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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. Coda wave interferometry for the measurement of thermally induced ultrasonic velocity variations in CFRP laminates

    NASA Astrophysics Data System (ADS)

    Livings, Richard; Dayal, Vinay; Barnard, Dan

    2016-02-01

    Ultrasonic velocity measurement is a well-established method to measure properties and estimate strength as well as detect and locate damage. Determination of accurate and repeatable ultrasonic wave velocities can be difficult due to the influence of environmental and experimental factors. Diffuse fields created by a multiple scattering environment have been shown to be sensitive to homogeneous strain fields such as those caused by temperature variations, and Coda Wave Interferometry has been used to measure the thermally induced ultrasonic velocity variation in concrete, aluminum, and the Earth's crust. In this work, we analyzed the influence of several parameters of the experimental configuration on the measurement of thermally induced ultrasonic velocity variations in a carbon-fiber reinforced polymer plate. Coda Wave Interferometry was used to determine the relative velocity change between a baseline signal taken at room temperature and the signal taken at various temperatures. The influence of several parameters of the experimental configuration, such as the material type, the receiver aperture size, and fiber orientation on the results of the processing algorithm was evaluated in order to determine the optimal experimental configuration.---This work is supported by the NSF Industry/University Cooperative Research Program of the Center for Nondestructive Evaluation at Iowa State University.

  4. 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.

  5. Premonitory Variations in S-Wave Velocity Anisotropy before Earthquakes in Nevada.

    PubMed

    Gupta, I N

    1973-12-14

    Application of nonhydrostatic stress to rock induces velocity anisotropy, causing the S wave to split into two components traveling with somewhat different velocities. Large premonitory changes in the extent of S-wave splitting have been observed for two earthquakes in Nevada. Observations of the difference between the two S-wave velocities may provide a simple method for pedicting earthquakes. PMID:17810815

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  7. 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.

  8. 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.

  9. Geological variation in S-wave velocity structures in Northern Taiwan and implications for seismic hazards based on ambient noise analysis

    NASA Astrophysics Data System (ADS)

    Lai, Ya-Chuan; Huang, Bor-Shouh; Huang, Yu-Chih; Yao, Huajian; Hwang, Ruey-Der; Huang, Yi-Ling; Chang, Wen-Yen

    2014-12-01

    Ambient noise analysis in Northern Taiwan revealed obvious lateral variations related to major geological units. The empirical Green's functions extracted from interstation ambient noise were regarded as Rayleigh waves, from which we analyzed the group velocities for period from 3 to 6 s. According to geological features, we divided Northern Taiwan into seven subregions, for which regionalized group velocities were derived by using the pure-path method. On average, the group velocities in mountain areas were higher than those in the plain areas. We subsequently inverted the S-wave velocity structure for each subregion down to 6 km in depth. Following the analysis, we proposed the first models of geology-dependent shallow S-wave structures in Northern Taiwan. Overall, the velocity increased substantially from west to east; specifically, the mountain areas, composed of metamorphic rocks, exhibited higher velocities than did the coastal plain and basin, which consist of soft sediment. At a shallow depth, the Western Coastal Plain, Taipei Basin, and Ilan Plain displayed a larger velocity gradient than did other regions. At the top 3 km of the model, the average velocity gradient was 0.39 km/s per km for the Western Coastal Plain and 0.15 km/s per km for the Central Range. These S-wave velocity models with large velocity gradients caused the seismic waves to become trapped easily in strata and, thus, the ground motion was amplified. The regionalized S-wave velocity models derived from ambient noises can provide useful information regarding seismic wave propagation and for assessing seismic hazards in Northern Taiwan.

  10. Eurasian surface wave tomography: Group velocities

    NASA Astrophysics Data System (ADS)

    Ritzwoller, Michael H.; Levshin, Anatoli L.

    1998-03-01

    This paper presents the results of a study of the dispersion characteristics of broadband fundamental surface waves propagating across Eurasia. The study is broader band, displays denser and more uniform data coverage, and demonstrates higher resolution than previous studies of Eurasia performed on this scale. In addition, the estimated group velocity maps reveal the signatures of geological and tectonic features never before displayed in similar surface wave studies. We present group velocity maps from 20 s to 200 s period for Rayleigh waves and from 20 s to 125 s for Love waves. Broadband waveform data from about 600 events from 1988 through 1995 recorded at 83 individual stations across Eurasia have produced about 9000 paths for which individual dispersion curves have been estimated. Dispersion curves from similar paths are clustered to reduce redundancy, to identify outliers for rejection, and to assign uncertainty estimates. On average, measurement uncertainty is about 0.030-0.040 km/s and is not a strong function of frequency. Resolution is estimated from "checker-board" tests, and we show that average resolutions across Eurasia range from 5 to 7.5 but degrade at periods above about 100 s and near the periphery of the maps. The estimated maps produce a variance reduction relative to the Preliminary Reference Earth Model (PREM) of more than 90% for Rayleigh waves below 60 s period but reduce to about 70% between 80 and 200 s period. For Love waves, variance reductions are similar, being above 90% for most periods below 100 s and falling to 70% at 150 s. Synthetic experiments are presented to estimate the biases that theoretical approximations should impart to the group velocity maps, in particular source group time shifts, azimuthal anisotropy, and systematic event mislocations near subducting slabs. The most significant problems are probably caused by azimuthal anisotropy, but above 100 s the effect of source group time shifts may also be appreciable. These effects are probably below the signal levels that we interpret here, however. Many known geological and tectonic structures are observed in the group velocity maps. Of particular note are the signatures of sedimentary basins, continental flood basalts, variations in crustal thickness, backarc spreading, downgoing slabs, and continental roots. Comparison of the estimated group velocity maps with those predicted by CRUST5.1/S16B30 is qualitatively good, but there are significant differences in detail which provide new information that should help to calibrate future crustal and upper mantle models of Eurasia.

  11. Seasonal cycles of seismic velocity variations detected using coda wave interferometry at Fogo volcano, So Miguel, Azores, during 2003-2004

    NASA Astrophysics Data System (ADS)

    Martini, Francesca; Bean, Christopher J.; Saccorotti, Gilberto; Viveiros, Fatima; Wallenstein, Nicolau

    2009-04-01

    Fogo volcano is an active central volcano, with a lake filled caldera, in the central part of So Miguel Island, Azores, whose current activity is limited to hydrothermal manifestations such as active fumarolic fields, thermal and CO 2 cold springs and soil diffuse degassing areas. It is affected by important active tectonic structures, with high seismic activity and practically continuous micro-seismicity. A recurrent feature from the seismicity observed in volcanic regions is the occurrence of clusters of similar earthquakes, whose origin can be attributed to the repeated action of a similar source mechanism at the same focal area. Doublets/multiplets were identified in this study within a catalogue of small magnitude (usually < 3) volcano tectonic events recorded in 2003-2004 by a selection of stations around Fogo volcano. All events have been cross-correlated and pairs whose waveforms exhibited a cross-correlation coefficient equal to or higher than 0.9 were analysed using the coda-wave interferometry technique. Subtle velocity variations found between events highlight a seasonal cycle of the velocity patterns, with lower velocity in winter time and higher velocity during summer months. Those results, together with quantitative differences between the same doublets at different stations, exhibit an excellent correlation with rainfall. A seasonal effect can also be broadly seen in the seismicity occurrence, and some of the swarms recorded over the two year period occur during the wettest season or close to episodes of abundant (above average) rainfall. Moreover, temporal and spatial analysis of several swarms highlighted the lack of any mainshock-aftershock sequence and organized migration of the hypocenters. This is suggestive of a very heterogeneous stress field. Vp/Vs is found to be lower than usually observed in volcanic areas, an occurrence likely related to the presence of steamy fluid associated with the geothermal system. Taken together, these observations suggest that pore pressurisation plays a major role in controlling a considerable part of the recorded seismicity. The geothermal fluids around Fogo massif have been identified as derived from meteoric water, which infiltrates through Fogo Lake and the volcano flanks and flows from south to north on the northern flank. All those elements seem to point to a role played by rainfall in triggering seismicity at So Miguel, possibly through pressure changes at depth in response to surface rain and/or an interaction with the geothermal system.

  12. 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).

  13. Anisotropic shear velocity structure beneath the Eastern Lau back-arc Spreading Center from joint Rayleigh and Love wave ambient noise tomography - Implications for the variation of mantle wedge melt distributions

    NASA Astrophysics Data System (ADS)

    Zha, Y.; Webb, S. C.; Wiens, D. A.; Blackman, D. K.; Dunn, R. A.; Conder, J. A.; Menke, W. H.

    2013-12-01

    We analyze Rayleigh and Love wave dispersion extracted from ambient noise correlation of OBS data to obtain a 3D shear velocity model beneath the Eastern Lau Spreading Center (ELSC). The ELSC is a 400-km-long back-arc spreading center lying close to the Tonga trench in the southwestern Pacific. Seafloor morphology, crustal thickness and lava composition data show systematic variations along the ridge as the ridge migrates away from the volcanic arc front to the north, indicating a decreasing influence of the subducting slab. Phase velocities for Rayleigh and Love waves were obtained from inter-station coherences of ambient noise recorded at 50 OBS stations. The phase velocity measurements were then inverted for anisotropic phase velocity maps and subsequently inverted for a 3D shear velocity model. Two separate low velocity zones (LVZs) are imaged beneath the back-arc basin. The shallow LVZ lies beneath the Tofua Volcanic Arc closer to the trench. The deeper LVZ underneath the back-arc spreading center widens and shifts laterally with respect to the ridge as the ridge migrates away from the volcanic arc. The two LVZs overlap to the south of 21 S but become distinct to the north, indicating that the northern ELSC segment is supplied by a different source of melt than the southern segment. Anisotropic Rayleigh wave velocity maps show fast directions sub-parallel to the trench, indicating possible along-trench mantle flow beneath the spreading center. (a) Bathymetry map of study area and locations of cross-sections shown in (b). (b) Seismic shear velocity variation at cross-sections shown in figure 1. The top three are perpendicular to the ridge and the bottom one is along the ridge.

  14. Local surface skimming longitudinal wave velocity and residual stress mapping.

    PubMed

    Sathish, Shamachary; Martin, Richard W; Moran, Thomas J

    2004-01-01

    Local variation in surface skimming longitudinal wave (SSLW) velocity has been measured using a scanning acoustic microscope. A very narrow width electrical impulse has been used to excite the transducer of the acoustic lens. This permits the separation of the SSLW signal from the direct reflected signal in the time domain. A simple method of measuring the time delay between the directly reflected signal and the SSLW signal at two defocuses has been utilized for the local measurement of SSLW velocity. The variation in the SSLW velocity measured over an area of the sample is scaled and presented as an image. The method has been implemented to image the variation of the SSLW velocity around a crack tip in a sample of Ti-6Al-4V. Since the SSLW velocity is known to change linearly with the stress, the SSLW velocity image is considered as a representation of the image of stress around the crack tip. Local stress variation in the same region of the crack tip is directly measured using x-ray diffraction. The SSLW velocity image is compared with the x-ray diffraction stress image. The contrast in the two images, spatial resolution, and the penetration depth into the sample of acoustic waves and x rays are discussed. PMID:14759007

  15. Local surface skimming longitudinal wave velocity and residual stress mapping

    NASA Astrophysics Data System (ADS)

    Sathish, Shamachary; Martin, Richard W.; Moran, Thomas J.

    2004-01-01

    Local variation in surface skimming longitudinal wave (SSLW) velocity has been measured using a scanning acoustic microscope. A very narrow width electrical impulse has been used to excite the transducer of the acoustic lens. This permits the separation of the SSLW signal from the direct reflected signal in the time domain. A simple method of measuring the time delay between the directly reflected signal and the SSLW signal at two defocuses has been utilized for the local measurement of SSLW velocity. The variation in the SSLW velocity measured over an area of the sample is scaled and presented as an image. The method has been implemented to image the variation of the SSLW velocity around a crack tip in a sample of Ti-6Al-4V. Since the SSLW velocity is known to change linearly with the stress, the SSLW velocity image is considered as a representation of the image of stress around the crack tip. Local stress variation in the same region of the crack tip is directly measured using x-ray diffraction. The SSLW velocity image is compared with the x-ray diffraction stress image. The contrast in the two images, spatial resolution, and the penetration depth into the sample of acoustic waves and x rays are discussed.

  16. 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.

  17. Phase velocities of plane waves in a pipe with a flow whose velocity varies along the radius

    NASA Astrophysics Data System (ADS)

    Butorin, V. M.

    2013-11-01

    The phase velocities of plane waves in a pipe filled with a moving acoustic medium are studied for different laws of flow velocity variation along the pipe radius. The wave equation is solved by the discretization method, which breaks the entire pipe volume into individual cylinders under the assumption that, within each of the cylinders, the flow velocity of the medium is constant. This approach makes it possible to reduce the solution to the wave problem to solving Helmholtz equations for individual cylinders. Based on boundary conditions satisfied at the boundaries between neighboring cylinders, a homogeneous system of linear algebraic equations is obtained. From this system, with the use of the scattering matrices, a simple dispersion equation is derived for determining the phase velocities of plane waves. The stability of the numerical solution to the dispersion equation with respect to the number of cylinders is investigated. The phase velocities of quasi-homogeneous and inhomogeneous waves in a pipe are numerically calculated and analyzed for different velocities of a moving medium and different laws of flow velocity variation along the radius. It is shown that the variation that occurs in the phase velocity of a homogeneous plane wave in a pipe due to the motion of the medium is identical to the mean flow velocity for different laws of flow velocity variation along the radius. For inhomogeneous plane waves, the phase velocity increment exceeds the mean flow velocity several times and depends on both the law of wave amplitude distribution along the radius and the law of the flow velocity variation along the radius.

  18. Wave Measurements Using GPS Velocity Signals

    PubMed Central

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

    2011-01-01

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

  19. Copernicus observations of Iota Herculis velocity variations

    NASA Technical Reports Server (NTRS)

    Rogerson, J. B., Jr.

    1984-01-01

    Observations of Iota Her at 109.61-109.67 nm obtained with the U1 channel of the Copernicus spectrophotometer at resolution 5 pm during 3.6 days in May, 1979, are reported. Radial-velocity variations are detected and analyzed as the sum of two sinusoids with frequencies 0.660 and 0.618 cycles/day and amplitudes 9.18 and 8.11 km/s, respectively. Weak evidence supporting the 13.9-h periodicity seen in line-profile variations by Smith (1978) is found.

  20. 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.

  1. 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.

  2. 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.

  3. Unexpected tidal variation of the ocean-acoustic velocity

    NASA Astrophysics Data System (ADS)

    Sugioka, H.; Fukao, Y.; Hibiya, T.

    2004-12-01

    Ocean sound velocity significantly varies at tidal frequency in not only shallow but also deep pert. Unexpected largely semidiurnal fluctuation of ocean-acoustic waves (T-waves), which propagate through the SOFAR channel, is found on the ocean bottom seismometer records for the 1999 submarine volcanic swarm in northern Mariana. The amplitude is one order larger than any previous artificial experiments. Here we report the first in situ evidence that T-wave travel time provide information about vertical movement of seawater due to internal tides. Numerical 3-D modelling shows the internal tide excited by external tidal forcing is particularly large along the Izu-Bonin-Mariana Ridge because of rough topography. A semidiurnal up-and-down movement associated with the internal tide cause an undulation of the SOFAR channel on the order of 100 m, which causes T-wave travel time variations consistent with the observed ones. The results are consistent with the observed travel time variations both in amplitude and phase, demonstrating that T-waves from volcanic swarms can be used to detect oceanic internal tides. Generation of internal tides is an important sink of the external tidal energy so that accurate estimate of conversion of the external to internal tides is essential to close the global tidal energy budget and to understand the Earth-Moon system evolution.

  4. ML shear wave velocity tomography for the Iranian Plateau

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  5. 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.

  6. 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.

  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. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Velocities of guided ultrasonic waves in heterogeneous medium

    NASA Technical Reports Server (NTRS)

    Touratier, M.

