pacific LLSVP using P(Pdiff)-waves. We find that the northern edge of the Pacific LLSVP is shallow dipping (26° relative to the horizontal) and diffuse (?120 km wide transition zone) whereas the eastern edge is steeper dipping (70°) and apparently sharp (?40 km wide). We trace the LLSVP boundary up to ?500 km above the CMB in most areas, and 700 km between 120° and 90°W at the eastern extent of the boundary. Apparent P-wave velocity drops are ?1-3% relative to PREM, indicating a strong influence of LLSVPs on P-wave velocity, at least in the high-frequency wavefield, in contrast to previous studies. A localised patch with a greater velocity drop of ?15-25% is detected, defined by large magnitude gradients of the travel-time residuals. We identify this as a likely location of an Ultra-Low Velocity Zone (ULVZ), matching the location of a previously detected ULVZ in this area. The boundary of a separate low velocity anomaly, of a similar height to the LLSVP, is detected in the north-west Pacific, matching tomographic images. This outlier appears to be connected to the main LLSVP through a narrow channel close to the CMB and may be in the process of joining or splitting from the main LLSVP. We also see strong velocity increases in the lower mantle to the east of the LLSVP, likely detecting subducted material beneath central America. The LLSVP P-wave boundary is similar to that determined in high-resolution S-wave studies and follows the -0.4% ?VS iso-velocity contour in the S40RTS tomography model. Additionally, the LLSVP boundary roughly matches the shape of the -0.4% ?VP iso-velocity contour of the P-wave model GyPSuM but defines an area more similar to that defined by the 0.0% VP iso-velocity contour. High resolution P-wave velocity determination allows for estimation of the ratio of P- and S-wave velocity anomalies (RS,P) which can be used to indicate dominantly thermal or chemical control of seismic velocities. Although the RS,P is found here to be approximately 2.4, which is indicative of a thermo-chemical anomaly. However, this result contains a large amount of uncertainty and the implications for the origin of LLSVPs likely remain inconclusive. Nonetheless, other observations of the Pacific LLSVP are consistent with a thermo-chemical anomaly whose shape and boundary sharpness are controlled by proximity to active and past subduction.

  7. Prediction of Building Limestone Physical and Mechanical Properties by Means of Ultrasonic P-Wave Velocity

    PubMed Central

    Concu, Giovanna; De Nicolo, Barbara; Valdes, Monica

    2014-01-01

    The aim of this study was to evaluate ultrasonic P-wave velocity as a feature for predicting some physical and mechanical properties that describe the behavior of local building limestone. To this end, both ultrasonic testing and compressive tests were carried out on several limestone specimens and statistical correlation between ultrasonic velocity and density, compressive strength, and modulus of elasticity was studied. The effectiveness of ultrasonic velocity was evaluated by regression, with the aim of observing the coefficient of determination r2 between ultrasonic velocity and the aforementioned parameters, and the mathematical expressions of the correlations were found and discussed. The strong relations that were established between ultrasonic velocity and limestone properties indicate that these parameters can be reasonably estimated by means of this nondestructive parameter. This may be of great value in a preliminary phase of the diagnosis and inspection of stone masonry conditions, especially when the possibility of sampling material cores is reduced. PMID:24511286

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

    PubMed

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

    2009-12-01

    Defining the mantle structure that lies beneath hot spots is important for revealing their depth of origin. Three-dimensional images of shear-wave velocity beneath the Hawaiian Islands, obtained from a network of sea-floor and land seismometers, show an upper-mantle low-velocity anomaly that is elongated in the direction of the island chain and surrounded by a parabola-shaped high-velocity anomaly. Low velocities continue downward to the mantle transition zone between 410 and 660 kilometers depth, a result that is in agreement with prior observations of transition-zone thinning. The inclusion of SKS observations extends the resolution downward to a depth of 1500 kilometers and reveals a several-hundred-kilometer-wide region of low velocities beneath and southeast of Hawaii. These images suggest that the Hawaiian hot spot is the result of an upwelling high-temperature plume from the lower mantle. PMID:19965755

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

    USGS Publications Warehouse

    Villasenor, A.; Benz, H.M.; Filippi, L.; De Luca, G.; Scarpa, R.; Patane, G.; Vinciguerra, S.

    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 a band of steeply-dipping seismicity, suggesting a magmatic conduit that feeds the summit eruptions. The most prominent structure is an approximately 8-km-diameter high-velocity body located between 2 and 12 km depth below the southeast flank of the volcano. This high-velocity body is interpreted as a remnant mafic intrusion that is an important structural feature influencing both volcanism and east flank slope stability and faulting.

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

    SciTech Connect

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

    2001-09-09

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

  11. 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.

  12. 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.

  13. 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).

  14. 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.

  15. 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.

  16. Crust and upper mantle heterogeneities in the southwest Pacific from surface wave phase velocity analysis

    NASA Astrophysics Data System (ADS)

    Pillet, R.; Rouland, D.; Roult, G.; Wiens, D. A.

    1999-02-01

    Direct earthquake-to-station Rayleigh and Love wave data observed on high gain broadband records are analyzed in order to improve the lateral resolution of the uppermost mantle in the southwest Pacific region. We used data of nine permanent Geoscope and Iris stations located in the southern hemisphere and nine other stations as part of two temporary networks, the first one installed in New Caledonia and Vanuatu (hereafter named Cavascope network) by ORSTOM and the EOST from Louis Pasteur University in Strasbourg (France) and the second one installed in the Fiji, Tonga and Niue islands (hereafter named Spase network) by Washington University in St. Louis (USA). In order to collect more significant details on the surficial structures, we included the analysis of short period waves down to 8 s. A multiple frequency filtering technique has been used to recover phase velocities of Rayleigh and Love waves for selected earthquakes with magnitude greater than 5.5 and with known centroid moment tensor (CMT). About 1100 well-distributed seismograms have been processed in the period range 8-100 s and corrections for topography and water depth have been applied to the observed phase velocities. The geographical distribution of phase velocity anomalies have then been computed using the tomographic method developed by Montagner [Montagner, J.P., 1986a. Regional three-dimensional structures using long-period surface waves. Ann. Geophys. 4 (B3), 283-294]. Due to a poor knowledge of dense, well-distributed, crustal thickness values and corresponding velocity models, we did not perform or speculate on the construction of an S-wave 3D velocity model; therefore, we limited this study to the interpretation of the phase velocity distribution. The location of phase velocity anomalies are well determined and the deviations are discussed within the framework of the geological context and compared with other tomographic models. At long periods, from 40 s to 100 s, our results agree well with most of previous studies: the tomographic imaging shows a large contrast between low and high phase velocities along the Solomon, New Hebrides and Fiji-Tonga trenches. The lowest phase velocity anomalies are distributed beneath northern and southern Fiji basins and the Lau basin (corresponding to the volume situated just above the dipping slabs), whereas the highest values are displayed beneath the Pacific plate and the eastern part of Indian plate downgoing under the North Fiji basin. At shorter periods, our results show that the phase velocity distributions are well correlated with the large structural crustal domains. The use of local temporary broadband stations in the central part of the studied area gives us the opportunity to observe surface waves showing well-dispersed trains, allowing extended velocity measurements down to 8 s although aliasing due to multipaths become important. The continental regions (Eastern Australia, New Guinea, Fiji islands and New Zealand) show low velocities which are likely due to thick continental crust, whereas the Tasmanian, D'Entrecasteaux, and the Northern and Southern Fiji basins are characterized by higher velocities suggesting thinner oceanic crust. Additional analysis including the anisotropic case and S-wave velocity inversion with depth is in progress.

  17. Identification of Upper--Mantle Velocity and Anisotropy Structures Beneath the Archean Superior Province Using Surface Waves

    NASA Astrophysics Data System (ADS)

    Sol, S.; Thomson, C. J.; Kendall, J.; Snell, C.; White, D.

    2004-05-01

    The Canadian Archean Western Superior Province (WSP) is composed of a number of east--west trending subprovinces progressing in age from south to north. Lithoprobe's Western Superior Transect aimed to better understand the significance of such geological architecture for Archean tectonics and included a portable broadband teleseismic array to complement conventional crustal geophysical studies. This N--S array of 17 instruments traversed subprovince boundaries and involved two more stations further north in the Trans--Hudson orogen (THO). Body wave teleseismic tomography and shear--wave splitting analysis have suggested the existence of laterally--varying lithospheric--mantle structures that may be associated with frozen Archean oceanic lithosphere and a high degree of anisotropy. In order to acquire additional constraints on this interesting lower--lithospheric environment we have examined surface waves from high--magnitude teleseismic events in two stages: a standard dispersion analysis along two near--orthogonal paths and a Love and Rayleigh polarization study. The W--E path was examined by incorporating data from CNSN station ULM. Variations in 15--80s Rayleigh fundamental mode group and phase velocities for S--N propagation indicate that the linear profile is best treated in three segments reflecting changes in lithospheric structure. Corresponding shear--wavespeed models inferred from independent isotropic inversions of Love (20--70s) and Rayleigh fundamental phase velocity are broadly coherent with the coincident R/WAR model of Musacchio et al. (in press, JGR, 2004). Both studies indicate crustal thinning moving northward (from 45 to 39 km), faster velocities in the E--W direction and the presence of a thin anisotropic high--velocity layer just below the Moho. While this layer is detected along the E--W path and in the middle and northern parts of the N--S line, there is no surface--wave indication of it in the southern section. It has been interpreted as a relic of oceanic lithosphere accreted during the Kenoran orogeny. Anisotropy is suggested both by comparing the observed Rayleigh phase velocities along the orthogonal paths and by a Rayleigh/Love discrepancy in each of the N--S and E--W isotropic inversions. In fact, inspection of the Rayleigh/Love particle motions in various frequency bands for surface--waves arriving from various azimuths brings into question the assumptions in isotropic analysis. Indicators such as quasi--Love waves and Love elliptical particle motion are seen at most of the stations. Numerical modelling indicates that plausible uppermost--mantle anisotropy has the potential to explain such observatons, especially given the large SKS splitting along the main array. Interestingly, despite a null SKS splitting result at the far north THO station BPW, surface--wave polarizations there provide evidence of significant anisotropy. Overall, the surface--wave data reinforce other techniques suggesting significant lateral variations and anisotropy in the WSP, with the upper 200km of the lithosphere capable of accounting for most of the latter. A true areal array extending across the WSP can be expected to reveal major structures.

  18. Lithospheric shear wave velocity and radial anisotropy beneath the northern part of North China from surface wave dispersion analysis

    NASA Astrophysics Data System (ADS)

    Fu, Yuanyuan V.; Gao, Yuan; Li, Aibing; Shi, Yutao

    2015-09-01

    Rayleigh and Love wave phase velocities in the northern part of the North China are obtained from ambient noise tomography in the period range of 8-35 s and two plane wave earthquake tomography at periods of 20-91 s using data recorded at 222 broadband seismic stations from the temporary North China Seismic Array and permanent China Digital Seismic Array. The dispersion curves of Rayleigh and Love wave from 8 to 91 s are jointly inverted for the 3-D shear wave structure and radial anisotropy in the lithosphere to 140 km depth. Distinct seismic structures is observed from the Fenhe Graben and Taihang Mountain to the North China Basin. The North China Basin from the lower crust to the depth of 140 km is characterized by high-velocity anomaly, reflecting mafic intrusion and residual materials after the extraction of melt, and by strong radial anisotropy with Vsh > Vsv, implying horizontal layering of intrusion and alignment of minerals due to vigorous extensional deformation and subsequent thermal annealing. However, low-velocity anomaly and positive radial anisotropy are observed in the Fenhe Graben and Taihang Mountain, suggesting the presence of partial melt in the lithosphere due to the mantle upwelling and horizontal flow pull.

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

    E-print Network

    Merlino, Robert L.

    Electrostatic ion-cyclotron waves driven by parallel velocity shear R. L. Merlinoa) Department cyclotron frequency propagating at large angles to the ambient magnetic field can be excited in a magnetized in determining the stability of shear-driven electrostatic ion-cyclotron EIC modes is also considered

  20. 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

  1. 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.

  2. Increase of shear wave velocity before the 1998 eruption of Merapi volcano (Indonesia)

    E-print Network

    Snieder, Roel

    Increase of shear wave velocity before the 1998 eruption of Merapi volcano (Indonesia) U. Wegler,1 of the edifice of Merapi volcano (Java, Indonesia) before its eruption in 1998 by analyzing multiply scattered eruption of Merapi volcano (Indonesia), Geophys. Res. Lett., 33, L09303, doi:10.1029/2006GL025928. 1

  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. 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.

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

    USGS Publications Warehouse

    Ismail, A.; Anderson, N.

    2007-01-01

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

  6. 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.

  7. Crustal S-wave structure beneath Eastern Black Sea Region revealed by Rayleigh-wave group velocities

    NASA Astrophysics Data System (ADS)

    Ç?nar, Hakan; Alkan, Hamdi

    2016-01-01

    In this study, the crustal S-wave structure beneath the Eastern Black Sea Region (including the Eastern Black Sea Basin (EBSB) and Eastern Pontides (EP)) has been revealed using inversion of single-station, fundamental-mode Rayleigh-wave group velocities in the period range of 4-40 seconds. We used digital broadband recordings of 13 regional earthquakes that recently occurred in the easternmost EBSB recorded at stations of the Kandilli Observatory and Earthquake Research Institute (KOERI). The average group-velocity-dispersion curves were generated from 26 paths for the EBSB, and 16 paths for the EP, and they were inverted to determine the average 1-D shear-wave structure of the region. We have created a pseudo-section, roughly depicting the crustal structure of the region based on the group velocity inversion results of all station-earthquake paths. The thickness of the sedimentary layer reaches 12 km in the center of EBSB (Vs = 2.5-3.1 km/s) and decreases 4 km in the EP. There is a thin sedimentary layer in the EP (Vs = 2.7 km/s). A consolidated thin crust that exists in the EBSB possesses a high seismic velocity (Vs = 3.8 km/s). While a thin (?26 km) and transitional crust exists beneath the EBSB, a thick (about 42 km) continental crust exists beneath the EP where the Conrad is clearly seen at about a 24 km depth. Thick continental crust in the EP region is clearly distinguished from a gradational velocity change (Vs = 3.4-3.8 km/s). The Moho dips approximately southwards, and the Vs velocity (4.25-4.15 km/s) beneath the Moho discontinuity decreases from the EBSB to the EP in the N-S direction. This may be an indication of a southward subduction.

  8. 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.

  9. 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.

  10. Near-surface Scholte wave velocities at Ekofisk from short noise recordings by seismic noise gradiometry

    NASA Astrophysics Data System (ADS)

    Ridder, S. A. L.; Biondi, B. L.

    2015-09-01

    We propose a new approach for imaging the subsurface using a stochastic wavefield of interface waves present in the ambient seismic field. Unlike seismic interferometry, our technique does not rely on cross correlations to obtain the Green's function between two seismic receivers. Rather, it relies on the local measurements of phase velocity obtained directly from the ratio between second-order temporal and spatial derivatives of the wavefield. We process 10 min of ambient seismic noise recording made using a large and dense array installed over Ekofisk. We image a subsidence-induced geomechanical imprint on the Scholte wave phase velocities in the near surface. This resulting phase velocity pattern is verified by comparison to results from a seismic-noise cross-correlation tomography.

  11. Generation of electromagnetic waves in the very low frequency band by velocity gradient

    SciTech Connect

    Ganguli, G. Tejero, E.; Crabtree, C.; Amatucci, W.; Rudakov, L.

    2014-01-15

    It is shown that a magnetized plasma layer with a velocity gradient in the flow perpendicular to the ambient magnetic field is unstable to waves in the Very Low Frequency band that spans the ion and electron gyrofrequencies. The waves are formally electromagnetic. However, depending on wave vector k{sup ¯}=kc/?{sub pe} (normalized by the electron skin depth) and the obliqueness, k{sub ?}/k{sub ||}, where k{sub ?,||} are wave vectors perpendicular and parallel to the magnetic field, the waves are closer to electrostatic in nature when k{sup ¯}?1 and k{sub ?}?k{sub ||} and electromagnetic otherwise. Inhomogeneous transverse flows are generated in plasma that contains a static electric field perpendicular to the magnetic field, a configuration that may naturally arise in the boundary layer between plasmas of different characteristics.

  12. A statistical study of fundamental toroidal mode standing Alfvén waves using THEMIS ion bulk velocity data

    NASA Astrophysics Data System (ADS)

    Takahashi, Kazue; Hartinger, Michael D.; Angelopoulos, Vassilis; Glassmeier, Karl-Heinz

    2015-08-01

    We have studied the statistical properties of toroidal mode standing Alfvén waves with a fundamental eigenmode structure along the field line, denoted T1 waves, in the L range 7-12, using THEMIS-D data for 2008-2013. T1 wave events were identified in hourly data segments using an automated procedure that detects narrowband oscillations in the azimuthal component of the ion bulk velocity. For each event we determined the frequency, amplitude, ellipticity, and the orientation angle of the polarization ellipse, and we examined the L and magnetic local time dependence of the detection rate and physical properties of the T1 waves. Confirming previous observations in space and on the ground, we found a pronounced dawn-dusk asymmetry in the wave detection rate and amplitude. The detection rate in the dawn sector is approximately twice as high as that in the dusk sector, and the amplitude in the dawn sector is larger by ˜50%. The same asymmetry is also evident in the velocity amplitude averaged in the fixed Pc5 band (1.7-6.7 mHz) and in the amplitude of the electric field and field line displacement that are derived from the velocity amplitude. The ellipticity and the orientation angle of the polarization ellipse are organized by local time, in accordance with the theoretical prediction of toroidal mode waves excited by field line resonance with tailward propagating waves in the magnetosphere, which are in turn driven by external sources. Although infrequently, T1 waves are also detected in the midnight sector, suggesting magnetotail sources for this subset of events.

  13. Viscoacoustic wave form inversion of transmission data for velocity and attenuation

    SciTech Connect

    Watanabe, Toshiki; Nihei, Kurt T.; Nakagawa, Seiji; Myer, Larry R.

    2003-12-01

    This study investigates the performance of a frequency domain viscoacoustic full wave form nonlinear inversion to obtain high resolution images of velocity and attenuation. An efficient frequency domain implementation is applied that consists of performing a series of single frequency inversions sweeping from low to high frequency. A cascaded inversion was adopted in which the real part of the velocity is first imaged using the phase information, then the quality factor (Q) is imaged using the amplitude information. Tests with synthetic data indicate that our approach yielded better images than the simultaneous determination of the real and imaginary parts of the complex velocity. The method is applied to laboratory data obtained in a water tank with suspended acrylic bars. Broadband 200 kHz data are obtained for a crosshole configuration with a computer-controlled scanning system and piezofilm source and detector. The velocity image produced by the full wave form inversion is compared to a curved ray travel time tomography velocity image, and was observed to possess higher resolution and more precise locations of the acrylic bars. The Q image shows a lower resolution than the velocity image, but recovers the correct Q for acrylic. This method can be applied for geophysical applications targeted to soil, unconsolidated rocks, and marine sediments and also nondestructive evaluation and medical applications.

  14. Second sound shock waves and critical velocities in liquid helium 2. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Turner, T. N.

    1979-01-01

    Large amplitude second-sound shock waves were generated and the experimental results compared to the theory of nonlinear second-sound. The structure and thickness of second-sound shock fronts are calculated and compared to experimental data. Theoretically it is shown that at T = 1.88 K, where the nonlinear wave steepening vanishes, the thickness of a very weak shock must diverge. In a region near this temperature, a finite-amplitude shock pulse evolves into an unusual double-shock configuration consisting of a front steepened, temperature raising shock followed by a temperature lowering shock. Double-shocks are experimentally verified. It is experimentally shown that very large second-sound shock waves initiate a breakdown in the superfluidity of helium 2, which is dramatically displayed as a limit to the maximum attainable shock strength. The value of the maximum shock-induced relative velocity represents a significant lower bound to the intrinsic critical velocity of helium 2.

  15. Condition Assessment of PC Tendon Duct Filling by Elastic Wave Velocity Mapping

    PubMed Central

    Liu, Kit Fook; Mehrabi, Nima; Yoshikazu, Kobayashi; Shiotani, Tomoki

    2014-01-01

    Imaging techniques are high in demand for modern nondestructive evaluation of large-scale concrete structures. The travel-time tomography (TTT) technique, which is based on the principle of mapping the change of propagation velocity of transient elastic waves in a measured object, has found increasing application for assessing in situ concrete structures. The primary aim of this technique is to detect defects that exist in a structure. The TTT technique can offer an effective means for assessing tendon duct filling of prestressed concrete (PC) elements. This study is aimed at clarifying some of the issues pertaining to the reliability of the technique for this purpose, such as sensor arrangement, model, meshing, type of tendon sheath, thickness of sheath, and material type as well as the scale of inhomogeneity. The work involved 2D simulations of wave motions, signal processing to extract travel time of waves, and tomography reconstruction computation for velocity mapping of defect in tendon duct. PMID:24737961

  16. 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.

  17. 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.

  18. 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.

  19. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  1. 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.

  2. Plane-wave diffraction at the periodically corrugated boundary of vacuum and a negative-phase-velocity material.

    PubMed

    Depine, Ricardo A; Lakhtakia, Akhlesh

    2004-05-01

    Considering the diffraction of a plane wave by a periodically corrugated half-space, we show that the transformation of the refracting medium from positive (negative) phase velocity to negative (positive) phase velocity type has an influence on the diffraction efficiencies. This effect increases with increasing corrugation depth, owing to the presence of evanescent waves in the troughs of the corrugated interface. PMID:15244981

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

    E-print Network

    Kawakatsu, Hitoshi

    Three-dimensional crustal S wave velocity structure in Japan using microseismic data recorded by Hi seismic noise. We applied this method to the recording of Hi-net tiltmeters in Japan at 679 stations from), Three-dimensional crustal S wave velocity structure in Japan using microseismic data recorded by Hi

  4. Magnetic antenna excitation of whistler modes. III. Group and phase velocities of wave packets

    NASA Astrophysics Data System (ADS)

    Urrutia, J. M.; Stenzel, R. L.

    2015-07-01

    The properties of whistler modes excited by single and multiple magnetic loop antennas have been investigated in a large laboratory plasma. A single loop excites a wavepacket, but an array of loops across the ambient magnetic field B0 excites approximate plane whistler modes. The single loop data are measured. The array patterns are obtained by linear superposition of experimental data shifted in space and time, which is valid in a uniform plasma and magnetic field for small amplitude waves. Phasing the array changes the angle of wave propagation. The antennas are excited by an rf tone burst whose propagating envelope and oscillations yield group and phase velocities. A single loop antenna with dipole moment across B0 excites wave packets whose topology resembles m = 1 helicon modes, but without radial boundaries. The phase surfaces are conical with propagation characteristics of Gendrin modes. The cones form near the antenna with comparable parallel and perpendicular phase velocities. A physical model for the wave excitation is given. When a wave burst is applied to a phased antenna array, the wave front propagates both along the array and into the plasma forming a "whistler wing" at the front. These laboratory observations may be relevant for excitation and detection of whistler modes in space plasmas.

  5. A physical model study of converted wave amplitude variation in a reservoir of systematically aligned vertical fractures

    NASA Astrophysics Data System (ADS)

    Chang, C.; Sun, L.; Lin, C.; Chang, Y.; Tseng, P.

    2013-12-01

    The existence of fractures not only provides spaces for the residence of oils and gases reside, but it also creates pathways for migration. Characterizing a fractured reservoir thus becomes an important subject and has been widely studied by exploration geophysicists and drilling engineers. In seismic anisotropy, a reservoir of systematically aligned vertical fractures (SAVF) is often treated as a transversely isotropic medium (TIM) with a horizontal axis of symmetry (HTI). Subjecting to HTI, physical properties vary in azimuth. P-wave reflection amplitude, which is susceptible to vary in azimuth, is one of the most popular seismic attributes which is widely used to delineate the fracture strike of an SAVF reservoir. Instead of going further on analyzing P-wave signatures, in this study, we focused on evaluating the feasibility of orienting the fracture strike of an SAVF reservoir using converted (C-) wave amplitude. For a C-wave is initiated by a downward traveling P-wave that is converted on reflection to an upcoming S-wave; the behaviors of both P- and S-waves should be theoretically woven in a C-wave. In our laboratory work, finite offset reflection experiments were carried out on the azimuthal plane of a HTI model at two different offset intervals. To demonstrate the azimuthal variation of C-wave amplitude in a HTI model, reflections were acquired along the principal symmetry directions and the diagonal direction of the HTI model. Inheriting from phenomenon of S-wave splitting in a transversely isotropic medium (TIM), P-waves get converted into both the fast (S1) and slow (S2) shear modes at all azimuths outside the vertical symmetry planes, thus producing split PS-waves (PS1 and PS2). In our laboratory data, the converted PS1- (C1-) wave were observed and identified. As the azimuth varies from the strike direction to the strike normal, C1-wave amplitude exhibits itself in a way of weakening and can be view from the common-reflection-point (CRP) gathers. Therefore, in conjunction with the azimuthal velocity and the amplitude variations in the P-wave and the azimuthal polarization of the S-wave, the azimuthal variation of C-wave amplitude which is experimentally demonstrated could be considered as a valuable seismic attribute in orienting the fracture strike of a SAVF reservoir. (Key words: converted wave, transversely isotropic medium, physical modeling, amplitude, fracture)

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

    PubMed Central

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

    2011-01-01

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

  7. Seismic wave velocity of rocks in the Oman ophiolite: constraints for petrological structure of oceanic crust

    NASA Astrophysics Data System (ADS)

    Saito, S.; Ishikawa, M.; Shibata, S.; Akizuki, R.; Arima, M.; Tatsumi, Y.; Arai, S.

    2010-12-01

    Evaluation of rock velocities and comparison with velocity profiles defined by seismic refraction experiments are a crucial approach for understanding the petrological structure of the crust. In this study, we calculated the seismic wave velocities of various types of rocks from the Oman ophiolite in order to constrain a petrological structure of the oceanic crust. Christensen & Smewing (1981, JGR) have reported experimental elastic velocities of rocks from the Oman ophiolite under oceanic crust-mantle conditions (6-430 MPa). However, in their relatively low-pressure experiments, internal pore-spaces might affect the velocity and resulted in lower values than the intrinsic velocity of sample. In this study we calculated the velocities of samples based on their modal proportions and chemical compositions of mineral constituents. Our calculated velocities represent the ‘pore-space-free’ intrinsic velocities of the sample. We calculated seismic velocities of rocks from the Oman ophiolite including pillow lavas, dolerites, plagiogranites, gabbros and peridotites at high-pressure-temperature conditions with an Excel macro (Hacker & Avers 2004, G-cubed). The minerals used for calculations for pillow lavas, dolerites and plagiogranites were Qtz, Pl, Prh, Pmp, Chl, Ep, Act, Hbl, Cpx and Mag. Pl, Hbl, Cpx, Opx and Ol were used for the calculations for gabbros and peridotites. Assuming thermal gradient of 20° C/km and pressure gradient of 25 MPa/km, the velocities were calculated in the ranges from the atmospheric pressure (0° C) to 200 MPa (160° C). The calculation yielded P-wave velocities (Vp) of 6.5-6.7 km/s for the pillow lavas, 6.6-6.8 km/s for the dolerites, 6.1-6.3 km/s for the plagiogranites, 6.9-7.5 km/s for the gabbros and 8.1-8.2 km/s for the peridotites. On the other hand, experimental results reported by Christensen & Smewing (1981, JGR) were 4.5-5.9 km/s for the pillow lavas, 5.5-6.3 km/s for the dolerites, 6.1-6.3 km/s for the plagiogranites, 6.5-7.7 km/s for the gabbros and 6.3-7.9 km/s for the peridotites. Although the two results are broadly comparable to each other for plagiogranites and gabbros, the calculated velocities are considerably higher than the experimental ones for pillow lavas, dolerites and peridotites. The discrepancy for the pillow lavas and dolerites can be attributed to the presence of pore-spaces in the experimental samples. On the other hand, serpentinization of peridotite samples likely resulted in lower velocities in experiments than in calculation. We compared our results with Vp structure of the oceanic crust and mantle (White et al. 1992, JGR). The calculated Vp of peridotites and gabbros are comparable to those of mantle and layer-3, respectively. The calculated Vp of dolerites is comparable to layer-3 and considerably higher than layer-2 velocities. However, recent deep drilling results (Holes 504B and 1256D) indicate the seismic layer-2 of oceanic crust mainly composed of dolerites, which is consistent with the experimental P-wave velocities of dolerites (Christensen & Smewing, 1981, JGR). These results imply that the velocity structure of seismic layer-2 reflects the distribution of pore-spaces in the upper oceanic crust.