    1984-01-01

    Experimental and theoretical examinations were performed of the longitudinal velocity characteristics of waves in trilaminar and encapsulated waveguides. The study was confined to waveguides with core material that featured transverse wave velocities much worse than the longitudinal wave velocities. The velocities were obtained using a dispersion equation, with consideration given to both the core and encapsulant. Asymptotic velocities were also calculated for bending and twisting in trilaminar waveguides. Trials were run with bimetallic waveguides for comparison with the theoretical predictions. Good agreement was found between the predicted velocity of the propagation of the fundamental mode and the measured velocities. The method was calculated valid for modes above four, confirming that the data were contained in either the core or outer layer, and were unsensitive to the encapsulant.

  13. Detailed Three-Dimensional P and S Wave Velocity Models for the New Madrid Seismic Zone

    NASA Astrophysics Data System (ADS)

    Powell, C.; Withers, M.; Vlahovic, G.

    2005-05-01

    Detailed P and S wave velocity models and Vp/Vs values have been determined for the New Madrid Seismic Zone (NMSZ) based upon arrival times recorded by the New Madrid seismic network and by PANDA stations. The combined data set consists of 11,778 P wave arrivals and 8,579 S wave arrivals recorded by 97 stations. We used a modified version of the Benz et al., 1996 algorithm that inverts simultaneously for both P and S velocities and hypocentral locations (Tryggvason et al., 2002). The ability to specify independent P and S wave starting velocity models, rather than an S wave model linked to the P wave model via a constant Vp/Vs ratio, is particularly important for the NMSZ because the surface sediments have highly variable Vp/Vs ratios. Block size was reduced to 2x2x2 km, yielding the most detailed image of the NMSZ ever obtained. Inversion results were tested using chessboard models, spike tests and reconstruction techniques. Intrusions are imaged in great detail. Low P wave velocity and high S wave velocity appear to be correlated with earthquake occurrence; this results in distinct regions of low Vp/Vs values that correspond to the major arms of seismicity. The unusual low Vp/Vs values could be due to lithology variations but may be related to fluid saturation and porosity variations.

  14. 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.

  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. 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.

  17. 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.

  18. Low Velocity Waves Inside and Outside of Plants

    NASA Astrophysics Data System (ADS)

    Wagner, Orvin

    2010-03-01

    I have been reporting organizing waves in plants for many years. In 1989 I reported wave travel between plants. The waves travel at near 25 m/s horizontally through air on earth. Recently I built my own transmitters and receivers and found that the waves will penetrate mountains. Monitoring plants suggest that there is constant communication between plants with the cacophony peaking during the summer months. The location of the sun has a direct influence. I hypothesize that the observed waves are waves in dark matter as well as the other media involved. Apparently dark matter not only interacts with gravity but has much to do with the organization of nature. The velocities of waves in plants peak vertically. For example in Ponderosa pine the ratio of the vertical to horizontal velocity is 3/1 making a tall spindly tree. In apple the ratio is 4/3 making a nearly round tree. The velocity anisotropy may suggest that dark matter interacts differently with respect to the gravity direction. The penetrating qualities of the waves may provide useful communication. There appears to be a rather large velocity distribution, however, when the waves travel far through dense matter.

  19. Estimating propagation velocity through a surface acoustic wave sensor

    DOEpatents

    Xu, Wenyuan; Huizinga, John S.

    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.

  20. Particle velocity measurements of powdered materials under shock wave loading

    NASA Astrophysics Data System (ADS)

    Kobayashi, Takamichi

    2015-11-01

    Velocity measurements of window/sample interface by velocity interferometer have been performed on a powdered material, Ce:YAG, under various shock loading conditions induced by flyer plate impact with a maximum impact velocity of 1.074 km/s (SUS304). The observed interface velocities are much higher than expected and increase with the impact velocity, indicating that the shock impedance of shock-compressed powder is much larger than that of the ambient powder mainly because the density is largely increased. It is suggested that the equilibrium state is reached quickly within a few shock wave reflections at sample boundaries.

  1. Nonlinear shock acceleration. III - Finite wave velocity, wave pressure, and entropy generation via wave damping

    NASA Technical Reports Server (NTRS)

    Eichler, D.

    1985-01-01

    The nonlinear theory of shock acceleration developed in earlier papers, which treated the waves as being completely frozen into the fluid, is generalized to include wave dynamics. In the limit where damping keeps the wave amplitude small, it is found that a finite phase velocity (V sub ph) of the scattering waves through the background fluid, tempers the acceleration generated by high Mach number shocks. Asymptotic spectra proportional to 1/E sq are possible only when the ratio of wave velocity to shock velocity is less than 0.13. For a given asymptotic spectrum, the efficiency of relativistic particle production is found to be practically independent of the value of V sub ph, so that earlier results concerning its value remain valid for finite V sub ph. In the limit where there is no wave damping, it is shown that for modest Alfven Mach numbers, approximately greater than 4 and less than 6, the magnetic field is amplified by the energetic particles to the point of being in rough equipartition with them, as models of synchrotron emission frequently take the field to be. In this case, the disordering and amplification of field energy may play a major role in the shock transition.

  2. Temporal Changes in S-Wave Velocity at Different Depths Near Parkfield, CA

    NASA Astrophysics Data System (ADS)

    Wu, C.; Delorey, A. A.; Brenguier, F.; Guyer, R. A.; Gomberg, J. S.; Johnson, P. A.

    2014-12-01

    The 2003 Mw6.5 San Simeon earthquake and the 2004 Mw6.0 Parkfield earthquake have been found to cause significant seismic velocity decreases along the San Andreas Fault (SAF). However, the depth range of the velocity decreases is hard to constrain based on traditional approaches and is still inclusive. In this study, we used noise interferometry (MSNoise) and surface wave inversion to measure the S-wave velocity changes at different depths near Parkfield after the two large earthquakes. We processed continuous seismic recordings from 15 stations near Parkfield from 2001 to 2011 to obtain the noise cross-correlation functions, and measured the temporal variations in Rayleigh wave phase velocities at 6 different frequency bands. We then invert the Rayleigh wave phase velocity changes at different frequencies using a series of Rayleigh wave sensitivity kernels, for the S-wave velocity changes at different depths. Our results indicate that the S-wave velocity decreases caused by the San Simeon earthquake are relatively small (up to ~0.1%), and they access depths of at least 6 km in the region of Parkfield. On the other hand, the S-wave velocity decrease caused by the Parkfield earthquake is larger (up to ~0.3%), but is dominated by elastic changes in the top 1-2 km of the crust. Our ongoing work is focused on constraining and understanding the physical mechanisms for the different depth ranges of velocity changes cause by the two large earthquakes, and characterization of the recovery processes at different depths after the Parkfield earthquake.

  3. Shear wave velocity structure in West Java, Indonesia as inferred from surface wave dispersion

    NASA Astrophysics Data System (ADS)

    Anggono, Titi; Syuhada

    2016-02-01

    We investigated the crust and upper mantle of West Java, Indonesia by measuring the group velocity dispersion of surface waves. We analyzed waveform from four teleseismic earthquake recorded at three 3-component broadband seismometers. We analyzed fundamental mode of Rayleigh and Love waves from vertical, radial, and transverse components using multiple filter technique. We inverted the measured group velocity to obtain shear wave velocity profile down to 200 km depth. We observed low shear wave velocity zone at depth of about 20 km. Shear velocity reduction is estimated to be 18% compared to the upper and lower velocity layer. The low velocity zone might be associated with the subducting slab of Indo-Australian Plate as similar characteristics of low velocity zones also observed at other subducting regions.

  4. 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).

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

    SciTech Connect

    Spence, W.L.

    1985-04-01

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

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

    USGS Publications Warehouse

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

    2003-01-01

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

  7. Effect of crack aperture on P-wave velocity and dispersion

    NASA Astrophysics Data System (ADS)

    Wei, Jian-Xin; Di, Bang-Rang; Ding, Pin-Bo

    2013-06-01

    We experimentally studied the effect of crack aperture on P-wave velocity, amplitude, anisotropy and dispersion. Experimental models were constructed based on Hudson's theory. Six crack models were embedded with equal-radius penny-shaped crack inclusions in each layer. The P-wave velocity and amplitude were measured parallel and perpendicular to the layers of cracks at frequencies of 0.1 MHz to 1 MHz. The experiments show that as the crack aperture increases from 0.1 mm to 0.34 mm, the amplitude of the P-waves parallel to the crack layers decreases linearly with increasing frequency and the P-wave velocity dispersion varies from 1.5% to 2.1%, whereas the amplitude of the P-wave perpendicular to the crack layers decreases quadratically with increasing frequency and the velocity dispersion varies from 1.9% to 4.7%. The variation in the velocity dispersion parallel and perpendicular to the cracks intensifies the anisotropy dispersion of the P-waves in the crack models (6.7% to 83%). The P-wave dispersion strongly depends on the scattering characteristics of the crack apertures.

  8. 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.; OShaughnessy, 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, Andr G.; Abecasis, Gonalo 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=?0.0750.012 SD/allele, P = 2.8 x 10?10; replication beta=?0.0860.020 SD/allele, P = 1.4 x 10?6). Combined results for rs7152623 from 11 cohorts gave beta=?0.0760.010 SD/allele, P=3.1x10?15. The association persisted when adjusted for mean arterial pressure (beta=?0.0600.009 SD/allele, P = 1.0 x 10?11). Results were consistent in younger (<55 years, 6 cohorts, N=13,914, beta=?0.0810.014 SD/allele, P = 2.3 x 10?9) and older (9 cohorts, N=12,026, beta=?0.0610.014 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

  9. 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.

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

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

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

  11. 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.

  12. 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.

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

    NASA Astrophysics Data System (ADS)

    Hirsch, Aaron C.; Dalton, Colleen A.; Ritsema, Jeroen

    2015-11-01

    Seismic models provide constraints on the thermal and chemical properties of the cratonic upper mantle. Depth profiles of shear velocity from global and regional studies contain positive velocity gradients in the uppermost mantle and often lack a low-velocity zone, features that are difficult to reconcile with the temperature structures inferred from surface heat flow data and mantle-xenolith thermobarometry. Furthermore, the magnitude and shape of the velocity profiles vary between different studies, impacting the inferences drawn about mantle temperature and composition. In this study, forward modeling is used to identify the suite of one-dimensional shear-velocity profiles that are consistent with phase-velocity observations made for Rayleigh waves traversing Precambrian cratons. Two approaches to the generation of 1-D models are considered. First, depth profiles of shear velocity are 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 lithosphere. Second, shear velocity-depth profiles are randomly generated. In both cases, Rayleigh wave phase velocity is calculated from the Earth models, and acceptable models are identified on the basis of comparison to observed phase velocity. The results show that it is difficult but not impossible to find acceptable Earth models that contain a low-velocity zone in the upper mantle and that temperature structures that are consistent with constraints from mantle xenoliths yield phase-velocity predictions lower than observed. For most acceptable randomly generated Earth models, shear velocity merges with the global average at approximately 300 km.

  14. 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, ε and δ, 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 δ. The second method is inversion method using linear approach where vertical velocity, δ, and ε is estimated simultaneously. Both methods are tested on synthetic models using ray-tracing forward modelling. Results show that δ value can be estimated appropriately using both methods. Meanwhile, inversion based method give better estimation for obtaining ε value. This study shows that estimation on anisotropic parameters rely on the accuracy of normal moveout velocity, residual moveout and offset to angle transformation.

  15. Analysis of GPR data: wave propagation velocity determination

    NASA Astrophysics Data System (ADS)

    Tillard, Sylvie; Dubois, Jean-Claude

    1995-01-01

    The detection of millimeter-wide discontinuities such as fissures in subsurface geological formations may be possible by means of GPR soundings, but establishing a law for the electromagnetic wave propagation velocity from field data in order to interpret radar data and to localize these discontinuities in depth is not easy. In order to optimize the interpretation of such radar surveys carried out at various sites, we turned our attention to the accuracy by which the electromagnetic wave propagation velocity may be determined. In a granitic quarry, with the help of a borehole cored 40 m deep, we were able to appraise the limits of velocity analysis based on normal move-out corrections. We characterized the degree of error caused by slightly dipping reflectors and we showed the instability of interval velocity calculations caused by uncertainties in reflection time and RMS velocity assessment. The velocity profile derived from laboratory measurements of dielectric permittivity of the granite samples, for various depths of cores, proved to be insufficient for an exact mapping of the fissure network. At a limestone quarry site, we showed that by working on several paths of electromagnetic waves, direct velocity determinations could help in differentiating rocks in the same formation, based on quality of the field data. Finally, velocities calculated in an anisotropic environment and in geological formations covered by a road or a concrete surface were analysed. Using data recorded in schists, we obtained an example of a non-uniform distribution of velocity in the same formation. Using data recorded in sands and in granite, we demonstrated that a surface material had negligible effect on the determination of the subjacent geological environment velocity.

  16. Acoustic Interferometer for Localized Rayleigh Wave Velocity Measurements

    NASA Astrophysics Data System (ADS)

    Martin, Richard W.; Sathish, Shamachary; Reibel, Richard; Moran, Thomas J.; Blodgett, Mark P.

    2003-03-01

    Two instrumentation systems for measurement of Rayleigh surface wave (RSW) velocity are described. The first system consists of a more conventional methodology using matched RF amplifiers and phase detector/mixer circuits. In the second system, a lock-in amplifier, operating at high frequency, replaces the matched RF amplifiers and phase detector/mixer circuit, therefore simplifying the instrumentation. Both systems have been used to measure relative Rayleigh wave velocity using a cylindrically focused acoustic transducer consisting of three elements. A high-precision relative velocity measurement of Rayleigh surface waves is performed by exciting the central element and one of the outer elements with a tone burst signal and measuring the phase difference between the two received signals.

  17. 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.

  18. 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.

  19. Relationship of D'' structure with the velocity variations near the inner-core boundary

    NASA Astrophysics Data System (ADS)

    Luo, Sheng-Nian; Ni, Sidao; Helmberger, Don

    2002-06-01

    Variations in regional differential times between PKiKP (i) and PKIKP (I) have been attributed to hemispheric P-velocity variations of about 1% in the upper 100 km of the inner core (referred to as HIC). The top of the inner core appears relatively fast beneath Asia where D'' is also fast. An alternative interpretation could be the lateral variation in P velocity at the lowermost outer core (HOC) producing the same differential times. To resolve this issue, we introduce the diffracted PKP phase near the B caustic (Bdiff) in the range of 139-145 epicenter distances, and the corresponding differential times between Bdiff and PKiKP and PKIKP as observed on broadband arrays. Due to the long-wavelength nature of Bdiff, we scaled the S-wave tomography model with k values (k ? dlnVs/dlnVp) to obtain large-scale P-wave velocity structure in the lower mantle as proposed by earlier studies. Waveform synthetics of Bdiff constructed with small k's predict complex waveforms not commonly observed, confirming the validity of large scaling factor k. With P-velocity in lower mantle constrained at large scale, the extra travel-time constraint imposed by Bdiff helps to resolve the HOC-HIC issue. Our preliminary results suggest k > 2 for the lowermost mantle and support HIC hypothesis. An important implication is that there appears to be a relationship of D'' velocity structures with the structures near the inner core boundary via core dynamics.

  20. 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.

  1. 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.

  2. Performance of velocity sensor for flexural wave reduction

    SciTech Connect

    Ko, S.H.

    1996-04-01

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

  3. 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.

  4. On electromagnetic waves with a negative group velocity

    SciTech Connect

    Makarov, V. P.; Rukhadze, A. A.; Samokhin, A. A.

    2010-12-15

    Recent publications devoted to the electrodynamics of media in which waves with a negative group velocity can exist are discussed. The properties of such waves have been studied from the beginning of the past century, and the most important results in this field were obtained by Soviet physicists in the 1940s-1950s. However, in most recent publications, this circumstance has not been taken into account.

  5. 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.

  6. An Examination of Rayleigh Wave Phase Velocities, South Shetland Islands

    NASA Astrophysics Data System (ADS)

    Robertson Maurice, S. D.; Wiens, D. A.; Lawrence, J. F.

    2003-12-01

    We examine the crustal and upper mantle structure of Bransfield Strait, the South Shetland Islands, and the Antarctic Peninsula using data from the Seismic Experiment in Patagonia and Antarctica (SEPA). We use Rayleigh wave phase velocity dispersion measurements from 20 teleseismic events to determine the interstation phase velocities at periods between 16 and 120 seconds. Maps of the velocities indicate crust with continental properties beneath the South Shetland Islands, the Antarctic Peninsula, and the area southwest of the Hero Fracture Zone. Thinner crust (less than 20 km thick) with backarc spreading mantle velocities lies within the Bransfield Basin proper. The seismic velocities indicate more established spreading in the northeastern portion of Bransfield Strait, and we see no evidence of anisotropy within the mantle.

  7. Fast magnetosonic waves driven by shell velocity distributions

    NASA Astrophysics Data System (ADS)

    Min, Kyungguk; Liu, Kaijun

    2015-04-01

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

  8. 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.

  9. SP12RTS: a degree-12 model of shear- and compressional-wave velocity for Earth's mantle

    NASA Astrophysics Data System (ADS)

    Koelemeijer, P.; Ritsema, J.; Deuss, A.; van Heijst, H.-J.

    2016-02-01

    We present the new model SP12RTS of isotropic shear-wave (VS) and compressional-wave (VP) velocity variations in the Earth's mantle. SP12RTS is derived using the same methods as employed in the construction of the shear-wave velocity models S20RTS and S40RTS, and the same data types. SP12RTS includes additional traveltime measurements of P-waves and new splitting measurements: 33 normal modes with sensitivity to the compressional-wave velocity and 9 Stoneley modes with sensitivity primarily to the lowermost mantle. Contrary to S20RTS and S40RTS, variations in VS and VP are determined without invoking scaling relationships. Lateral velocity variations in SP12RTS are parametrised using spherical harmonics up to degree 12, to focus on long-wavelength features of VS and VP and their ratio R. Large-low-velocity provinces (LLVPs) are observed for both VS and VP. SP12RTS also features an increase of R up to 2500 km depth, followed by a decrease towards the core-mantle boundary. A negative correlation between the shear-wave and bulk-sound velocity variations is observed for both the LLVPs and the surrounding mantle. These characteristics can be explained by the presence of post-perovskite or large-scale chemical heterogeneity in the lower mantle.

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

    NASA Astrophysics Data System (ADS)

    Krupi?ski, Adam

    2012-10-01

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

  11. 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.}

  12. 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

  13. 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].

  14. 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 38N 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 112.8E, the 38N 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.

  15. 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.

  16. Dip-movement processing for depth-variable velocity. [Correction for variation of velocity with depth

    SciTech Connect

    Artley, C.T.

    1992-12-01

    Dip-moveout correction (DMO) has become commonplace in the seismic processing flow. The goal of DMO processing is to transform the NMO-corrected data to zero-offset, so that the application of zero-offset (poststack) migration is equivalent to full prestack migration of the recorded data. Nearly all DMO implementations assume that the seismic velocity is constant. Usually, this is an acceptable tradeoff because of the tremendous cost savings of DMO and poststack migration versus prestack migration. Where the velocity changes rapidly with depth, however, this constant velocity theory can yield inadequate results. For many areas, such as the Gulf Coast, a velocity function that varies with depth is a reasonable approximation to the true velocity field. Using ray tracing, I find the raypaths from the source and receiver to the reflection point with the given recording time. The time along the corresponding zero-offset ray gives the DMO correction. The relationships between the three rays are expressed by a system of nonlinear equations. By simultaneously solving the equations via Newton-Raphson iteration, I determine the mapping that transforms nonzero-offset data to zero-offset. Unlike previous schemes that approximately handle vertical velocity variation, this method makes no assumptions about the offset, dip, or hyperbolic moveout.

  17. P-wave velocity structure beneath the northern Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Park, Y.; Kim, K.; Jin, Y.

    2010-12-01

    We have imaged tomographically the tree-dimensional velocity structure of the upper mantle beneath the northern Antarctic Peninsula using teleseismic P waves. The data came from the seven land stations of the Seismic Experiment in Patagonia and Antarctica (SEPA) campaigned during 1997-1999, a permanent IRIS/GSN station (PMSA), and 3 seismic stations installed at scientific bases, Esperanza (ESPZ), Jubany (JUBA), and King Sejong (KSJ), in South Shetland Islands. All of the seismic stations are located in coast area, and the signal to noise ratios (SNR) are very low. The P-wave model was inverted from 95 earthquakes resulting in 347 ray paths with P- and PKP-wave arrivals. The inverted model shows a strong low velocity anmaly beneath the Bransfield Strait, and a fast anomaly beneath the South Shetland Islands. The low velocity anomaly beneath the Bransfield might be due to a back arc extension, and the fast velocity anomaly beneath the South Shetland Islands could indicates the cold subducted slab.

  18. 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

  19. Seismic velocity variation along the Izu-Bonin arc estaimated from traveltime tomography using OBS data

    NASA Astrophysics Data System (ADS)

    Obana, K.; Tamura, Y.; Takahashi, T.; Kodaira, S.

    2014-12-01

    The Izu-Bonin (Ogasawara) arc is an intra-oceanic island arc along the convergent plate boundary between the subducting Pacific and overriding Philippine Sea plates. Recent active seismic studies in the Izu-Bonin arc reveal significant along-arc variations in crustal structure [Kodaira et al., 2007]. The thickness of the arc crust shows a remarkable change between thicker Izu (~30 km) and thinner Bonin (~10 km) arcs. In addition to this, several geological and geophysical contrasts, such as seafloor topography and chemical composition of volcanic rocks, between Izu and Bonin arc have been reported [e.g., Yuasa 1992]. We have conducted earthquake observations using ocean bottom seismographs (OBSs) to reveal seismic velocity structure of the crust and mantle wedge in the Izu-Bonin arc and to investigate origin of the along-arc structure variations. We deployed 40 short-period OBSs in Izu and Bonin area in 2006 and 2009, respectively. The OBS data were processed with seismic data recorded at routine seismic stations on Hachijo-jima, Aoga-shima, and Chichi-jima operated by National Research Institute for Earth Science and Disaster Prevention (NIED). More than 5000 earthquakes were observed during about three-months observation period in each experiment. We conducted three-dimensional seismic tomography using manually picked P- and S-wave arrival time data. The obtained image shows a different seismic velocity structures in the mantle beneath the volcanic front between Izu and Bonin arcs. Low P-wave velocity anomalies in the mantle beneath the volcanic front in the Izu arc are limited at depths deeper than those in the Bonin arc. On the other hand, P-wave velocity in the low velocity anomalies beneath volcanic front in the Bonin arc is slower than that in the Izu arc. These large-scale along-arc structure variations in the mantle could relate to the geological and geophysical contrasts between Izu and Bonin arcs.

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

    PubMed Central

    Varghese, Tomy; Madsen, Ernest L.

    2011-01-01

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

  1. Waves in microstructured solids and negative group velocity

    NASA Astrophysics Data System (ADS)

    Peets, T.; Kartofelev, D.; Tamm, K.; Engelbrecht, J.

    2013-07-01

    Waves with negative group velocity (NGV) were discovered in optics by Sommerfeld and Brillouin, and experimentally verified in many cases, for example in left-handed media. For waves in solids, such an effect is described mostly in layered media. In this paper, it is demonstrated that in microstructured solids, waves with NGV may also exist leading to backwards pulse propagation. Two physical cases are analysed: a Mindlin-type hierarchical (a scale within a scale) material and a felt-type (made of fibres) material. For both cases, the dispersion analysis of one-dimensional waves shows that there exists certain ranges of physical parameters which lead to NGV. The results can be used in dispersion engineering for designing materials with certain properties.

  2. 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.

  3. 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 (ω(pe) > ω(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 ω(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 ω - k([parallel])v([parallel]) = ω(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

  4. Lifting the Seismic Lid Beneath Cameroon Volcanic Line Using 1D Shear Wave Velocities

    NASA Astrophysics Data System (ADS)

    Tokam Kamga, Alain; Durrheim, Ray; Tabod, Charles; Nyblade, Andrew; Nguiya, Severin

    2014-05-01

    The composition of the lithosphere beneath Cameroon and the origin of the Cameroon Volcanic Line (CVL) is a matter of debate. Although many studies based on regional or global observations provide models for the setting of the CVL, none of them are strong enough to be considered as definitive. We used the joint inversion of Rayleigh wave group velocities and Rayleigh wave group velocities to derive shear wave velocity profiles of the lithosphere beneath Cameroon andshow that lithosphere is, on average, faster beneath the Congo Craton than beneath the Pan-African age crust. Using recently published dispersion curves, we extend the depth of investigation from 60 to 200 km. The calculated velocity-depth profiles do not show any sharp discontinuity that could be interpreted as the lithosphere-asthenosphere transition. Furthermore, there is no clear evidence of the existence of a low velocity zone beneath any geologic province within Cameroon. The smooth velocity variations observed on the velocity models are believed to be influenced by lateral mantle heterogeneities rather than vertical ones. The shear wave velocities for the uppermost mantle are in general greater than 4.3 km/s at all stations. This is higher than the values obtained in the Main Ethiopian Rift, and suggest that the perturbation of the by thermal anomalies does not extend as far as the CVL. This suggests that the source of volcanism along the CVL is from small scale convection in the asthenosphere and controlled by lithospheric fractures that are probably driven by the cold (and fast) edge of the Congo Craton.

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

    NASA Astrophysics Data System (ADS)

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

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

  6. 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.

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

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

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

  8. Variation of Seismic Velocity Structure and Topical Low Velocity Anomalies near the 660 km Discontinuity: Inference and Observational Uncertainties

    NASA Astrophysics Data System (ADS)

    Tajima, F. C.; Sigloch, K.; Nakagawa, T.

    2009-12-01

    Seismic tomography models published in the past two decades led to the findings of common long-wavelength features while there is still large variation of relatively short wavelength features among the models. On the other hand, laboratory experiments show clear difference in the measured properties for synthetic subducted mantle minerals under dry and hydrous conditions, i.e., seismic speeds and phase transformation depths while the water content in the mantle transition zone (MTZ) or the mechanisms of hydration and dehydration through subduction process are still poorly known. Nonetheless, the tomography images or electrical conductivity distributions have been interpreted rather equivocally in terms of thermal structure and water content (or fluid distribution) in the mantle. Thus, in an attempt to validate and supplement the resolution of tomography models, we carried out waveform modeling focusing on the MTZ using reflectivity and finite difference synthetics with relatively short-wavelength body waves (~1 Hz). Results show variation of seismic structure as well as highly localized low velocity anomalies (LVA’s) at the bottom of the MTZ where pronounced flattened high velocity anomalies (HVA’s), stagnant slabs, have been visualized by recent tomography studies. The effects of the LVA zones can be significant on P waveforms as SV converted or scattered waves in a relatively high frequency band while the image of local LVA’s embedded in HVA’s may not be necessarily captured in travel-time tomography studies alone. These LVA’s may indicate dehydration induced melts or fluids which were predicted from high pressure experiments for major subducted slab minerals, i.e., olivine under hydrous conditions. Given possible lateral temperature variation under slab geotherm, the LVA could be highly local. However, the waveform modeling along spotty single high frequency rays alone does not have resolving power of the lateral extent of structural variation or topical anomalies. Accordingly, we address sensitivity issues and apply a finite-frequency approach to remedy the lack of ability to constrain the lateral extent of anomaly or structural variation. Here, the radii of the Fresnel zones of the P wave data at 1 Hz are from 60 to 70 km approximately. Our preliminary analysis performed in different frequency bands indicates promising results to distinguish seismic properties of the area with an LVA zone, and suggests clues to the inhomogeneous distribution of fluids which may be associated with deep dehydration under slab geotherm.

  9. 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.

  10. A variational principle for the scattered wave.

    PubMed

    Freund, D E; Farrell, R A

    1990-05-01

    A Schwinger-type variational principle is presented for the scattered field in the case of scalar wave scattering with an arbitrary field incident on an object of arbitrary shape with homogeneous Dirichlet boundary conditions. The result is variationally invariant at field points ranging from the surface of the scatterer to the farfield and is an important extension of the usual Schwinger variational principle for the scattering amplitude, which is a farfield quantity. Also, a generic procedure, physically motivated by the general principles of boundary conditions and shadowing, is presented for constructing simple trial functions to approximate the fields. The variational principle and the trial function design are tested for the special case of a spherical scatterer and accurate answers are found over the entire frequency range. PMID:2348017

  11. 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.

  12. Initial Free-Surface Velocities Imparted by Grazing Detonation Waves

    NASA Astrophysics Data System (ADS)

    Backofen, Joseph; Weickert, Chris

    1999-06-01

    The initial velocity imparted by normal (head-on) impact of detonation waves with plates was found to be predictable by two equations as a result of analysis involving ten materials and nineteen explosives. (See ``The Effects of Plate Thickness and Explosive Properties on Projection from the End of a Charge", 16th International Symposium on Ballistics, 1996.) The current paper will present an examination of initial free-surface velocities imparted by grazing (side-on) detonation waves which, surprisingly, were found to be predictable using the previously developed equations by simply dividing by 2. In other words, two equations having a change-over point at one specific ratio of plate thickness to charge length (t/L) (charge thickness for side-on) were found to represent and predict the initial free-surface velocity for a range 0.001 < t/L < 10 for both head-on and side-on propulsion. Such a simple relationship for the initial free-surface velocities implies that a detonation's high-pressure zone behaves as if it is a Poisson-like solid.

  13. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  15. Photospheric logarithmic velocity spirals as MHD wave generation mechanisms

    NASA Astrophysics Data System (ADS)

    Mumford, S. J.; Erdlyi, R.

    2015-05-01

    High-resolution observations of the solar photosphere have identified a wide variety of spiralling motions in the solar plasma. These spirals vary in properties, but are observed to be abundant at the solar surface. In this work, these spirals are studied for their potential as magnetohydrodynamic (MHD) wave generation mechanisms. The inter-granular lanes, where these spirals are commonly observed, are also regions where the magnetic field strength is higher than average. This combination of magnetic field and spiralling plasma is a recipe for the generation of Alfvn waves and other MHD waves. This work employs numerical simulations of a self-similar magnetic flux tube embedded in a realistic, gravitationally stratified, solar atmosphere to study the effects of a single magnetic flux tube perturbed by a logarithmic velocity spiral driver. The expansion factor of the logarithmic spiral driver is varied and multiple simulations are run for a range of values of the expansion factor centred around observational constraints. The simulations are analysed using `flux surfaces' constructed from the magnetic field lines so that the vectors perpendicular, parallel and azimuthal to the local magnetic field vector can be calculated. The results of this analysis show that the Alfvn wave is the dominant wave for lower values of the expansion factor, whereas for the higher values the parallel component is dominant. This transition occurs within the range of the observational constraints, meaning that spiral drivers, as observed in the solar photosphere, have the potential to generate a variety of MHD wave modes.

  16. Measurements of wind velocity and pressure with a wave follower during Marsen

    NASA Technical Reports Server (NTRS)

    Hsiao, S. V.; Shemdim, O. H.

    1983-01-01

    Air pressure data are used in determining the rate of momentum transfer from wind to waves. On the basis of the wind velocity measurements, the wave-induced airflow and its coherence with waves are obtained for various wind velocities and phase speeds of the ocean waves. The pressure results suggest that momentum transfer to waves can be specified by a certain relation, which is given. The wind-velocity results suggest that the wave-induced airflow is much smaller than the mean wind speed. An empirical equation is proposed for the modulation of atmospheric transfer to short waves caused by the orbital velocity of long waves.

  17. The measurements of the compressional wave velocity of soils during unconsolidated-undrained triaxial testing

    NASA Astrophysics Data System (ADS)

    Lu, Zhiqu; Hickey, C. J.; Sabatier, J. M.