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

    NASA Astrophysics Data System (ADS)

    Danesi, S.; Morelli, A.

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

  9. An anisotropic shear velocity model of the Earth's mantle using normal modes, body waves, surface waves and long-period waveforms

    NASA Astrophysics Data System (ADS)

    Moulik, P.; Ekström, G.

    2014-12-01

    We use normal-mode splitting functions in addition to surface wave phase anomalies, body wave traveltimes and long-period waveforms to construct a 3-D model of anisotropic shear wave velocity in the Earth's mantle. Our modelling approach inverts for mantle velocity and anisotropy as well as transition-zone discontinuity topographies, and incorporates new crustal corrections for the splitting functions that are consistent with the non-linear corrections we employ for the waveforms. Our preferred anisotropic model, S362ANI+M, is an update to the earlier model S362ANI, which did not include normal-mode splitting functions in its derivation. The new model has stronger isotropic velocity anomalies in the transition zone and slightly smaller anomalies in the lowermost mantle, as compared with S362ANI. The differences in the mid- to lowermost mantle are primarily restricted to features in the Southern Hemisphere. We compare the isotropic part of S362ANI+M with other recent global tomographic models and show that the level of agreement is higher now than in the earlier generation of models, especially in the transition zone and the lower mantle. The anisotropic part of S362ANI+M is restricted to the upper 300 km in the mantle and is similar to S362ANI. When radial anisotropy is allowed throughout the mantle, large-scale anisotropic patterns are observed in the lowermost mantle with vSV > vSH beneath Africa and South Pacific and vSH > vSV beneath several circum-Pacific regions. The transition zone exhibits localized anisotropic anomalies of ˜3 per cent vSH > vSV beneath North America and the Northwest Pacific and ˜2 per cent vSV > vSH beneath South America. However, small improvements in fits to the data on adding anisotropy at depth leave the question open on whether large-scale radial anisotropy is required in the transition zone and in the lower mantle. We demonstrate the potential of mode-splitting data in reducing the trade-offs between isotropic velocity and anisotropy in the lowermost mantle for the even-degree variations. Spurious anisotropic variations in the mid-mantle are also suppressed with the addition of mode-splitting data.

  10. Daily variation of the fractal dimension of the velocity components in the turbulent surface layer

    NASA Astrophysics Data System (ADS)

    Tijera, M.; Maqueda, G.; Yagüe, C.; Cano, J. L.

    2012-04-01

    The turbulence is a dominant property within the Planetary Boundary Layer (PBL). It is the main characteristic of the mixing in the lower atmosphere since the atmospheric turbulent fluxes are more efficient than the molecular diffusion. Turbulence can be observed in time series of meteorological variables (wind velocity for example). The sampling rate of observation in that time series has to be high in order to detect the turbulent regime. The analysis of these series presents a self-similarity structure, so the wind velocity can be considered as a fractal magnitude. This work shows a study of the fractal dimension of the wind perturbation series u'and w'components of the wind speed. Fractal dimension of velocity components can be related to others turbulent characteristics of the fluxes close to the ground. Fluctuation of longitudinal and, specially, vertical components depend on stability and, therefore, on the solar cycle. In consequence, the behaviour of fractal dimension should be in agreement with that cycle also. These series have been obtained once it has carried out the necessary transformation to get the mean wind series in short intervals, namely 5 minutes, to ensure the consistent properties of turbulence. The original records available were taken every thirty minutes by sonic anemometers (20 Hz sampling rate) during a week of a field campaign. The data analysed was recorded in the experimental campaign SABLES-98 at the Research Centre for the Lower Atmosphere (CIBA), located in Valladolid province (Spain). It has been calculated the fractal dimension (Komolgorov capacity or box- counting dimension) of the time series of fluctuations of the velocity component along of the mean wind direction and the vertical component (u' = u-U, w' = w -W), both in the physical spaces (velocity-time). It has been studied the time evolution of the fractal dimension during several days and at three levels above the ground (5.8 m, 13.5 m, 32 m). The fractal dimension of theu' and w' components of wind velocity series have been studied, as well as the influence of different turbulent parameters depending on daily cycle: turbulent kinetic energy, friction velocity, difference of temperature between the extreme of the layer studied close of the surface (?T50-0.22m),etc. It has been observed that there is a possible correlation between the fractal dimension and some of these turbulent parameters. Finally, it has been analysed the variation of the fractal dimension versus stability obtained from the Richardson number along of the day.

  11. Effect of phase transitions on compressional-wave velocities in the Earth's mantle.

    PubMed

    Li, Li; Weidner, Donald J

    2008-08-21

    The velocities of seismic waves in the Earth are governed by the response of the constituent mineral assemblage to perturbations in pressure and stress. The effective bulk modulus is significantly lowered if the pressure of the seismic wave drives a volume-reducing phase transformation. A comparison between the amount of time required by phase transitions to reach equilibrium and the sampling period thus becomes crucial in defining the softening and attenuation of compressional waves within such a two-phase zone. These phenomena are difficult to assess experimentally, however, because data at conditions appropriate to the Earth's deep interior are required. Here we present synchrotron-based experimental data that demonstrate softening of the bulk modulus within the two-phase loop of olivine-ringwoodite on a timescale of 100 s. If the amplitude of the pressure perturbation and the grain size are scaled to those expected in the Earth, the compressional-wave velocities within the discontinuities at 410, 520 and, possibly, 660 km are likely to be significantly lower than otherwise expected. The generalization of these observations to aluminium-controlled phase transitions raises the possibility of large velocity perturbations throughout the upper 1,000 km of the mantle. PMID:18719587

  12. In vivo noninvasive method for measuring local wave velocity in femoral arteries of pig

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoming; Kinnick, Randall; Pislaru, Cristina; Fatemi, Mostafa; Greenleaf, James

    2005-09-01

    We have proposed generating a bending wave in the arterial wall using ultrasound radiation force and measuring the wave velocity along the arterial wall [Zhang et al., IEEE Trans. Ultrason. Ferroelectr. Freq. Control 52, 642-652 (2005)]. Here, we report the results of in vivo studies on pigs. The pig was anesthetized, and a micromanometer tip catheter was inserted into the femoral artery to measure luminal pressure. A water bath was created on the animal's groin to allow unimpeded access of the ultrasound beams to the femoral artery. The femoral artery was first located using a 13-MHz linear-array transducer. Then, a vibro-acoustography image was obtained to ensure precise positioning of the excitation force relative to the artery. The artery was excited by the force transducer and the resulting vibration of the arterial wall was measured by a sensing Doppler transceiver. Measured wave velocity was 3.1 m/s at 300 Hz. With this new method wave velocity over a distance of 5 mm, and therefore stiffness of arteries, can be measured locally and non-invasively. Measurement time is short in a few tens of milliseconds, which allows pressure dependence and pharmacological effect on the wall properties to be measured at different cardiac times.

  13. Velocity structure and variations in the region of quiet solar filaments

    NASA Astrophysics Data System (ADS)

    Mashnich, G. P.; Bashkirtsev, V. S.; Khlystova, A. I.

    2009-04-01

    We study the velocity fields in the region of quiet solar filaments using spectral observations at the Sayan Solar Observatory (ISTP, Irkutsk). Once the series of spectral images have been processed, maps of the two-dimensional distribution of the velocity and its variations in the chromosphere (in the H ? ? = 486.13 nm line) and the photosphere (in the Fe I ? = 486.37 nm line) are constructed. The motions in the filaments have been found to consist of steady and periodic components. Our analysis of the spatial distributions of various oscillation modes shows that the short-period (<10 min) oscillations propagate mainly vertically and are observed at the filament edges, on scales of several arcseconds. The quasi-hour (>40 min) oscillations propagate mostly along the filament at a small angle to its axis. The intensity in the H ? core in individual fragments of some filaments varies with a period of about one hour. The observed velocity structures in the filaments and the imbalance of steady motions on the opposite sides of the filaments can be explained in terms of the model of a twisted fine-structure magnetic flux tube.

  14. Focused terahertz waves generated by a phase velocity gradient in a parallel-plate waveguide.

    PubMed

    McKinney, Robert W; Monnai, Yasuaki; Mendis, Rajind; Mittleman, Daniel

    2015-10-19

    We demonstrate the focusing of a free-space THz beam emerging from a leaky parallel-plate waveguide (PPWG). Focusing is accomplished by grading the launch angle of the leaky wave using a PPWG with gradient plate separation. Inside the PPWG, the phase velocity of the guided TE1 mode exceeds the vacuum light speed, allowing the wave to leak into free space from a slit cut along the top plate. Since the leaky wave angle changes as the plate separation decreases, the beam divergence can be controlled by grading the plate separation along the propagation axis. We experimentally demonstrate focusing of the leaky wave at a selected location at frequencies of 100 GHz and 170 GHz, and compare our measurements with numerical simulations. The proposed concept can be valuable for implementing a flat and wide-aperture beam-former for THz communications systems. PMID:26480453

  15. wave velocity group velocity

    E-print Network

    Walker, D. Greg

    Time scales device size phonon mean free path Length scales ion track gate drainsource Transverse Engineering 1.1eV per pair 1.4eV kinetic 2.2eV phonon Ionization energy symmetry/insulated boundary ion track thermalized boundary · · · · Partitioning of phonon energy to electronic energy is comparable Localized phonon

  16. 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.

  17. Long-term variations in solar wind velocity and radiation belt electrons

    NASA Astrophysics Data System (ADS)

    Reeves, Geoff; Morley, Steve; Cunningham, Greg

    2013-03-01

    In this paper we analyze the relationship between yearly variations in MeV radiation belt electron fluxes and solar wind velocity (Vsw). We find that the long-term trends have properties that are important for physical understanding of solar wind-magnetosphere coupling processes and, potentially, for improvements of short-term space weather forecasts. A statistical analysis of solar wind velocity shows that years with high average solar wind velocity are not high simply due to a larger number of days with high Vsw. Rather the entire distribution (median and percentiles) shifts along with the mean Vsw. Similar behavior is seen in the MeV geosynchronous electron fluxes. By subtracting out a 365 day running average baseline, we show that the distribution of log fluxes around the mean is remarkably stable from year to year within a solar cycle and from one solar cycle to another. In contrast, the long-term trends in the baseline show significant changes from year to year and from one solar cycle to another suggesting that solar wind coupling to radiation belt fluxes is not constant but varies over long, as well as short, time scales. In some epicycles, the mean flux is strongly dependent on Vsw while in others the dependence is weak. Similarly, a given average Vsw may produce high average fluxes in one epicycle and low average fluxes in another. Future study of these epicycles and the relative variations within them may improve both physical understanding of solar wind-magnetosphere coupling and space weather forecasting.

  18. Velocity of an electric-field-induced synclinic solitary wave invading the anticlinic liquid crystal phase.

    PubMed

    Bhatt, N S; Zhang, S; Keast, S S; Neubert, M E; Rosenblatt, C

    2001-06-01

    The electric-field dependence of the velocity of synclinic fingers invading the anticlinic phase is determined by a time-of-flight technique. The time delay for a rapid increase in the transmitted optical intensity through the sample is measured between two points as a function of their separation along the trajectory of the solitary wave. The data are quantitatively consistent with the rapid velocities deduced from a previous measurement [Liq. Cryst. 27, 249 (2000)], demonstrating that the previous data were not affected by multiple nucleation sites occurring at higher fields. PMID:11415154

  19. Observation of low shear-wave velocity at the base of the polar ice sheets: evidence for enhanced anisotropy

    NASA Astrophysics Data System (ADS)

    Farra, Véronique; Wittlinger, Gérard

    2013-04-01

    The subglacial structure of the arctic and antarctic continents remains widely unknown because of the presence of the thick ice caps. Geological direct investigations are almost impossible and seismological studies of the structure underneath are open to misinterpretations because of the strong reverberations of the seismic waves inside the ice layer. Knowing the thickness and the elastic parameters of the ice layer is important in order to analyze properly the seismic data in studies of the deeper crust structure. Here we analyse seismic data from the broadband stations located on the Antarctic and Greenland ice sheets in order to determine the large-scale seismic parameters of the polar ice sheets. The P-to-S converted waves at the ice/rock interface and inside the ice sheets and their multiples (the P-receiver functions) are used to estimate the in-situ P-velocity Vp and the P-to-S velocity ratio Vp/Vs of the polar ice. The thickness of the whole ice layer is precisely known either from Radio Echo Soundings or from ice core drillings allowing thus an accurate determination of Vp and Vp/Vs. At some places in and near the Wilkes Basin, a sedimentary layer is probably squeezed between the ice and the bedrock. We find that the polar ice caps have a two-layer structure, the upper layer of variable thickness about 2/3 of the total thickness with velocities very close to the ice standard values and the lower layer preserving a standard Vp but with about 25% smaller shear-wave velocity and a more or less constant thickness. The shear-velocity drop in the lower layer may be the evidence of a strong anisotropy induced by preferred orientation of ice crystals and by fine layering of soft and hard ice layers. Enhanced water content may also play a significant role. A large variation of ice viscosity with depth is therefore expected and heterogeneous flowing of the polar ice sheet. This heterogeneous flowing may invalidate the use at great depth of the ice dating models based on monotonic layer thinning.

  20. 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.

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

    E-print Network

    Zeng, Chong

    2011-05-18

    gentle topography changes with insignificant errors. Finally, many near-surface features with strong lateral heterogeneity such as dipping interfaces, faults, and tunnels can be imaged by the waveform inversion of Rayleigh waves for shallow S...

  2. 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.

  3. 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.

  4. 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.

  5. Flute mode waves near the lower hybrid frequency excited by ion rings in velocity space

    NASA Technical Reports Server (NTRS)

    Cattell, C.; Hudson, M.

    1982-01-01

    Discrete emissions at the lower hybrid frequency are often seen on the S3-3 satellite. Simultaneous observation of perpendicularly heated ions suggests that these ions may provide the free energy necessary to drive the instability. Studies of the dispersion relation for flute modes excited by warm ion rings in velocity space show that waves are excited with real frequencies near the lower hybrid frequency and with growth rates ranging from about 0.01 to 1 times the ion cyclotron frequency. Numerical results are therefore consistent with the possibility that the observed ions are the free energy source for the observed waves.

  6. DETERMINATION OF ELASTIC WAVE VELOCITY AND RELATIVE HYPOCENTER LOCATIONS USING REFRACTED WAVES. I. METHODOLOGY.

    USGS Publications Warehouse

    Shedlock, Kaye M.; Roecker, Steven W.

    1985-01-01

    An arrival time difference method utilizing refracted arrivals from earthquakes in a homogeneous, layered earth model has been developed for the simultaneous determination of near-source (in situ) velocity and relative locations of earthquakes. The method is particularly applicable when analyzig data from arrays in which most of the recording stations are far (i. e. , several focal depths) from a group of events. This iterative scheme locates earthquakes relative to a master event and performs an inversion for in situ velocity using a generalized inverse-least squares estimation procedure.

  7. Dispersion curves of shear horizontal wave surface velocities in multilayer piezoelectric systems

    NASA Astrophysics Data System (ADS)

    Calás, H.; Rodriguez-Ramos, R.; Otero, J. A.; Leija, L.; Ramos, A.; Monsivais, G.

    2010-02-01

    A precise knowledge of the frequency responses, velocity dispersion, and distinct vibration modes in multilayer piezoelectric structures would permit the optimization of new designs for electromechanical sensor, actuator, and surface acoustic wave (SAW) filter devices under broad and narrow band conditions. In this paper, the singular-value decomposition technique, combined with the global matrix method and scaling procedure, are applied for studying the solutions of shear stationary waves in symmetric multilayer composite piezoelectric systems. This approach eliminates numerical instabilities sometimes appearing in the analysis of this type of piezoelectric systems, by using a multiple scaling strategy in the global matrix processing. The dispersion curves of the surface velocities, obtained by application of the proposed approach, have shown the presence of clearly separated odd and even bands in such a type of piezoelectric devices, which is explained by considering the eigenstates of the system. Details of this bands pattern are calculated and analyzed.

  8. The velocity of the arterial pulse wave: a viscous-fluid shock wave in an elastic tube

    PubMed Central

    Painter, Page R

    2008-01-01

    Background The arterial pulse is a viscous-fluid shock wave that is initiated by blood ejected from the heart. This wave travels away from the heart at a speed termed the pulse wave velocity (PWV). The PWV increases during the course of a number of diseases, and this increase is often attributed to arterial stiffness. As the pulse wave approaches a point in an artery, the pressure rises as does the pressure gradient. This pressure gradient increases the rate of blood flow ahead of the wave. The rate of blood flow ahead of the wave decreases with distance because the pressure gradient also decreases with distance ahead of the wave. Consequently, the amount of blood per unit length in a segment of an artery increases ahead of the wave, and this increase stretches the wall of the artery. As a result, the tension in the wall increases, and this results in an increase in the pressure of blood in the artery. Methods An expression for the PWV is derived from an equation describing the flow-pressure coupling (FPC) for a pulse wave in an incompressible, viscous fluid in an elastic tube. The initial increase in force of the fluid in the tube is described by an increasing exponential function of time. The relationship between force gradient and fluid flow is approximated by an expression known to hold for a rigid tube. Results For large arteries, the PWV derived by this method agrees with the Korteweg-Moens equation for the PWV in a non-viscous fluid. For small arteries, the PWV is approximately proportional to the Korteweg-Moens velocity divided by the radius of the artery. The PWV in small arteries is also predicted to increase when the specific rate of increase in pressure as a function of time decreases. This rate decreases with increasing myocardial ischemia, suggesting an explanation for the observation that an increase in the PWV is a predictor of future myocardial infarction. The derivation of the equation for the PWV that has been used for more than fifty years is analyzed and shown to yield predictions that do not appear to be correct. Conclusion Contrary to the theory used for more than fifty years to predict the PWV, it speeds up as arteries become smaller and smaller. Furthermore, an increase in the PWV in some cases may be due to decreasing force of myocardial contraction rather than arterial stiffness. PMID:18664288

  9. Race, Psychosocial Factors, and Aortic Pulse Wave Velocity: The Health, Aging, and Body Composition Study

    PubMed Central

    Sutton-Tyrrell, Kim; Penninx, Brenda W.; Vogelzangs, Nicole; Harris, Tamara B.; Vaidean, Georgeta D.; Ayonayon, Hilsa N.; Kim, Lauren; Lakatta, Edward G.; Newman, Anne B.

    2010-01-01

    Background. Increasingly, researchers have begun to explore pathways through which psychosocial factors might influence cardiovascular disease, with some emphasis on early markers. The current study examined the cross-sectional association between psychosocial factors and aortic pulse wave velocity (an early marker of cardiovascular disease) in a biracial cohort of older adults. We were particularly interested in determining whether the association between psychosocial factors and aortic pulse wave velocity differed for older blacks compared with whites. Methods. Participants were 2,488 (40% black and 52% female) older adults from the Health, Aging, and Body Composition Study. Carotid–femoral aortic pulse wave velocity was assessed using standard methodologies. Depressive symptoms, anxiety symptoms, negative life events, and inadequate emotional support were assessed, and a summary psychosocial risk index was created. Results. In multivariable linear regression models, psychosocial risk was not associated with aortic pulse wave velocity (Estimate [Est] = .00, p = .83), but there was a significant Race × Psychosocial risk interaction (Est = .07, p = .01), after adjusting for age, race, sex, and education. Further analyses revealed that this association was driven by the inadequate emotional support component of psychosocial risk (Race × Inadequate emotional support, p = .005). In race-stratified analyses, inadequate emotional support was associated with higher levels of arterial stiffness in older blacks (Est = .05, p = .04) but not whites (Est = ?.04, p = .13). This association persisted after adjusting for demographics, cardiovascular risk factors, and social network characteristics. Conclusions. Findings suggest that older blacks may be particularly vulnerable to the effects of inadequate emotional support on vascular health. Interventions aimed at increasing social support among this population might be beneficial in reducing cardiovascular disease risk. PMID:20522528

  10. Piezooptic Coefficients and Acoustic Wave Velocities in Sn2P2S6 Crystals

    E-print Network

    O. Mys; I. Martynyuk-Lototska; A. Grabar; Yu. Vysochanskii; R. Vlokh

    2007-06-28

    Piezooptic coefficients of Sn2P2S6 crystals are experimentally determined for l=623.8 nm and T=293 K with the aid of interferometric technique. The components of the elastic stiffness tensor for these crystals are calculated on the basis of studies for the acoustic wave velocities. It is shown that acoustooptic figure of merit can achieve extremely high values for Sn2P2S6 crystals (M2 - 2x10-12s3/kg2).

  11. Autoresonant excitation and evolution of nonlinear waves: The variational approach L. Friedland

    E-print Network

    Friedland, Lazar

    Autoresonant excitation and evolution of nonlinear waves: The variational approach L. Friedland waves can be excited and controlled in adia- batically varying systems driven by an externally launched pump wave. The excitation proceeds via the trapping into the resonance, while later the nonlinear wave

  12. 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.

  13. Limits of Line VISAR data interpretation with large spatial velocity variations.

    NASA Astrophysics Data System (ADS)

    Furnish, Michael

    2015-06-01

    Line-imaging velocimetry provides information on position dependence of velocity histories, and in turn on grain anisotropies, texture, variability, and nonplanar material motion. In recent experiments on copper bicrystals, strong position dependence of motion created complicated fringe patterns not amenable to conventional analysis methods (mock quadrature or FFT). The data were initially interpreted by hand. Subsequently, a Matlab-based program was prepared to reduce such records by a fringe-trace method, as well as to extract precise wave-transit time information. Limits and capabilities of such analyses will be discussed and set in the context of other methods, using experimental and synthetic data. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  14. Rock physics model-based prediction of shear wave velocity in the Barnett Shale formation

    NASA Astrophysics Data System (ADS)

    Guo, Zhiqi; Li, Xiang-Yang

    2015-06-01

    Predicting S-wave velocity is important for reservoir characterization and fluid identification in unconventional resources. A rock physics model-based method is developed for estimating pore aspect ratio and predicting shear wave velocity Vs from the information of P-wave velocity, porosity and mineralogy in a borehole. Statistical distribution of pore geometry is considered in the rock physics models. In the application to the Barnett formation, we compare the high frequency self-consistent approximation (SCA) method that corresponds to isolated pore spaces, and the low frequency SCA-Gassmann method that describes well-connected pore spaces. Inversion results indicate that compared to the surroundings, the Barnett Shale shows less fluctuation in the pore aspect ratio in spite of complex constituents in the shale. The high frequency method provides a more robust and accurate prediction of Vs for all the three intervals in the Barnett formation, while the low frequency method collapses for the Barnett Shale interval. Possible causes for this discrepancy can be explained by the fact that poor in situ pore connectivity and low permeability make well-log sonic frequencies act as high frequencies and thus invalidate the low frequency assumption of the Gassmann theory. In comparison, for the overlying Marble Falls and underlying Ellenburger carbonates, both the high and low frequency methods predict Vs with reasonable accuracy, which may reveal that sonic frequencies are within the transition frequencies zone due to higher pore connectivity in the surroundings.

  15. Prediction of rocks thermal conductivity from elastic wave velocities, mineralogy and microstructure

    NASA Astrophysics Data System (ADS)

    Pimienta, Lucas; Sarout, Joel; Esteban, Lionel; Piane, Claudio Delle

    2014-05-01

    While knowledge on Thermal Conductivity (TC) of rocks is of interest in many fields, determining this property remains challenging. In this paper, a modelling approach for TC prediction from Elastic Wave Velocity (EWV) measurements is reported. To this end, a new effective TC model for a typical sedimentary rock is introduced that explicitly accounts for the presence of pores, pressure-sensitive microcracks (or grain contacts) and formation fluids. A model of effective elasticity is also devised for this same rock that links its microstructural characteristics to the velocity of elastic waves. The two models are based on the same effective medium approach and involve the same microstructural parameters. A workflow based on this explicit modelling approach is devised that allows for the prediction of the TC of a reservoir rock using (i) the elastic waves velocities, (ii) the dominant mineral content and (iii) the bulk porosity. This workflow is validated using experimental data reported in the literature for dry and water-saturated Fontainebleau and Berea sandstones. The datasets include measurements of TC and EWV as a function of effective pressure. In addition, it is shown that the dependence of TC on the rock microstructure is formally and practically similar to that of EWV. It is also demonstrated that the accuracy of TC predictions from EWV increases with effective pressure (burial depth). The underlying assumptions and limitations of the present approach together with the effect of burial are discussed.

  16. 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.

  17. 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.

  18. TU-A-9A-02: Analysis of Variations in Clinical Doppler Ultrasound Peak Velocity Measurements

    SciTech Connect

    Zhang, Y; Stekel, S; Tradup, D; Hangiandreou, N

    2014-06-15

    Purpose: Doppler ultrasound (US) peak velocity (Vmax) measurements show considerable variations due to intrinsic spectral broadening with different scanning techniques, machines and manufacturers. We developed a semi-automated Vmax estimation method and used this method to investigate the performance of a US system for clinical Doppler Vmax measurement. Methods: Semi-automated Vmax is defined as the velocity at which the computed mean spectral profile falls to within 1 background standard deviation of the background mean. GE LOGIQ E9 system with 9L and ML6-15 probes were studied with steady flow (5.3 – 12.5 ml/s) in a Gammex OPTIMIZER 1425A phantom. All Doppler spectra were acquired by 1 operator at the distal end of 5 mm angular tube using a modified clinical carotid artery protocol. Repeatability and variation of Vmax to scanning parameters and probes were analyzed and reported as percentage, i.e. (max-min)/mean. Results: Vmax estimation had good repeatability (3.1% over 6 days for 9L, and 3.6% for ML6-15). For 9L probe, varying gain, compression, scale, SV depth and length, and frequency had minimal impact on Vmax (all variations less than 4.0%). Beam steering had slightly higher influence (largest variations across flow rates were 4.9% for 9L and 6.9% for ML6-15). For both probes, Doppler angle had the greatest effect on Vmax. Percentage increase of Vmax was largely independent of actual flow rates. For Doppler angle varied from 30 to 60°, Vmax increased 24% for 9L, and 20% for ML6-15. Vmax measured by ML6-15 were lower than that by 9L at each Doppler angle with differences less than 5%. Conclusion: The proposed Vmax estimation method is shown to be a useful tool to evaluate clinical Doppler US system performance. For the tested system and probes, Doppler angle had largest impact in measured Vmax.

  19. Sensitivity bias in the mass-radius distribution from Transit Timing Variations and Radial Velocity measurements

    E-print Network

    Steffen, Jason H

    2015-01-01

    Motivated by recent discussions, both in private and in the literature, we use a Monte Carlo simulation of planetary systems to investigate sources of bias in determining the mass-radius distribution of exoplanets for the two primary techniques used to measure planetary masses---Radial Velocities (RVs) and Transit Timing Variations (TTVs). We assert that mass measurements derived from these two methods are comparably reliable---as the physics underlying their respective signals is well understood. Nevertheless, their sensitivity to planet mass varies with the properties of the planets themselves. We find that for a given planet size, the RV method tends to find planets with higher mass while the sensitivity of TTVs is more uniform. This ``sensitivity bias'' implies that a complete census of TTV systems is likely to yield a more robust estimate of the mass-radius distribution provided there are not important physical differences between planets near and far from mean-motion resonance. We discuss differences in...

  20. Generation of lower hybrid and whistler waves by an ion velocity ring distribution

    SciTech Connect

    Winske, D.; Daughton, W.

    2012-07-15

    Using fully kinetic simulations in two and three spatial dimensions, we consider the generation and nonlinear evolution of lower hybrid waves produced by a cold ion ring velocity distribution in a low beta plasma. We show that the initial development of the instability is very similar in two and three dimensions and not significantly modified by electromagnetic effects, consistent with linear theory. At saturation, the level of electric field fluctuations is a small fraction of the background thermal energy; the electric field and corresponding density fluctuations consist of long, field-aligned striations. Energy extracted from the ring goes primarily into heating the background ions and the electrons at comparable rates. The initial growth and saturation of the magnetic components of the lower hybrid waves are related to the electric field components, consistent with linear theory. As the growing electric field fluctuations saturate, parallel propagating whistler waves develop by the interaction of two lower hybrid waves. At later times, these whistlers are replaced by longer wavelength, parallel propagating whistlers that grow through the decay of the lower hybrid fluctuations. Wave matching conditions demonstrate these conversion processes of lower hybrid waves to whistler waves. The conversion efficiency (=ratio of the whistler wave energy to the energy in the saturated lower hybrid waves) is computed and found to be significant ({approx}15%) for the parameters of the three-dimensional simulation (and even larger in the two-dimensional simulation), although when normalized in terms of the initial kinetic energy in the ring ions the overall efficiency is very small (<10{sup -4}). The results are compared with relevant linear and nonlinear theory.

  1. 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.

  2. 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.

  3. Control of Periodic Variations in Saturn's Magnetosphere By Compressional Waves

    NASA Astrophysics Data System (ADS)

    Jia, X.; Kivelson, M.

    2014-12-01

    Many of the periodic variations observed in Saturn's magnetosphere can be linked directly to the presence of a rotating pattern of field-aligned currents that link the northern and southern ionospheres with each other and with the magnetosphere. Such a current system is incorporated in a magnetohydrodynamic simulation that has previously been shown to reproduce many of the observed periodic properties of the system (Jia et al., 2012; Jia and Kivelson, 2012). Here the simulation is used to investigate a range of phenomena that can be attributed to the effects of compressional waves launched from the rotating current sources. The compressional waves are found to drive the flapping of the plasma sheet and the expansion and contraction of the magnetopause in each rotation period. Because the compressional perturbations weaken as they rotate from morning to evening around the day side of the magnetosphere, the boundary develops a strong morning-evening asymmetry. A fit to the shape is provided that may be useful in further investigation of magnetopause properties, but there is already evidence of the proposed asymmetry in the Cassini observations of Clarke et al. [2010].

  4. Aspherical heterogeneity of the mantle from phase velocities of mantle waves

    NASA Technical Reports Server (NTRS)

    Nakanishi, I.; Anderson, D. L.

    1984-01-01

    Long-period surface waves are used to map the lateral heterogeneity of the upper 100-600 km of the mantle. There is good correlation of velocity with surface tectonics and heat flow. Convergence regions are generally slow for Love waves and fast for Rayleigh waves. Back arc basins have slower than average shallow mantle. Some island arcs show evidence of fast material at greater depth. Deep-seated slow anomalies underlie the Red Sea-Afar region of north-east Africa, western North American-northern East Pacific Rise, Indian Ocean triple junction and the Tasman Sea-Campbell Plateau regions. The fastest regions are in the north central Australia-New Guinea and the South Atlantic.

  5. The nonlinear theory of slow-wave electron cyclotron masers with inclusion of the beam velocity spread

    SciTech Connect

    Kong, Ling-Bao; Beijing Key Laboratory of Environmentally Harmful Chemicals Assessment, Beijing University of Chemical Technology, Beijing 100029 ; Wang, Hong-Yu; Hou, Zhi-Ling; Beijing Key Laboratory of Environmentally Harmful Chemicals Assessment, Beijing University of Chemical Technology, Beijing 100029 ; Jin, Hai-Bo; Du, Chao-Hai

    2013-12-15

    The nonlinear theory of slow-wave electron cyclotron masers (ECM) with an initially straight electron beam is developed. The evolution equation of the nonlinear beam electron energy is derived. The numerical studies of the slow-wave ECM efficiency with inclusion of Gaussian beam velocity spread are presented. It is shown that the velocity spread reduces the interaction efficiency. -- Highlights: •The theory of slow-wave electron cyclotron masers is considered. •The calculation of efficiency under the resonance condition is presented. •The efficiency under Gaussian velocity spreads has been obtained.

  6. Variations in Gravitational Field, Tidal Force, Electromagnetic Waves and Earthquakes

    NASA Astrophysics Data System (ADS)

    Strasser, Valentino

    2010-12-01

    This paper is the report on an experiment carried out between the month of December 2009 and the month of April 2010 between the Venetian Lagoon and the Northern Apennines in Italy, to check on a potential relationship between earthquakes and variations in the local gravitational field, the effect on the tide exercised by the interaction between the moon and the Sun, the appearance of anomalous light effects in the atmosphere ("Earth lights"), and the emission of radio waves caused by stresses in the Earth's crust. The cases studied show that there is indeed some concomitance between the periodic rising and falling of the sea level and the terrestrial tide effect, due to the gravitational attraction of the moon and sun on the Earth. In fact, changes in the local force of gravity coincided with the cycle of high and low tides and, in certain cases, with a variation in the electromagnetic field that preceded the occurrence of a seismic event by just a few hours. The o! bservations in the article are limited to the magnitude range discussed in the paper.

  7. A model for seasonal changes in GPS positions and seismic wave speeds due to thermoelastic and hydrologic variations

    USGS Publications Warehouse

    Tsai, V.C.

    2011-01-01

    It is known that GPS time series contain a seasonal variation that is not due to tectonic motions, and it has recently been shown that crustal seismic velocities may also vary seasonally. In order to explain these changes, a number of hypotheses have been given, among which thermoelastic and hydrology-induced stresses and strains are leading candidates. Unfortunately, though, since a general framework does not exist for understanding such seasonal variations, it is currently not possible to quickly evaluate the plausibility of these hypotheses. To fill this gap in the literature, I generalize a two-dimensional thermoelastic strain model to provide an analytic solution for the displacements and wave speed changes due to either thermoelastic stresses or hydrologic loading, which consists of poroelastic stresses and purely elastic stresses. The thermoelastic model assumes a periodic surface temperature, and the hydrologic models similarly assume a periodic near-surface water load. Since all three models are two-dimensional and periodic, they are expected to only approximate any realistic scenario; but the models nonetheless provide a quantitative framework for estimating the effects of thermoelastic and hydrologic variations. Quantitative comparison between the models and observations is further complicated by the large uncertainty in some of the relevant parameters. Despite this uncertainty, though, I find that maximum realistic thermoelastic effects are unlikely to explain a large fraction of the observed annual variation in a typical GPS displacement time series or of the observed annual variations in seismic wave speeds in southern California. Hydrologic loading, on the other hand, may be able to explain a larger fraction of both the annual variations in displacements and seismic wave speeds. Neither model is likely to explain all of the seismic wave speed variations inferred from observations. However, more definitive conclusions cannot be made until the model parameters are better constrained. Copyright ?? 2011 by the American Geophysical Union.

  8. Strong seismic wave scattering in the low-velocity anomaly associated with subduction of oceanic plate

    NASA Astrophysics Data System (ADS)

    Takemura, Shunsuke; Yoshimoto, Kazuo

    2014-05-01

    Analyses of dense seismic records in Kanto, Japan, revealed distinct pulse broadening and peak delay of high-frequency S waves at central Chiba. These phenomena are observed at frequency range of 1-8 Hz and exist only for ray paths passing through the low-velocity (LV) zone at depth of 20-40 km beneath northwestern Chiba. To obtain a more detailed understanding of these phenomena, we conducted 2-D and 3-D finite difference method simulations of seismic wave propagation using a realistic heterogeneous structure model. Through numerous simulations we demonstrated that strong seismic scattering, due to localized strong small-scale heterogeneities in the LV zone and in the oceanic crust, is a major cause of strong pulse broadening and peak delay of high-frequency S waves. After comparing simulation results with observations, the most preferable small-scale velocity heterogeneity in the LV zone is characterized by a Gaussian power spectral density function (PSDF) with correlation distance a of 1-2 km and rms value ? = 0.07-0.09, superposed on a background exponential PSDF (a = 3 km, ? = 0.07). Assuming strong velocity heterogeneities, observed amplitude decay at Chiba is also well explained by strong scattering attenuation in the LV zone. Because the LV zone, which has been reported by seismic tomography studies, is interpreted as being constructed by the dehydration of the subducting oceanic crust of the Philippine Sea Plate, strong small-scale velocity heterogeneity in the LV zone may be related to the random distribution of fluid in this volume.

  9. 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.

  10. 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.

  11. Long-lived, long-period radial velocity variations in Aldebaran: A planetary companion and stellar activity

    NASA Astrophysics Data System (ADS)

    Hatzes, A. P.; Cochran, W. D.; Endl, M.; Guenther, E. W.; MacQueen, P.; Hartmann, M.; Zechmeister, M.; Han, I.; Lee, B.-C.; Walker, G. A. H.; Yang, S.; Larson, A. M.; Kim, K.-M.; Mkrtichian, , D. E.; Döllinger, M.; Simon, , A. E.; Girardi, L.

    2015-08-01

    Aims: We investigate the nature of the long-period radial velocity variations in ? Tau first reported over 20 yr ago. Methods: We analyzed precise stellar radial velocity measurements for ? Tau spanning over 30 yr. An examination of the H? and Ca II ?8662 spectral lines, and Hipparcos photometry was also done to help discern the nature of the long-period radial velocity variations. Results: Our radial velocity data show that the long-period, low amplitude radial velocity variations are long-lived and coherent. Furthermore, H? equivalent width measurements and Hipparcos photometry show no significant variations with this period. Another investigation of this star established that there was no variability in the spectral line shapes with the radial velocity period. An orbital solution results in a period of P = 628.96 ± 0.90 d, eccentricity, e = 0.10 ± 0.05, and a radial velocity amplitude, K = 142.1 ± 7.2 m s-1. Evolutionary tracks yield a stellar mass of 1.13 ± 0.11 M?, which corresponds to a minimum companion mass of 6.47 ± 0.53 MJup with an orbital semi-major axis of a = 1.46 ± 0.27 AU. After removing the orbital motion of the companion, an additional period of ?520 d is found in the radial velocity data, but only in some time spans. A similar period is found in the variations in the equivalent width of H? and Ca II. Variations at one-third of this period are also found in the spectral line bisector measurements. The ~520 d period is interpreted as the rotation modulation by stellar surface structure. Its presence, however, may not be long-lived, and it only appears in epochs of the radial velocity data separated by ~10 yr. This might be due to an activity cycle. Conclusions: The data presented here provide further evidence of a planetary companion to ? Tau, as well as activity-related radial velocity variations. Based in part on observations obtained at the 2-m-Alfred Jensch Telescope at the Thüringer Landessternwarte Tautenburg and the telescope facilities of McDonald Observatory.Tables 3-9 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/580/A31

  12. Alternative dust-ion acoustic waves in a magnetized charge varying dusty plasma with nonthermal electrons having a vortex-like velocity distribution

    NASA Astrophysics Data System (ADS)

    Hadjaz, Idir; Tribeche, Mouloud

    2014-06-01

    Alternative localized dust-ion acoustic waves are investigated in a magnetized charge varying dusty plasma with nonthermal electrons having a vortex-like velocity distribution. The correct non-Maxwellian charging currents are obtained based on the well-known orbit limited motion theory. Following the standard reductive perturbation technique, a Schamel-Zakharov Kuznetsov Burgers (S-ZKB) equation is derived. It is shown that due to an interplay between trapping and nonthermality, our dusty plasma model may support solitary as well as shock waves the main quantities (phase velocity, amplitude and width) of which are drastically influenced by trapping, nonthermality and charge variation. Due to the flexibility provided by the outlined distribution function (two concepts of non isothermality), we stress that our model should provide a good fit of the space observations.

  13. Resonant-to-nonresonant transition in electrostatic ion-cyclotron wave phase velocity

    NASA Astrophysics Data System (ADS)

    Carroll, J. J., III; Koepke, M. E.; Zintl, M. W.; Gavrishchaka, V.

    Because of the implications for plasmas in the laboratory and in space, attention has been drawn to inhomogeneous energy-density driven (IEDD) waves that are sustained by velocity-shear-induced inhomogeneity in cross-field plasma flow. These waves have a frequency vr in the lab frame within an order of magnitude of the ion gyrofrequency vci, propagate nearly perpendicular to the magnetic field (kz /k^ << 1), and can be Landau resonant (0 < v1/kz < nd) with a parallel drifting electron population (drift speed nd), where subscripts 1 and r indicate frequency in the frame of flowing ions and in the lab frame, respectively, and kz is the parallel component of the wavevector. A transition in phase velocity from 0 < v1/kz < nd to 0 > v1/kz > nd for a pair of IEDD eigenmodes is observed as the degree of in-homogeneity in the transverse E × B flow is increased in a magnetized plasma column. For weaker velocity shear, both eigenmodes are dissipative, i.e. in Landau resonance, with kz nd > 0. For stronger shear, both eigenmodes become reactive, with one's wavevector component kz remaining parallel, but with v1/kz > nd , and the other's wavevector component kz becoming anti-parallel, so that 0 > v1/kz . For both eigenmodes, the transition (1) involves a small frequency shift and (2) does not involve a sign change in the wave energy density, which is proportional to vr v1, both of which are previously unrecognized aspects of inhomogeneous energy-density driven waves.

  14. Heart-Carotid Pulse Wave Velocity a Useful Index of Atherosclerosis in Chinese Hypertensive Patients

    PubMed Central

    Li, Chunyue; Xiong, Huahua; Pirbhulal, Sandeep; Wu, Dan; Li, Zhenzhou; Huang, Wenhua; Zhang, Heye; Wu, Wanqing

    2015-01-01

    Abstract This study was designed to investigate the relationship between heart-carotid pulse wave velocity (hcPWV) and carotid intima-media thickness (CIMT) in hypertensive patients, and also to examine the effect of pre-ejection period (PEP) on it. Doppler ultrasound device was used to measure CIMT in left common carotid artery. Hypertensive patients were divided into normal (n?=?36, CIMT ?0.8?mm) and thickened (n?=?31, CIMT?>?0.8?mm) group. Electrocardiogram R-wave-based carotid pulse wave velocity (rcPWV) and aortic valve-carotid pulse wave velocity (acPWV) were calculated as the ratio of the travel length to the pulse transit time with or without PEP, respectively. CIMT has significant relations with rcPWV (r?=?0.611, P?

  15. Heart-Carotid Pulse Wave Velocity a Useful Index of Atherosclerosis in Chinese Hypertensive Patients.

    PubMed

    Li, Chunyue; Xiong, Huahua; Pirbhulal, Sandeep; Wu, Dan; Li, Zhenzhou; Huang, Wenhua; Zhang, Heye; Wu, Wanqing

    2015-12-01

    This study was designed to investigate the relationship between heart-carotid pulse wave velocity (hcPWV) and carotid intima-media thickness (CIMT) in hypertensive patients, and also to examine the effect of pre-ejection period (PEP) on it. Doppler ultrasound device was used to measure CIMT in left common carotid artery. Hypertensive patients were divided into normal (n?=?36, CIMT ?0.8?mm) and thickened (n?=?31, CIMT?>?0.8?mm) group. Electrocardiogram R-wave-based carotid pulse wave velocity (rcPWV) and aortic valve-carotid pulse wave velocity (acPWV) were calculated as the ratio of the travel length to the pulse transit time with or without PEP, respectively. CIMT has significant relations with rcPWV (r?=?0.611, P?

  16. Estimate of shear wave velocity, and its time-lapse change, from seismic data recorded at the SMNH01 station of KiK-net using seismic interferometry

    E-print Network

    Snieder, Roel

    Estimate of shear wave velocity, and its time-lapse change, from seismic data recorded at the SMNH of the most important seismic networks which is located in Japan, to estimate effective shear wave velocities of this paper is to use seismic interferometry based on deconvolution to obtain effective shear wave velocities

  17. Predicting the Intra-Cyclic Variation of the Velocity of the Centre of Mass from Segmental Velocities in Butterfly Stroke: A Pilot Study

    PubMed Central

    Barbosa, Tiago M.; Fernandes, Ricardo J.; Morouco, Pedro; Vilas-Boas, Joao P.

    2008-01-01

    The purpose of this study was to analyze the relationship between the intra-cycle variation of the horizontal velocity of displacement of the center of mass (dV), the hand's and feet's velocity, as well as, to identify the variables that most predict the dV's, in butterfly stroke. The study was divided in two parts. The aim of Part I was to investigate the behavior of variables in study at slow swimming velocities and the purpose of Part II was the same but at high swimming velocities. 3 male Portuguese swimmers and 1 female swimmer, of international level were studied in Part I. The swimmers were submitted to an incremental set of 200 m butterfly swims. In the Part II, 7 Portuguese male swimmers of national and international level were studied. Each swimmer performed two maximal 25 m butterfly swims. Both protocols were recorded from four different plans, allowing a 3D analysis. It was calculated the dV, the 3D components (Vx, Vy, Vz) of the hand's velocity and the 2D components (Vx, Vy) of the feet's velocity. Several variables presented significant correlation coefficients with dV at all selected velocities (high velocity ranged from r = 0.58 for Vx-out to r = 0.82 for Vy-1dwn; slow velocity ranged from r = -0.45 for Vx-1dwn to r=0.73 for Vx-ups; overall velocity ranged from r= 0.34 for Vz-ent to r = 0.82 for Vx-ins). It was also computed a regression model to predict dV. For high velocity (up to 1.75 ± 0.09 m.s-1), the variables that best predict dV were Vy during the first downbeat, Vx and Vy during the arm's insweep (r2 = 0.93). At slow velocity (up to 1.48 m.s-1), the variables included in the forward step-by-step regression model were Vx during upsweep, Vy and Vx during insweep (r2 = 0.69). For overall velocity, the variables that most fit the regression model were Vx during upsweep, Vy during second downbeat and Vz during entry (r2= 0.94). In order to reduce dV, butterfliers should increase hand's velocity in all orthogonal components at the end of the underwater path, should increase the vertical velocity during the downbeats and decrease the velocity during the hand's entry. Key pointsSegmental velocities are a determinant phenomenon for swimming performance and should be carefully analyzed by coaches and butterfliers.Butterfliers must finish the last phase of the underwater path with a high hand's velocity in order to reduce the speed fluctuation and increase the swimming velocity.Butterfliers should also pay more attention to downbeats, since they are important to reduce the speed fluctuation during the hand's entry, as well as, the arm's recovery. PMID:24149450

  18. 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

  19. 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.

  20. Shear velocity and intrinsic Q structure of the shallow crust in southeastern New England from Rg wave dispersion

    SciTech Connect

    Saikia, C.K. ); Kafka, A.L.; Gnewuch, S.C.; McTigue, J.W. )

    1990-06-10

    In this study, the authors analyzed 0.5-2.0 s period Rayleigh waves (Rg) generated by quarry and construction blasting in southern New England (SNE). The paths crossing the Hartford Rift basin (HRB) show an obvious correlation between geology and Rg dispersion. The entire region in the southeastern New England comprising a wide range of geological structures and rock types from the Bronson Hill Anticlinorium to the Avalonian Terrane can be represented as one dispersion region. Therefore the relationship between lateral changes in geologic structures mapped on the surface and Rg dispersion is not as straightforward as might be expected for a best fitting flat-layered model of the shallow crust. The shear wave velocities appear to vary between 2.55 and 3.63 km/s within the upper 2.5 km except for the central HRB where the variation is between 2.12 and 2.7 km/s. Intrinsic Q structure is considered to be the primary means for the loss of energy in the shallow crust and was analyzed by modeling the waveforms of several of the observed seismograms. For this aspect of our study, the authors used a modal summation of Rayleigh waves assuming a far-field radiation approximation. The observed seismograms were dominated primarily by contributions from the fundamental mode, but higher modes were also included in the synthesis of the waveform. They were unable to model the absolute amplitudes of the waveforms because of the problems with the instrument calibration. It is clear, however, that to predict correct waveforms, the shear wave Q values in the upper few tenths of a kilometer of the crust must be about an order of magnitude smaller than Q values at the depth of 1-3 km which is of order of 100-250.

  1. Spatial Parallelism of a 3D Finite Difference, Velocity-Stress Elastic Wave Propagation Code

    SciTech Connect

    MINKOFF,SUSAN E.

    1999-12-09

    Finite difference methods for solving the wave equation more accurately capture the physics of waves propagating through the earth than asymptotic solution methods. Unfortunately. finite difference simulations for 3D elastic wave propagation are expensive. We model waves in a 3D isotropic elastic earth. The wave equation solution consists of three velocity components and six stresses. The partial derivatives are discretized using 2nd-order in time and 4th-order in space staggered finite difference operators. Staggered schemes allow one to obtain additional accuracy (via centered finite differences) without requiring additional storage. The serial code is most unique in its ability to model a number of different types of seismic sources. The parallel implementation uses the MP1 library, thus allowing for portability between platforms. Spatial parallelism provides a highly efficient strategy for parallelizing finite difference simulations. In this implementation, one can decompose the global problem domain into one-, two-, and three-dimensional processor decompositions with 3D decompositions generally producing the best parallel speed up. Because i/o is handled largely outside of the time-step loop (the most expensive part of the simulation) we have opted for straight-forward broadcast and reduce operations to handle i/o. The majority of the communication in the code consists of passing subdomain face information to neighboring processors for use as ''ghost cells''. When this communication is balanced against computation by allocating subdomains of reasonable size, we observe excellent scaled speed up. Allocating subdomains of size 25 x 25 x 25 on each node, we achieve efficiencies of 94% on 128 processors. Numerical examples for both a layered earth model and a homogeneous medium with a high-velocity blocky inclusion illustrate the accuracy of the parallel code.

  2. Spatial parallelism of a 3D finite difference, velocity-stress elastic wave propagation code

    SciTech Connect

    Minkoff, S.E.

    1999-12-01

    Finite difference methods for solving the wave equation more accurately capture the physics of waves propagating through the earth than asymptotic solution methods. Unfortunately, finite difference simulations for 3D elastic wave propagation are expensive. The authors model waves in a 3D isotropic elastic earth. The wave equation solution consists of three velocity components and six stresses. The partial derivatives are discretized using 2nd-order in time and 4th-order in space staggered finite difference operators. Staggered schemes allow one to obtain additional accuracy (via centered finite differences) without requiring additional storage. The serial code is most unique in its ability to model a number of different types of seismic sources. The parallel implementation uses the MPI library, thus allowing for portability between platforms. Spatial parallelism provides a highly efficient strategy for parallelizing finite difference simulations. In this implementation, one can decompose the global problem domain into one-, two-, and three-dimensional processor decompositions with 3D decompositions generally producing the best parallel speedup. Because I/O is handled largely outside of the time-step loop (the most expensive part of the simulation) the authors have opted for straight-forward broadcast and reduce operations to handle I/O. The majority of the communication in the code consists of passing subdomain face information to neighboring processors for use as ghost cells. When this communication is balanced against computation by allocating subdomains of reasonable size, they observe excellent scaled speedup. Allocating subdomains of size 25 x 25 x 25 on each node, they achieve efficiencies of 94% on 128 processors. Numerical examples for both a layered earth model and a homogeneous medium with a high-velocity blocky inclusion illustrate the accuracy of the parallel code.

  3. Measurements of Spatially Resolved Velocity Variations in Shock Compressed Heterogeneous Materials Using a Line-Imaging Velocity Interferometer

    SciTech Connect

    ASAY,JAMES R.; CHHABILDAS,LALIT C.; KNUDSON,MARCUS D.; TROTT,WAYNE M.

    1999-09-01

    Relatively straightforward changes in the optical design of a conventional optically recording velocity interferometer system (ORVIS) can be used to produce a line-imaging velocity interferometer wherein both temporal and spatial resolution can be adjusted over a wide range. As a result line-imaging ORVIS can be tailored to a variety of specific applications involving dynamic deformation of heterogeneous materials as required by the characteristic length scale of these materials (ranging from a few {micro}m for ferroelectric ceramics to a few mm for concrete). A line-imaging ORVIS has been successfully interfaced to the target chamber of a compressed gas gun driver and fielded on numerous tests in combination with simultaneous measurements using a dual delay-leg, ''push-pull'' VISAR system. These tests include shock loading of glass-reinforced polyester composites, foam reverberation experiments (measurements at the free surface of a thin aluminum plate impacted by foam), and measurements of dispersive velocity in a shock-loaded explosive simulant (sugar). Comparison of detailed spatially-resolved material response to the spatially averaged VISAR measurements will be discussed.

  4. Large-scale Observations of a Subauroral Polarization Stream by Midlatitude SuperDARN Radars: Instantaneous Longitudinal Velocity Variations

    NASA Technical Reports Server (NTRS)

    Clausen, L. B. N.; Baker, J. B. H.; Sazykin, S.; Ruohoniemi, J. M.; Greenwald, R. A.; Thomas, E. J.; Shepherd, S. G.; Talaat, E. R.; Bristow, W. A.; Zheng, Y.; Coster, A. J.

    2012-01-01

    We present simultaneous measurements of flow velocities inside a subauroral polarization stream (SAPS) made by six midlatitude high-frequency SuperDARN radars. The instantaneous observations cover three hours of universal time and six hours of magnetic local time (MLT). From velocity variations across the field-of-view of the radars we infer the local 2D flow direction at three different longitudes. We find that the local flow direction inside the SAPS channel is remarkably constant over the course of the event. The flow speed, however, shows significant temporal and spatial variations. After correcting for the radar look direction we are able to accurately determine the dependence of the SAPS velocity on magnetic local time. We find that the SAPS velocity variation with magnetic local time is best described by an exponential function. The average velocity at 00 MLT was 1.2 km/s and it decreased with a spatial e-folding scale of two hours of MLT toward the dawn sector. We speculate that the longitudinal distribution of pressure gradients in the ring current is responsible for this dependence and find these observations in good agreement with results from ring current models. Using TEC measurements we find that the high westward velocities of the SAPS are - as expected - located in a region of low TEC values, indicating low ionospheric conductivities.

  5. 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. )

    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

  6. Pressure wave and fluid velocity in a bend-mode inkjet nozzle with double PZT actuators

    NASA Astrophysics Data System (ADS)

    Kim, Sungu; Sung, Jaeyong; Lee, Myeong Ho

    2013-02-01

    A new concept of bend-mode inkjet nozzle with double PZT (lead zirconate titanate) actuators has been designed and fabricated in the present study. Then the pressure wave and fluid velocity at the nozzle exit have been investigated. The complex pressure behavior inside the channel was solved numerically based on the narrow channel acoustic theory. The two PZTs attached to a rectangular channel were actuated sequentially by setting the waveforms of each PZT to be center-aligned with various pulse widths. As a result, the double PZT actuation is superior to the single PZT actuation in view of strong momentum force and fast dissipation of residual pressure. The maximum fluid velocity at the nozzle exit is observed when the respective pulse widths equal to their optimum pulse widths. The numerical results are supported by the experimental results with the fabricated inkjet device by measuring the speed of meniscus just out of the nozzle.