    2003-04-01

    In this study, a conventional triaxial cell was modified to measure the compressional wave velocity during a triaxial test. Two air-dry remolded soils taken from the counties in Sharkey and Neshoba, MS, were chosen for the study. Unconsolidated-undrained triaxial tests with pore pressure measurement were carried out. Soil samples were isotropically consolidated up to three different cell pressures, axially compressed with the axial strain up to 22%, and subjected to the unload-reload stress path cycles before and after soil failures. The velocity of the compressional wave in the axial direction as a function of the axial strain was measured along with the measurement of the stress-strain response. A comparison of the load-deformation behavior with the load-acoustic velocity behavior was made. The variation of the acoustic velocity with the effective stresses during the isotropic loading, normally consolidated compression and unload-reload stress path cycles were examined. Several empirical expressions of the compressional wave velocity in terms of the effective stresses and the over-consolidation ratio were proposed and examined with the measured data.

  18. Observations of Rapid Velocity Variations in the Slow Solar Wind

    NASA Astrophysics Data System (ADS)

    Hardwick, S. A.; Bisi, M. M.; Davies, J. A.; Breen, A. R.; Fallows, R. A.; Harrison, R. A.; Davis, C. J.

    2013-07-01

    The technique of interplanetary scintillation (IPS) is the observation of rapid fluctuations of the radio signal from an astronomical compact source as the signal passes through the ever-changing density of the solar wind. Cross-correlation of simultaneous observations of IPS from a single radio source, received at multiple sites of the European Incoherent SCATter (EISCAT) radio antenna network, is used to determine the velocity of the solar wind material passing over the lines of sight of the antennas. Calculated velocities reveal the slow solar wind to contain rapid velocity variations when viewed on a time-scale of several minutes. Solar TErrestrial RElations Observatory (STEREO) Heliospheric Imager (HI) observations of white-light intensity have been compared with EISCAT observations of IPS to identify common density structures that may relate to the rapid velocity variations in the slow solar wind. We have surveyed a one-year period, starting in April 2007, of the EISCAT IPS observing campaigns beginning shortly after the commencement of full science operations of the STEREO mission in a bid to identify common density structures in both EISCAT and STEREO HI datasets. We provide a detailed investigation and presentation of joint IPS/HI observations from two specific intervals on 23 April 2007 and 19 May 2007 for which the IPS P-Point (point of closest approach of the line of sight to the Sun) was between 72 and 87 solar radii out from the Sun's centre. During the 23 April interval, a meso-scale (of the order of 105 km or larger) transient structure was observed by HI-1A to pass over the IPS ray path near the P-Point; the observations of IPS showed a micro-scale structure (of the order of 102 km) within the meso-scale transient. Observations of IPS from the second interval, on 19 May, revealed similar micro-scale velocity changes, however, no transient structures were detected by the HIs during that period. We also pose some fundamental thoughts on the slow solar wind structure itself.

  19. Estimation of S-wave velocity structure by array microtremor measurements in San Fernando Valley, CA, USA

    NASA Astrophysics Data System (ADS)

    Iwata, T.; Kawase, H.; Matsushima, S.; Nagato, K.; Miyake, H.; Sekiguchi, H.; Kataoka, S.; Aoi, S.; Satoh, T.; Pitarka, A.; Graves, R.; Somerville, P. G.

    2001-12-01

    After the 1994 Northridge and the 1995 Kobe earthquakes, the importance of modeling both 3-D crustal structure and subsurface structure has been widely recognized for ground motion evaluation in frequency range responsible for damage to buildings and urban structures. Urban areas often extend over large-scale sediment structures and S-wave velocity is a parameter of highest importance for estimation of ground motion amplification factor. Microtremor array observation is a strong tool to investigate subsurface S-wave velocity structures and has been adopted. In 2000, we conducted microtormor array measurements at several sites in the San Fernando Valley which were severely damaged during the 1994 Northridge earthquake. Formally, Kawase et al.(1998) performed microtremor array measurements at severely damaged sites in the center of San Fernando Valley, Sherman Oaks, and Los Angeles basin during the 1994 Northridge earthquake. Recently, SCEC proposed the crustal velocity structure model in the south California area. The aim of our observation is to obtain spatial variation of S-wave velocity structure in San Fernando Valley by combining with preexisting underground structure information at limited sites and compare it with the damage distribution. There are few underground structure information in San Fernando city area and we try to estimate S-wave velocity structure in that area. We did simultaneous array observations in Sherman Oaks and San Fernando city area By F-K analysis, we estimated phase velocity dispersion. Underground S-wave velocity structure is modeled by fitting the dispersion curve of the observed phase velocity with theoretical one for fundamental Rayleigh wave. We estimate S-wave velocity structures down to about 1km depth at those three sites. Estimated S-wave velocity structures are compared with the SCEC model and those by Kawase et al(1998). There are difference between the SCEC model and our model. Site amplifications from those structure models will be discussed.

  20. 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.

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

    NASA Astrophysics Data System (ADS)

    Karato, Shun-ichiro

    2013-04-01

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

  2. 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.

  3. Blood pulse wave velocity measured by photoacoustic microscopy

    NASA Astrophysics Data System (ADS)

    Yeh, Chenghung; Hu, Song; Maslov, Konstantin; Wang, Lihong V.

    2013-03-01

    Blood pulse wave velocity (PWV) is an important indicator for vascular stiffness. In this letter, we present electrocardiogram-synchronized photoacoustic microscopy for in vivo noninvasive quantification of the PWV in the peripheral vessels of mice. Interestingly, strong correlation between blood flow speed and ECG were clearly observed in arteries but not in veins. PWV is measured by the pulse travel time and the distance between two spot of a chose vessel, where simultaneously recorded electrocardiograms served as references. Statistical analysis shows a linear correlation between the PWV and the vessel diameter, which agrees with known physiology. Keywords: photoacoustic microscopy, photoacoustic spectroscopy, bilirubin, scattering medium.

  4. In Vitro Validation of Rapid MR Measurement of Wave Velocity

    PubMed

    Kraft; Fatouros; Corwin; Fei

    1997-05-01

    A one-dimensional time-of-flight MR sequence, having a total acquisition time of approximately 60 ms, has been employed to determine flow-wave propagation velocities for pulsatile flow in compliant latex tubes. The results were compared with those of two independent methods and were found to be in good agreement. An extension of the same MR method was used to test the validity of the "water-hammer" relationship as a means to assess pulse pressure. Very good agreement was found with direct manometric determinations of pulse pressure. PMID:9252279

  5. Surface wave and shear wave velocity structure beneath Kekexili area in northern Tibet

    NASA Astrophysics Data System (ADS)

    He, W.; Chen, Y. J.; Fan, W.; Tang, Y.; Seismotectonics at Peking University

    2011-12-01

    While several portable seismic arrays had been deployed in Tibet during the last decade most of these arrays covered the southern and eastern region of the plateau, leaving the central northern part of the plateau, the Kekexili area, out of the inversion range of most of these tomographic studies. In 2008 following the 2008 Ms 7.3Yutian earthquake Peking University deployed a temporal seismic array along the southern boundary of the Tarim basin. Here we report preliminary results of a surface wave study utilizing the ray paths between this PKU Yutian array and the on-going Indepth IV passive array (also known as the ASCENT array) to invert for the average shear-wave velocity structure of this little studied Kekexili area. We also show the results of the average shear-wave velocity structure of the Tarim basin using the surface waves pasting through the PKU Yutian array and the CEA provincial permanent stations in the Tianshan region. We divide the ray paths into two groups that have sampled the northern and southern Kekexili region separated by the Kunlun fault zone. Phase- and group-velocity curves of the Rayleigh waves were measured at the periods of 15 to 125 s using conventional two-station method. Further inversion of phase velocities yields one-dimensional model of the average shear wave velocity structure for the northern and southern Kekexili areas. Both of the phase- and group-velocities measured for the ray paths in the northern Kekexili area are higher than that in the southern Kekexili area for periods shorter than 75 s and however, the difference is insignificant at periods longer than 75 s. The inverted Moho depth is about 50 km for the northern Kekexili area, and about 65 km for the southern Kekexili area. There exists a high velocity zone at depths of 50-70 km near the Moho in the northern Kekexili area. Finally, the measured phase velocities for the ray paths across the Tarim basin are significantly lower than the AK135 global average model at periods less than 75 seconds. The inverted Moho depth is about 50 km and the shear wave velocities in the crust is lower than the AK135 model for the Tarim basin.

  6. Three-Dimensional Velocity Structure in Southern California from Teleseismic Surface Waves and Body Waves.

    NASA Astrophysics Data System (ADS)

    Prindle-Sheldrake, K. L.; Tanimoto, T.

    2003-12-01

    Analysis of teleseismic waves generated by large earthquakes worldwide across the Southern California TriNet Seismic Broadband Array has yielded high quality measurements of both surface waves and body waves. Rayleigh waves and Love waves were previously analyzed using a spectral fitting technique (Tanimoto. and Prindle-Sheldrake, GRL 2002; Prindle-Sheldrake and Tanimoto, submitted to JGR), producing a three-dimensional S-wave velocity structure. Features in our velocity structure show some regional contrasts with respect to the starting model (SCEC 2.2), which has detailed crustal structure, but laterally homogeneous upper mantle structure. The most prominent of which is a postulated fast velocity anomaly located west of the Western Transverse Ranges that could be related to a rotated remnant plate from Farallon subduction. Analysis indicates that, while Rayleigh wave data are mostly sensitive to mantle structure, Love wave data require some modifications of crustal structure from SCEC 2.2 model. Recent advances in our velocity structure focus on accommodation of finite frequency effect, and the addition of body waves to the data. Thus far, 118 events have been analyzed for body waves. A simple geometrical approach is used to represent the finite frequency effect in phase velocity maps. Due to concerns that, for seismic phases between 10-100 seconds, structure away from the ray theoretical is also sampled by a propagating surface wave, we have adopted a technique which examines a normal mode formula in its asymptotic limit (Tanimoto, GRL 2003 in press). An ellipse, based on both distance from source to receiver and wavelength, can be used to approximate the effect on the structure along the ray path and adjacent structure. Three models were tested in order to select the appropriate distribution within the ellipse; the first case gives equal weight to all blocks within the ellipse; case 2 incorporates a Gaussian function which falls off perpendicular to the ray path, allowing the amplitude to peak at the receiver; case 3 is the same as case 2, yet removes the effect of the peak at the receiver. A major improvement is that the locale under consideration has expanded due to the effect of ray paths spreading over a larger area than the ray theoretical. Comparison of the three techniques yields very similar results, and all techniques show an exceptional correlation to the ray theoretical phase velocity maps. After analyzing our data in terms of the finite frequency effect, we find that little change has occurred as a result of employing this technique other than expanding our region of study. P-wave measurements were obtained from the data set for 118 events. Preliminary results show systematic patterns. We have successfully measured 30 S-wave events which we plan to incorporate into our velocity structure. Our goal is to proceed with a joint inversion of P-waves, S-waves and Surface waves for a collective Southern California velocity structure.

  7. 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.

  8. 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

  9. Network locational testing and velocity variations in central Virginia

    SciTech Connect

    Sibol, M.S.; Bollinger, G.A.

    1983-01-01

    Twenty-four blasts from three quarries operating in the central Virginia area were used, first to test the location capabilities of the Central Virginia - North Anna Network and then to generate relative station delay suits for network stations. Using two different methods of approximating blast origin times, the Closest Station Method (CSM) and the Single Iteration Method (SIM), station delays were derived for different areas within central Virginia. Application of these station delay suites reduced locational errors in the general area from an average of 3.0 +- 1.2 to 1.7 +- 0.6 km (95% cofidence level). In both cases, the average equivalent radii, a linear measure of error ellipse size, were 1.3 km. However, this result depends primarily on the improvement at one of the three quarries, where the location error was reduced from 6.5 km to 2.6 km. Utilizing one of these methods (the SIM), lateral variational patterns in velocity were inferred and determined to be velocity banding similar to that observed in the Piedmont province in Georgia, North and South Carolina.

  10. 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.

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

    USGS Publications Warehouse

    Hotovec-Ellis, Alicia J.; Gomberg, Joan S.; Vidale, John; Creager, Ken C.

    2014-01-01

    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.

  12. 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.

  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. 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 Alfvn 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.

  15. 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.

  16. Mapping Tectonic features beneath the Gulf of California using Rayleigh and Love Waves Group Velocities

    NASA Astrophysics Data System (ADS)

    Persaud, P.; Di Luccio, F.; Clayton, R. W.

    2012-12-01

    This study contributes to our understanding of the Pacific-North America lithospheric structure beneath the Gulf of California and its western and eastern confining regions, by mapping fundamental mode surface wave group velocities. We measure the dispersion of Rayleigh and Love surface waves to create a series of 2D maps of group velocities, which provide important information on the earth structure beneath the study region. Although several surface waves studies were published in the last decade, all of them were done using phase velocity measurements based on the two stations method. Here we combine dispersion measurements at the regional scale with data at teleseismic distances to provide a more complete dataset for studies of earth structure. We also analyze group velocities from short to long periods in order to define structural features at both crustal and mantle scales. Our study uses earthquakes recorded by the Network of Autonomously Recording Seismographs (NARS-Baja), a set of 14 broadband seismic stations that flank the Gulf of California. From the NEIC bulletin we selected 140 events recorded by the NARS-Baja array. In order to have dispersion measurements in a wide range of periods, we used regional earthquakes with M > 4.2 and teleseismic events with M > 6.9. We first computed the dispersion curves for the surface wave paths crossing the region. Then, the along path group velocity measurements for multiple periods are converted into tomographic images using kernels which vary in off-path width with the square root of the period. Dispersion measurements show interesting and consistent features for both Rayleigh and Love waves. At periods equal to or shorter than 15 s, when surface waves are primarily sensitive to shear velocity in the upper 15 km of the crust, slow group velocities beneath the northern-central Gulf reveal the presence of a thick sedimentary layer, relative to the southern Gulf. Group velocities beneath the northwestern side of Baja are faster than the rest of the peninsula. At deeper crustal levels, group velocities become faster in the northern Gulf, whereas in the central Gulf a slow velocity patch becomes more localized. At periods of 30 s and longer, tomographic maps become more complex, reflecting the variation in lithospheric structure beneath the study area. Above 40 s, two areas of high velocity are clearly incoming from the Pacific. Going even deeper into the mantle (60-100 s), the velocity pattern becomes less heterogeneous and relatively slow. The separation between low velocities beneath the East Pacific Rise and the Rivera Transform fault zone and high velocities beneath the northern tip of the Rivera plate is clear at these periods. At even longer periods, tomographic maps are relatively homogeneous beneath Baja and the Gulf, as well as onshore and offshore.

  17. 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.

  18. 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.

  19. Average shear-wave velocity structure of the Kamchatka peninsula from the dispersion of surface waves

    NASA Astrophysics Data System (ADS)

    Shapiro, N. M.; Gorbatov, A. V.; Gordeev, E.; Dominguez, J.

    2000-09-01

    An average shear-wave velocity structure has been estimated for the path between the Kamchatka Isthmus and Petropavlovsk-Kamchatski. It is obtained from the Monte Carlo inversion of the Rayleigh and Love wave group velocity dispersion curves measured using broad-band seismograms of events in Northern Kamchatka recorded by the IRIS station PET in Petropavlovsk-Kamchatski. The Moho interface was found at a depth of 355 km and the Konrad one at 184 km. An important feature of the found structure is a low velocity in the upper mantle. This result is coherent with the recent and present-% day volcanic activity in Kamchatka. Synthetic long period seismograms computed for the obtained structure are in good agreement with observed ones.

  20. 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.

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

    NASA Astrophysics Data System (ADS)

    Berge, P. A.