  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

    SciTech Connect

    Kono, Yoshio; Yamada, Akihiro; Inoue, Toru; Wang Yanbin; Yu, Tony

    2011-02-15

    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 deg. 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 deg. Y-cut LiNbO{sub 3} transducer attached to the end of the lower anvil. Combined ultrasonic and microtomographic measurements were carried out for SiO{sub 2} glass up to 2.6 GPa and room temperature. A decrease in elastic wave velocities of the SiO{sub 2} 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 (K{sub s}) and shear (G) moduli as a function of pressure. K{sub s} and G of the SiO{sub 2} glass also decreased with increasing pressure. The negative pressure dependence of K{sub s} is stronger than that of G, and as a result the value of K{sub s} 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-K{sub s}-G-(T) equations of state for noncrystalline materials.

  9. Combined ultrasonic elastic wave velocity and microtomography measurements at high pressures

    SciTech Connect

    Kono, Yoshio; Yamada, Akihiro; Wang, Yanbin; Yu, Tony; Inoue, Toru

    2011-09-16

    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{sup o} 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{sup o} Y-cut LiNbO{sub 3} transducer attached to the end of the lower anvil. Combined ultrasonic and microtomographic measurements were carried out for SiO{sub 2} glass up to 2.6 GPa and room temperature. A decrease in elastic wave velocities of the SiO{sub 2} 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 (K{sub s}) and shear (G) moduli as a function of pressure. K{sub s} and G of the SiO{sub 2} glass also decreased with increasing pressure. The negative pressure dependence of K{sub s} is stronger than that of G, and as a result the value of K{sub s} 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.

  10. Continuous wave cavity ring-down spectroscopy for velocity distribution measurements in plasma

    NASA Astrophysics Data System (ADS)

    McCarren, D.; Scime, E.

    2015-10-01

    We report the development of a continuous wave cavity ring-down spectroscopic (CW-CRDS) diagnostic for real-time, in situ measurement of velocity distribution functions of ions and neutral atoms in plasma. This apparatus is less complex than conventional CW-CRDS systems. We provide a detailed description of the CW-CRDS apparatus as well as measurements of argon ions and neutrals in a high-density (109 cm-3 < plasma density <1013 cm-3) plasma. The CW-CRDS measurements are validated through comparison with laser induced fluorescence measurements of the same absorbing states of the ions and neutrals.

  11. Negative-phase-velocity propagation of electromagnetic waves in the relativisitic context

    NASA Astrophysics Data System (ADS)

    Lakhtakia, Akhlesh; Mackay, Tom G.; Setiawan, Sandi

    2005-08-01

    This paper focuses on the recently established phenomenon of negative-phase-velocity (NPV) propagation of electromagnetic waves in the context of relativity, both special and general. Different observers in different states of uniform motion with respect to a material fragment may arrive at different conclusions on the possibility or impossibility of NPV propagation in that material. Also, conditions for NPV propagation may be satisfied in gravitationally affected vacuum. NPV propagation may thus be possible in scenarios encompassing space exploration, navigation, and communication; remotely guided extraterrestrial manufacturing industries; and the unraveling of the evolution of our universe after the last Big Bang.

  12. Experimental demonstration of noncontact pulse wave velocity monitoring using multiple Doppler radar sensors.

    PubMed

    Lu, Li; Li, Changzhi; Lie, Donald Y C

    2010-01-01

    In this paper, two Doppler radars are used to monitor the pulse movements at the heart and the calf in order to measure the pulse wave velocity (PWV) wirelessly. Both simulation and experiment have been performed to demonstrate the feasibility of the proposed noncontact PWV monitoring. A three-stage calibration procedure, including DC offset calibration, circuit delay calibration and antenna radiation pattern calibration, has been developed for reliable long-term PWV monitoring. The measurement results have been verified by wired contact measurement with pulse transducers. PMID:21096684

  13. Velocity Shift of Surface Acoustic Waves due to Interaction with Composite Fermions in a Modulated Structure

    NASA Astrophysics Data System (ADS)

    Mirlin, A. D.; Wölfle, P.; Levinson, Y.; Entin-Wohlman, O.

    1998-08-01

    We study the effect of a periodic density modulation on surface acoustic wave (SAW) propagation along a 2D electron gas near Landau level filling ? = 1/2. Within the composite fermion theory, the problem is described in terms of fermions subject to a spatially modulated magnetic field and scattered by a random magnetic field. We find that a few percent modulation induces a large peak in the SAW velocity shift, as observed recently by Willett et al. As further support of this theory we find the dc resistivity to be in good agreement with recent data of Smet et al.

  14. Rayleigh and Love waves phase velocity measurements in central Europe from seismic ambient noise

    NASA Astrophysics Data System (ADS)

    Verbeke, J.; Fry, B.; Boschi, L.; Kissling, E. H.

    2009-12-01

    We present a new database of surface-wave phase-velocity dispersion curves derived from seismic ambient noise, cross-correlating continuous seismic recordings from the Swiss Network, the German Regional Seismological Network (GRSN), and from the Italian national broadband network operated by the the Istituto Nazionale di Geofisica e Vulcanologia (INGV), plus some stations from the Mediterranean Very Broadband Seismographic Network (MedNet) and from the Austrian Central Institute for Meteorology and Geodynamics (ZAMG). In order to increase the aperture of the station array, additional measurements from the French, Bulgarian, Hungarian, Romanian and Greek stations obtained throught Orfeus are also included. The ambient noise we are using to assemble our database was recorded at the mentioned stations between January 2006 and December 2007. The Green function method, applied to continuous signal recorded at pairs of stations allows to extract from ambient noise coherent surface-wave signal travelling between the two stations. Usually the ambient-noise cross-correlation technique allows to have infomation at periods of 30 s or shorter. Our efforts are focused on extending this technique to longer periods. At this point we are able to obtain coherent dispersion curves at periods from 8 to 35 s. At a second stage, the data set of phase delays associated with a certain frequency of Rayleigh or Love waves are inverted, to determine 2-dimensional phase-velocity maps of the European region. Inversions are conducted by means of a linearized tomographic inversion algorithm. We are now able to obtain 2D Rayleighs and Loves waves phase-velocity maps at periods between 8 and 35 s. We compare these maps with those that we obtain from teleseismic measurements made at the same stations, and with independantly observed geological features in Europe and the Moho depth. Combining ambient-noise and teleseismic observations, our efforts will help to determine a 3D consensus model of the European crust and of vertically and horizontally polarized shear velocity in the underlying upper mantle period. This model will represent an important improvement over exisiting models, in that it will simultaneously explain observations made at very different frequencies, providing, in particular, a very high-resolution map of the lithosphere-asthenosphere boundary region.

  15. 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.

  16. Mixed augmented variational formulation (MAVF) for lower hybrid full-wave calculations

    E-print Network

    Labrunie, Simon

    Mixed augmented variational formulation (MAVF) for lower hybrid full-wave calculations P. Bertrand is considered. Keywords: Full wave, Lower hybrid, Finite element PACS: 52.35.Hr, 41.20.Jb, 52.64.-y INTRODUCTION The propagation and the absorption of the lower hybrid electromagnetic wave is a pow- erful method to generate

  17. Theory on excitations of drift Alfvn waves by energetic particles. I. Variational formulation

    E-print Network

    Zonca, Fulvio

    Theory on excitations of drift Alfvén waves by energetic particles. I. Variational formulation on excitations of drift Alfvén waves by energetic particles. II. The general fishbone-like dispersion relation: 192.107.52.30 On: Mon, 21 Jul 2014 13:32:03 #12;Theory on excitations of drift Alfven waves

  18. Variational Calculation on the Helium Atom Using a Trigonometric Trial Wave Function Frank Rioux

    E-print Network

    Rioux, Frank

    Variational Calculation on the Helium Atom Using a Trigonometric Trial Wave Function Frank Rioux Chemistry Department CSB|SJU Trigonometric Trial Wave Function: r ,( ) 3 3 3 sech r( ):= Demonstrate the wave function is normalized. 0 r r ,( )2 4 r 2 d assume 0>, simplify 1 The terms

  19. Variational Calculation on the Helium Atom Using a Hydrogenic Trial Wave Function Frank Rioux

    E-print Network

    Rioux, Frank

    Variational Calculation on the Helium Atom Using a Hydrogenic Trial Wave Function Frank Rioux Chemistry Department CSB|SJU Gaussian Trial Wave Function: r ,( ) 3 exp - r( ):= Demonstrate the wave function is normalized. 0 r r ,( )2 4 r 2 d assume 0>, simplify 1 The terms

  20. Shear velocity model for the Kyrgyz Tien Shan from joint inversion of receiver function and surface wave data

    E-print Network

    Gilligan, Amy; Roecker, Steven W.; Priestley, Keith F.; Nunn, Ceri

    2014-07-09

    model shows a variation in crustal thickness across the range. We ?nd that crustal velocities extend to ? 75 km beneath the Kokshaal Range, which we attribute to underthrusting of the Tarim Basin beneath the southern Tien Shan. This result supports...

  1. Effect of pore pressure on the velocity of compressional waves in low-porosity rocks.

    NASA Technical Reports Server (NTRS)

    Todd, T.; Simmons, G.

    1972-01-01

    The velocity V sub p of compressional waves has been measured in rock samples of low porosity to confining pressures P sub c of 2 kb for a number of different constant pore pressures P sub p. An effective pressure defined by P sub e = P sub c-nP sub p, n less than or equal to 1, is found to be the determining factor in the behavior of V sub p rather than an effective pressure defined simply by the differential pressure Delta P = P sub c-P sub p. As pore pressure increases at constant effective pressure, the value of n increases and approaches 1, but as effective pressure increases at constant pore pressure, the value of n decreases. These observations are consistent with Biot's theory of the propagation of elastic waves in a fluid-saturated porous solid.

  2. 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.

  3. First high resolution P wave velocity structure beneath Tenerife Island, (Canary Islands, Spain)

    NASA Astrophysics Data System (ADS)

    Garcia-Yeguas, Araceli; Ivan, Koulakov; Ibañez Jesus, M.; Valenti, Sallarès.

    2010-05-01

    3D velocity structure distribution has been imaged for first time using high resolution traveltime seismic tomography of the active volcano of Tenerife Island (Canary Islands, Spain). It is located in the Atlantic Ocean. In this island is situated the Teide stratovolcano (3718 m high) that is part of the Cañadas-Teide-Pico Viejo volcanic complex. Las Cañadas is a caldera system more than 20 kilometers wide where at least four distinct caldera processes have been identified. Evidence for many explosive eruptions in the volcanic complex has been found; the last noticeable explosive eruption (sub-plinean) occurred at Montaña Blanca around 2000 years ago. During the last 300 years, six effusive eruptions have been reported, the last of which took place at Chinyero Volcano on 18 November 1909. In January 2007, a seismic active experiment was carried out as part of the TOM-TEIDEVS project. About 6850 air gun shots were fired on the sea and recorded on a dense local seismic land network consisting of 150 independent (three component) seismic stations. The good quality of the recorded data allowed identifying P-wave arrivals up to offsets of 30-40 km obtaining more than 63000 traveltimes used in the tomographic inversion. The images have been obtained using ATOM-3D code (Koulakov, 2009). This code uses ray bending algorithms in the ray tracing for the forward modelling and in the inversion step it uses gradient methods. The velocity models show a very heterogeneous upper crust that is usual in similar volcanic environment. The tomographic images points out the no-existence of a magmatic chamber near to the surface and below Pico Teide. The ancient Las Cañadas caldera borders are clearly imaged featuring relatively high seismic velocity. Moreover, we have found a big low velocity anomaly in the northwest dorsal of the island. The last eruption took place in 1909 in this area. Furthermore, in the southeast another low velocity anomaly has been imaged. Several resolution and accuracy tests were carried out to quantify the reliability of the final velocity models. Checkerboard tests show that the well-resolved are located up to 6-8 km depth. Also we carried out synthetic tests in which we successfully reproduce single anomalies observed in the velocity models. Especially we have study carefully the low velocity anomalies found in the NW and SE, which have been recovered successfully. The jack-knife technique have been used and our results are stable if we remove the 50% of the data for different stations, but if we reject all the data for some stations, the velocity models can change. These tests assure the uniqueness of the first 3D velocity model that characterizes the internal structure of the Tenerife Island. As main conclusions of our work we can remark: a) This is the first 3-D velocity image of the area; b) we have observed low velocity anomalies near to surface that could be associated to the presence of magma, water reservoirs and volcanic landslides; c) high velocity anomalies could be related to ancient volcanic episodes or basement structures; d) our results could help to resolve many questions relate to the evolution of the volcanic system, as the presence or not of big landslides, calderic explosions or others; e) this image is a very important tool to improve the knowledge of the volcanic hazard, and therefore volcanic risk. We would like to highlight the importance of take into account the risk of eruption in other areas besides Pico Teide-Las Cañadas system.

  4. Improved Pulse Wave Velocity Estimation Using an Arterial Tube-Load Model

    PubMed Central

    Gao, Mingwu; Zhang, Guanqun; Olivier, N. Bari; Mukkamala, Ramakrishna

    2015-01-01

    Pulse wave velocity (PWV) is the most important index of arterial stiffness. It is conventionally estimated by non-invasively measuring central and peripheral blood pressure (BP) and/or velocity (BV) waveforms and then detecting the foot-to-foot time delay between the waveforms wherein wave reflection is presumed absent. We developed techniques for improved estimation of PWV from the same waveforms. The techniques effectively estimate PWV from the entire waveforms, rather than just their feet, by mathematically eliminating the reflected wave via an arterial tube-load model. In this way, the techniques may be more robust to artifact while revealing the true PWV in absence of wave reflection. We applied the techniques to estimate aortic PWV from simultaneously and sequentially measured central and peripheral BP waveforms and simultaneously measured central BV and peripheral BP waveforms from 17 anesthetized animals during diverse interventions that perturbed BP widely. Since BP is the major acute determinant of aortic PWV, especially under anesthesia wherein vasomotor tone changes are minimal, we evaluated the techniques in terms of the ability of their PWV estimates to track the acute BP changes in each subject. Overall, the PWV estimates of the techniques tracked the BP changes better than those of the conventional technique (e.g., diastolic BP root-mean-squared-errors of 3.4 vs. 5.2 mmHg for the simultaneous BP waveforms and 7.0 vs. 12.2 mmHg for the BV and BP waveforms (p < 0.02)). With further testing, the arterial tube-load model-based PWV estimation techniques may afford more accurate arterial stiffness monitoring in hypertensive and other patients. PMID:24263016

  5. Ion Bernstein waves in a plasma with a kappa velocity distribution

    SciTech Connect

    Nsengiyumva, F.; Mace, R. L.; Hellberg, M. A.

    2013-10-15

    Using a Vlasov-Poisson model, a numerical investigation of the dispersion relation for ion Bernstein waves in a kappa-distributed plasma has been carried out. The dispersion relation is found to depend significantly on the spectral index of the ions, ?{sub i}, the parameter whose smallness is a measure of the departure from thermal equilibrium of the distribution function. Over all cyclotron harmonics, the typical Bernstein wave curves are shifted to higher wavenumbers (k) if ?{sub i} is reduced. For waves whose frequency lies above the lower hybrid frequency, ?{sub LH}, an increasing excess of superthermal particles (decreasing ?{sub i}) reduces the frequency, ?{sub peak}, of the characteristic peak at which the group velocity vanishes, while the associated k{sub peak} is increased. As the ratio of ion plasma to cyclotron frequency (?{sub pi}/?{sub ci}) is increased, the fall-off of ? at large k is smaller for lower ?{sub i} and curves are shifted towards larger wavenumbers. In the lower hybrid frequency band and harmonic bands above it, the frequency in a low-?{sub i} plasma spans only a part of the intraharmonic space, unlike the Maxwellian case, thus exhibiting considerably less coupling between adjacent bands for low ?{sub i}. It is suggested that the presence of the ensuing stopbands may be a useful diagnostic for the velocity distribution characteristics. The model is applied to the Earth's plasma sheet boundary layer in which waves propagating perpendicularly to the ambient magnetic field at frequencies between harmonics of the ion cyclotron frequency are frequently observed.

  6. The thin section rock physics: Modeling and measurement of seismic wave velocity on the slice of carbonates

    SciTech Connect

    Wardaya, P. D. Noh, K. A. B. M. Yusoff, W. I. B. W.; Ridha, S.; Nurhandoko, B. E. B.

    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.

  7. 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.

  8. Estimations of the S-wave velocity structures in Chia-Yi City, Taiwan, using the array records of microtremors

    NASA Astrophysics Data System (ADS)

    Huang, H.-C.; Wu, C.-F.

    2006-11-01

    Shear-wave velocities (VS) have been widely used for the site characterization of earthquake ground motion. We report here our investigation of the S-wave velocity structures of Chia-Yi City, Taiwan using the array records of microtremors at seven sites. The dispersion curves at these sites were first calculated using the F-K method proposed by Capon (1969); the S-wave velocity structures in Chia-Yi City were then estimated by employing the surface wave inversion technique (Herrmann, 1991). At frequencies lower than about 1 Hz, the propagation directions are concentrated in the northwest and southwest quadrants. The generation of these may be attributed to the ocean waves of the Taiwan Strait. The harder site (CBA) has higher phase velocities, while the softer sites (CWB, SHP and YRU) have lower phase velocities, especially at frequencies between 1 and 5 Hz. The shallow velocity structures (0-1,500 m) can be roughly divided into four to five layers. The depth of the alluvium gradually increases from east to west and from north to south.

  9. Estimations of the S-Wave Velocity Structures at the Puli Area, Taiwan, Using the Array Records of Microtremors

    NASA Astrophysics Data System (ADS)

    Huang, H.; Wu, C.

    2007-12-01

    In Puli, the collapse of many structures during the Chi-Chi earthquake was very closely related to the site effects (Huang and Tarng, 2005). The Shallow Shear-wave velocities have widely been used for earthquake ground- motion site characterization. Thus, the S-wave velocity structures of the Puli area are investigated using the array records of microtremors at three sites (CUH, NAK and PUL). The dispersion curves at these sites are calculated using the F-K method (Capon, 1969); then, the S-wave velocity structures at the Puli area are estimated by employing the surface wave inversion technique (Herrmann, 1991). Compared with CUH and NAK, PUL has higher phase velocities at frequencies of 2-6 Hz and lower values at frequencies of 0.3-1.3Hz. If the S-wave velocity of bedrock is assumed to be 2000m/sec, the depths of the alluvium at the Puli area are between 450m (NAK) and 660m (PUL). Besides, three distinct interfaces (330-420m, 570-630m, and 800-840m) exist in the shallow velocity structure. The above results are in good agreement with those using the seismic exploration method (Wang et al., 2002).

  10. The effects of pressure, temperature, and pore water on velocities in Westerly granite. [for seismic wave propagation

    NASA Technical Reports Server (NTRS)

    Spencer, J. W., Jr.; Nur, A. M.

    1976-01-01

    A description is presented of an experimental assembly which has been developed to conduct concurrent measurements of compressional and shear wave velocities in rocks at high temperatures and confining pressures and with independent control of the pore pressure. The apparatus was used in studies of the joint effects of temperature, external confining pressure, and internal pore water on sonic velocities in Westerly granite. It was found that at a given temperature, confining pressure has a larger accelerating effect on compressional waves in dry rock, whereas at a given confining pressure, temperature has a larger retarding effect on shear waves.

  11. 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.

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

    USGS Publications Warehouse

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

    2013-01-01

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

  13. Direct Estimation of Love Wave Phase Velocities Using Circular-Array Records of Ambient Noise

    NASA Astrophysics Data System (ADS)

    Tada, T.; Cho, I.; Shinozaki, Y.

    2008-12-01

    We have derived simple and novel formulae to directly infer phase velocities of Love waves using two- component, horizontal-motion, circular-array seismograms of ambient noise (microtremors). Our formulae have been derived as an extension of the SPAC method (Aki, 1957), a popular technique of ambient noise exploration using circular arrays. Most commonly, the SPAC method is used to infer phase velocities of Rayleigh waves (and their dispersion curves) on the basis of vertical-motion data. When three-component seismograms are available, it also provides the possibility to infer phase velocities of Love waves (and their dispersion curves), a useful, additional constraint on the subsurface soil structure (Okada and Matsushima, 1989; Matsushima and Okada, 1990; Ferrazzini et al., 1991; Métaxian et al., 1997; Chouet et al., 1998; Yamamoto, 2000; Saccorotti et al., 2003; Köhler et al., 2007). In the three-component SPAC method, however, the Love-wave phase velocities have to be inferred only as part of the solution of a nonlinear system of equations, in which the Rayleigh-wave phase velocities and the Rayleigh/Love power partition ratios also appear as unknowns to be solved for. The Love-wave phase velocities are the only unknown to appear in our formulae. All we need as the input is the two-component, horizontal-motion records of ambient noise around a circle of radius r and at its center. We first define R(t,r,?) and T(t,r,?) as the radial and tangential components, respectively, of the horizontal-motion seismogram at radius r and azimuth ? as seen from the array center. The time series R1(t,r), T1(t,r) and T0(t,r) are then defined as their weighted and non-weighted azimuthal averages: R1(t,r)=?-?? R(t,r,?)exp(-i?)d? T1(t,r)=?-?? T(t,r,?)exp(-i?)d? T0(t,r)=?-?? T(t,r,?)d? Our new formulae state: GR1T0(r,r;?)/GR1T0(0,r;?)=(J0+J2)(r?/cL(?)) (SPAC+L method) GT1T0(r,r;?)/GT1T0(0,r;?)=(J0-J2)(r?/cL(?)) (SPAC-L method) GT1T0(r,r;?)/GR1T0(r,r;?)=+i[(J0-J2)/(J0+J2)](r?/cL(?)) (CCA-L method). On the left-hand side, GR1T0(r',r;?) (where r'=r or 0) is the correlation function between R1(t,r') and T0(t,r), while GT1T0(r',r;?) is the correlation function between T1(t,r') and T0(t,r) (? denotes the frequency). On the right-hand side, J0 and J2 are the zeroth- and second-order Bessel functions of the first kind, while cL(?) denotes the phase velocity of Love waves. Once the quantity on the left-hand side is known from measurement records, it is quite straightforward to infer cL(?) by simple inversion. We tentatively name the ambient noise methods, based on our new formulae, as marked to the right of each equation above --- SPAC+L, SPAC-L and CCA-L. Although earlier works have also presented elaborate circular-array ambient noise methods to infer Love-wave phase velocities directly (Tada et al., 2006; García-Jerez et al., 2008), the ones we are presenting here are by far simpler. We have tested the practical utility of our formulae by applying them to both artificial and real ambient noise data. Preliminary results have suggested that the SPAC+L method has the best performance, followed by CCA-L and SPAC-L.

  14. 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.

  15. Statistical correlations of shear wave velocity and penetration resistance for soils

    NASA Astrophysics Data System (ADS)

    Dikmen, Ünal

    2009-03-01

    In this paper, the correlation between shear wave velocity and standard penetration test blow counts (SPT-N) is investigated. The study focused primarily on the correlation of SPT-N and shear wave velocity (Vs) for several soil categories: all soils, sand, silt and clay-type soils. New empirical formulae are suggested to correlate SPT-N and Vs, based on a dataset collected in a part of Eski?ehir settlement in the western central Anatolia region of Turkey. The formulae are based on geotechnical soundings and active and passive seismic experiments. The new and previously suggested formulae showing correlations between uncorrected SPT-N and Vs have been compared and evaluated by using the same dataset. The results suggest that better correlations in estimation of Vs are acquired when the uncorrected blow counts are used. The blow count is a major parameter and the soil type has no significant influence on the results. In cohesive soils, the plasticity contents and, in non-cohesive soils except for gravels, the graded contents have no significant effect on the estimation of Vs. The results support most of the conclusions of earlier studies. These practical relationships developed between SPT-N and Vs should be used with caution in geotechnical engineering and should be checked against measured Vs.

  16. Prediction of shear wave velocity using empirical correlations and artificial intelligence methods

    NASA Astrophysics Data System (ADS)

    Maleki, Shahoo; Moradzadeh, Ali; Riabi, Reza Ghavami; Gholami, Raoof; Sadeghzadeh, Farhad

    2014-06-01

    Good understanding of mechanical properties of rock formations is essential during the development and production phases of a hydrocarbon reservoir. Conventionally, these properties are estimated from the petrophysical logs with compression and shear sonic data being the main input to the correlations. This is while in many cases the shear sonic data are not acquired during well logging, which may be for cost saving purposes. In this case, shear wave velocity is estimated using available empirical correlations or artificial intelligent methods proposed during the last few decades. In this paper, petrophysical logs corresponding to a well drilled in southern part of Iran were used to estimate the shear wave velocity using empirical correlations as well as two robust artificial intelligence methods knows as Support Vector Regression (SVR) and Back-Propagation Neural Network (BPNN). Although the results obtained by SVR seem to be reliable, the estimated values are not very precise and considering the importance of shear sonic data as the input into different models, this study suggests acquiring shear sonic data during well logging. It is important to note that the benefits of having reliable shear sonic data for estimation of rock formation mechanical properties will compensate the possible additional costs for acquiring a shear log.

  17. Optical measurement of velocity and drag coefficient of droplets accelerated by shock waves

    NASA Astrophysics Data System (ADS)

    Hirahara, H.; Kawahashi, M.

    2005-02-01

    The drag coefficient of micron-sized droplets accelerated by a shock wave has been investigated. The motion of the droplets was studied by an optical measurement system, and an inertial relaxation in the mist flow is discussed in detail. An expansion-shock tube was employed in the present experiment, in which water droplets were produced by a homogeneous condensation when humid nitrogen gas expanded adiabatically in the test section. The local mean diameter and local number density of the droplet cloud were 1.0 ?m and on the order of 1012 particles/m3, respectively, as estimated using a light scattering measurement in a preliminary experiment. The droplet cloud accelerated behind a shock wave was observed using a direct shadowgraph method with a spatial filter. Since the intensity of transmitted light through the mist flow is a function of the radius and number density of droplets, we can obtain the locally averaged number density distribution under an adequate approximation. The transmitted light intensity was related to the velocity distribution of droplets under the adequate assumption. So, the acceleration of droplets was estimated from the velocity ratio between the droplets and gas flow. Then, the drag coefficient was calculated for the particle Reynolds number. The experimental result was also compared to a numerical prediction.

  18. 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.

  19. 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.

  20. High-resolution seismic tomography of compressional wave velocity structure at Newberry Volcano, Oregon Cascade Range

    SciTech Connect

    Achauer, U.; Evans, J.R.; Stauber, D.A.

    1988-09-10

    Compressional wave velocity structure is determined for the upper crust beneath Newberry Volcano, central Oregon, using a high-resolution active-source seismic-tomography method. Newberry Volcano is a bimodal shield volcano east of the axis of the Cascade Range. It is associated both with the Cascade Range and with northwest migrating silicic volcanism in southeast Oregon. High-frequency (approx.7 Hz) crustal phases, nominally Pg and a midcrustal reflected phase, travel upward through a target volume beneath Newberry Volcano to a dense array of 120 seismographs. This arrangement is limited by station spacing to 1- to 2-km resolution in the upper 5 to 6 km of the crust beneath the volcano's summit caldera. The experiment tests the hypothesis that Cascade Range volcanoes are underlain only by small magma chambers. A small low-velocity anomaly delineated abosut 3 km below the summit caldera supports this hypothesis for Newberry Volcano and is interpreted as a possible magma chamber of a few to a few tens of km/sup 3/ in volume. A ring-shaped high-velocity anomaly nearer the surface coincides with the inner mapped ring fractures of the caldera. It also coincides with a circular gravity high, and we interpret it as largely subsolidus silicic cone sheets. The presence of this anomaly and of silicic vents along the ring fractures suggests that the fractures are a likely eruption path between the small magma chamber and the surface.

  1. 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.

  2. Control of plasma waves associated with the space shuttle by the angle between the orbiter's velocity vector and the magnetic field

    SciTech Connect

    Cairns, I.H.; Gurnett, D.A. )

    1991-05-01

    The interaction between water outgassed from the space shuttle and the ionospheric plasma leads to production of water ions by charge exchange and an active and complex plasma wave environment for the space shuttle. The authors show that the amplitude and spectral character of some of these waves are controlled by the angle between the magnetic field and the shuttle's velocity vector V{sub T} relative to the ionospheric plasma. When the flow is approximately perpendicular to the magnetic field (V{sub {parallel}}/V{sub T}{approximately}0), large wave amplitudes and characteristic mushroom wave structures are observed, whereas more nearly parallel flows {vert bar}V{parallel}{vert bar} {approximately} V{sub {perpendicular}} are characterized by low wave levels. They show that linear instability theory predicts the growth of Doppler-shifted lower hybrid waves in the observed frequency range when driven by the ring and/or beam distributions of water ions produced by charge exchange in the vicinity of the space shuttle. Two mutually compatible interpretations for the V{sub {parallel}}/V{sub T} effect exist. The first interpretation involves the path lengths available for growth of waves driven by pickup ions varying with the quantity V{sub {parallel}}/V{sub T} and being limited by spatial variations in the water ion distribution. The second interpretation follows directly from the linear theory: decreasing the ring/beam speed V{sub {perpendicular}} of the pickup ions driving the waves (increasing V{sub {parallel}}/V{sub T} results in smaller growth rates), with zero growth rate below some threshold value of V{sub {perpendicular}}.These results have immediate implications for future shuttle missions and orbiting platforms subject to outgassing of water. If these facilities are used for ionospheric plasma studies or active experiments involving plasma waves, the plasma wave background due to pickup ions associated with the orbiter should be minimized.

  3. Three-dimensional P- and S-wave velocity structure along the central Alpine Fault, South Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Guo, B.; Thurber, C. H.; Roecker, S. W.; Townend, J.; Rawles, C.; Chamberlain, C. J.; Boese, C. M.; Bannister, S. C.

    2014-12-01

    The Deep Fault Drilling Project (DFDP) on the central Alpine Fault, South Island, New Zealand, has motivated a broad range of geophysical and geological studies aiming to characterize the fault system in the locality of the drill site at various scales. We have been developing three-dimensional P- and S-wave velocity models of the region by double-difference tomography utilizing datasets from multiple seismic networks (WIZARD, SAMBA, ALFA, GeoNet, and others). In our previous work, the quality of the S-wave model has been poor due to the small number of available S-wave picks. We have utilized a new high-accuracy automatic S-wave picker to increase the number of usable S arrivals by an order of magnitude, thereby dramatically improving the S-wave velocity model. Compared to previous studies, e.g. Eberhart-Phillips and Bannister (2002) and Feenstra et al (2013), our updated P-wave model shows a clear high Vp body (Vp > 6km/s) at depths of 5-15 km near the drill site. With our better resolved S-wave velocity model, we can see a sharp high Vs body (Vs > 3.7 km/s) in the same region. The newly added S-picks help to improve the accuracy of the relocations of the earthquakes . This in turn has highlighted the presence of earthquake swarms within the low velocity zone. Together with the updated earthquake relocations, the P- and S-wave tomography results reveal the Alpine Fault to be marked by a velocity contrast throughout most of the study region. The fault dips steeply from 5 to 20 km depth with an average dip of 50-60° SE, as inferred from the velocity structure and the seismicity.

  4. 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.

  5. Radial variation in sap velocity as a function of stem diameter and sapwood thickness in yellow-poplar trees.

    PubMed

    Wullschleger, Stan D.; King, Anthony W.

    2000-04-01

    Canopy transpiration and forest water use are frequently estimated as the product of sap velocity and cross-sectional sapwood area. Few studies, however, have considered whether radial variation in sap velocity and the proportion of sapwood active in water transport are significant sources of uncertainty in the extrapolation process. Therefore, radial profiles of sap velocity were examined as a function of stem diameter and sapwood thickness for yellow-poplar (Liriodendron tulipifera L.) trees growing on two adjacent watersheds in eastern Tennessee. The compensation heat pulse velocity technique was used to quantify sap velocity at four equal-area depths in 20 trees that ranged in stem diameter from 15 to 69 cm, and in sapwood thickness from 2.1 to 14.8 cm. Sap velocity was highly dependent on the depth of probe insertion into the sapwood. Rates of sap velocity were greatest for probes located in the two outer sapwood annuli (P1 and P2) and lowest for probes in closest proximity to the heartwood (P3 and P4). Relative sap velocities averaged 0.98 at P1, 0.66 at P2, 0.41 at P3 and 0.35 at P4. Tree-specific sap velocities measured at each of the four probe positions, divided by the maximum sap velocity measured (usually at P1 or P2), indicated that the fraction of sapwood functional in water transport (f(S)) varied between 0.49 and 0.96. There was no relationship between f(S) and sapwood thickness, or between f(S) and stem diameter. The fraction of functional sapwood averaged 0.66 +/- 0.13 for trees on which radial profiles were determined. No significant depth-related differences were observed for sapwood density, which averaged 469 kg m(-3) across all four probe positions. There was, however, a significant decline in sapwood water content between the two outer probe positions (1.04 versus 0.89 kg kg(-1)). This difference was not sufficient to account for the observed radial variation in sap velocity. A Monte-Carlo analysis indicated that the standard error in estimated mean f(S) declined rapidly with increasing sample size. At n = 10, the coefficient of variation in mean f(S) was 7% and at n = 15 it was slightly less than 5%. These observations indicate that radial variation in sap velocity is an important, albeit often overlooked, source of uncertainty in the scaling process. Failure to recognize that not all sapwood is functional in water transport will introduce systematic bias into estimates of both tree and stand water use. Future studies should devise sampling strategies for assessing radial variation in sap velocity and such strategies should be used to identify the magnitude of this variation in a range of non-, diffuse- and ring-porous trees. PMID:12651431

  6. Full waveform inversion of diving & reflected waves for velocity model building with impedance inversion based on scale separation

    NASA Astrophysics Data System (ADS)

    Zhou, Wei; Brossier, Romain; Operto, Stéphane; Virieux, Jean

    2015-09-01

    Full waveform inversion (FWI) aims to reconstruct high-resolution subsurface models from the full wavefield, which includes diving waves, post-critical reflections and short-spread reflections. Most successful applications of FWI are driven by the information carried by diving waves and post-critical reflections to build the long-to-intermediate wavelengths of the velocity structure. Alternative approaches, referred to as reflection waveform inversion (RWI), have been recently revisited to retrieve these long-to-intermediate wavelengths from short-spread reflections by using some prior knowledge of the reflectivity and a scale separation between the velocity macromodel and the reflectivity. This study presents a unified formalism of FWI, named as Joint FWI, whose aim is to efficiently combine the diving and reflected waves for velocity model building. The two key ingredients of Joint FWI are, on the data side, the explicit separation between the short-spread reflections and the wide-angle arrivals and, on the model side, the scale separation between the velocity macromodel and the short-scale impedance model. The velocity model and the impedance model are updated in an alternate way by Joint FWI and waveform inversion of the reflection data (least-squares migration), respectively. Starting from a crude velocity model, Joint FWI is applied to the streamer seismic data computed in the synthetic Valhall model. While the conventional FWI is stuck into a local minimum due to cycle skipping, Joint FWI succeeds in building a reliable velocity macromodel. Compared with RWI, the use of diving waves in Joint FWI improves the reconstruction of shallow velocities, which translates into an improved imaging at deeper depths. The smooth velocity model built by Joint FWI can be subsequently used as a reliable initial model for conventional FWI to increase the high-wavenumber content of the velocity model.

  7. VizieR Online Data Catalog: Aldebaran radial velocity variations (Hatzes+, 2015)

    NASA Astrophysics Data System (ADS)

    Hatzes, A. P.; Cochran, W. D.; Endl, M.; Guenther, E. W.; MacQueen, P.; Hartmann, M.; Zechmeister, M.; Han, I.; Lee, B.-C.; Walker, G. A. H.; Yang, S.; Larson, A. M.; Kim, K.-M.; Mkrtichian, D. E.; Dollinger, M.; Simon, A. E.; Girardi, L.

    2015-07-01

    Seven independent data sets of high precision radial velocity data were used for our analysis. Precise RV measurements were also made with a Hydrogen-Fluoride (H-F) cell as part of the CFHT survey (hereafter the "CFHT" data set) of Walker et al. (1989ApJ...343L..21W) as well as additional measurements from the Dominion Astrophysical Observatory (hereafter "DAO" data set) using the same technique. See Campbell & Walker (1979PASP...91..540C) and Larson et al. (1993PASP..105..825L) for a description of the H-F measurements. For the remaining five RV data sets an iodine (I2) cell provided the wave- length reference. These include the original measurements using the McDonald Observatory 2.1m telescope (here-after "McD-2.1m" data set) and the coude spectrograph in the so-called "cs11" focus (hereafter "McD-CS11" data set) of the 2.7m telescope at McDonald Observatory. We should note that the we did not include the McDonald data that were used for the bisector measurements of Hatzes & Cochran (1998MNRAS.293..469H). These were taken using telluric lines as a wavelength reference which had a lower precision than the iodine wavelength calibration or H-F methods. The latest McDonald measurements were taken using the Tull Spectrograph at the so-called "cs23" focus (here-after the "McD-Tull" data set) as part of a long-term planet search program (e.g. Cochran et al., 1997ApJ...483..457C; Endl et al., 2004ApJ...611.1121E; Robertson et al., 2012ApJ...749...39R). (7 data files).

  8. Laser Light Scattering Diagnostic for Measurement of Flow Velocity in Vicinity of Propagating Shock Waves

    NASA Technical Reports Server (NTRS)

    Seasholtz, Richard G.; Buggele, Alvin E.

    2002-01-01

    A laser light scattering diagnostic for measurement of dynamic flow velocity at a point is described. The instrument is being developed for use in the study of propagating shock waves and detonation waves in pulse detonation engines under development at the NASA Glenn Research Center (GRC). The approach uses a Fabry-Perot interferometer to measure the Doppler shift of laser light scattered from small (submicron) particles in the flow. The high-speed detection system required to resolve the transient response as a shock wave crosses the probe volume uses fast response photodetectors, and a PC based data acquisition system. Preliminary results of measurements made in the GRC Mach 4, 10 by 25 cm supersonic wind tunnel are presented. Spontaneous condensation of water vapor in the flow is used as seed. The tunnel is supplied with continuous air flow at up to 45 psia and the flow is exhausted into the GRC laboratory-wide altitude exhaust system at pressures down to 0.3 psia.

  9. Non-Contact Determination of Antisymmetric Plate Wave Velocity in Ceramic Matrix Composites

    NASA Technical Reports Server (NTRS)

    Kautz, Harold E.

    1996-01-01

    A 13 mJ NdYAG 1064 nm, 4 ns, laser pulse was employed to produce ultrasonic plate waves in 20 percent porous SiC/SiC composite tensile specimens of three different architectures. An air coupled 0.5 MHz transducer was used to detect and collect the waveforms which contained first antisymmetric plate wave pulses for determining the shear wave velocity (VS). These results were compared to VS values determined on the same specimens with 0.5 MHz ultrasonic transducers with contact coupling. Averages of four noncontact determinations on each of 18 specimens were compared to averages of four contact values. The noncontact VS's fall in the same range as the contact. The standard deviations for the noncontact VS's averaged 2.8 percent. The standard deviations for the contact measurements averaged 2.3 percent, indicating similar reproducibility. Repeated laser pulsing at the same location always lead to deterioration of the ulu-"nic signal. The signal would recover in about 24 hr in air however, indicating that no permanent damage was produced.

  10. Scheme for measuring experimentally the velocity of pilot waves and the discreteness of time

    SciTech Connect

    He Guangping

    2010-12-22

    We consider the following two questions. Suppose that a quantum system suffers a change of the boundary condition or the potential at a given space location. Then (1)when will the wavefunction shows a response to this change at another location? And (2)how does the wavefunction changes?The answer to question (1) could reveal how a quantum system gets information on the boundary condition or the potential. Here we show that if the response takes place immediately, then it can allow superluminal signal transfer. Else if the response propagates in space with a finite velocity, then it could give a simple explanation why our world shows classicality on the macroscopic scale. Furthermore, determining the exact value of this velocity can either clarify the doubts on static experiments for testing Bell's inequality, or support the pilot-wave interpretation of quantum mechanics. We propose a feasible experimental scheme for measuring this velocity, which can be implemented with state-of-art technology, e.g., single-electron biprism interferometry.Question (2) is studied with a square-well potential model, and we find a paradox between the impossibility of superluminal signal transfer and the normalization condition of wavefunctions. To solve the paradox, we predict that when a change of the potential occurs at a given space location, the system will show no response to this change at all, until after a certain time interval. Otherwise either special relativity or quantum mechanics will be violated. As a consequence, no physical process can actually happen within Planck time. Therefore it gives a simple proof that time is discrete, with Planck time being the smallest unit. Combining with the answer to question (1), systems with a larger size and a slower velocity could have a larger unit of time, making it possible to test the discreteness of time experimentally. Our result also sets a limit on the speed of computers, and gives instruction to the search of quantum gravity theories.

  11. Downward Link of Solar Activity Variations Through Wave Driven Equatorial Oscillations (QBO and SAO)

    NASA Technical Reports Server (NTRS)

    Mengel, J. G.; Mayr, H. G.; Chan, K. L.; Porter, H. S.; Einaudi, Franco (Technical Monitor)

    2000-01-01

    Signatures of the 11-year solar activity/irradiance cycle are observed in the Quasi Biennial Oscillation (QBO) of the lower stratosphere. At these altitudes, the QBO is understood to be the result of "downward control" exerted by the wave mean flow interactions that drive the phenomenon. It is reasonable then to speculate that the QBO is a natural conduit to lower altitudes of solar activity variations in radiance (SAV). To test this hypothesis, we conducted experiments with a 2D version of our Numerical Spectral Model that incorporates Hines' Doppler Spread Parameterization for small-scale gravity waves (GW). To account for the SAV, we change the solar heating rate on a logarithmic scale from 0.1% at the surface to 1% at 50 kin to 10% at 100 km. With the same GW flux, we then conduct numerical experiments to evaluate the magnitude of the solar activity irradiance effect (SAE) on the zonal circulation at low latitudes. The numerical results obtained show that, under certain conditions, the SAE is significant in the zonal circulation and does extend to lower altitudes where the SAV is small. The differences in the wind velocities can be as large as 5 m/s at 20 kin. We carried out two numerical experiments with integrations over more than 20 years: 1) With the QBO period "tuned" to be 30 months, of academic interest but instructive, the seasonal cycle in the solar forcing [through the Semi-annual Oscillation (SAO)] acts as a strong pacemaker to produce a firm lock on the period and phase of the QBO. The SAE then shows up primarily as a distinct but relatively weak amplitude modulation. 2) With the QBO period between 30 and 34 (or less than 30, presumably) months, the seasonal phase lock is weak compared with (1). The SAV in the seasonal cycle then causes variations in the QBO period and phase, and this amplifies the SAE to produce relatively large variations in the wind field. We conclude that, under realistic conditions as in (2), the solar seasonal forcing, with activity variations in radiance, causes the phase and period of the QBO to change to produce a relatively large solar activity effect in the zonal circulation at low latitudes and low altitudes.

  12. Ambient noise analysis along the North Anatolian Fault Zone in Turkey: Lateral variations of the crustal velocity field

    NASA Astrophysics Data System (ADS)

    Acarel, D.; Bulut, F.; Bohnhoff, M.

    2013-12-01

    We analyze the ambient seismic noise field in order to investigate crustal structure and seismic anisotropy at the North Anatolian Fault Zone (NAFZ) in NW Turkey. We focus on the eastern Sea of Marmara section of the NAFZ representing a pre-seismic phase of the seismic cycle just prior to an expected major (M>7) earthquake. We apply cross-correlation analysis of the seismic ambient noise to determine spectral dependence of the seismic velocity in order to image crustal structure at seismogenic depths. Time-domain cross correlations are calculated for all available stations pairs in the target area. Inter-station distances span 0.3-90 km. Only the vertical component is analyzed in order to recover fundamental mode Rayleigh waves in the frequency range of 0.05-1.1 Hz. Group velocity dispersion curves are obtained for selected correlation paths in particular to address the directional dependency of the velocity field. In the frequency band of interest, average group velocities range between ~1.8 and 3.5 km/s. Dispersion curves corresponding to the NS-trending paths crossing the main NAFZ fault branch below the eastern Sea of Marmara show low group velocities between ~1.5 and 1.8 km/s well explained by the 3-4 km-deep Çinarcik Basin directly south of the fault. In contrast, ray paths restricted to within the mainland Istanbul and Armutlu peninsulas (primarily trending EW) show higher group velocities up to 3.2 km/s. By averaging the dispersion curves we determine an optimized 1-D S-wave velocity model for the eastern Sea of Marmara region allowing for a significant improvement in hypocenter determination.

  13. Estimation of shallow S-wave velocity structure in the Puli basin, Taiwan, using array measurements of microtremors

    NASA Astrophysics Data System (ADS)

    Wu, Cheng-Feng; Huang, Huey-Chu

    2012-05-01

    The September 21, 1999, Chi-Chi earthquake induced strong shaking, resulting in severe damage in the Puli area. According to Huang and Tarng (2005), the collapse of many structures during the earthquake was very closely related to site effects. Shallow shear-wave velocities are widely used for earthquake ground-motion site characterization. Thus, we investigate S-wave velocity structures for the Puli area by performing microtremor array measurements at 16 sites. Dispersion curves at these sites are calculated using the F-K method (Capon, 1969) for the vertical component; S-wave velocity structures for the Puli area are then estimated by surface wave inversion (Herrmann, 1991). If the S-wave velocity of the bedrock is assumed to be 2000 m/s, the depths of the Quaternary sediments in the Puli area are between 300 m (FAL, PIP) and 870 m (DAH). Moreover, there are 3˜6 distinct interfaces in the shallow velocity structure (0˜1000 m). The depth of the bedrock gradually increases from the edge (SIN, PIP) to the center (PUL, DAH) of the basin and the thickest Quaternary sediments appear near Heng-Chih-Cheng (DAH).

  14. Ambient noise surface wave tomography to determine the shallow shear velocity structure at Valhall: depth inversion with a Neighbourhood Algorithm

    NASA Astrophysics Data System (ADS)

    Mordret, A.; Landès, M.; Shapiro, N. M.; Singh, S. C.; Roux, P.

    2014-09-01

    This study presents a depth inversion of Scholte wave group and phase velocity maps obtained from cross-correlation of 6.5 hr of noise data from the Valhall Life of Field Seismic network. More than 2 600 000 vertical-vertical component cross-correlations are computed from the 2320 available sensors, turning each sensor into a virtual source emitting Scholte waves. We used a traditional straight-ray surface wave tomography to compute the group velocity map. The phase velocity maps have been computed using the Eikonal tomography method. The inversion of these maps in depth are done with the Neighbourhood Algorithm. To reduce the number of free parameters to invert, geological a priori information are used to propose a power-law 1-D velocity profile parametrization extended with a gaussian high-velocity layer where needed. These parametrizations allowed us to create a high-resolution 3-D S-wave model of the first 600 m of the Valhall subsurface and to precise the locations of geological structures at depth. These results would have important implication for shear wave statics and monitoring of seafloor subsidence due to oil extraction. The 3-D model could also be a good candidate for a starting model used in full-waveform inversions.

  15. The effect of nickel on the properties of iron at the conditions of Earth's inner core: Ab initio calculations of seismic wave velocities of

    E-print Network

    Vocadlo, Lidunka

    calculations of seismic wave velocities of Fe­Ni alloys Benjami´ Martorell n , John Brodholt, Ian G. Wood such as Si, C, O and S ($2%; Birch, 1964; Poirier, 1994). Although data for seismic wave velocities through­Ni alloy high pressure high temperature inner core elastic properties compressional and shear wave

  16. Method to measure a relative transverse velocity of a source-lens-observer system using gravitational lensing of gravitational waves

    SciTech Connect

    Itoh, Yousuke; Futamase, Toshifumi; Hattori, Makoto

    2009-08-15

    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 wavelengths 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.

  17. One-dimensional particle-in-cell simulations of electrostatic Bernstein waves in plasmas with kappa velocity distributions

    NASA Astrophysics Data System (ADS)

    Abdul, R. F.; Mace, R. L.

    2015-10-01

    Electrostatic Bernstein waves that propagate exactly perpendicularly to a static magnetic field in an electron-ion plasma are investigated using one-and-two-halves dimensional particle-in-cell simulations. An ion-to-electron mass ratio of mi/me = 100 is used, allowing sufficient separation of the electron and ion time scales while still accounting for the ion dynamics without resorting to exceptionally long simulation run times. As a consequence of the mass ratio used, both the high frequency electron Bernstein wave and the lower frequency ion Bernstein wave are resolved within a single simulation run. The simulations presented here use isotropic three-dimensional kappa velocity distributions as well as the widely used Maxwellian velocity distribution, and the results from using each of these velocity distributions are analysed and compared. The behaviour of the Bernstein waves is found to be significantly dependent on the spectral index, ?, of the kappa distribution in all frequency domains of the Bernstein waves. In both the Maxwellian and kappa cases, spectral analysis of the electric field (wave) intensities, as a function of ? and k, show very good agreement between the simulation results and the linear dispersion relation for Bernstein waves. This agreement serves to validate the simulation techniques used, as well as the theory of Bernstein waves in plasmas with a kappa velocity distribution. The intensity of the field fluctuations in the simulations containing an abundance of superthermal particles, i.e., where the plasma has a kappa velocity distribution with a low kappa index, is slightly higher compared to the simulations of plasmas with higher kappa values. The plasmas with low kappa values also exhibit a broader region in frequency space of high intensity field fluctuations.

  18. Variation in Differential and Total Cross Sections Due to Different Radial Wave Functions

    ERIC Educational Resources Information Center

    Williamson, W., Jr.; Greene, T.

    1976-01-01

    Three sets of analytical wave functions are used to calculate the Na (3s---3p) transition differential and total electron excitation cross sections by Born approximations. Results show expected large variations in values. (Author/CP)

  19. Traveling-wave electrokinetic micropumps: velocity, electrical current, and impedance measurements.

    PubMed

    García-Sánchez, P; Ramos, A; Green, N G; Morgan, H

    2008-09-01

    An array of microelectrodes covered in an electrolyte and energized by a traveling-wave potential produces net movement of the fluid. Arrays of platinum microelectrodes of two different characteristic sizes have been studied. For both sizes of arrays, at low voltages (<2 V pp) the electrolyte flow is in qualitative agreement with the linear theory of ac electroosmosis. At voltages above a threshold, the direction of fluid flow is reversed. The electrical impedance of the electrode-electrolyte system was measured after the experiments, and changes in the electrical properties of the electrolyte were observed. Measurements of the electrical current during pumping of the electrolyte are also reported. Transient behaviors in both electrical current and fluid velocity were observed. The Faradaic currents probably generate conductivity gradients in the liquid bulk, which in turn give rise to electrical forces. These effects are discussed in relation to the fluid flow observations. PMID:18672919

  20. Surface acoustic wave velocity of gold films deposited on silicon substrates at different temperatures

    SciTech Connect

    Salas, E.; Jimenez Rioboo, R. J.; Prieto, C.; Every, A. G.

    2011-07-15

    Au thin films have been deposited by DC magnetron sputtering on Si (001) substrates at different substrate temperatures, ranging from 200 K to 450 K. With increasing temperature, the expected crystallinity and morphology of the Au thin film are clearly improved, as shown by x ray diffraction, atomic force microscopy and scanning electron microscopy experiments. Parallel to this, the surface acoustic wave propagation velocity shows a clear enhancement toward the ideal values obtained from numerical simulations of a Au thin film on Si (001) substrate. Moreover, a very thin and slightly rough interlayer between the Si (001) substrate and the Au thin film is developed for temperatures above 350 K. The composition and nature of this interlayer is not known. This interlayer may be responsible for the steep change in the structural and elastic properties of the Au thin films at the higher temperatures and possibly also for an improvement of the adhesion properties of the Au on the Si (001) substrate.

  1. Inferring subasthenospheric mantle flow velocity from shear-wave splitting near midocean ridges

    NASA Astrophysics Data System (ADS)

    Ribe, N.; Silver, P.; Kaminski, E.

    2003-04-01

    Seismic anisotropy is one of the few geophysical observables that can provide direct constraints on the pattern of upper mantle flow. Theory and experiment show that in simple shear, the seismically fast axes of olivine crystals rapidly align with the flow direction, which will then correspond to the fast direction, ?, of shear-wave splitting (SWS). If the anisotropy is concentrated within a low-viscosity asthenosphere that decouples the lithosphere from the mantle below, ? will give the orientation (± 180o) of the differential velocity between the lithosphere V_L and subasthenospheric mantle velocity, V_M. SWS measurements on a rigid lithosphere are insufficient to infer V_M or (equivalently) the sense of shear within the asthenosphere. However, such inferences can in principle be made from SWS measurements on a deforming lithosphere (Silver and Holt, 2002) or on opposite sides of a spreading ridge (Bjarnason et al., 2002), given idealized assumptions about the mantle flow field. In order to evaluate the feasibility of inferring mantle flow velocity in a realistic oceanic setting, we consider a simple upper mantle model comprising a low-viscosity layer (asthenosphere) above a higher viscosity layer and below a rigid lithosphere. The (analytically determined) flow in both layers is the sum of a ridge-like corner flow and a horizontal simple shear with arbitrary strength and direction induced by applying a constant velocity boundary condition at the base of the lower layer. The evolution of olivine/enstatite lattice preferred orientation along streamlines is determined using the method of Kaminski and Ribe (2001), and is then used to calculate the full anisotropic elastic tensor at each point in the model domain. Synthetic profiles of SWS across the ridge are then calculated using the method of Rümpker and Silver (1998). The calculated profiles exhibit striking asymmetries that reflect directly the flow velocity within the subasthenospheric layer. We will report the results of a systematic study to evaluate the ability to invert for V_M as a function of the strength and direction of the shear and on the interlayer viscosity contrast.

  2. Dip-moveout error in transversely isotropic media with linear velocity variation in depth

    SciTech Connect

    Larner, K.L. . Dept. of Geophysics)

    1993-10-01

    Levin modeled the moveout, within common-mid-point (CMP) gathers, of reflection from plane-dipping reflectors beneath homogeneous, transversely isotropic media. For some media, when the axis of symmetry for the anisotropy was vertical, the author found departures in stacking velocity from predictions based upon the familiar cosine-of-dip correction for isotropic media. Here, the author does similar tests, again with transversely isotropic models with vertical axis of symmetry, but now allowing the medium velocity of vary linearly with depth. Results for the same four anisotropic media studied by Levin show behavior of dip-corrected stacking velocity with reflector dip that, for all velocity gradients considered, differs little from that for the counterpart homogeneous media. As with isotropic media, travel times in an inhomogeneous, transversely isotropic medium can be modeled adequately with a homogeneous model with vertical velocity equal to the vertical rms velocity of the inhomogeneous medium. In practice, dip-moveout (DMO) is based on the assumption that either the medium is homogeneous or its velocity varies with depth, but in both cases isotropy is assumed. It turns out that for only one of the traversely isotropic media considered here--shale-limestone--would v(z) DMO fail to give an adequate correction within CMP gathers. For the shale-limestone, fortuitously the constant-velocity DMO gives a better moveout correction than does the v(z) DMO.