    2001-12-01

    Recent advances in seismic surveys have provided ways to image shallow structure in highly attenuating soils and near-surface rock. Applications include using surface wave methods to find tunnels; mapping landfills with seismic refraction methods; finding faults, the water table, or other strong heterogeneities using seismic reflection surveys. Recent improvements in laboratory ultrasonic measurement techniques have provided reliable data on compressional and shear wave velocities in soils at low pressures analogous to the top few meters to tens of meters of the subsurface. The availability of these data points the way for development of interpretation methods that may allow seismologists to obtain more information from their data in the future. For environmental applications, improvements to interpretation methods could lead to reliable detection of second-order features such as changes in soil saturation, presence of dense non-aqueous phase liquids, or changes in clay content. Traditional modeling techniques developed in the oil industry are optimized for consolidated materials at pressures and depths greater than those typical for environmental applications. The shallow subsurface velocities are highly nonlinear and the soils are highly attenuating, and these characteristics must be considered when modeling velocities (and also when processing seismic data). Various factors, including grain contact roughness, location of clay with respect to sand grains, location of fluid in the partially-saturated case, loose vs. dense packing, all affect the compressional and shear wave velocities and attenuation and their pressure (depth) dependence. Care must be taken when applying effective medium theories or grain-contact theories to model shallow soil velocity behavior. Unconsolidated materials at low pressures show much greater variation in compressional vs. shear wave properties than consolidated materials and high-pressure applications would show. Despite the modeling difficulties, progress in seismic interpretation may be made if data are available for both compressional and shear waves. Examples of pitfalls and methods for successful soil velocity modeling will be presented using lab and field velocity data from the literature, for sands, silty sands, and other unconsolidated materials. The goal is to develop techniques to improve interpretation of seismic data from the vadose zone. This work was performed under the auspices of the U.S. Department of Energy by the University of California Lawrence Livermore National Laboratory under contract W-7405-ENG-48 and supported specifically by the DOE Environmental Management Science Program. >http://www.llnl.gov/ees/esd/expgeoph/Berge/EMSP/

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

    SciTech Connect

    Williams, R.S.; Grant, S.K. . Dept. of Geology and Geophysics); Haas, C.J. . Dept. of Mining Engineering)

    1993-03-01

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

  3. 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. PMID:26587459

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

    NASA Astrophysics Data System (ADS)

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

    2011-09-01

    Endothelial function can be assessed non-invasively with ultrasound, analyzing the change of brachial diameter in response to transient forearm ischemia. We propose a new technique based in the same principle, but analyzing a continuous recording of carotid-radial pulse wave velocity (PWV) instead of diameter. PWV was measured on 10 healthy subjects of 222 years before and after 5 minutes forearm occlusion. After 59 31 seconds of cuff release PWV decreased 21 9% compared to baseline, reestablishing the same after 533 65 seconds. There were no significant changes observed in blood pressure. When repeating the study one hour later in 5 subjects, we obtained a coefficient of repeatability of 4.8%. In conclusion, through analysis of beat to beat carotid-radial PWV it was possible to characterize the temporal profiles and analyze the acute changes in response to a reactive hyperemia. The results show that the technique has a high sensitivity and repeatability.

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

    PubMed

    Clamond, Didier

    2012-04-13

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

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

    SciTech Connect

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

    1982-04-10

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

  7. 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.

  8. 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.

  9. 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.

  10. 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, CAGSBaiwanzhuang 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.

  11. 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.

  12. Variational wave functions for homogenous Bose systems

    NASA Astrophysics Data System (ADS)

    St?, Andrs; Szpfalusy, Pter

    2008-02-01

    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 Bogoliubovs canonical transformation for each k . In another case, inspired by Nozires 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 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.

  13. Determination of the specific area of liquid gas and the velocity of weak pressure waves in aqueous foams

    NASA Technical Reports Server (NTRS)

    Saint-Cloud, Jean; Guerraud, Claude; Moreau, Michel; Manson, Numa

    1988-01-01

    The specific area of an aqueous foam contained in a tube is obtained by determining the fraction of the quantity of light emitted by a source and diffused by the specific area of the column of the foam. The velocity of the waves of weak pressure (which propagate in the air with the velocity of sound) is measured by noticing the moment when the wave penetrates the column and the moment when, having reached the opposite side, it determines a variation of the light diffused by the area of the latter.

  14. Probabilistic Seismic Hazard Maps of Seattle, Washington, Including 3D Sedimentary Basin Effects and Rupture Directivity: Implications of 3D Random Velocity Variations (Invited)

    NASA Astrophysics Data System (ADS)

    Frankel, A. D.; Stephenson, W. J.; Carver, D.; Odum, J.; Williams, R. A.; Rhea, S.

    2010-12-01

    We have produced probabilistic seismic hazard maps of Seattle for 1 Hz spectral acceleration, using over five hundred 3D finite-difference simulations of earthquakes on the Seattle fault, Southern Whidbey Island fault, and Cascadia subduction zone, as well as for random deep and shallow earthquakes at various locations. The 3D velocity model was validated by modeling the observed waveforms for the 2001 M6.8 Nisqually earthquake and several smaller events in the region. At these longer periods (≥ 1 sec) that are especially important to the response of buildings of ten stories or higher, seismic waves are strongly influenced by sedimentary basins and rupture directivity. We are investigating how random spatial variations in the 3D velocity model affect the simulated ground motions for M6.7 earthquakes on the Seattle fault. A fractal random variation of shear-wave velocity with a Von Karman correlation function produces spatial variations of peak ground velocity with multiple scale lengths. We find that a 3D velocity model with a 10% standard deviation in shear-wave velocity in the top 1.5 km and 5% standard deviation from 1.5-10 km depth produces variations in peak ground velocities of as much as a factor of two, relative to the case with no random variations. The model with random variations generally reduces the peak ground velocity of the forward rupture directivity pulse for sites near the fault where basin-edge focusing of S-waves occurs. It also tends to reduce the peak velocity of localized areas where basin surface waves are focused. However, the medium with random variations also causes small-scale amplification of ground motions over distances of a few kilometers. We are also evaluating alternative methods of characterizing the aleatory uncertainty in the probabilistic hazard calculations.

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

    NASA Astrophysics Data System (ADS)

    Liang, X.; Sandvol, E. A.; Shen, Y.; Gao, H.; Zhang, Z.

    2013-12-01

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

  16. S-wave velocity structure beneath the High Lava Plains, Oregon, from Rayleigh-wave dispersion inversion

    NASA Astrophysics Data System (ADS)

    Warren, Linda M.; Snoke, J. Arthur; James, David E.

    2008-09-01

    The High Lava Plains (HLP) "hotspot" track is a prominent volcanic lineament that extends from the southeast corner of Oregon in the northern Great Basin to Newberry volcano in the eastern Cascades. With the age of silicic volcanism decreasing along track to the northwest, the HLP and Newberry volcano are a rough mirror image to the Eastern Snake River Plain and Yellowstone but, in the case of the HLP, at an orientation strongly oblique to North American plate motion. Since this orientation is incompatible with plate motion over a fixed hotspot, other proposed origins for the HLP, such as asthenospheric inflow around a steepening slab, residual effects of a Columbia River/Steens plume, backarc spreading, and Basin and Range extension, relate it to various tectonic features of the Pacific Northwest. To begin distinguishing between these hypotheses, we image upper-mantle structure beneath the HLP and adjacent tectonic provinces with fundamental-mode Rayleigh waves recorded by stations of the USArray Transportable Array, the recently-initiated HLP seismic experiment, the United States National Seismograph Network, and the Berkeley seismic network. We estimate phase velocities along nearly 300 two-station propagation paths that lie within and adjacent to the HLP and cross the region along two azimuths, parallel to and perpendicular to the HLP track. The dispersion curves, which typically give robust results over the period range 16-171 seconds, are grouped by tectonic region, and the composite curves are inverted for S-wave velocity as a function of depth. We also fit a single plane wave to phase delays across the region to identify laterally homogeneous subregions. The resulting variations in upper-mantle structure correlate with variations in surface volcanism and tectonics. The lowest velocities ( 4.1 km/s) occur at 50 km depth in the SE corner of Oregon, where there has been extensive basaltic volcanism in the past 2-5 kyr, and suggest uppermost mantle temperatures sufficient to produce basaltic partial melting. While the seismic velocities of the uppermost mantle beneath the volcanic High Lava Plains are low relative to the standard Tectonic North America (TNA) model, they are only slightly lower than those found for the adjacent northern Great Basin and they appear to be significantly higher than upper-mantle velocities beneath the Eastern Snake River Plain. Our results provide no evidence for a residual plume signature beneath the HLP region, leaving open questions as to the origin of the HLP volcanic track itself.

  17. Analysis of Surface Wave Phase Velocity and Azimuth Anomalies using Wave Gradiometry for USArray

    NASA Astrophysics Data System (ADS)

    Yang, Y.; Langston, C. A.

    2014-12-01

    We investigate the phase velocity and surface wave arrival angle anomalies observed on the US Array Transportable Array (TA) incorporating wave gradiometry (WG) and frequency wavenumber (fk) methods. For WG, there are two crucial points: computing the spatial gradient over a subarray and acquiring an accurate reference station amplitude. In order to get a stable spatial gradient with small error we use up to a fifth order Taylor's series expansion of the wavefield for subarrays of 22 stations or more. Reference station amplitudes are regularized using a beam forming method to increase the SNR. Synthetic surface waves are generated using the SPECFEM3D globe algorithm with models S362ANI and CRUST2.0 with additional random ambient noise added as input. Stability in WG parameters are tested assuming different reducing sloweness. Stability of phase velocity estimates is improved by incorporating the higher order Taylor series terms. In application to stations of the TA, outcomes from WG and fk all show similar arrival angle anomalies. However, phase velocity determined from fk is higher and is spatially coarser than results from WG. Performance of WG improves with decreasing frequency as expected. Using this analysis flow, WG gives stable results for waves generated by earthquakes from different directions. Comparison of synthetic and observed maps of azimuth and phase velocity anomaly shows general agreement although some important local differences are observed. These differences will provide invaluable information for improving understanding of Earth structure. An approach for using WG parameters in Earth model inversion is outlined based on our stability analysis.

  18. Lateral variations in mantle velocity structure and discontinuities determined from P, PP, S, SS and SS - S{sub d}S travel time residuals

    SciTech Connect

    Vasco, D.W.; Johnson, L.R.; Pulliam, J.

    1995-12-10

    The arrival times of seismic P- and S-waves are used in constructing a mantle velocity model and a model of boundary topography of the 410-km and 660-km discontinuities. Travel times obtained from events listed in the catalog of the International Seismology Centre (ISC) are relocated relative to the velocity model of the International Association of Seismology and Physics of the Earth`s Interior 1991 (IASP91). The role of perturbations of the 410-km and 660-km discontinuities on the models of P- and S-wave velocity variations is discussed. Correlations are not evident when velocity anomalies are plotted as a function of transition zone thickness.

  19. 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

  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. 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.

  2. 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.

  3. Crustal shear wave velocity and radial anisotropy beneath the Rio Grande rift from ambient noise tomography

    NASA Astrophysics Data System (ADS)

    Fu, Yuanyuan V.; Li, Aibing

    2015-02-01

    Shear wave velocity and radial anisotropy beneath New Mexico are obtained from ambient seismic noise tomography using data from the Transportable Array. Besides the distinct seismic structure imaged across the Rio Grande rift from the Colorado Plateau to the Great Plains, both velocity and anisotropy models also reveal significant variations along the rift. The rift at Albuquerque is characterized by remarkably low velocity in the shallow crust, high velocity and strong positive anisotropy in the middle and lower crust, and low velocity in the upper mantle. These observations can be interpreted as magma accumulation in the shallow crust and significant mafic underplating in the lower crust with abundant melt supply from the hot mantle. We propose that the Albuquerque region has recently been experiencing the most vigorous extensional deformation in the rift. Positive anisotropy with Vsh > Vsv appears in the central and southern rifts with a stronger anisotropy beneath younger volcanoes, reflecting layering of magma intrusion due to past and recent rifting activities. The low velocities in the uppermost mantle are observed under high-elevation places, the Jemez Lineament, northern rift, and east rift boundary, implying that the buoyancy of hot mantle largely compensates the local high topography. Low mantle velocities appear at the boundary of the southern rift, corresponding to the large lithosphere thickness change, instead of the rift center, consistent with the prediction from the small-scale, edge-driven mantle convection model. We conclude that the edge-driven upper mantle convection is probably the dominant mechanism for the recent and current rifting and uplift in the Rio Grande rift.

  4. Imaging seismic velocities for hydrate-bearing sediments using converted waves near Yuan-An Ridge, off southwest Taiwan

    NASA Astrophysics Data System (ADS)

    Cheng, W. B.; Shih, T. Y.; Lin, W. Y.; Wang, T. K.; Liu, C. S.; Wang, Y.

    2014-10-01

    Data from P-waves and from S-waves generated by P-S conversion on reflection from airgun shots recorded along four lines of ocean bottom seismometers were used to construct 2-D velocity sections near the Yuan-An Ridge, off southwest Taiwan. The locations of the ocean bottom seismometers were determined to high accuracy by an inversion based on the shot traveltimes. Traveltime inversion and forward modeling of multicomponent wide-angle seismic data result in detailed P-wave (Vp) and S-wave (Vs) velocities of hydrate-bearing sediment layers. The inversion indicates a relatively high P-wave velocity beneath topographic ridges which represent a series of thrust-cored anticlines develop in the accretionary wedge. S-wave velocities of the sediments over the entire section, down to 400 m below seafloor, range from 320 to 570 ms-1. We suggested the lateral variation in Vp/Vs profiles in the hydrate-affected zones may be related to the migration conduit of gas-rich fluid and a characteristic of hydrate content. We model Vp using equations based on a modification of Woods equation to estimate the gas hydrate saturation. The hydrate saturation varies from 5% at the top ?200 m below the seafloor to 10-15% of pore space close to the bottom simulating reflector (BSR) in the survey area.

  5. 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.

  6. Interferometric methods for measurement of ultrasonic wave velocity: Classification, characteristics and basic defects

    NASA Technical Reports Server (NTRS)

    Kozlowski, Z.

    1974-01-01

    Interferometric methods may be considered to include all methods in which the time necessary for a signal to pass through a medium is determined on the basis of the period of oscillation of which the signal consists, while the distance is determined by noting the coincidence between (1) interference between the measured signal and its reflection and ultrasonic interference, or between another signal serving as a reference and electrical interference in the electronic part of the device. In general, all interferometric methods are relatively simple and permit a high degree of accuracy. Theoretically 48 different variations may be distinguished, about 30 of which are capable of practical application. For liquids, where transverse waves do not exist, the number of possible variations is limited to 40, assuming that absolute velocity measurement is desired.

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

    NASA Astrophysics Data System (ADS)

    Liang, X.; Sandvol, E. A.; Shen, Y.

    2012-12-01

    Variations in the subduction angle of the Nazca plate beneath the South American plate has lead to different modes of deformation along the strike of the Andean active margin including the formation of the Central Andean Plateau. There is a volcanic gap between the central and southern Andean volcanic zones, where the subducting Nazca slab changes from 30-degree dipping slab beneath the Puna plateau to a horizontal slab geometry beneath the Sierras Pampeanas, and then to a 30-degree dipping slab beneath the south Andes from north to south. The Pampean flat-slab subduction correlates spatially with the track of the Juan Fernandez Ridge, and is associated with the inboard migration of crustal deformation. In the Puna plateau a major Pliocene delamination event has previously been inferred from geochemical and geological and preliminary geophysical data beneath the southern Puna plateau. The transition between dipping- and flat-subduction slab and the mountain building process of the central Andean plateau are probably key issues to understanding this type of Andean-type orogenic process. We combined both body-wave and ambient-noise measurements together to invert the upper mantle velocity structure by using a full-waveform simulation approach. The broadband waveform data from several temporary networks: PUNA, SIEMBRA, CHARGE, RAMP, and several permanent stations are used. The preliminary results show that the low upper mantle velocities north of 29S and south of 35S, corresponding to the low velocity mantle wedge of dipping-subduction. We also observe what appears to be an isolate high velocity below the southern Puna where the Pliocene delamination event may have occurred. At the same time the intermediate to high velocity is beneath the Sierras Pampeanas, which is well correlated with the Pampeanas flat-slab, however we observe substantial heterogenity within this flat slab.