  3. Association of brachial-ankle pulse wave velocity with cardiovascular risk factors in systemic lupus erythematosus.

    PubMed

    Tso, T K; Huang, W N; Huang, H Y; Chang, C K

    2005-01-01

    Systemic lupus erythematosus (SLE) is associated with premature atherosclerosis. Increasing arterial stiffness is closely associated with atherosclerotic cardiovascular diseases, and pulse wave velocity (PWV) is considered to be an indicator of arterial stiffness. The objective of this study was to identify the relationship between brachial-ankle pulse wave velocity (baPWV) and cardiovascular risk factors in patients with SLE. Age, body mass index (BMI), systolic blood pressure (SBP), diastolic blood pressure (DBP), fasting blood glucose (FBS), plasma lipid profile, plasma homocysteine, thiobarbituric acid reactive substances (TBARS), baPWV, ankle-brachial index (ABI), and SLE-related factors were determined in a total of 83 SLE patients (12 males and 71 females). All SLE patients were further classified into two subgroups according to baPWV value (baPWV < 1400 cm/s, n=37 versus baPWV > 1400 cm/s, n=46). The mean baPWV value of studied SLE patients was 1520 +/- 381 cm/s. Age, BMI, SBP, DBP, FBS, TBARS and homocysteine levels were significantly higher in SLE patients with baPWV value > 1400cm/s than in SLE patients with baPWV value < 1400cm/s. In addition, baPWV correlated significantly with age, SBP, DBP, FBS and homocysteine. Moreover, stepwise multiple regression analysis showed that age and SBP were independently associated with baPWV. The results of this study indicate a possible link between vascular stiffness measured by baPWV and cardiovascular risk factors in patients with SLE. PMID:16335579

  4. Quantitative Assessment of In-situ Salt Karstification Using Shear Wave Velocity, Dead Sea

    NASA Astrophysics Data System (ADS)

    Ezersky, Michael; Legchenko, Anatoly

    2014-09-01

    The Dead Sea (DS) coastal areas have been dramatically affected by sinkhole formation since around 1990. Such sinkholes along both Israeli and Jordanian shores are linked to karst cavities that form through slow salt dissolution. A quantitative estimate of such in-situ salt karstification would be an important indicator of sinkhole hazard. One of the indications of salt karstification is its increased hydraulic conductivity, caused by the development of dissolution cavities forming conducting channels within the salt layer. We measured the hydraulic conductivity (K) versus shear-wave velocity (Vs) of DS salt in situ for estimating the actual salt karstification in areas of sinkhole development. These parameters were measured with the Magnetic Resonance Sounding (MRS) and Multichannel Analysis of Surface Waves (MASW) methods, respectively. Understanding of the field relationships was augmented by similar inter-relations obtained in the laboratory on samples of DS salt. In-situ salt velocities Vs vary from 750 m/s to over 1650 m/s, while hydraulic conductivity (K) in the same zones varies between about 10- 4 m/s to slightly over 10- 8 m/s. Both field and laboratory K and Vs values fit the exponential function ln(K) = - 0.0045 ? Vs - 5.416 with a determination coefficient (R2) of 0.88. A classification based on Vs and K was generated for salt conditions and the corresponding degrees of sinkhole hazard, which was verified in the Mineral Beach sinkhole development area. The mapping of sinkhole sites shows that they form within highly conductive zones with K ? 5.5 ? 10- 5. It is suggested that this methodology, with some modification, can be used for evaluating the conductive properties of karstified rock and associated sinkhole hazards.

  5. Seismic velocity anisotropy and heterogeneity beneath the Mantle Electromagnetic and Tomography Experiment (MELT) region of the East Pacific Rise from analysis of P and S body waves

    USGS Publications Warehouse

    Hammond, W.C.; Toomey, D.R.

    2003-01-01

    We use teleseismic P and S delay times and shear wave splitting measurements to constrain isotropic and anisotropic heterogeneity in the mantle beneath the southern East Pacific Rise (SEPR). The data comprise 462 P and S delay times and 18 shear wave splitting observations recorded during the Mantle Electromagnetic and Tomography (MELT) Experiment. We estimate the mantle melt content (F) and temperature (T) variation from the isotropic velocity variation. Our results indicate that the maximum variation in F beneath our array is between zero and ???1.2%, and maximum variation in T is between zero and ???100 K. We favor an explanation having partial contributions from both T and F. We approximate the seismic anisotropy of the upper mantle with hexagonal symmetry, consistent with the assumption of two dimensionality of mantle flow. Our new tomographic technique uses a nonlinear inversion of P and slow S polarization delay times to simultaneously solve for coupled VP and VS heterogeneity throughout the model and for the magnitude of anisotropy within discrete domains. The domain dimensions and the dip of the anisotropy are fixed for each inversion but are varied in a grid search, obtaining the misfit of the models to the body wave delay data and to split times of vertically propagating S waves. The data misfit and the isotropic heterogeneity are sensitive to domain dimensions and dip of anisotropy. In a region centered beneath the SEPR the best average dip of the hexagonal symmetry axis is horizontal or dipping shallowly (<30??) west. Given the resolution of our data, a subaxial region characterized by vertically aligned symmetry axes may exist but is limited to be <80 km deep. We infer that the mantle flow beneath the SEPR is consistent with shallow asthenospheric return flow from the direction of the South Pacific superswell.

  6. 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.

  7. 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.

  8. Study on creating hydraulic tomography for crystalline rock using frequency dependent elastic wave velocity

    SciTech Connect

    Yoshimura, K.; Sakashita, S.; Ando, K.; Bruines, P.; Blechschmidt, I.; Kickmaier, W.; Onishi, Y.; Nishiyama, S.

    2007-07-01

    The objective of this study is to establish a technique to obtain hydraulic conductivity distribution in granite rock masses using seismic tomography. We apply the characteristic that elastic wave velocity disperses in fully saturated porous media on frequency and this velocity dispersion is governed by the hydraulic conductivity - this characteristic has been confirmed in laboratory experiments. The feasibility and design of the field experiment was demonstrated in a first step with numerical simulations. In a second step we applied the technique to the fractured granite at the Grimsel Test Site in Switzerland. The emphasis of the field campaign was on the evaluation of the range of applicability of this technique. The field campaign was structured in three steps, each one corresponding to a larger spatial scale. First, the seismic tomography was applied to a small area - the two boreholes were located at a distance of 1.5 m. In the following step, we selected a larger area, in which the distance of the boreholes amounts to 10 m and the field corresponds to a more complex geology. Finally we applied the testing to a field where the borehole distance was of the order of 75 m. We also drilled a borehole to confirm hydraulic characteristic and reviewed hydraulic model in the 1.5 m cross-hole location area. The results from the field campaign are presented and their application to the various fields are discussed and evaluated. (authors)

  9. Independent association between brachial-ankle pulse wave velocity and global longitudinal strain of left ventricle.

    PubMed

    Kim, Hack-Lyoung; Seo, Jae-Bin; Chung, Woo-Young; Kim, Sang-Hyun; Kim, Myung-A; Zo, Joo-Hee

    2015-12-01

    Data regarding the influence of arterial stiffness on left ventricular (LV) long-axis function has been scarce. This study was performed to investigate the association between brachial-ankle pulse wave velocity (baPWV) and LV global longitudinal strain (GLS). A total of 248 subjects (mean age 59.2 ± 12.3 years; 50 % were men) without structural heart problems were retrospectively evaluated. LV GLS was measured by 2-dimensional speckle-tracking echocardiography. baPWV measurements were made on the same day of echocardiography. The incidences of hypertension, diabetes mellitus, and dyslipidemia were 51.2, 19.4, and 22.2 %, respectively. The mean value of baPWV was 1557 ± 285 cm/s. In simple linear regression analysis, baPWV had a significant positive association with LV GLS (? = 0.215, P = 0.001). In multiple linear regression analysis, baPWV was independently associated with LV GLS even after controlling for potential confounders, including age, gender, body mass index, systolic blood pressure, heart rate, HbA1c, total cholesterol, estimated glomerular filtration rate, left ventricular mass index, E/A, septal e' velocity and pulmonary artery systolic pressure (? = 0.211, P = 0.028). The results of this study suggest that baPWV may be independently associated with LV GLS, supporting the evidence of a close interaction between arterial stiffness and LV function. Increased arterial stiffness may result in impaired LV longitudinal function. PMID:26298315

  10. Low-amplitude and long-period radial velocity variations in giants HD 3574, 63 Cygni, and HD 216946

    NASA Astrophysics Data System (ADS)

    Lee, B.-C.; Han, I.; Park, M.-G.; Hatzes, A. P.; Kim, K.-M.

    2014-06-01

    Aims: We study the low-amplitude and long-period variations in evolved stars using precise radial velocity measurements. Methods: The high-resolution, fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) was used from September 2004 to May 2014 as part of the exoplanet search program at the Bohyunsan Optical Astronomy Observatory (BOAO). Results: We report the detection of low-amplitude and long-period orbital radial velocity variations in three evolved stars, HD 3574, 63 Cyg, and HD 216946. They have periods of 1061, 982, and 1382 days and semi-amplitudes of 376, 742, and 699 m s-1, respectively. Based on observations made with the BOES instrument on the 1.8 m telescope at Bohyunsan Optical Astronomy Observatory in Korea.Tables 2-4 are available in electronic form at http://www.aanda.org

  11. 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.

  12. Lithospheric instability and the source of the Cameroon Volcanic Line: Evidence from Rayleigh wave phase velocity tomography

    NASA Astrophysics Data System (ADS)

    Adams, Aubreya N.; Wiens, Douglas A.; Nyblade, Andrew A.; Euler, Garrett G.; Shore, Patrick J.; Tibi, Rigobert

    2015-03-01

    The Cameroon Volcanic Line (CVL) is a 1800 km long volcanic chain, extending SW-NE from the Gulf of Guinea into Central Africa, that lacks the typical age progression exhibited by hot spot-related volcanic tracks. This study investigates the upper mantle seismic structure beneath the CVL and surrounding regions to constrain the origin of volcanic lines that are poorly described by the classic plume model. Rayleigh wave phase velocities are measured at periods from 20 to 182 s following the two-plane wave methodology, using data from the Cameroon Seismic Experiment, which consists of 32 broadband stations deployed between 2005 and 2007. These phase velocities are then inverted to build a model of shear wave velocity structure in the upper mantle beneath the CVL. Results show that phase velocities beneath the CVL are reduced at all periods, with average velocities beneath the CVL deviating more than -2% from the regional average and +4% beneath the Congo Craton. This distinction is observed for all periods but is less pronounced for the longest periods measured. Inversion for shear wave velocity structure indicates a tabular low velocity anomaly directly beneath the CVL at depths of 50 to at least 200 km and a sharp vertical boundary with faster velocities beneath the Congo Craton. These observations demonstrate widespread infiltration or erosion of the continental lithosphere beneath the CVL, most likely caused by mantle upwelling associated with edge-flow convection driven by the Congo Craton or by lithospheric instabilities that develop due to the nearby edge of the African continent.

  13. Stationary Planetary Wave and Nonmigrating Tidal Composition of Ionospheric Wave-3 & Wave-4 variations in 2007-2011 FORMOSAT-3/COSMIC observations

    NASA Astrophysics Data System (ADS)

    Chang, L. C.; Lin, C.; Yue, J.; Liu, J. G.; Lin, J.

    2013-12-01

    The wave-3 and wave-4 modulations of the Equatorial Ionization Anomalies (EIAs) are a robust feature of the low latitude ionosphere, when viewed in a constant local time reference frame. Although initially associated respectively with the DE2 and DE3 nonmigrating diurnal tides coupling upwards from the mesosphere and lower thermosphere (MLT) region alone, recent results have suggested that the wave-3 and wave-4 components may also have significant contributions from other nonmigrating tidal and stationary planetary wave (SPW) components. In this study, we present observations of tidal and SPW components comprising the ionospheric wave-3 and wave-4 structures from FORMOSAT-3 / COSMIC Total Electron Content (TEC) from 2007-2011. We find that the wave-3 (wave-4) feature is comprised predominately by DE2 (DE3) and SPW3 (SPW4) throughout the entire five year period, with contributions from SE1 (SE2) being less significant. Additionally, the wave-3 component also has recurring contributions from a DW4 component during December/January. The absolute amplitudes of all the aforementioned components are positively correlated to the level of solar activity, as well as the semiannual variation in zonal mean TEC. After normalizing by the zonal mean TEC, the relative amplitudes of the wave-4 related components show an anti-correlation to solar activity through 2010, which is not seen with the wave-3 related components. The seasonal variation and phase relations of the main constituents of wave-3 and wave-4 are consistent from year to year, as evidenced by the inter-annual recurrence in the peak and trough locations of the ionospheric wave-3 and wave-4. Relative amplitudes of DE3 (black) and SPW4 (blue) in COSMIC TECs as a function of time at 15°N (a) and 15°S (b). Units % of maximum daily zonal mean TEC. Range of uncertainties denoted by dotted lines.

  14. Binaries at Birth: Stellar multiplicity in embedded clusters from radial velocity variations in the IN-SYNC survey

    NASA Astrophysics Data System (ADS)

    Oskar Jaehnig, Karl; Stassun, Keivan; Tan, Jonathan C.; Covey, Kevin R.; Da Rio, Nicola

    2016-01-01

    We study the nature of stellar multiplicity in young stellar systems using the INfrared Spectroscopy of Young Nebulous Clusters (IN-SYNC) survey, carried out in SDSS III with the APOGEE spectrograph. Multi-epoch observations of thousands of low-mass stars in Orion A, NGC2264, NGC1333 and IC348 have been carried out, yielding H-band spectra with R=22,500 for sources with H<12 mag. Radial velocity sensitivities ~0.3 km/s can be achieved, depending on the spectral type of the star. We search the IN-SYNC radial velocity catalog to identify sources with radial velocity variations indicative of spectroscopically undetected companions, analyze their spectral properties and discuss the implications for the overall multiplicity of stellar populations in young, embedded star clusters.

  15. 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.

  16. Diffractive Nonlinear Geometrical Optics for Variational Wave Equations and the Einstein Equations

    E-print Network

    Giuseppe Ali; John K. Hunter

    2005-11-02

    We derive an asymptotic solution of the vacuum Einstein equations that describes the propagation and diffraction of a localized, large-amplitude, rapidly-varying gravitational wave. We compare and contrast the resulting theory of strongly nonlinear geometrical optics for the Einstein equations with nonlinear geometrical optics theories for variational wave equations.

  17. 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

  18. 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.

  19. Augmentation index and aortic pulse wave velocity in patients with abdominal aortic aneurysms

    PubMed Central

    Durmus, Ismet; Kazaz, Zeynep; Altun, Gokalp; Cansu, Aysegul

    2014-01-01

    Background: Abdominal aortic aneurysm (AAA) is a severe disease that can prove fatal. Factors such as advanced age, male gender, family history and cigarette use increase the risk of AAA. These factors associated with AAA development also increase arterial stiffness. Aortic pulse-wave velocity (PWV) was measured as an index of aortic stiffness. The heart rate-corrected augmentation index (AIx@75) was estimated as a composite marker of wave reflections and arterial stiffness. Elevated arterial stiffness increases the risk of development of cardiovascular events and impairs cardiovascular functions. In this study we investigated whether arterial stiffness rises in patients with AAA by measuring aortic PWV and AIx@75 parameters. Methods: Eighteen patients with AAA (age 69 ± 4 years) and 20 patients with no aneurysm (age 66 ± 6) were included. AAA was diagnosed using computerized tomography. Arterial stiffness was measured non-invasively in all patients using a SphygmoCor device. Aortic PWV and AIx@75 were used as arterial stiffness parameters. Results: There was no significant difference between the two groups in terms of demographic characteristics. AIx@75 (33.2 ± 8.9 vs 25.1 ± 7.8, p=0.008) and aortic PWV (14.8 ± 4.9 vs 10.0 ± 1.7, p=0.002) were significantly elevated in the AAA group compared to the control group. Conclusion: Elevated AIx@75 and aortic PWV shows that arterial stiffness increases in patients with AAA. PMID:24600499

  20. Shear wave velocity analysis of a deep seated gravel landslide structure using the microtremor survey method

    NASA Astrophysics Data System (ADS)

    Su, L.; Xu, X.; Liao, H.; Geng, X.-Y.

    2015-09-01

    The depth and geometry of potential failure surface is the fundamental for evaluating the mechanisms of a landslide. Traditional techniques to acquire information on potential sliding surface are mainly drilling, pitting, and trenching, but these techniques are time consuming and expensive. In this study, microtremor signals and the dispersion curves of surface wave are extracted from the vertical component of microtremor records using the spatial autocorrelation (SPAC) method to estimate shear wave velocity structure. The results suggest that the buried depth of phyllite bedrock is approximately 47.4m, and the thickness of weathered bedrock layer is about 9.9m at about 57.3m deep, which could be interpreted as the potential sliding surface of this landslide, in accordance with borehole data. The microtremor survey method (MSM) is flexible, non-invasive, relatively quick and deployable on the landslide. It clearly demonstrat that it is an effective tool to improve the drilling success rate, and hence allow a large scale and high density investigation of structure characteristics of a deep seated landslide.

  1. 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.

  2. Joint Bayesian inversion of free oscillations and body waves for Earth's radial velocity and density structure

    NASA Astrophysics Data System (ADS)

    De Wit, R. W.; Valentine, A. P.; Trampert, J.

    2013-12-01

    Existing 1-D seismic models are the basis for 3-D seismic tomography and most earthquake location algorithms. It is therefore important to evaluate the quality of such 1-D reference models, yet quantifying uncertainties in seismological models is challenging. Ideally, quality assessment is an integral part of the inverse method. Our aim in this study is two-fold: (i) we show one approach to solving a Bayesian non-linear inverse problem and quantifying model uncertainties, and (ii) we analyse the constraint on radial P and S-wave velocity and density structure provided by normal mode and travel time data. We jointly invert body-wave travel times from the EHB bulletin (phases Pn, P, PP, PKP, Sn and S) and centre frequencies of recently measured splitting functions for the Earth's free oscillations up to 10 mHz. We adopt a machine learning approach to extract all information on the 1-D model that is available in the seismic data. We use artificial neural networks, which are very common in pattern recognition problems and can be used to approximate an arbitrary function. We obtain probability density functions (pdfs), which provide a quantitative description of our knowledge of the individual earth model parameters.

  3. Stereoscopy of dust density waves under microgravity: Velocity distributions and phase-resolved single-particle analysis

    SciTech Connect

    Himpel, Michael Killer, Carsten; Melzer, André; Bockwoldt, Tim; Piel, Alexander; Ole Menzel, Kristoffer

    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.

  4. Joint Inversion of Geoid Anomaly and Teleseismic P-Wave Delay Times: Modeling Density and Velocity Perturbations Beneath the Parana Magmatic Province

    NASA Astrophysics Data System (ADS)

    Chaves, C. A. M.; Ussami, N.; Ritsema, J.

    2014-12-01

    The Parana Magmatic Province (PMP) is one of the largest continental igneous provinces (LIP) on Earth. It is well dated at 133 Ma preceding the opening of the South Atlantic Ocean, but the causative geodynamic processes are still poorly understood. Although a low-velocity anomaly has been imaged by seismic tomography in the northeast region of the PMP and interpreted as a fossil conduct of a mantle plume that is related to the flood basalt eruptions, geochemical data indicate that such magmatism is caused by the melting of a heterogeneous and enriched lithospheric mantle with no deep plume participation. Models of density perturbations in the upper mantle estimated from joint inversion of geoid anomalies and P-wave delay times will offer important constraints on mantle dynamics. A new generation of accurate global geopotential models derived from satellite-missions (e.g. GRACE, GOCE) allows us to estimate density distribution within the Earth from geoid inversion. In order to obtain the residual geoid anomaly related to the density structure of the mantle, we use the EGM2008 model removing estimated geoid perturbations owing to variations in crustal structure (i.e., topographical masses, Moho depth, thickness of sediments and basalts). Using a spherical-Earth approximation, the density model space is represented by a set of tesseroids and the velocity model is parameterized in nodes of a spherical grid where cubic B-splines are utilized as an interpolation function. To constrain the density inversion, we add more than 10,000 manually picked teleseismic P-wave delay times. During the inversion procedure, density and P-wave velocity are linked through the optimization of a constant linear factor correlating density and velocity perturbation. Such optimization will be performed using a probability density function (PDF) [Tarantola, 2005]. We will present the preliminary results of this joint inversion scheme and hypothesize on the geodynamic processes responsible for the flood basalt eruptions.

  5. Ultrasonic elastic wave velocity measurements of polycrystalline pyrope garnet up to 20 GPa and 1700 K

    NASA Astrophysics Data System (ADS)

    Zou, Y.; Irifune, T.; Greaux, S.; Whitaker, M. L.; Ohfuji, H.; Shinmei, T.; Higo, Y.; Li, B.

    2012-12-01

    Pyrope Mg3Al2(SiO4)3 garnet is considered a significant magnesium end-member of garnets group. Elastic properties of pyrope garnet for both single crystal and synthetic polycrystalline samples have been measured by various techniques, including ultrasonic interferometry, Brillouin scattering and static compression methods. However, to date, direct measurements of the elastic wave velocities of pyrope garnet based on in situ high P-T experiments have been still limited. Previous studies were carried out either at high pressure or high temperature. Moreover, the earlier studies on the elastic properties, i.e. the pressure and temperature dependence of bulk modulus and shear modulus are not well constrained. It is thus of great importance to carry out further studies for pyrope garnet at elevated pressures and temperatures. Recently, the elasticity and sound velocities of synthetic polycrystalline pyrope garnet have been measured up to 20 GPa and 1700 K, equivalent to the middle part of the mantle transition zone, by using ultrasonic interferometry combined with energy-dispersive synchrotron X-ray diffraction in a Kawai-type multi-anvil apparatus. Compressional (VP) and shear wave (VS) velocities as well as the bulk (KS) and shear (G) moduli exhibit monotonic increase with pressure, and decrease with temperature, respectively. Two-dimensional linear fittings yield the following parameters: KS0 = 170.0(2) GPa, dKs/dP = 4.51(2), dKs/dT = -0.0170(1) GPa/K, G0= 93.2(1) GPa, dG/dP = 1.51(2), and dG/dT = -0.0107(1) GPa/K. Moreover, we have observed a linear temperature dependence in both VP and VS, which is consistent with that in grossular (Kono et al. 2010), but in contrast to that in pyrolite majorite where a non-linear temperature dependence was observed (Irifune et al. 2008). The non-linear temperature dependence may be due to the effect of the complex multi-component system, but not the garnet structure itself.

  6. 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.

  7. Zonal concentration of some geophysical process intensity caused by tides and variations in the Earth's rotation velocity

    NASA Astrophysics Data System (ADS)

    Levin, B.; Domanski, A.; Sasorova, E.

    2014-01-01

    We analyzed what kind of fundamental physical phenomena can be responsible for the generation of the anomalous latitudinal zones of the seismic activity, and the hotspots, and some other geophysical processes. The assessment of tidal effect contribution to the earthquake preparation process is discussed. A disk model of the Earth's rotation was proposed. The model is acceptable for the homogeneous Earth and for the heterogeneous one. The disk model explains the nucleation of two maximums of the gradient of the moment of inertia over latitude with respect to the Equator. Effects of the variations in the Earth's rotation angular velocity were estimated and the possible features caused by the rotation velocity instability were described. The variations in the relative velocity of the Earth's rotation (dimensionless value ? ? (T - P)/P) are approximately equal upon the average to 10-8, where T is the observed length of day for the Earth, and P is the astronomical day. These variations lead to the occurrence of the additional energy estimated as 1020 J. The authors proposed the hypothesis of a pulsating geoid based on effects of the Earth's rotation features, and tidal forces, and conception of critical latitudes in the solid Earth. This hypothesis may highlight the phenomenon of zonal intensification of some geological processes in the solid Earth (the seismic activity, and hotspot location, and major ore deposit locations).

  8. 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.

  9. LONG-TERM VARIATION IN THE SUN'S ACTIVITY CAUSED BY MAGNETIC ROSSBY WAVES IN THE TACHOCLINE

    E-print Network

    Usoskin, Ilya G.

    LONG-TERM VARIATION IN THE SUN'S ACTIVITY CAUSED BY MAGNETIC ROSSBY WAVES IN THE TACHOCLINE (10Be and 14C) on the Earth reveal the variation of the Suns magnetic activity over hundreds during the first half of this century. Key words: Sun: activity ­ Sun: interior ­ Sun: oscillations 1

  10. Gravity wave variations during the 2009 stratospheric sudden warming as revealed by ECMWFT799 and observations

    E-print Network

    Chu, Xinzhao

    Gravity wave variations during the 2009 stratospheric sudden warming as revealed by ECMWFT799 (GW) variations during the 2009 stratospheric sudden warming (SSW) in the Arctic. The magnitude and occurrence of GWs correlate with the location and strength of the polar vortex that is strongly disturbed

  11. Estimating the free gas content in Baltic Sea sediments using compressional wave velocity from marine seismic data

    NASA Astrophysics Data System (ADS)

    Tóth, Zsuzsanna; Spiess, Volkhard; Mogollón, José M.; Jensen, Jørn Bo

    2014-12-01

    A 2-D high-resolution velocity field was obtained from marine seismic data to quantify free gas content in shallow muddy sediments at in situ pressure and temperature. The velocities were acquired applying Migration Velocity Analysis on prestack time-migrated data. Compressional wave velocities are highly sensitive to free gas as very small amounts of gas can cause a significant decrease in the medium velocity. The analyzed profile crosses a depression filled with organic-rich Holocene mud in the Bornholm Basin, Baltic Sea. The interval velocity field reveals two low-velocity patches, which extend from the reversed polarity reflections marking the top of the gassy sediment layer down to the base of the Holocene mud. Average interval velocities within the gassy mud are lower than the seafloor migration velocity by up to ˜500 m/s. This decrease, using a geoacoustic model, is caused by an average 0.046% gas volume fraction. The interval velocities in individual cells of the velocity field are reduced to ˜200 m/s predicting up to 3.4% gas content. The velocity field is limited in resolution due to velocity determination at and between reflections; however, together with the stratigraphic interpretation, geological units containing free gas could be identified. Shallow gas occurs vertically throughout most of the Holocene mud in the gassy area. Comparison with biogeochemical studies at other Baltic Sea sites suggests that the distribution of free gas is likely to be patchy in the sediment, but the gas concentration may peak below the sulfate-methane transition zone and gradually decrease below.

  12. Estimation of Relative Amplification Effect by Shear Wave Velocity (Vs30): A Case Study from Eskisehir, Turkey

    NASA Astrophysics Data System (ADS)

    Mutlu, Sunay; Tün, Muammer; Güney, Yücel; Ecevito?lu, Berkan

    2014-05-01

    Turkey, which is one of the world's most active earthquake zones located within the Alpine-Himalayan seismic belt. The major part of the territory of the country is at risk of earthquakes that causes damage and loss of life. The important indication of this danger is the past earthquakes resulted with losses. Turkey has experienced many destructive earthquakes in the last 15 years. In 1999 Gölcük Earthquake with the magnitude of 7.4, Düzce Earthquake with the magnitude of 7.2 and in 2011 Van Earthquake with the magnitude of 7.2-Van resulted with thousands of loss of life and damage to property as billions of thousand liras. It is quite important to doing microzonation works in these areas and estimation of behaviors during the earthquake in order to prevent occurring damages in settlements and areas will be settle. Soil amplification comes from the most basic parameter used in the microzonation works. This study was made in Eskisehir urban area which is one of the most urbanized and industrialized cities of Turkey in recent years. This study aim to amplification that may occur due to the earthquake to effects of Eskisehir region. It was used that seismic refraction data in 23 different location and 96 borehole data in settlement. Local soil properties variation upon amplification influence was investigated depending on SPT-N values and wave velocity data from seismic refraction. Average shear wave velocities for each type of surface to 30 m were found that each borehole point by equations ?yisan (1996), and Jafari et al. (1997) using the resulting values. In addition, relative amplifications has been calculated by Midorikawa (1987) and Borcherdt et al's (1991) approaches. Then, these parameters have been mapped spatial changes using GIS (Geographical Information Systems) techniques. Porsuk river and its surroundings might have caused a high soil amplification result due to the low speed and soft soil when analyze the results of maps. In addition, it is thought that the results of this study will be clear up determination of risk areas where used city center urban regeneration studies in Eskisehir.