  8. Shear wave velocity prediction using seismic attributes and well log data

    NASA Astrophysics Data System (ADS)

    Gholami, Raoof; Moradzadeh, Ali; Rasouli, Vamegh; Hanachi, Javid

    2014-08-01

    Formation's properties can be estimated indirectly using joint analysis of compressional and shear wave velocities. Shear wave data is not usually acquired during well logging, which is most likely for cost saving purposes. Even if shear data is available, the logging programs provide only sparsely sampled one-dimensional measurements: this information is inadequate to estimate reservoir rock properties. Thus, if the shear wave data can be obtained using seismic methods, the results can be used across the field to estimate reservoir properties. The aim of this paper is to use seismic attributes for prediction of shear wave velocity in a field located in southern part of Iran. Independent component analysis (ICA) was used to select the most relevant attributes to shear velocity data. Considering the nonlinear relationship between seismic attributes and shear wave velocity, multi-layer feed forward neural network was used for prediction of shear wave velocity and promising results were presented.

  9. 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.

  10. 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.

  11. 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

  12. 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

  13. 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

  14. Finite element solution for pressure and velocity wave propagation

    SciTech Connect

    Lucas, S.

    1987-01-01

    As part of the development of utility thermal-hydraulics capabilities, the microcomputer is becoming a more powerful tool for analysis. Water-hammer and single-phase flow problems have been analyzed with large computer codes such as RELAP5, TRAC, or method of characteristics codes. These analyses can now be performed on a microcomputer for a fraction of the manpower as before and at essentially no cost. This can be done by using finite element (weighted residual) types of methods. A finite element (weighted residual) type of solution is outlined for solving the continuity (mass) and momentum equations for pressure wave propagation. The method uses a staggered grid. A staggered grid is one in which the scalar variables (such as pressure) and the vector variables (velocity, mass flux) are solved for at different points in the computational grid. The method presented here is termed the elimination method, since for two equations (mass and momentum), one of the dependent variables is eliminated in terms of the other, resulting in, essentially, a higher order equation in one dependent variable.

  15. Rayleigh and Love wave phase velocity maps of Iceland from combined ambient noise and teleseismic surface wave analysis.

    NASA Astrophysics Data System (ADS)

    Harmon, N.

    2014-12-01

    Iceland is one of the few regions where ridge-plume interaction can be examined with a terrestrial seismic array. Velocity structure from broadband surface wave dispersion measurements can be used to constrain the complicated crustal and upper mantle structure caused by the plume enhanced rifting activity. Here I use data from the ICEMELT and HOTSPOT arrays on Iceland to generate phase velocity dispersion maps of both Rayleigh and Love waves from ambient noise cross correlation and teleseismic events. I invert Rayleigh and Love wave dispersion observed from ambient noise for tomographic velocity structure. For teleseismic Rayleigh waves I use the two-plane wave approximation array-based method of Forsyth and Li [2005]. I also develop and adapt this method for teleseismic Love waves. This requires additional preprocessing of the data to estimate the amplitude and phase for teleseismic Love waves. Specifically, for each station, the vertical component phase observation of the fundamental mode Rayleigh is used to predict and remove the horizontal components of Rayleigh waves. Then I invert for the maximum amplitude and apparent back azimuth at each period of interest of the Love wave from the transverse and radial components. The amplitude and phase measurement is then inverted for phase velocity structure using a modified version of the two plane-wave approximation. Preliminary results indicate a low velocity region at short periods (8-15 s) in both the Rayleigh and Love wave phase velocity maps beneath the active volcanic centers in the middle of the island. At longer periods (20-125 s) a low velocity region is visible beneath central Iceland. The velocity minimum is located to the north of Iceland in the Rayleigh wave maps. These observations are consistent with previous studies in the region.

  16. 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.

  17. Seismic velocities at the core-mantle boundary inferred from P waves diffracted around the core

    NASA Astrophysics Data System (ADS)

    Sylvander, Matthieu; Ponce, Bruno; Souriau, Annie

    1997-05-01

    The very base of the mantle is investigated with core-diffracted P-wave (P diff) travel times published by the International Seismological Centre (ISC) for the period 1964-1987. Apparent slownesses are computed for two-station profiles using a difference method. As the short-period P diff mostly sample a very thin layer above the core-mantle boundary (CMB), a good approximation of the true velocity structure at the CMB can be derived from the apparent slownesses. More than 27000 profiles are built, and this provides an unprecedented P diff sampling of the CMB. The overall slowness distribution has an average value of 4.62 s/deg, which corresponds to a velocity more than 4% lower than that of most mean radial models. An analysis of the residuals of absolute ISC P and P diff travel times is independently carried out and confirms this result. It also shows that the degree of heterogeneities is significantly higher at the CMB than in the lower mantle. A search for lateral velocity variations is then undertaken; a first large-scale investigation reveals the presence of coherent slowness anomalies of very large dimensions of the order of 3000 km at the CMB. A tomographic inversion is then performed, which confirms the existence of pronounced (8-10%) lateral velocity variations and provides a reliable map of the heterogeneities in the northern hemisphere. The influence of heterogeneity in the overlying mantle, of noise in the data and of CMB topography is evaluated; it seemingly proves minor compared with the contribution of heterogeneities at the CMB. Our results support the rising idea of a thin, low-velocity laterally varying boundary layer at the base of the D? layer. The two principal candidate interpretations are the occurrence of partial melting, or the presence of a chemically distinct layer, featuring infiltrated core material.

  18. 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.

  19. 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.

  20. Ultrasonic Velocity Variations with Soil Composition for Moisture Measurement

    NASA Technical Reports Server (NTRS)

    Metzl, R.; Choi, J.; Aggarwal, M. D.; Manu, A.

    1998-01-01

    Soil moisture content may be measured by many methods, but the presently available techniques all have drawbacks when used in ground truth measurements for remote sensing. Ultrasonic velocity varies with soil moisture content, and may be used as the basis of a new measurement technique. In order to characterize a sensor capable of field use, soil particle size distribution data are compared to ultrasonic velocity in a variety of soils over a wide moisture range.

  1. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  3. 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.

  4. 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.

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

    NASA Astrophysics Data System (ADS)

    Dinh, Tra; Podglajen, Aurlien; 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 Krmer (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 Krmer, 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.

  6. 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.

  7. 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.

  8. 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 Hα 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

  9. 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.

  10. Elastic wave velocities and permeability evolution during compaction of Bleuswiller sandstone.

    NASA Astrophysics Data System (ADS)

    Fortin, J.; Schubnel, A.; Gueguen, Y.

    2004-05-01

    Field observations and laboratory experiments have recently documented the formation of compaction bands in porous sandstones ([Mollema and Antonellini, 1996],[Olsson and Holcomb, 2000], [Besuelle, 2001a], [Klein et al., 2001]). It has been observed experimentally ([Wong et al., 2001], [Baud et al., 2003],[Fortin et al., 2003] that under axisymmetric compression, compaction bands develop sub-perpendicular to the main compressive stress which is predicted theoretically in the framework of strain localization theory ([Bsuelle, 2001a],[Issen and Rudnicki, 2000]). Volumetric strain, fluid transport and elastic properties are intimately coupled to one another, for they all depend on few intrinsic parameters such as the porosity, the crack density, and the matrix and fluid elastic properties. On one hand, [Scott et al., 1993] showed that elastic wave velocities were clearly affected during the deformation of porous sandstones. On the other hand, [Zhu and Wong, 1997] showed that the relation between the evolution of permeability and volumetric strain during compaction of sandstones was not straightforward. In this tudy, we present for the first time the simultaneous evolution of volumetric strain, elastic wave velocities and permeability for a set of deformation experiments of Bleuswiller sandstone. We show that, although very coherent to one another, those three sets are not systematically correlated. Indeed, inelastic compaction, whether it is distributed or localized, is accompanied by a drastic decrease of elastic wave velocities due to grain crushing, a decrease of permeability and porosity due to pore collapse. Using simple statistical physics concepts based on [Kachanov, 1993] and [Guguen and Dienes, 1989], we try to understand and address the issue of coupling/decoupling between volumetric strain (mainly sensitive to equant porosity variations), elastic properties (mainly sensitive to crack density) and permeability (theoretically sensitive to both) during the formation of compaction bands. Finally, we show that the mineral composition of a sandstone is a key parameter controlling the effective pressure at which the onset of pore collapse P* takes place.

  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. Investigation of coseismic and postseismic processes using in situ measurements of seismic velocity variations in an underground mine

    NASA Astrophysics Data System (ADS)

    Olivier, G.; Brenguier, F.; Campillo, M.; Roux, P.; Shapiro, N. M.; Lynch, R.

    2015-11-01

    The in situ mechanical response of a rock mass to a sudden dynamic and static stress change is still poorly known. To tackle this question, we conducted an experiment in an underground mine to examine (1) the influence of dynamic and static stress perturbations on seismic velocities, (2) elastic static stress changes, and (3) induced earthquake activity associated with the blast and removal of a portion of hard rock. We accurately (0.01%) measured seismic velocity variations with ambient seismic noise correlations, located aftershock activity, and performed elastic static stress modeling. Overall, we observe that the blast induced a sudden decrease in seismic velocities over the entire studied area, which we interpreted as the damage due to the passing of strong seismic waves. This sudden process is followed by a slow relaxation lasting up to 5 days, while seismic activity returns to its background level after 2 days. In some locations, after the short-term effects of the blast have subsided, the seismic velocities converge to new baseline levels and permanent changes in seismic velocity become visible. After comparing the spatial pattern of permanent seismic velocity changes with elastic static stress modeling, we infer that the permanent seismic velocity changes are due to the change in the static volumetric stress induced by the removal of a solid portion of rock by the blast. To our knowledge, this is the first observation of noise-based permanent seismic velocity changes associated with static stress changes.

  13. 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

  14. 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.

  15. 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.

  16. 3D P-Wave Velocity Structure of the Deep Galicia Rifted Margin

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  17. 3D P-Wave Velocity Structure of the Deep Galicia Rifted Margin

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  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. 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.

  20. Ultra Low-Velocity Control of a Surface Acoustic Wave Linear Motor

    NASA Astrophysics Data System (ADS)

    Kotani, Hiroyuki; Takasaki, Masaya; Ishino, Yuji; Mizuno, Takeshi

    A surface acoustic wave (SAW) linear motor is a kind of ultrasonic motor. The advantages of the SAW linear motor are thin structure, high thrust force, high velocity and precise positioning. The relationship between applied current and output velocity is, however, unstable in the low velocity range due to the friction drive principle. Therefore the SAW linear motor cannot obtain stable driving without feedback control in the low-velocity region. In this research, to realize low velocity, a pulse width modulation (PWM) control and flexible slider structure are employed. Flexible structure is installed to cancel vibration due to the PWM carrier wave. A lower velocity in the unstable range is realized. Moreover we change the calculation algorithm for the slider velocity measurement. As a result, the SAW linear motor can be driven at an ultra low velocity of 30?m/s. Additionally, driving characteristics are improved using a feedforward controller.

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

    NASA Technical Reports Server (NTRS)

    Bolton, Scott J.

    1990-01-01

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

  2. 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.

  3. 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.

  4. Estimation of sea-floor wave velocities and density from pressure and particle velocity by AVO analysis

    SciTech Connect

    Amundsen, L.; Reitan, A.

    1995-09-01

    The authors propose a new method for inferring the density and P- and S-wave velocities at the sea bottom. The technique is based on estimating these parameters from the acoustic/elastic reflection coefficient calculated from point-source measurements of pressure and vertical component of particle velocity recorded at the sea floor. The data may be collected either by using a fixed source and two-component receiver and a moving source. By spectral division of the two-component recordings transformed to the frequency-radial wavenumber domain, they obtain an estimate of the slowness-dependant reflection coefficient, containing AVO information, which is inverted in a least-squares sense with respect to wave velocities and density. In the following, the theoretical framework with related inversion procedure is outlined briefly. The viability of the inversion method is demonstrated by means of synthetic data.

  5. Estimation of spatiotemporal variation of acoustic velocity in ocean and its modeling for GPS/Acoustic seafloor positioning

    NASA Astrophysics Data System (ADS)

    Sugimoto, S.; Tadokoro, K.; Ikuta, R.; Watanabe, T.; Okuda, T.; Sayanagi, K.; Miyata, K.; Nagao, T.

    2009-12-01

    We have been developing an observation system with the GPS/Acoustic combination technique for monitoring of seafloor crustal deformation. We installed two sets of triangular array of acoustic transponders as geodetic reference sites on the Suruga trough, central Japan, where the Philippine Sea plate is subducting beneath the Eurasian plate at a rate of 2 cm/yr. In our campaign observation, we measured ranges to acoustic transponders from an on-board acoustic transducer whose position was determined by kinematic GPS. Repeated our campaign observations can reveal directly seafloor crustal deformation in focal area of subduction zone. Present analysis method simultaneously estimates temporal variation of acoustic velocity and positions of acoustic transponders assuming the horizontally-layered structure of acoustic velocity. However, actual structure might have stable spatial variation due to oceanic current and internal wave. The stable spatial variation causes bias error on the positioning. For reduction of the bias error and shortening observation time, we should measure and/or estimate the spatial variation of acoustic velocity. In this presentation, for an investigation of horizontal scales of the spatial variation of acoustic velocity, we estimated spectrum of oceanic internal wave using by continuous measurements of temperature and pressure in ocean. In addition, we evaluate a new seafloor positioning method which simultaneously estimates spatiotemporal variation of acoustic velocity through numerical experiments. The continuous measurements in parallel with acoustic ranging were conducted by mooring temperature and pressure sensors attached rope with an interval of 50 m. The continuous measurements were made for five hours with a sampling interval of three seconds in each day in August and October 2008. For reduction of measurement noise, we carried out two-dimensional B-spline fitting of temperature and pressure with ABIC minimization. By the fitting, we could carry out spectral analysis for time-series of temperature (or pressure) at arbitrary depth (or temperature). As a result, several spectra were consistent with Garrett-Munk Spectrum. We could estimated the frequency of internal wave of 10^-4 Hz and phase velocity of isothermal surface was ~1.5 cm/s. Accordingly, the horizontal wavelength of the internal wave was about less than1 km at one of the sites in consideration of inertial and buoyancy frequency. In the new seafloor positioning method, spatial variation of acoustic velocity was regarded as two-dimensional lateral gradient, and this method estimate position of seafloor transponder, temporal variation and, two-dimensional lateral gradient of acoustic velocity. In numerical experiment, for example, we first assumed certain temporal variation and one-dimensional (NS component) gradient which was 0.75 m/s in distance of about 2 km and synthesized dataset of travel-time which was given certain Gaussian error. As a preliminary result, we reproduced given positions of seafloor transponder within 3 cm under that condition.

  6. New statistical analysis of the horizontal phase velocity distribution of gravity waves observed by airglow imaging

    NASA Astrophysics Data System (ADS)

    Matsuda, Takashi S.; Nakamura, Takuji; Ejiri, Mitsumu K.; Tsutsumi, Masaki; Shiokawa, Kazuo

    2014-08-01

    We have developed a new analysis method for obtaining the power spectrum in the horizontal phase velocity domain from airglow intensity image data to study atmospheric gravity waves. This method can deal with extensive amounts of imaging data obtained on different years and at various observation sites without bias caused by different event extraction criteria for the person processing the data. The new method was applied to sodium airglow data obtained in 2011 at Syowa Station (69S, 40E), Antarctica. The results were compared with those obtained from a conventional event analysis in which the phase fronts were traced manually in order to estimate horizontal characteristics, such as wavelengths, phase velocities, and wave periods. The horizontal phase velocity of each wave event in the airglow images corresponded closely to a peak in the spectrum. The statistical results of spectral analysis showed an eastward offset of the horizontal phase velocity distribution. This could be interpreted as the existence of wave sources around the stratospheric eastward jet. Similar zonal anisotropy was also seen in the horizontal phase velocity distribution of the gravity waves by the event analysis. Both methods produce similar statistical results about directionality of atmospheric gravity waves. Galactic contamination of the spectrum was examined by calculating the apparent velocity of the stars and found to be limited for phase speeds lower than 30 m/s. In conclusion, our new method is suitable for deriving the horizontal phase velocity characteristics of atmospheric gravity waves from an extensive amount of imaging data.

  7. 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.

  8. Effects of stress on magnetically induced velocity changes for surface waves in steels

    NASA Astrophysics Data System (ADS)

    Kwun, H.

    1985-11-01

    Results of an experimental investigation of the effects of uniaxial stress on the magnetically induced velocity changes for 5-MHz surface (Rayleigh) waves in specimens of ASTM A-36, SAE 4340, and HY-80 steel are described. Like the magnetically induced velocity changes for ultrasonic shear and longitudinal waves, the magnetically induced velocity changes for surface waves exhibited characteristic stress effects which were dependent on the magnitude and the sign (tensile or compressive) of the stress as well as on the relative orientation of the stress, the magnetic field, and the wave propagation directions. The observed characteristic stress effects indicated potential applicability of the magnetically induced velocity changes for surface waves to nondestructive measurements of residual surface stresses in ferromagnetic structural steels.

  9. Formation of damage zone and seismic velocity variations during hydraulic stimulation: numerical modelling and field observations

    NASA Astrophysics Data System (ADS)

    Shalev, Eyal; Cal, Marco; Lyakhovsky, Vladimir

    2013-11-01

    During hydraulic stimulations, a complex interaction is observed between the injected flux and pressure, number and magnitude of induced seismic events, and changes in seismic velocities. In this paper, we model formation and propagation of damage zones and seismicity patterns induced by wellbore fluid injection. The model includes the coupling of poroelastic deformation and groundwater flow with damage evolution (weakening and healing) and its effect on the elastic and hydrologic parameters of crystalline rocks. Results show that three subsequent interactions occur during stimulation. (1) Injected flux-pressure interaction: typically, after a flux increase, the wellbore pressure also rises to satisfy the flux conditions. Thereafter, the elevated pore pressure triggers damage accumulation and seismic activity, that is, accompanied by permeability increase. As a result, wellbore pressure decreases retaining the target injected flux. (2) Wellbore pressure-seismicity interaction: damage processes create an elongated damage zone in the direction close to the main principal stress. The rocks within the damage zone go through partial healing and remain in a medium damage state. Damage that originates around the injection well propagates within the damage zone away from the well, raising the damage state of the already damaged rocks, and is followed by compaction and fast partial healing back to a medium damage state. This `damage wave' behaviour is associated with the injected flux changes only in early stages while fracture's height (h) is larger than its length (l). The ratio h/l controls the deformation process that is responsible for several key features of the damage zone. (3) Stress- and damage-induced variations of the seismic P-wave velocities (Vp). Vp gradually decreases as damage is accumulated and increases after rock failure as the shear stress is released and healing and compaction are dominant. Typically, Vp decreases within the damage zone and increases in most regions outside the damage zone. After a `damage wave' that is originated at the well, Vp rises back and may exceeds its initial values. Similar transient variations of the elastic parameters and the effects of h/l are observed at the Soultz-sous-Forts Enhanced Geothermal System (EGS) records of induced seismicity during hydraulic injection.

  10. Anisotropic P-wave velocity analysis and seismic imaging in onshore Kutch sedimentary basin of India

    NASA Astrophysics Data System (ADS)

    Behera, Laxmidhar; Khare, Prakash; Sarkar, Dipankar

    2011-08-01

    The long-offset P-wave seismic reflection data has observable non-hyperbolic moveout, which depend on two parameters such as normal moveout velocity ( Vnmo) and the anisotropy parameter( ?). Anisotropy (e.g., directional dependence of velocity at a fixed spatial location in a medium) plays an important role in seismic imaging. It is difficult to know the presence of anisotropy in the subsurface geological formations only from P-wave seismic data and special analysis is required for this. The presence of anisotropy causes two major distortions of moveout in P-wave seismic reflection data. First, in contrast to isotropic media, normal-moveout (NMO) velocity differs from the vertical velocity; and the second is substantial increase of deviations in hyperbolic moveout in an anisotropic layer. Hence, with the help of conventional velocity analysis based on short-spread moveout (stacking) velocities do not provide enough information to determine the true vertical velocity in a transversely isotropic media with vertical symmetry axis (VTI media). Therefore, it is essential to estimate the single anisotropic parameter ( ?) from the long-offset P-wave seismic data. It has been demonstrated here as a case study with long-offset P-wave seismic data acquired in onshore Kutch sedimentary basin of western India that suitable velocity analysis using Vnmo and ? can improve the stacking image obtained from conventional velocity analysis.

  11. 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.

  12. Spatial and seasonal variation in wave attenuation over Zostera noltii

    NASA Astrophysics Data System (ADS)

    Paul, M.; Amos, C. L.

    2011-08-01

    Wave attenuation is a recognized function of sea grass ecosystems which is believed to depend on plant characteristics. This paper presents field data on wave attenuance collected over a 13 month period in a Zostera noltii meadow. The meadow showed a strong seasonality with high shoot densities in summer (approximately 4,600 shoots/m2) and low densities in winter (approximately 600 shoots/m2). Wave heights and flow velocities were measured along a transect at regular intervals during which the site was exposed to wind waves and boat wakes that differ in wave period and steepness. This difference was used to investigate whether wave attenuation by sea grass changes with hydrodynamic conditions. A seasonal change in wave attenuation was observed from the data. Results suggest that a minimum shoot density is necessary to initiate wave attenuation by sea grass. Additionally, a dependence of wave attenuation on hydrodynamics was found. Results suggest that the threshold shoot density varies with wave period and a change in energy dissipation toward the shore was observed once this threshold was exceeded. An attempt was made to quantify the bed roughness of the meadow; the applicability of this roughness value in swaying vegetation is discussed. Finally, the drag coefficient for the meadow was computed: A relationship between wave attenuance and vegetation Reynolds number was found which allows comparing the wave attenuating effect of Zostera noltii to other plant species.

  13. Constraining Anisotropic Shear-Wave Velocity and Its Scaling to Compressional Velocity and Density throughout the Mantle Using Wide-Spectrum Seismic Data

    NASA Astrophysics Data System (ADS)

    Moulik, P.; Ekstrom, G.

    2014-12-01

    We use a large dataset of normal-mode splitting functions, surface-wave phase anomalies, long-period waveforms, and body-wave travel times to investigate the resolution of anisotropic velocities, density and discontinuity topography in the Earth's mantle. Our starting point is our new anisotropic shear-wave-velocity model S362ANI+M, which is an update to the model S362ANI (Kustowski et al., 2008). S362ANI+M was derived using additional normal-mode splitting-function observations. The isotropic part of the new model has strong variations in the transition zone and is well correlated with several recent global tomographic models. 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. 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 that mode-splitting data reduce tradeoffs between isotropic velocity and anisotropy in the lowermost mantle for the even-degree variations. Anisotropic variations in the mid mantle are also suppressed with the addition of mode-splitting data. The seismic observables used in this study have different sensitivity to mantle heterogeneity; the long-period mantle waveforms and mode-splitting data, for example, are also sensitive to VP and ? structure. Most tomographic models adopt a priori scaling relationships between variations in shear velocity and other elastic parameters. We introduce an approach to estimate the scaling ratios from seismic data wherein we impose, with increasing weights, a priori correlations between variations in VS and that of VP and ?. The VS-VP and VS-? correlations and corresponding fit to data are examined to estimate depth-dependent scaling ratios. This approach allows us to investigate the resolution of scaling ratios from current datasets in different regions of the Earth's mantle.

  14. Shear wave velocities in the Pampean flat-slab region from Rayleigh wave tomography: Implications for slab and upper mantle hydration

    NASA Astrophysics Data System (ADS)

    Porter, Ryan; Gilbert, Hersh; Zandt, George; Beck, Susan; Warren, Linda; Calkins, Josh; Alvarado, Patricia; Anderson, Megan

    2012-11-01

    The Pampean flat-slab region, located in central Argentina and Chile between 29 and 34S, is considered a modern analog for Laramide flat-slab subduction within western North America. Regionally, flat-slab subduction is characterized by the Nazca slab descending to 100 km depth, flattening out for 300 km laterally before resuming a more "normal" angle of subduction. Flat-slab subduction correlates spatially with the track of the Juan Fernandez Ridge, and is associated with the inboard migration of deformation and the cessation of volcanism within the region. To better understand flat-slab subduction we combine ambient-noise tomography and earthquake-generated surface wave measurements to calculate a regional 3D shear velocity model for the region. Shear wave velocity variations largely relate to changes in lithology within the crust, with basins and bedrock exposures clearly defined as low- and high-velocity regions, respectively. We argue that subduction-related hydration plays a significant role in controlling shear wave velocities within the upper mantle. In the southern part of the study area, where normal-angle subduction is occurring, the slab is visible as a high-velocity body with a low-velocity mantle wedge above it, extending eastward from the active arc. Where flat-slab subduction is occurring, slab velocities increase to the east while velocities in the overlying lithosphere decrease, consistent with the slab dewatering and gradually hydrating the overlying mantle. The hydration of the slab may be contributing to the excess buoyancy of the subducting oceanic lithosphere, helping to drive flat-slab subduction.

  15. Effect of film elasticity on the drift velocity of capillary-gravity waves

    NASA Astrophysics Data System (ADS)

    Weber, Jan Erik; Saetra, yvind

    1995-02-01

    The effect of an insoluble, elastic surface film on the drift velocity of capillary-gravity waves is studied theoretically on the basis of a Lagrangian description of motion. There is no forcing from the atmosphere, and the wave amplitude is taken to attenuate in time. Defining a nondimensional parameter ?, which combines film elasticity, fluid viscosity, and wave frequency, maximum damping of the linear waves occurs when ?=1 (the Marangoni effect). In this case the frequency of capillary-gravity waves nearly coincides with that of elastic film waves. The nonlinear drift velocity is obtained for general values of ?. In particular, it is found that the absolute maximum of the transient drift current is located below the surface when ??2/3. At the surface, maximum drift velocity (in time domain) occurs for values of ? that are somewhat less than one.

  16. 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.

  17. 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.

  18. 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.

  19. 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 (103E-111E, 44N-49N) 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 0.5x0.5 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)

  20. Estimating wave orbital velocity through the azimuth cutoff from space-borne satellites

    NASA Astrophysics Data System (ADS)

    Stopa, Justin E.; Ardhuin, Fabrice; Chapron, Bertrand; Collard, Fabrice

    2015-11-01

    It has been long accepted that ocean wave conditions recorded from synthetic aperture radar (SAR) aboard satellites resolve large scale swells. SARs make use of its displacement to achieve fine resolution; however the random surface motions can reduce its nominal azimuthal resolution. Accordingly, the SAR spectral azimuth response mirrors the probability distribution of the radial velocity component of the scatters. This effect, quantified in a measure called the azimuth cutoff, is estimated by defining a scale based on the fitting of a Gaussian function to the radar cross section azimuth spectrum. The independent measure provides additional sea state information related to the root mean square surface orbital wave velocity. We use data recorded from the European Space Agency's ENVISAT advanced SAR in the C-band spanning its lifetime 2003-2012. Our purpose is to first establish the validity of the azimuth cutoff using both colocated buoys and modeled wave data. Some systematic biases are corrected using other SAR derived parameters, improving the accuracy of the estimate. Despite our efforts, errors exist in the presence of swell, extreme wind waves, and related to the wave direction. Under the majority of the sea states the parameter is well behaved. As a final point, applications using the wave orbital velocities are described in terms of diagnosing a spectral wave model and the wave climate. As illustrated, the returned radar signal provides useful sea state information that resolves wind speeds, wave orbital velocities from the wind waves, and swells.

  1. Surface-wave phase-velocity models of the United States: Expanding with USArray coverage

    NASA Astrophysics Data System (ADS)

    Foster, A. E.; Ekstrom, G.; Nettles, M.

    2014-12-01

    We update our models of Love and Rayleigh wave phase-velocity structure using USArray data through mid 2014. We make measurements of the phase at periods from 25 to 100 s using a two-station method that assumes a great-circle arrival path for Love waves, and uses the estimated arrival angle for Rayleigh waves to correct the two-station calculation. Arrival-angle estimates are made with a mini-array method that employs a grid search to select the back-azimuth to the source that best predicts the phase observed on a local subset of stations. The two-station phase data with inter-station path lengths between 350 and 750 km are inverted to produce phase-velocity models at discrete periods. The new data set expands the modeled area, covering the entire contiguous United States. The mini-array method also produces an estimate of the local phase-velocity. We calculate this local phase-velocity for both Love and Rayleigh waves, and compare the measurements with the maps resulting from the inversion of the two-station measurements. The local phase velocities, two-station phase velocities, and two-station phase-velocity models are all examined for bias resulting from overtone interference. Based on previous work, we expect overtone interference to affect Love wave measurements but not Rayleigh wave measurements, and to affect the local measurements more than the two-station models.

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

    NASA Astrophysics Data System (ADS)

    Carlson, Richard L.; Gangi, Anthony F.

    1985-09-01

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

  3. 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.

  4. Guided wave observations and evidence for the low-velocity subducting crust beneath Hokkaido, northern Japan

    NASA Astrophysics Data System (ADS)

    Shiina, Takahiro; Nakajima, Junichi; Toyokuni, Genti; Matsuzawa, Toru

    2014-12-01

    At the western side of the Hidaka Mountain range in Hokkaido, we identify a clear later phase in seismograms for earthquakes occurring at the uppermost part of the Pacific slab beneath the eastern Hokkaido. The later phase is observed after P-wave arrivals and has a larger amplitude than the P wave. In this study, we investigate the origin of the later phase from seismic wave observations and two-dimensional numerical modeling of wave fields and interpret it as a guided P wave propagating in the low-velocity subducting crust of the Pacific plate. In addition, the results of our numerical modeling suggest that the low-velocity subducting crust is in contact with a low-velocity material beneath the Hidaka Mountain range. Based on our interpretation for the later phase, we estimate P-wave velocity in the subducting crust beneath the eastern part of Hokkaido by using the differences in the later phase travel times and obtain velocities of 6.8 to 7.5 km/s at depths of 50 to 80 km. The obtained P-wave velocity is lower than the expected value based on fully hydrated mid-ocean ridge basalt (MORB) materials, suggesting that hydrous minerals are hosted in the subducting crust and aqueous fluids may co-exist down to depths of at least 80 km.

  5. Variations of seismic velocities in the Kachchh rift zone, Gujarat, India, during 2001-2013

    NASA Astrophysics Data System (ADS)

    Mandal, Prantik

    2016-03-01

    We herein study variations of seismic velocities in the main rupture zone (MRZ) of the Mw 7.7 2001 Bhuj earthquake for the time periods [2001-05, 2006-08, 2009-10 and 2011-13], by constructing dVp(%), dVs(%) and d(Vp/Vs)(%) tomograms using high-quality arrival times of 28,902 P- and 28,696 S-waves from 4644 precise JHD (joint hypocentral determination) relocations of local events. Differential tomograms for 2001-05 reveal a marked decrease in seismic velocities (low dVp, low dVs and high d(Vp/Vs)) in the MRZ (at 5-35 km depths) during 2001-10, which is attributed to an increase in crack/fracture density (higher pore fluid pressure) resulted from the intense fracturing that occurred during the mainshock and post-seismic periods. While we observe a slight recovery or increase in seismic velocities 2011-13, this could be related to the healing process (lower pore fluid pressure due to sealing of cracks) of the causative fault zone of the 2001 Bhuj mainshock. The temporal reduction in seismic velocities is observed to be higher at deeper levels (more fluid enrichment under near-lithostatic pressure) than that at shallower levels. Fluid source for low velocity zone (LVZ) at 0-10 km depths (with high d(Vp/Vs)) could be attributed to the presence of meteoric water or soft alluvium sediments with higher water content, while fluid source for LVZ at 10-35 km depths could be due to the presence of brine fluids (released from the metamorphic dewatering) and volatile CO2 (emanating from the crystallization of carbonatite melts in the asthenosphere), in fractures and pores. We also imaged two prominent LVZs associated with the Katrol Hill fault zone and Island Belt fault zone, extending from shallow upper-crust to sub-crustal depth, which might be facilitating the deeper circulation of metamorphic fluids/volatile CO2, thereby, the generation of lower crustal earthquakes occurring in the Kachchh rift zone.