  13. Variational divergence in wave scattering theory with Kirchhoffean trial functions

    NASA Technical Reports Server (NTRS)

    Bird, J. F.

    1986-01-01

    In a recent study of variational improvement of the Kirchhoff approximation for electromagnetic scattering by rough surfaces, a key ingredient in the variational principle was found to diverge for important configurations (e.g., backscatter) if the polarization had any vertical component. The cause and a cure of this divergence are discussed here. The divergence is demonstrated to occur for arbitrary perfectly conducting scatterers and its universal characterstics are determined, by means of a general divergence criterion that is derived. A variational cure for the divergence is prescribed, and it is tested successfully on a standard scattering model.

  14. Tomographic P wave velocity and vertical velocity gradient structure across the geothermal site Groß Schönebeck (NE German Basin): Relationship to lithology, salt tectonics, and thermal regime

    NASA Astrophysics Data System (ADS)

    Bauer, K.; Moeck, I.; Norden, B.; Schulze, A.; Weber, M.; Wirth, H.

    2010-08-01

    Seismic wide-angle data were collected along a 40-km-long profile centered at the geothermal research well GrSk 3/90 in the Northeast German Basin. Tomographic inversion of travel time data provided a velocity and a vertical velocity gradient model, indicative of Cenozoic to Pre-Permian sediments. Wide-angle reflections are modeled and interpreted as top Zechstein and top Pre-Permian. Changes in velocity gradients are interpreted as the transition from mechanical to chemical compaction at 2-3 km depth, and localized salt structures are imaged, suggesting a previously unknown salt pillow in the southern part of the seismic profile. The Zechstein salt shows decreased velocities in the adjacent salt pillows compared to the salt lows, which is confirmed by sonic log data. This decrease in velocity could be explained by the mobilization of less dense salt, which moved and formed the salt pillows, whereas the denser salt remained in place at the salt lows. We interpret a narrow subvertical low-velocity zone under the salt pillow at GrSk 3/90 as a fault in the deep Permian to Pre-Permian. This WNW-ESE trending fault influenced the location of the salt tectonics and led to the formation of a fault-bounded graben in the Rotliegend sandstones with optimal mechanical conditions for geothermal production. Thermal modeling showed that salt pillows are related to chimney effects, a decrease in temperature, and increasing velocity. The assumed variations in salt lithology, density, and strain must thus be even higher to compensate for the temperature effect.

  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. Variation of Pressure Waveforms in Measurements of Extracorporeal Shock Wave Lithotripter

    NASA Astrophysics Data System (ADS)

    Inose, Naoto; Ide, Masao

    1993-05-01

    In this paper, we describe measurement of variation in pressure waveforms of the acoustic field of an extra-corporeal shock-wave lithotripter (ESWL). Variations in the measured acoustic fields and pressure waveform of an underwater spark-gap-type ESWL with an exhausted spark plug electrode have been reported by researchers using crystal sensors. If the ESWL spark plugs become exhausted, patients feel pain during kidney, biliary stone disintegration. We studied the relationship between exhaustion of electrodes and the variation of pressure waveforms and shock-wave fields of the ESWL using a newly developed hydrophone.

  17. Correlation of Arterial Stiffness and Bone Mineral Density by Measuring Brachial-Ankle Pulse Wave Velocity in Healthy Korean Women

    PubMed Central

    Kim, Nam-Lee

    2015-01-01

    Background An association between arterial stiffness and osteoporosis has previously been reported. Therefore, we investigated the relationship between arterial stiffness, measured by brachial-ankle pulse wave velocity, and bone mineral density in a sample of healthy women undergoing routine medical checkup. Methods We retrospectively reviewed the medical charts of 135 women who had visited the Health Promotion Center (between May 2009 and December 2012). Brachial-ankle pulse wave velocity was measured using an automatic wave analyzer. Bone mineral density of the lumbar spine (L1-L4) and femur was measured by dual-energy X-ray absorptiometry. Metabolic syndrome was defined according to National Cholesterol Education Program-Adult Treatment Panel III criteria, using body mass index >25 kg/m2 instead of waist circumference >88.9 cm. Results Pearson's correlation analysis revealed significant inverse relationships between pulse wave velocity and bone mineral density of the lumbar spine (r=-0.335, P<0.001), femur neck (r=-0.335, P<0.001), and total femur (r=-0.181, P=0.04). Pulse wave velocity showed the strongest association with age (r=0.586, P<0.001). Multiple regression analysis identified an independent relationship between pulse wave velocity and lumbar spine bone mineral density in women after adjusting for age, metabolic syndrome, body mass index, smoking status, alcohol intake, and exercise (r=-0.229, P=0.01). Conclusion This study confirmed an association between arterial stiffness and bone mineral density in women. PMID:26634100

  18. 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.

  19. S-wave velocity and Poisson's ratio model in Southern Chile along a transect at 38°15'S from active and passive TIPTEQ data

    NASA Astrophysics Data System (ADS)

    Ramos, Catalina; Mechie, James

    2015-04-01

    Using active and passive seismology data from project TIPTEQ (from The Incoming Plate to mega-Thrust EarthQuake processes) we derive a shear (S) wave velocity and a Poisson's ratio (?) model across the Chilean convergent margin along 38°15'S, where the Mw 9.5 Valdivia earthquake is believed to have occurred. The obtained S-wave velocity model consists of three different tomographic images that were merged together. In the upper part (0 - 5 km depth), controlled source data from explosions were used to obtain a S-wave travel-time tomography. In the middle part (5 - 20 km depth) a dispersion analysis and then a noise tomography were carried out in two different ways: one used the dispersion curves to obtain a 3D S-wave velocity model in one step and the other used the dispersion curves to obtain surface-wave velocity tomographic images for different periods and then used the surface-wave velocity values every 10 km along the profile to obtain 1D S-wave velocity profiles every 10 km that were then interpolated to obtain a 2D S-wave tomography. Both methods produce similar S-wave travel-times. In the lower part (20 - 75 km depth, depending on the longitude) an already existent S-wave velocity model from local earthquake tomography was merged with the other two sections. The final S-wave velocity model and already existent compressional (P) wave velocity models along the same transect allowed us to obtain a Poisson's ratio model. The results show that the velocities and Poisson's ratios in this part of the Chilean convergent margin can all be explained in terms of normal rock types. There is no requirement to call on the existence of significant amounts of present-day fluids in the continental lithosphere above the plate interface in this part of the Chilean convergent margin, to explain the derived velocities and Poisson's ratios.

  20. Diurnal and seasonal variation of vertical velocity pattern in boundary layer over a high altitude site in central Himalayan region

    NASA Astrophysics Data System (ADS)

    Shukla, Krishna Kumar; phanikumar, D. v.; newsom, Rob k.; niranjan kumar, K.; kotamarthi, V. r.

    2015-04-01

    During the Indo-US collaborative Ganges Valley Aerosol Experiment (GVAX) a Doppler lidar (DL) was operated continuously from June 2011 to March 2012 at a high altitude site on Manora Peak (29.4o N; 79.2o E; 1958 m above mean sea level (amsl)) in the the Himalayan foothills. The lidar provided height-resolved measurements of vertical velocity and attenuated backscatter above the site. This study investigates seasonal and diurnal variations of vertical velocity and attenuated backscatter in the local boundary layer height ~1 km above ground level (agl) during the monsoon(June-August) ,post-monsoon (September-November), winter (December-February) and premonsoon (March) periods. The upslope flows were observed during the daytime and down slope flows were are observed during the nighttime. The magnitude of the vertical velocity varied between 0.1-0.4 m.s-1 in all seasons. The vertical velocity variances ranged from 0.2 to 1.5 m-2s-2. Variances were higher during the daytime due to convection. At night, the variance decreased due to cooling at the surface. There is good correlation (R2 ~ 0.26, 0.66 and 0.4) between the daily mean attenuated backscatter and relative humidity during post-monsoon, winter and pre-monsoon seasons respectively and an anti-correlation (R2 ~0.03) between the attenuated backscatter and relative humidity in monsoon season. There are very less co-relation (R2 ~0.06, 0.19, 0.002 and 0.12) between daily mean vertical velocity and attenuated backscatter in all the seasons respectively. The mean diurnal vertical velocity component is modulated by the terdiurnal (8-hour) component in all the seasons. We investigate the impact of variable weather conditions on vertical velocity.

  1. Estimation of elastic moduli in a compressible Gibson half-space by inverting Rayleigh-wave phase velocity

    USGS Publications Warehouse

    Xia, J.; Xu, Y.; Miller, R.D.; Chen, C.

    2006-01-01

    A Gibson half-space model (a non-layered Earth model) has the shear modulus varying linearly with depth in an inhomogeneous elastic half-space. In a half-space of sedimentary granular soil under a geostatic state of initial stress, the density and the Poisson's ratio do not vary considerably with depth. In such an Earth body, the dynamic shear modulus is the parameter that mainly affects the dispersion of propagating waves. We have estimated shear-wave velocities in the compressible Gibson half-space by inverting Rayleigh-wave phase velocities. An analytical dispersion law of Rayleigh-type waves in a compressible Gibson half-space is given in an algebraic form, which makes our inversion process extremely simple and fast. The convergence of the weighted damping solution is guaranteed through selection of the damping factor using the Levenberg-Marquardt method. Calculation efficiency is achieved by reconstructing a weighted damping solution using singular value decomposition techniques. The main advantage of this algorithm is that only three parameters define the compressible Gibson half-space model. Theoretically, to determine the model by the inversion, only three Rayleigh-wave phase velocities at different frequencies are required. This is useful in practice where Rayleigh-wave energy is only developed in a limited frequency range or at certain frequencies as data acquired at manmade structures such as dams and levees. Two real examples are presented and verified by borehole S-wave velocity measurements. The results of these real examples are also compared with the results of the layered-Earth model. ?? Springer 2006.

  2. Vertical vibration of a circular footing on a linear-wave-velocity B. B. GUZINA and R. Y. S. PAKy

    E-print Network

    Guzina, Bojan

    Vertical vibration of a circular footing on a linear-wave-velocity half-space B. B. GUZINAÃ and R. Y. S. PAKy An exact treatment is presented for the problem of a rigid surface foundation vibrating; soilastructure interaction; vibration. Les auteurs abordent le probleÁme de la vibra- tion verticale de

  3. Experimental study on monitoring CO2 sequestration by conjoint analysis of the P-wave velocity and amplitude.

    PubMed

    Chen, Hao; Yang, Shenglai; Huan, Kangning; Li, Fangfang; Huang, Wei; Zheng, Aiai; Zhang, Xing

    2013-09-01

    CO2 sequestration has been considered to be one of the most straightforward carbon management strategies for industrial CO2 emission. Monitoring of the CO2 injection process is one of the best ways to make sure the safety storage but is also a major challenge in CO2 geological sequestration. Previous field and laboratory researches have shown that seismic methods are among the most promising monitoring methods because of the obvious reduction in P-wave velocities caused by CO2 injection. However, as CO2 injection continues, the P-wave velocity becomes increasingly insensitive according to the pilot projects when CO2 saturation is higher than 20-40%. Therefore, the conventional seismic method needs improvement or replacement to solve its limitations. In this study, P-wave velocity and amplitude responses to supercritical CO2 injection in brine-saturated core samples from Jilin oilfield were tested using core displacement and an ultrasonic detection integrated system. Results showed that neither the P-wave velocity nor amplitude could simply be used to monitor the CO2 injection process because of the insensitive or nonmonotonous response. Consequently, a new index was established by synthetically considering these two parameters to invert and monitor the CO2 process, which can be thought of as a newer and more effective assessment criterion for the seismic method. PMID:23915233

  4. Derivation of site-specific relationships between hydraulic parameters and p-wave velocities based on hydraulic and seismic tomography

    SciTech Connect

    Brauchler, R.; Doetsch, J.; Dietrich, P.; Sauter, M.

    2012-01-10

    In this study, hydraulic and seismic tomographic measurements were used to derive a site-specific relationship between the geophysical parameter p-wave velocity and the hydraulic parameters, diffusivity and specific storage. Our field study includes diffusivity tomograms derived from hydraulic travel time tomography, specific storage tomograms, derived from hydraulic attenuation tomography, and p-wave velocity tomograms, derived from seismic tomography. The tomographic inversion was performed in all three cases with the SIRT (Simultaneous Iterative Reconstruction Technique) algorithm, using a ray tracing technique with curved trajectories. The experimental set-up was designed such that the p-wave velocity tomogram overlaps the hydraulic tomograms by half. The experiments were performed at a wellcharacterized sand and gravel aquifer, located in the Leine River valley near Göttingen, Germany. Access to the shallow subsurface was provided by direct-push technology. The high spatial resolution of hydraulic and seismic tomography was exploited to derive representative site-specific relationships between the hydraulic and geophysical parameters, based on the area where geophysical and hydraulic tests were performed. The transformation of the p-wave velocities into hydraulic properties was undertaken using a k-means cluster analysis. Results demonstrate that the combination of hydraulic and geophysical tomographic data is a promising approach to improve hydrogeophysical site characterization.

  5. Fluid Distribution in Synthetic Wet Halite Rocks : Inference from Measured Elastic Wave Velocity and Electrical Conductivity

    NASA Astrophysics Data System (ADS)

    Watanabe, T.; Kitano, M.

    2011-12-01

    Intercrystalline fluid can significantly affect rheological and transport properties of rocks. Its influences are strongly dependent on its distribution. The dihedral angle between solid and liquid phases has been widely accepted as a key parameter that controls solid-liquid textures. The liquid phase is not expected to be interconnected if the dihedral angle is larger than 60 degree. However, observations contradictory to dihedral angle values have been reported. Watanabe (2010) suggested the coexistence of grain boundary fluid with a positive dihedral angle. For good understanding of fluid distribution, it is thus critical to study the nature of grain boundary fluid. We have developed a high pressure and temperature apparatus for study of intercrystalline fluid distribution. It was specially designed for measurements of elastic wave velocities and electrical conductivity. The apparatus mainly consists of a conventional cold-seal vessel with an external heater. The pressure medium is silicon oil of the viscosity of 0.1 Pa s. The pressure and temperature can be controlled from 0 to 200 MPa and from 20 to 200 C, respectively. Dimensions of a sample are 9 mm in diameter, and 15 mm in length. Halite-water system is used as an analog for crustal rocks. The dihedral angle has been studied systematically at various pressure and temperature conditions [Lewis and Holness, 1996]. The dihedral angle is larger than 60 degree at lower pressure and temperature. It decreases to be smaller than 60 degree with increasing pressure and temperature. A sample is prepared by cold-pressing and annealing of wet NaCl powder. Optical examination has shown that synthesized samples are microstructurally homogeneous. Grains are polygonal and equidimensional with a mean diameter of 100 micrometer. Grain boundaries vary from straight to bowed and 120 degree triple junctions are common. Gas and fluid bearing inclusions are visible on the grain boundaries. There are spherical inclusions or isolated worm-like channels. In this presentation, we will report preliminary results of compressional wave velocity and electrical conductivity measurements.

  6. Short-period Rayleigh wave group and phase velocities of the Reno-Truckee Meadows basin from ambient seismic noise

    NASA Astrophysics Data System (ADS)

    Noriega Salmon, R.; Moschetti, M. P.; Stephenson, W. J.; Meremonte, M. E.

    2013-12-01

    The Reno-Truckee Meadows basin in western Nevada experiences high seismicity rates, exposing the population to significant seismic hazards. We expect that earthquake ground-motions are amplified in this basin, however current-generation ground motion prediction equations were developed with few measurements from sensors sited within deep sedimentary basins. Improved estimates of ground motion require detailed knowledge of 3D basin structure and the use of 3D numerical ground motion simulations. The main goal of this work is to develop a 3D shear wave velocity model of the near surface (depths less than 2 km) of the Reno basin using ambient seismic noise analyses. In order to investigate shallow structures in the Reno basin, we deployed 12 broadband seismic stations, with average station spacings ranging 2-3 km, and recorded continuous ground velocities between late February and March 2011. We calculate interstation Green's functions from ambient seismic noise and report on the progress of our analyses here. We cross-correlate vertical component time series to recover 91 empirical Green's functions (EGFs). EGFs contain surface wave energy in 0.5-5 s period band, with inter-station distances ranging from 2-18 km. From the frequency content of the cross-correlations, we expect to resolve shear wave velocity structures above 2 km. Based on the asymmetry of the EGFs, ambient seismic noise sources 2-3 s period appear to locate west of the array, and perhaps originate near the coastlines; shorter period signals show greater symmetry in the EGFs and may result from local, possibility cultural, sources. However, further work will be required to definitively identify the locations of the noise sources. We measure surface wave group and phase velocities by frequency-time analyses and find clear agreements between the lateral distributions of surface wave speeds and the inferred basin depths. Future work will focus on inversion of the inter-station surface wave dispersion measurements for lateral distribution of surface wave speeds, and inversion for 3D shear wave velocity structure. Most previous ambient noise tomography studies obtain group and phase surface velocity dispersion measurements at periods T > 5-10 s (i.e. Shapiro and Campillo (2004); Yao et al., (2006); Yang et al. (2008)), which are longer that those used in this study. As a result, a secondary goal of this study is to investigate the ability of a small, temporary, broadband seismic array to characterize the shallow subsurface at depths beyond those retrieved by standard geotechnical methods.

  7. Blood pressure and obesity exert independent influences on pulse wave velocity in youth.

    PubMed

    Lurbe, Empar; Torro, Isabel; Garcia-Vicent, Consuelo; Alvarez, Julio; Fernández-Fornoso, José Antonio; Redon, Josep

    2012-08-01

    The objective was to analyze pulse wave velocity (PWV) in normotensive, high-normal, and hypertensive youths by using aortic-derived parameters from peripheral recordings. The impact of obesity on vascular phenotypes was also analyzed. A total of 501 whites from 8 to 18 years of age were included. The subjects were divided according to BP criteria: 424 (85%) were normotensive, 56 (11%) high-normal, and 21 (4%) hypertensive. Obesity was present in 284 (56%) and overweight in 138 (28%). Pulse wave analysis using a SphygmoCor device was performed to determine central blood pressure (BP), augmentation index, and measurement of PWV. Among the BP groups, differences appeared in age, sex, and height but not in body mass index. Significant differences in peripheral and central systolic and diastolic BPs and pulse pressures were observed within groups. A graded increase in PWV was present across the BP strata without differences in augmentation index. Using a multiple regression analysis, age, BP groups, and obesity status were independently associated with PWV. Older and hypertensive subjects had the highest PWV, whereas, from normal weight status to obesity, PWV decreased. Likewise, PWV was positively related to peripheral or central systolic BP and negatively related to body mass index z score. For 1 SD of peripheral systolic BP, PWV increased 0.329 m/s, and for 1 SD of body mass index z score PWV decreased 0.129 m/s. In conclusion, PWV is increased in hypertensive and even in high-normal children and adolescents. Furthermore, obesity, the factor most frequently related to essential hypertension in adolescents, blunted the expected increment in PWV of hypertensive and high-normal subjects. PMID:22733475

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

    NASA Astrophysics Data System (ADS)

    Yordkayhun, Sawasdee; Sujitapan, Chedtaporn; Chalermyanont, Tanit

    2015-02-01

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

  9. S-Wave Velocity Structure of the Taiwan Chelungpu Fault Drilling Project (TCDP) Site Using Microtremor Array Measurements

    NASA Astrophysics Data System (ADS)

    Wu, Cheng-Feng; Huang, Huey-Chu

    2015-10-01

    The Taiwan Chelungpu Fault Drilling Project (TCDP) drilled a 2-km-deep hole 2.4 km east of the surface rupture of the 1999 Chi-Chi earthquake ( M w 7.6), near the town of Dakeng. Geophysical well logs at the TCDP site were run over depths ranging from 500 to 1,900 m to obtain the physical properties of the fault zones and adjacent damage zones. These data provide good reference material for examining the validity of velocity structures using microtremor array measurement; therefore, we conduct array measurements for a total of four arrays at two sites near the TCDP drilling sites. The phase velocities at frequencies of 0.2-5 Hz are calculated using the frequency-wavenumber ( f- k) spectrum method. Then the S-wave velocity structures are estimated by employing surface wave inversion techniques. The S-wave velocity from the differential inversion technique gradually increases from 1.52 to 2.22 km/s at depths between 585 and 1,710 m. This result is similar to those from the velocity logs, which range from 1.4 km/s at a depth of 597 m to 2.98 km/s at a depth of 1,705 m. The stochastic inversion results are similar to those from the seismic reflection methods and the lithostratigraphy of TCDP-A borehole, comparatively. These results show that microtremor array measurement provides a good tool for estimating deep S-wave velocity structure.

  10. Quasi-biennial variation of equatorial waves as seen in satellite remote sensing data

    NASA Astrophysics Data System (ADS)

    Chen, Zeyu

    The quasi-biennial oscillation (QBO) in zonal winds in the lower stratosphere at the Equator is the most prominent inter-annual variation signal in the middle atmosphere. Theoretically, it is driven by the drag from the damping of equatorial waves including the equatorially trapped planetary scale waves, such as Kelvin waves propagating eastward and Rossby-gravity waves propagating westward, inertio-gravity waves and gravity waves. In current research, the tem-perature data collected by the SABER/TIMED mission in 2002-2009 are used to investigate the equatorial waves activities. The Fast Fourier Synoptic Mapping (FFSM) method is applied to delineate planetary wave components with the zonal wavenumber spanning over -6 to +6, hereby, positive (negative) wavenumber is assigned to westward (eastward) propagating waves. Limited by the SABER/TIMED sampling scheme, only the waves with periods longer than one day can be resolved. Focusing on the height region 70-10 hPa where the QBO signal is most significant, it is clearly observed that the composite activity of all the eastward waves exhibit QBO like variation. Specifically, for each QBO cycle, the activity at 50 hPa level is characterized by the occurrence of a substantially clear minimum that coincides to the fast downward propagation of the westerly phase, the typical pattern of the QBO phenomenon. Phase speed spectra are derived by using the FFSM analysis results. And vertical shear of the zonal wind is derived by using the rawinsonde data at Singapore. Comparison of the phase speed spectra and the wind shear indicates that the minimum is due to the westerly shear below 30 hPa. Between the minimum, significant wave activities emerge, thus the property for the components are investigated. Results show that in height range 70-10 hPa, both wave 1 to wave 3 are prominent during the inter-minimum period for each QBO cycle. At 50 hPa level, wave 1 component exhibits amplitude spectral peak at three kinds of period, 8, 11 and 20 day. Meanwhile, shifting to shorter period is seen as wave number increases, for example, the 20-day period spectrum is attenuated substantially for wave 2 and wave 3 components. Moreover, results also show that although with small amplitude, wave 4 and wave 5 with shorter periods of 4-7 days are discernable in particular in the inter-minimum period. Further details will be presented in the talk.

  11. Variation in Angular Velocity and Angular Acceleration of a Particle in Rectilinear Motion

    ERIC Educational Resources Information Center

    Mashood, K. K.; Singh, V. A.

    2012-01-01

    We discuss the angular velocity ([image omitted]) and angular acceleration ([image omitted]) associated with a particle in rectilinear motion with constant acceleration. The discussion was motivated by an observation that students and even teachers have difficulty in ascribing rotational motion concepts to a particle when the trajectory is a…

  12. Seasonal variations in lower stratospheric gravity wave energy above the Falkland Islands

    NASA Astrophysics Data System (ADS)

    Moffat-Griffin, T.; Jarvis, M. J.; Colwell, S. R.; Kavanagh, A. J.; Manney, G. L.; Daffer, W. H.

    2013-10-01

    gravity wavefield in the lower stratosphere (between 15 km and 22 km altitude) above Mount Pleasant Airport (51°49'S, 58°26'W) on the Falkland Islands is studied using over 2100 high-resolution radiosonde soundings from 2002 to 2010. The seasonal variation in vertical direction of propagation shows a small decrease in numbers of upward propagating waves that is related to critical level filtering; however, there is a very large increase in numbers of downward propagating waves between July and September; this is attributed to the proximity of the edge of the polar vortex. There is a seasonal variation in gravity wave energy density, with a large peak during the austral autumn equinox; this is markedly different to results in the literature both from Rothera, on the Antarctic Peninsula, and stations on the main Antarctic continent. This seasonal pattern has been shown to be linked to variations in the sources of upward propagating gravity waves. The seasonal variation in gravity wave characteristics above Mount Pleasant Airport seen in our results suggests that the gravity wavefield in this region is determined by a combination of different gravity wave sources located above and below the lower stratosphere.

  13. Migration error in transversely isotropic media with linear velocity variation in depth

    SciTech Connect

    Larner, K.; Cohen, J.K.

    1992-10-01

    Given the sensitivity of imaging accuracy to the velocity used in migration, migration founded (as in practice) on the erroneous assumption that a medium is isotropic can be expected to be inaccurate for steep reflectors. Here, we estimate errors in interpreted reflection time and lateral position as a function of reflector dip for transversely isotropic models in which the axis of symmetry is vertical and the medium velocity varies linearly with depth. We limit consideration to media in which ratios of the various elastic moduli are independent of depth. Tests with reflector dips up to 120 degrees on a variety of anisotropic media show errors that axe tens of wavelengths for dips beyond 90 degrees when the medium (unrealistically) is homogeneous. For a given anisotropy, the errors are smaller for inhomogeneous media; the larger the velocity gradient, the smaller the errors. For gradients that are representative of the subsurface, lateral-position errors tend to be minor for dips less than about 60 degrees, growing to two to five wavelengths as dip passes beyond 90 degrees. These errors depend on reflector depth and average velocity to the reflector only through their ratio, i.e., migrated reflection time. Migration error, which is found to be unrelated to the ratio of horizontal to vertical velocity, is such that reflections with later migrated reflection times tend to be more severely over-migrated than are those with earlier ones. Over a large range of dips, migration errors that arise when anisotropy is ignored but inhomogeneity is honored tend to be considerably smaller than those encountered when inhomogeneity is ignored in migrating data from isotropic, inhomogeneous media.

  14. Migration error in transversely isotropic media with linear velocity variation in depth

    SciTech Connect

    Larner, K.; Cohen, J.K.

    1992-01-01

    Given the sensitivity of imaging accuracy to the velocity used in migration, migration founded (as in practice) on the erroneous assumption that a medium is isotropic can be expected to be inaccurate for steep reflectors. Here, we estimate errors in interpreted reflection time and lateral position as a function of reflector dip for transversely isotropic models in which the axis of symmetry is vertical and the medium velocity varies linearly with depth. We limit consideration to media in which ratios of the various elastic moduli are independent of depth. Tests with reflector dips up to 120 degrees on a variety of anisotropic media show errors that axe tens of wavelengths for dips beyond 90 degrees when the medium (unrealistically) is homogeneous. For a given anisotropy, the errors are smaller for inhomogeneous media; the larger the velocity gradient, the smaller the errors. For gradients that are representative of the subsurface, lateral-position errors tend to be minor for dips less than about 60 degrees, growing to two to five wavelengths as dip passes beyond 90 degrees. These errors depend on reflector depth and average velocity to the reflector only through their ratio, i.e., migrated reflection time. Migration error, which is found to be unrelated to the ratio of horizontal to vertical velocity, is such that reflections with later migrated reflection times tend to be more severely over-migrated than are those with earlier ones. Over a large range of dips, migration errors that arise when anisotropy is ignored but inhomogeneity is honored tend to be considerably smaller than those encountered when inhomogeneity is ignored in migrating data from isotropic, inhomogeneous media.

  15. Reference Values of Pulse Wave Velocity in Healthy People from an Urban and Rural Argentinean Population

    PubMed Central

    Díaz, Alejandro; Galli, Cintia; Tringler, Matías; Ramírez, Agustín; Cabrera Fischer, Edmundo Ignacio

    2014-01-01

    In medical practice the reference values of arterial stiffness came from multicenter registries obtained in Asia, USA, Australia and Europe. Pulse wave velocity (PWV) is the gold standard method for arterial stiffness quantification; however, in South America, there are few population-based studies. In this research PWV was measured in healthy asymptomatic and normotensive subjects without history of hypertension in first-degree relatives. Normal PWV and the 95% confidence intervals values were obtained in 780 subjects (39.8 ± 18.5 years) divided into 7 age groups (10–98 years). The mean PWV found was 6.84?m/s ± 1.65. PWV increases linearly with aging with a high degree of correlation (r2 = 0.61; P < 0.05) with low dispersion in younger subjects. PWV progressively increases 6–8% with each decade of life; this tendency is more pronounced after 50 years. A significant increase of PWV over 50 years was demonstrated. This is the first population-based study from urban and rural people of Argentina that provides normal values of the PWV in healthy, normotensive subjects without family history of hypertension. Moreover, the age dependence of PWV values was confirmed. PMID:25215227

  16. Pulse wave velocity and age- and gender-dependent aortic wall hardening in fowl

    PubMed Central

    Ruiz-Feria, Ciro A.; Yang, Yimu; Thomason, Donald B.; White, Jarred; Su, Guibin; Nishimura, Hiroko

    2009-01-01

    Before sexual maturation, chickens (Gallus gallus) show high blood pressure (BP) and neointimal plaques in the lower abdominal aortae (AbA). We investigated age/sex-related changes in pulse wave velocity (PWV), elastin, collagen, and protein levels in AbA, and cardiac morphology to determine whether PWV increases during incremental increases in BP of maturing fowl, while arterial stiffness becomes dominant with aging. PWV (m/s) was significantly greater in male chicks (6-7 wk, 9.3 ± 0.8; females, 6.1 ± 0.5) and remained high in cockerels (13 wk), young (27-28 wk), and adults (44-66 wk). PWV increased in prepubertal pullets (10.0 ± 0.9), dropped significantly in young hens, and remained low in adults. In contrast, medial thickness, protein levels, and collagen levels increased, while elastin/collagen ratios decreased, with maturation/aging. Males had heavier ventricular mass and thicker ventricular walls than females at all ages; left ventricular thickness decreased with maturation/aging. Thus, sustained high BP may have caused progressive medial hypertrophy, increased aortic rigidity, and enlarged hearts with left ventricular dilation. PWV of AbA was already greater in male chicks at an age when both sexes have similar collagen levels and low protein levels, suggesting that a factor other than structural stiffness may be an important determinant of PWV. PMID:19689927

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

    NASA Astrophysics Data System (ADS)

    Rocabado, V.; Schmitz, M.

    2013-05-01

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

  18. Investigating the effect of glucose on aortic pulse wave velocity using pancreatic clamping methodology.

    PubMed

    Puzantian, Houry; Teff, Karen; Townsend, Raymond R

    2015-05-01

    Aortic stiffness, determined by carotid-femoral pulse wave velocity (cfPWV), independently predicts cardiovascular outcomes. Recent studies suggest that glucose levels influence arterial stiffness indices. It is not clear, however, whether glucose affects cfPWV independently of glucoregulatory hormones. The aim of this study was to utilize a pancreatic clamping approach to determine whether plasma glucose independently predicts cfPWV. Healthy participants (N = 10) underwent pancreatic clamping to control glucose at varying concentrations using a 20% dextrose infusion while suppressing endogenous glucagon, insulin, and growth hormone by octreotide and replacing the hormones intravenously to achieve basal concentrations. Tonometric cfPWV, blood pressure, heart rate, plasma glucose, glucagon, insulin, growth hormone, and vasoactive biomarkers were measured. Plasma glucose levels of 150 mg/dl at 1 hr and 200 mg/dl at 2 hr postbaseline were achieved. There were no significant changes in cfPWV (5.8 m/s at 0 hr, 5.9 m/s at 1 hr, and 5.9 m/s at 2 hr) with increased glucose levels. There were small increases in insulin secretion. A definitive role for glucose in cfPWV modulation was not determined; there is a potential role for insulin as a cfPWV modulator. Continued efforts in clarifying the independent roles of glucose and insulin can elucidate novel vessel-related targets for cardiovascular disease prevention and management in patients with impaired glucose tolerance and diabetes. PMID:25802385

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

    E-print Network

    Way, Francis

    2000-01-01

    surface piercing wave gages. Particle velocities were measured at 49 positions with a side looking three-dimensional acoustic Doppler velocimeter. A spectral analysis was performed on each free surface time series to obtain H[m]?, as well as first...

  20. Variational Calculation on the Simple Harmonic Oscillator in Momentum Space The following normalized trial wave function is proposed for a variational calculation on the

    E-print Network

    Rioux, Frank

    normalized trial wave function is proposed for a variational calculation on the harmonic oscillator. x a = 0, indicating that the wave function is not wellbehaved and therefore cannot be used for quantum mechanical calculations. 5 0 5 x 1,( ) x Therefore, the wave function is Fourier transformed

  1. Coupled pulsing of lava fountains: Video monitoring reveals systematic height and velocity variations of adjacent vents

    NASA Astrophysics Data System (ADS)

    Witt, Tanja; Walter, Thomas R.

    2014-05-01

    Lava fountains are a common eruption form at basaltic volcanoes. Many of the lava fountains occur at fissure eruptions, associated with the alignment of active vents. We observed that the lava fountain pulses may occur in chorus at several adjacent vents, implying that activity at these vents is coupled. The mechanisms behind such a coupling of adjacent lava fountains and the underlying connection between the different craters are not fully understood, however. Here we employ video images to measure the height, width and velocity of the ejecta leaving the vent. With a Sobel edge-detection algorithm, our aim is to measure the height of the different fountains occurring along fissure eruptions. Video data acquired from Puu'oo (Hawaii) and from Eyjafjallajökull (Iceland) are showing major similarities in fountaining behavior. Based on the fountain activity times series we estimate the sign and degree of correlation of the different vents. We find that the height and velocity of adjacent lava fountains are often in chorus. The velocity is calculated by a correlation in the Fourier space of contiguous images. We observed that episodically and sporadically the correlation regime can change. Despite these changes, both the frequency of the lava pulses and the eruption and rest time between the pulses remain similar for adjacent lava fountains, implying, a controlling process in the magma feeder system itself. We interpret the initial vertical velocity at the vent to be proportional to the extent of bubbles, and layers of bubbles rising. Lateral migration of fountains and their dynamics, in turn, is associated to lateral magma and gas flow or inclined layers of bubbles developing along the fissure at depth. Systematic recording and analysis of video data from different volcanoes hence result in a better understanding of the mechanisms of parallel and non-parallel lava fountain pulses.

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

  3. The Potential Temporal Variations in Crustal Seismic Velocity Correlated with the 2010 Jiasian Earthquake and Non-volcanic Tremors in Southern Central Range of Taiwan

    NASA Astrophysics Data System (ADS)

    Wu, S.; Hung, S.

    2013-12-01

    Different from those found in major plate boundary zones around the Pacific Rim, NVT and low-frequency earthquakes (LFEs) have been discovered in the lower crust beneath the southern segment of the CR, which comprises part of the fold-and-thrust orogenic belt in Taiwan as a product the collision between the Eurasian plate and Luzon arc. The Mw 6.0 Jiasian earthquake occurred at a focal depth of 23 km to the southwest of the identified LFEs on March 4, 2010 and ruptured upward toward the northwest, appearing accompanied by enhanced NVT activity. To investigate potential changes and causes in crustal strains and rock properties associated with the earthquake rupture and energy level of NVT after the Jiasian earthquake, we construct empirical Green's functions (EGFs) from auto- and cross-correlation functions of continuous ambient noise between available station pairs near the epicenter from the short-period Central Weather Bureau Seismic Network (CWBSN) and the Broadband Array in Taiwan for Seismology (BATS) during 2009-2011. The temporal variations in seismic velocity perturbations are estimated by measuring the relative time delay of late-arriving coda waves between short-term and long-term stacked EGFs. The resulting EGFs at 0.1-0.9 Hz show the statistically significant coseismic velocity reduction only at station pairs with the interstation paths traversing through the region exposed to the Jiasian aftershock zone, where the GPS and peak-ground acceleration (PGA) observations and finite-fault rupture model all indicate large slip and ground shaking during the main shock rupture propagation. The measured relative velocity variation is slightly temporally correlated with the daily energy calculated by squares of the velocity amplitudes in 2-7 Hz, the frequency band characteristic of main NVT energy from previously located tremor groups in southern Central Range and northeastern Taiwan. Compared with strain perturbations induced from coseismic slip distribution and tremor activities, we will discuss the possible mechanisms responsible for the changes of crustal properties during earthquake and tremor occurrences in the atypical seismogenic zone of southern Taiwan.

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

    SciTech Connect

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

    2008-11-11

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

  5. Shear-wave velocity model of the Chukuo fault zone, Southwest Taiwan, from cross correlation of seismic ambient noise

    NASA Astrophysics Data System (ADS)

    Yeh, Yu-Lien; Wen, Strong; Lee, Kung-Jer; Chen, Chau-Huei

    2013-10-01

    The Chia-Nan (Chiayi-Tainan) area is in the southwestern Taiwan, and is located at the active deformation front of the collision of the Eurasian continental plate and the Philippine Sea plate, which causes complex folds as well as thrust fault systems in the area. The Chukuo fault zone is a boundary between the Western Foothill and the Western Coastal Plain in the Chia-Nan area. The nature of the crustal structure beneath the fault zone, especially the eastern part of the fault zone with mountain topography, has not been well known in detailed due to lack of drilling data as well as its limitation in using other geophysical methods, such as active source survey. In this study, we deployed an array with 11 broadband seismic stations to monitor the seismicity of the Chukuo fault zone. The array has recorded more than 1000 microearthquakes around this area. It provides an opportunity to use P- and S-wave travel time data to investigate the both the crustal P- and S-velocity in the fault zone, however due to the nature of the earthquake distribution, the ray density is relatively low at depth between 0 and 7 km. In addition, the uncertainty of S-wave reading for small earthquake also a limit in building precise S-velocity profile, Thus, we take the advantages of using cross-correlation of seismic ambient noise to investigate crustal S-velocity profile in the Chukuo fault area, especially in the mountain area where crustal faulting is a dominated phenomenon. The results indicate that S-wave velocity in the uppermost crust in the Chukuo fault zone is shown to be slower than previous studies. A low velocity layer exists at depth between 1 and 2 km in the east of the Chukuo Fault. The low S-velocity is related to a highly fractured upper crust due to intensive deformation caused by the orogenic process.

  6. Shock wave velocity measuring system based on vernier VISAR-type interferometers

    NASA Astrophysics Data System (ADS)

    Gubskii, K. L.; Koshkin, D. S.; Antonov, A. S.; Mikhailuk, A. V.; Pirog, V. A.; Kuznetsov, A. P.

    2015-11-01

    The paper presents a multi-line diagnostic system for measuring the surface velocity in shock physics experiments. This system is designed for simultaneous measurement of surface velocity at multiple points. It is free from ambiguity caused by harmonic dependence of interference signals on the velocity and has a time resolution of 0.8 ns.

  7. On the velocity of the TE-polarized light wave to propagate through a homogeneous dielectric layer

    E-print Network

    N. L. Chuprikov

    2013-06-18

    We present a novel model of elastic scattering of the plane TE-polarized light wave on a homogeneous dielectric layer. This wave is shown can be uniquely decomposed into a coherent superposition of two 'subprocess' TE waves to describe transmission and reflection in all spatial regions. Each of them has one incoming and one outgoing waves connected 'causally' to each other on the midplane of the layer -- namely, with keeping the continuity of the complex-valued electrical field strength and the corresponding energy flow density (averaged over an oscillation period). This model unlike the conventional one fulfills the mandatory physical requirements: in this scattering problem, the velocity of the energy transfer through the layer must be the same on mirror-symmetric planes, as well as it must be always subluminal, including the case of a frustrated total internal reflection (FTIR).

  8. Evaluation of the Thickness and Bond Quality of Three-Layered Media using Zero-Group-Velocity Lamb Waves

    NASA Astrophysics Data System (ADS)

    Cho, H.; Hara, Y.; Matsuo, T.

    2014-06-01

    Bonding conditions such as jointing agent thickness and bond strength (quality) at the interface between two components is a critical concern in an assembled product because the jointing area is often the weakest component in products. Using a laser ultrasonic technique, zero-group-velocity (ZGV) Lamb waves were utilized to characterize the thickness of an adhesive layer for an epoxy-bonded sample and the bond quality for brazed samples. Using two modes of the ZGV Lamb waves, the thickness of the adhesive layer ranging from 0.2 to 0.8 mm can be estimated with high accuracy. In bond quality measurements, poor bond quality lowered the frequency of ZGV Lamb waves. The decrease in the frequency depended on the amount of shear stress along the interface caused by ZGV Lamb waves.

  9. Generalizations of wave equations to multidimensional variational problems

    E-print Network

    A. V. Stoyanovsky

    2015-06-18

    This is a survey paper based on previous results of the author. In the paper, we define and discuss the generalizations of linear partial differential equations to multidimensional variational problems. We consider two examples of such equations: first, the generalized Schr\\"odinger equation which is a natural candidate for the mathematical equation of quantum field theory, and second, the quantum Plato problem which is a natural candidate for a simplest mathematical equation of string theory and, more generally, theory of $D$-branes. We propose a way to give a mathematical sense to these equations.

  10. AWESoMe: A code for the calculation of phase and group velocities of acoustic waves in homogeneous solids

    NASA Astrophysics Data System (ADS)

    Muñoz-Santiburcio, Daniel; Hernández-Laguna, Alfonso; Soto, Juan I.

    2015-07-01

    We present AWESoMe, an implementation of a method for the evaluation of acoustic wave velocities in homogeneous solid media. The code computes the phase and group velocities for all the possible propagation directions, as well as some related parameters such as the polarization vectors, the power flow angle and the enhancement factor. The code is conveniently interfaced with GNUPLOT, thus offering immediate visualization of the results. AWESoMe is open-source software, available under the GNU General Public License v3.

  11. SOAP 2.0: a tool to estimate the photometric and radial velocity variations induced by stellar spots and plages

    SciTech Connect

    Dumusque, X.; Boisse, I.; Santos, N. C.

    2014-12-01

    This paper presents SOAP 2.0, a new version of the Spot Oscillation And Planet (SOAP) code that estimates in a simple way the photometric and radial velocity (RV) variations induced by active regions. The inhibition of the convective blueshift (CB) inside active regions is considered, as well as the limb brightening effect of plages, a quadratic limb darkening law, and a realistic spot and plage contrast ratio. SOAP 2.0 shows that the activity-induced variation of plages is dominated by the inhibition of the CB effect. For spots, this effect becomes significant only for slow rotators. In addition, in the case of a major active region dominating the activity-induced signal, the ratio between the FWHM and the RV peak-to-peak amplitudes of the cross correlation function can be used to infer the type of active region responsible for the signal for stars with v sin i ?8 km s{sup –1}. A ratio smaller than three implies a spot, while a larger ratio implies a plage. Using the observation of HD 189733, we show that SOAP 2.0 manages to reproduce the activity variation as well as previous simulations when a spot is dominating the activity-induced variation. In addition, SOAP 2.0 also reproduces the activity variation induced by a plage on the slowly rotating star ? Cen B, which is not possible using previous simulations. Following these results, SOAP 2.0 can be used to estimate the signal induced by spots and plages, but also to correct for it when a major active region is dominating the RV variation.

  12. SOAP 2.0: A Tool to Estimate the Photometric and Radial Velocity Variations Induced by Stellar Spots and Plages

    NASA Astrophysics Data System (ADS)

    Dumusque, X.; Boisse, I.; Santos, N. C.

    2014-12-01

    This paper presents SOAP 2.0, a new version of the Spot Oscillation And Planet (SOAP) code that estimates in a simple way the photometric and radial velocity (RV) variations induced by active regions. The inhibition of the convective blueshift (CB) inside active regions is considered, as well as the limb brightening effect of plages, a quadratic limb darkening law, and a realistic spot and plage contrast ratio. SOAP 2.0 shows that the activity-induced variation of plages is dominated by the inhibition of the CB effect. For spots, this effect becomes significant only for slow rotators. In addition, in the case of a major active region dominating the activity-induced signal, the ratio between the FWHM and the RV peak-to-peak amplitudes of the cross correlation function can be used to infer the type of active region responsible for the signal for stars with v sin i <=8 km s-1. A ratio smaller than three implies a spot, while a larger ratio implies a plage. Using the observation of HD 189733, we show that SOAP 2.0 manages to reproduce the activity variation as well as previous simulations when a spot is dominating the activity-induced variation. In addition, SOAP 2.0 also reproduces the activity variation induced by a plage on the slowly rotating star ? Cen B, which is not possible using previous simulations. Following these results, SOAP 2.0 can be used to estimate the signal induced by spots and plages, but also to correct for it when a major active region is dominating the RV variation. . The work in this paper is based on observations made with the MOST satellite, the HARPS instrument on the ESO 3.6 m telescope at La Silla Observatory (Chile), and the SOPHIE instrument at the Observatoire de Haute Provence (France).

  13. A regional view of urban sedimentary basins in Northern California based on oil industry compressional-wave velocity and density logs

    USGS Publications Warehouse

    Brocher, T.M.

    2005-01-01

    Compressional-wave (sonic) and density logs from 119 oil test wells provide knowledge of the physical properties and impedance contrasts within urban sedimentary basins in northern California, which is needed to better understand basin amplification. These wire-line logs provide estimates of sonic velocities and densities for primarily Upper Cretaceous to Pliocene clastic rocks between 0.1 - and 5.6-km depth to an average depth of 1.8 km. Regional differences in the sonic velocities and densities in these basins largely 1reflect variations in the lithology, depth of burial, porosity, and grain size of the strata, but not necessarily formation age. For example, Miocene basin filling strata west of the Calaveras Fault exhibit higher sonic velocities and densities than older but finer-grained and/or higher-porosity rocks of the Upper Cretaceous Great Valley Sequence. As another example, hard Eocene sandstones west of the San Andreas Fault have much higher impedances than Eocene strata, mainly higher-porosity sandstones and shales, located to the east of this fault, and approach those expected for Franciscan Complex basement rocks. Basement penetrations define large impedence contrasts at the sediment/basement contact along the margins of several basins, where Quaternary, Pliocene, and even Miocene deposits directly overlie Franciscan or Salinian basement rocks at depths as much as 1.7 km. In contrast, in the deepest, geographic centers of the basins, such logs exhibit only a modest impedance contrast at the sediment/basement contact at depths exceeding 2 km. Prominent (up to 1 km/sec) and thick (up to several hundred meters) velocity and density reversals in the logs refute the common assumption that velocities and densities increase monotonically with depth.

  14. Seismic velocity variations along the rupture zone of the 1989 Loma Prieta earthquake, California

    E-print Network

    Lin, Guoqing

    of picks per event and reduced random picking errors compared with traditional master events. Our final P-wave/s in the southeast rupture zone of the main shock. The 3-D Vp/Vs model, however, has different features, with low Vp/Vs at shallow depths to be granitic rocks, whereas at greater depths the areas of higher Vp/Vs (around 1

  15. Noncontact Determination of Antisymmetric Plate Wave Velocity in Ceramic Matrix Composites

    NASA Technical Reports Server (NTRS)

    Kautz, Harold E.

    1998-01-01

    High-temperature materials are of increasing importance in the development of more efficient engines and components for the aeronautics industry. In particular, ceramic matrix composite (CMC) and metal matrix composite (MMC) structures are under active development for these applications. The acousto-ultrasonic (AU) method has been shown to be useful for assessing mechanical properties in composite structures. In particular, plate wave analysis can characterize composites in terms of their stiffness moduli. It is desirable to monitor changes in mechanical properties that occur during thermomechanical testing and to monitor the health of components whose geometry or position make them hard to reach with conventional ultrasonic probes. In such applications, it would be useful to apply AU without coupling directly to the test surface. For a number of years, lasers have been under investigation as remote ultrasonic input sources and ultrasound detectors. The use of an ultrasonic transducer coupled through an air gap has also been under study. So far at the NASA Lewis Research Center, we have been more successful in using lasers as ultrasonic sources than as output devices. On the other hand, we have been more successful in using an air-coupled piezoelectric transducer as an output device than as an input device. For this reason, we studied the laser in/air-coupled-transducer out combination-using a pulsed NdYAG laser as the ultrasonic source and an air-coupled-transducer as the detector. The present work is focused on one of the AU parameters of interest, the ultrasonic velocity of the antisymmetric plate-wave mode. This easily identified antisymmetric pulse can be used to determine shear and flexure modulus. It was chosen for this initial work because the pulse arrival times are likely to be the most precise. The following schematic illustrates our experimental arrangement for using laser in/air-transducer out on SiC/SiC composite tensile specimens. The NdYAG pulse was directed downward by a 90 infrared prism to the top of the specimen, but at the edge of one end. An energy sensor measured a single pulse at 13 millijoules (mJ) before it passed through the prism, which attenuated 15 percent of its energy. It also provided an output trigger for the waveform time-delay synthesizer.

  16. AEC for scanning digital mammography based on variation of scan velocity

    SciTech Connect

    Aaslund, Magnus; Cederstroem, Bjoern; Lundqvist, Mats; Danielsson, Mats

    2005-11-15

    A theoretical evaluation of nonuniform x-ray field distributions in mammography was conducted. An automatic exposure control (AEC) is proposed for a scanning full field digital mammography system. It uses information from the leading part of the detector to vary the scan velocity dynamically, thus creating a nonuniform x-ray field in the scan direction. Nonuniform radiation fields were also created by numerically optimizing the scan velocity profile to each breast's transmission distribution, with constraints on velocity and acceleration. The goal of the proposed AEC is to produce constant pixel signal-to-noise ratio throughout the image. The target pixel SNR for each image could be set based on the breast thickness, breast composition, and the beam quality as to achieve the same contrast-to-noise ratio between images for structures of interest. The results are quantified in terms of reduction in entrance surface air kerma (ESAK) and scan time relative to a uniform x-ray field. The theoretical evaluation was performed on a set of 266 mammograms. The performance of the different methods to create nonuniform fields decreased with increased detector width, from 18% to 11% in terms of ESAK reduction and from 30% to 25% in terms of scan time reduction for the proposed AEC and detector widths from 10 to 60 mm. Some correlation was found between compressed breast thickness and the projected breast area onto the image field. This translated into an increase of the ESAK and decrease of the scan time reduction with breast thickness. Ideally a nonuniform field in two dimensions could reduce the entrance dose by 39% on average, whereas a field nonuniform in only the scanning dimension ideally yields a 20% reduction. A benefit with the proposed AEC is that the risk of underexposing the densest region of the breast can be virtually eliminated.

  17. A basic program to compute seismic surface-wave group-velocity dispersion curves

    NASA Astrophysics Data System (ADS)

    Jin, Doo Jung; Colby, Richard J.

    In usual exploration seismic surveys, body waves are used to derive information about the subsurface. Seismic surface waves are treated as noise, usually troublesome noise. Because the amplitudes of surface waves are many times greater than those of body waves, they conceal the body waves in seismic records and make it difficult to process and interpret the body-wave data. It may be necessary to conduct a test survey and design, on the basis of test-survey results, an elaborate data acquisition and processing scheme in order to record useful body waves with surface waves suppressed. Generally body-wave data are not usable in some areas in spite of painstaking acquisition and processing efforts. However, the nature of the surface waves that makes them troublesome in exploration surveys may be harnessed to the geophysicist's advantage. Because their amplitudes are several or more times greater than those of body waves, seismic surface waves present far fewer problems in data acquisition and processing. Also, because seismic surface waves sample the near surface of the Earth rather than deep Earth, they are especially suitable to use in surveys for environmental or geotechnical applications. Probably the best way of using seismic surface waves in extracting information on the subsurface is to compute their dispersion relationships and then to apply an inversion scheme to the obtained dispersion curves. This paper presents a computer program written in BASIC to obtain dispersion curves. It is based on an algorithm termed multiple filter analysis.

  18. Wave propagation through a random array of pinned dislocations: Velocity change and attenuation in a generalized Granato and Luecke theory

    SciTech Connect

    Maurel, Agnes; Pagneux, Vincent; Barra, Felipe; Lund, Fernando

    2005-11-01

    A quantitative theory of the elastic wave damping and velocity change due to interaction with dislocations is presented. It provides a firm theoretical basis and a generalization of the Granato and Luecke model [J. Appl. Phys. 27, 583 (1956)]. This is done considering the interaction of transverse (T) and longitudinal (L) elastic waves with an ensemble of dislocation segments randomly placed and randomly oriented in an elastic solid. In order to characterize the coherent wave propagation using multiple scattering theory, a perturbation approach is used, which is based on a wave equation that takes into account the dislocation motion when forced by an external stress. In our calculations, the effective velocities of the coherent waves appear at first order in perturbation theory while the attenuations have a part at first order due to the internal viscosity and a part at second order due to the energy that is taken away from the incident direction. This leads to a frequency dependence law for longitudinal and transverse attenuations that is a combination of quadratic and quartic terms instead of the usual quadratic term alone. Comparison with resonant ultrasound spectroscopy (RUS) and electromagnetic acoustic resonance (EMAR) experiments is proposed. The present theory explains the difference experimentally observed between longitudinal and transverse attenuations [Ledbetter, J. Mater. Res. 10, 1352 (1995)].

  19. Changes of shear-wave velocity by interferon-based therapy in chronic hepatitis C

    PubMed Central

    Osakabe, Keisuke; Ichino, Naohiro; Nishikawa, Toru; Sugiyama, Hiroko; Kato, Miho; Shibata, Ai; Asada, Wakana; Kawabe, Naoto; Hashimoto, Senju; Murao, Michihito; Nakano, Takuji; Shimazaki, Hiroaki; Kan, Toshiki; Nakaoka, Kazunori; Takagawa, Yuka; Ohki, Masashi; Kurashita, Takamitsu; Takamura, Tomoki; Yoshioka, Kentaro

    2015-01-01

    AIM: To evaluate the changes of shear-wave velocity (Vs) by acoustic radiation force impulse after treatment in chronic hepatitis C. METHODS: Eighty-seven patients with chronic hepatitis C were consecutively treated with combinations of interferon (IFN) plus ribavirin (RBV). Vs value (m/s) was measured with acoustic radiation force impulse before treatment, at end of treatment (EOT), 1 year after EOT, and 2 years after EOT. RESULTS: In patients with a sustained virological response (SVR) (n = 41), Vs significantly decreased at EOT [1.19 (1.07-1.37), P = 0.0004], 1 year after EOT [1.10 (1.00-1.22), P = 0.0001], and 2 years after EOT [1.05 (0.95-1.16), P < 0.0001] compared with baseline [1.27 (1.11-1.49)]. In patients with a relapse (n = 26), Vs did not significantly decrease at EOT [1.23 (1.12-1.55)], 1 year after EOT [1.20 (1.12-1.80)], and 2 years after EOT [1.41 (1.08-2.01)] compared with baseline [1.39 (1.15-1.57)]. In patients with a nonvirological response (n = 20), Vs did not significantly decrease at EOT [1.64 (1.43-2.06)], 1 year after EOT [1.66 (1.30-1.95)], and 2 years after EOT [1.61 (1.36-2.37)] compared with baseline [1.80 (1.54-2.01)]. Among genotype 1 patients, baseline Vs was significantly lower in SVR patients [1.28 (1.04-1.40)] than in non-SVR patients [1.56 (1.20-1.83)] (P = 0.0142). CONCLUSION: Reduction of Vs values was shown in SVR patients after IFN-plus-RBV therapy by acoustic radiation force impulse. PMID:26401087