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

    PubMed Central

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

    2014-01-01

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

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

    PubMed Central

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

    2015-01-01

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

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

    PubMed

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  10. 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…

  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. Variational Water Wave Modelling: from Continuum to Experiment

    NASA Astrophysics Data System (ADS)

    Bokhove, Onno; Kalogirou, Anna

    2015-04-01

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

  13. Characterization of guided wave velocity and attenuation in anisotropic materials from wavefield measurements

    NASA Astrophysics Data System (ADS)

    Williams, Westin B.; Michaels, Thomas E.; Michaels, Jennifer E.

    2016-02-01

    The behavior of guided waves propagating in anisotropic composite panels can be substantially more complicated than for isotropic, metallic plates. The angular dependency of wave propagation characteristics need to be understood and quantified before applying methods for damage detection and characterization. This study experimentally investigates the anisotropy of wave speed and attenuation for the fundamental A0-like guided wave mode propagating in a solid laminate composite panel. A piezoelectric transducer is the wave source and a laser Doppler vibrometer is used to measure the outward propagating waves along radial lines originating at the source transducer. Group velocity, phase velocity and attenuation are characterized as a function of angle for a single center frequency. The methods shown in this paper serve as a framework for future adaptation to damage imaging methods using guided waves for structural health monitoring.

  14. 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.

  15. Downdip velocity changes in subducted oceanic crust beneath Northern Japaninsights from guided waves

    NASA Astrophysics Data System (ADS)

    Garth, Tom; Rietbrock, Andreas

    2014-09-01

    Dispersed P-wave arrivals observed in the subduction zone forearc of Northern Japan suggest that low velocity subducted oceanic crustal waveguide persists to depths of at least 220 km. First arrivals from events at 150-220 km depth show that the velocity contrast of the waveguide reduces with depth. High frequency energy (>2 Hz) is retained and delayed by the low velocity crustal waveguide while the lower frequency energy (<0.5 Hz) travels at faster velocities of the surrounding mantle material. The guided wave energy then decouples from the low velocity crustal waveguide due to the bend of the slab and is seen at the surface 1-2 s after the low frequency arrival. Dispersive P-wave arrivals from WBZ earthquakes at 150-220 km depth are directly compared to synthetic waveforms produced by 2-D and 3-D full waveform finite difference simulations. By comparing both the spectrogram and the velocity spectra of the observed and synthetic waveforms we are able to fully constrain the dispersive waveform, and so directly compare the observed and synthetic waveforms. Using this full waveform modelling approach we are able to tightly constrain the velocity structures that cause the observed guided wave dispersion. Resolution tests using 2-D elastic waveform simulations show that the dispersion can be accounted for by a 6-8 km thick low velocity oceanic crust, with a velocity contrast that varies with depth. The velocities inferred for this variable low velocity oceanic crust can be explained by lawsonite bearing assemblages, and suggest that low velocity minerals may persist to greater depth than previously thought. 2-D simulations are benchmarked to 3-D full waveform simulations and show that the structures inferred by the 2-D approximation produce similar dispersion in 3-D. 2-D viscoelastic simulations show that including elevated attenuation in the mantle wedge can improve the fit of the dispersed waveform. Elevated attenuation in the low velocity layers can however be ruled out.

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

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

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

  17. 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

  18. Variational principle for nonlinear wave propagation in dissipative systems

    NASA Astrophysics Data System (ADS)

    Dierckx, Hans; Verschelde, Henri

    2016-02-01

    The dynamics of many natural systems is dominated by nonlinear waves propagating through the medium. We show that in any extended system that supports nonlinear wave fronts with positive surface tension, the asymptotic wave-front dynamics can be formulated as a gradient system, even when the underlying evolution equations for the field variables cannot be written as a gradient system. The variational potential is simply given by a linear combination of the occupied volume and surface area of the wave front and changes monotonically over time.

  19. 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.

  20. 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

  1. 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

  2. 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.

  3. Surface waves in an incompressible fluid - Resonant instability due to velocity shear

    NASA Technical Reports Server (NTRS)

    Hollweg, Joseph V.; Yang, G.; Cadez, V. M.; Gakovic, B.

    1990-01-01

    The effects of velocity shear on the resonance absorption of incompressible MHD surface waves are studied. It is found that there are generally values of the velocity shear for which the surface wave decay rate becomes zero. In some cases, the resonance absorption goes to zero even for very small velocity shears. It is also found that the resonance absorption can be strongly enhanced at other values of the velocity shear, so the presence of flows may be generally important for determining the effects of resonance absorption, such as might occur in the interaction of p-modes with sunspots. Resonances leading to instability of the global surface mode can exist, and instability can occur for velocity shears significantly below the Kelvin-Helmholtz threshold. These instabilities may play a role in the development or turbulence in regions of strong velocity shear in the solar wind or the earth's magnetosphere.

  4. Surface waves in an incompressible fluid - Resonant instability due to velocity shear

    SciTech Connect

    Hollweg, J.V.; Yang, G.; Cadez, V.M.; Gakovic, B. Institut za Fiziku, Belgrade Sarajevo Univerzitet )

    1990-01-01

    The effects of velocity shear on the resonance absorption of incompressible MHD surface waves are studied. It is found that there are generally values of the velocity shear for which the surface wave decay rate becomes zero. In some cases, the resonance absorption goes to zero even for very small velocity shears. It is also found that the resonance absorption can be strongly enhanced at other values of the velocity shear, so the presence of flows may be generally important for determining the effects of resonance absorption, such as might occur in the interaction of p-modes with sunspots. Resonances leading to instability of the global surface mode can exist, and instability can occur for velocity shears significantly below the Kelvin-Helmholtz threshold. These instabilities may play a role in the development or turbulence in regions of strong velocity shear in the solar wind or the earth's magnetosphere. 27 refs.

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

    SciTech Connect

    Vatulin, V. V.; Zhidkov, N. V.; Kravchenko, A. G.; Kuznetsov, P. G.; Litvin, D. N.; Mis'ko, V. V.; Pinegin, A. V.; Pleteneva, N. P.; Senik, A. V.; Starodubtsev, K. V.; Tachaev, G. V.

    2010-05-15

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

  6. 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.

  7. Imaging subtle microstructural variations in ceramics with precision ultrasonic velocity and attenuation measurements

    NASA Technical Reports Server (NTRS)

    Generazio, Edward R.; Roth, Don J.; Baaklini, George Y.

    1987-01-01

    Acoustic images of a silicon carbide ceramic disk were obtained using a precision scanning contact pulse echo technique. Phase and cross-correlation velocity, and attenuation maps were used to form color images of microstructural variations. These acoustic images reveal microstructural variations not observable with X-ray radiography.

  8. 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 21N 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.

  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. 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.

  11. 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 Gralp 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.

  12. Wave Packets of Controlled Velocity Perturbations at Laminar Flow Separation

    NASA Astrophysics Data System (ADS)

    Dovgal, Alexander; Sorokin, Alexander

    Experimental data on controlled time-periodic disturbances of the laminar flow separating at a 2D backward-facing step on a flat plate are reported. Windtunnel results were obtained at low subsonic velocity through hot-wire measurements. It is found that vorticity perturbations generated locally behind the step contaminate an extended flow region downstream and upstream of their origin. One expects this could provide a feedback involved in self-sustained oscillations of the separation bubble.

  13. The relationship between shear wave velocity, temperature, attenuation and viscosity in the shallow part of the mantle

    NASA Astrophysics Data System (ADS)

    Priestley, Keith; McKenzie, Dan

    2013-11-01

    Surface wave tomography, using the fundamental Rayleigh wave velocities and those of higher modes between 1 and 4 and periods between 50 and 160 s, is used to image structures with a horizontal resolution of ˜250 km and a vertical resolution of ˜50 km to depths of ˜300 km in the mantle. A new model, PM_v2_2012, obtained from 3×106 seismograms, agrees well with earlier lower resolution models. It is combined with temperature estimates from oceanic plate models and with pressure and temperature estimates from the mineral compositions of garnet peridotite nodules to generate a number of estimates of SV(P,T) based on geophysical and petrological observations alone. These are then used to estimate the unrelaxed shear modulus and its derivatives with respect to pressure and temperature, which agree reasonably with values from laboratory experiments. At high temperatures relaxation occurs, causing the shear wave velocity to depend on frequency. This behaviour is parameterised using a viscosity to obtain a Maxwell relaxation time. The relaxation behaviour is described using a dimensionless frequency, which depends on an activation energy E and volume Va. The values of E and Va obtained from the geophysical models agree with those from laboratory experiments on high temperature creep. The resulting expressions are then used to determine the lithospheric thickness from the shear wave velocity variations. The resolution is improved by about a factor of two with respect to earlier models, and clearly resolves the thick lithosphere beneath active intracontinental belts that are now being shortened. The same expressions allow the three dimensional variations of the shear wave attenuation and viscosity to be estimated.

  14. 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.

  15. 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

  16. Simultaneous structure and elastic wave velocity measurement of SiO[subscript 2] glass at high pressures and high temperatures in a Paris-Edinburgh cell

    SciTech Connect

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

    2015-02-19

    An integration of multi-angle energy-dispersive x-ray diffraction and ultrasonic elastic wave velocity measurements in a Paris-Edinburgh cell enabled us to simultaneously investigate the structures and elastic wave velocities of amorphous materials at high pressure and high temperature conditions. We report the first simultaneous structure and elastic wave velocity measurement for SiO{sub 2} glass at pressures up to 6.8 GPa at around 500 C. The first sharp diffraction peak (FSDP) in the structure factor S(Q) evidently shifted to higher Q with increasing pressure, reflecting the shrinking of intermediate-range order, while the Si-O bond distance was almost unchanged up to 6.8 GPa. In correlation with the shift of FSDP position, compressional wave velocity (Vp) and Poisson's ratio increased markedly with increasing pressure. In contrast, shear wave velocity (Vs) changed only at pressures below 4 GPa, and then remained unchanged at {approx}4.0-6.8 GPa. These observations indicate a strong correlation between the intermediate range order variations and Vp or Poisson's ratio, but a complicated behavior for Vs. The result demonstrates a new capability of simultaneous measurement of structures and elastic wave velocities at high pressure and high temperature conditions to provide direct link between microscopic structure and macroscopic elastic properties of amorphous materials.

  17. 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.

  18. 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.

  19. 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.

  20. Site-effect estimations for Taipei Basin based on shallow S-wave velocity structures

    NASA Astrophysics Data System (ADS)

    Chen, Ying-Chi; Huang, Huey-Chu; Wu, Cheng-Feng

    2016-03-01

    Shallow S-wave velocities have been widely used for earthquake ground-motion site characterization. Thus, the S-wave velocity structures of Taipei Basin, Taiwan were investigated using array records of microtremors at 15 sites (Huang et al., 2015). In this study, seven velocity structures are added to the database describing Taipei Basin. Validity of S-wave velocity structures are first examined using the 1D Haskell method and well-logging data at the Wuku Sewage Disposal Plant (WK) borehole site. Basically, the synthetic results match well with the observed data at different depths. Based on S-wave velocity structures at 22 sites, theoretical transfer functions at five different formations of the sedimentary basin are calculated. According to these results, predominant frequencies for these formations are estimated. If the S-wave velocity of the Tertiary basement is assumed to be 1000 m/s, the predominant frequencies of the Quaternary sediments are between 0.3 Hz (WUK) and 1.4 Hz (LEL) in Taipei Basin while the depths of sediments between 0 m (i.e. at the edge of the basin) and 616 m (i.e. site WUK) gradually increase from southeast to northwest. Our results show good agreement with available geological and geophysical information.

  1. Multiparameter full waveform inversion of multicomponent ocean-bottom-cable data from the Valhall field. Part 2: imaging compressive-wave and shear-wave velocities

    NASA Astrophysics Data System (ADS)

    Prieux, Vincent; Brossier, Romain; Operto, Stéphane; Virieux, Jean

    2013-09-01

    Multiparameter elastic full waveform inversion (FWI) is a promising technology that allows inferences to be made on rock and fluid properties, which thus narrows the gap between seismic imaging and reservoir characterization. Here, we assess the feasibility of 2-D vertical transverse isotropic visco-elastic FWI of wide-aperture multicomponent ocean-bottom-cable data from the Valhall oil field. A key issue is to design a suitable hierarchical data-driven and model-driven FWI workflow, the aim of which is to reduce the nonlinearity of the FWI. This nonlinearity partly arises because the shear (S) wavespeed can have a limited influence on seismic data in marine environments. In a preliminary stage, visco-acoustic FWI of the hydrophone component is performed to build a compressional (P)-wave velocity model, a density model and a quality-factor model, which provide the necessary background models for the subsequent elastic inversion. During the elastic FWI, the P and S wavespeeds are jointly updated in two steps. First, the hydrophone data are inverted to mainly update the long-to-intermediate wavelengths of the S wavespeeds from the amplitude-versus-offset variations of the P-P reflections. This S-wave velocity model is used as an improved starting model for the subsequent inversion of the better-resolving data recorded by the geophones. During these two steps, the P-wave velocity model is marginally updated, which supports the relevance of the visco-acoustic FWI results. Through seismic modelling, we show that the resulting visco-elastic model allows several P-to-S converted phases recorded on the horizontal-geophone component to be matched. Several elastic quantities, such as the Poisson ratio, and the ratio and product between the P and S wavespeeds, are inferred from the P-wave and S-wave velocity models. These attributes provide hints for the interpretation of an accumulation of gas below lithological barriers.

  2. Wave equation tomographic velocity inversion method based on the Born/Rytov approximation

    NASA Astrophysics Data System (ADS)

    Zhang, Kai; Yin, Zheng; Li, Zhen-Chun; Chen, Yong-Rui

    2013-06-01

    This paper discusses Born/Rytov approximation tomographic velocity inversion methods constrained by the Fresnel zone. Calculations of the sensitivity kernel function and traveltime residuals are critical in tomographic velocity inversion. Based on the Born/Rytov approximation of the frequency-domain wave equation, we derive the traveltime sensitivity kernels of the wave equation on the band-limited wave field and simultaneously obtain the traveltime residuals based on the Rytov approximation. In contrast to single-ray tomography, the modified velocity inversion method improves the inversion stability. Tests of the near-surface velocity model and field data prove that the proposed method has higher accuracy and Computational efficiency than ray theory tomography and full waveform inversion methods.

  3. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

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

  5. 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.

  6. Near-surface Shear-wave Velocities using Passive and Active Surface-wave Methods in Chunchon, Korea

    NASA Astrophysics Data System (ADS)

    Kim, K. Y.; Kim, W.; Park, Y.

    2011-12-01

    To investigate near-surface shear-wave velocities (Vs) near an agricultural well in Chunchon, Korea, both passive and active surface-wave data were recorded. Ambient surface waves (microtremors) were recorded for 5 minutes at 10-ms sampling intervals using four 1-Hz vertical velocity sensors in triangular arrays with radii of 5, 10, 20, and 40 m. Synthetic surface waves, generated by a sledgehammer, were detected with a linear array of 24 4.5-Hz geophones separated at 2 m intervals and recorded for 2 s at a 2-ms sampling interval. Rayleigh wave phase-velocities were independently derived from the passive data using the Spatial Autocorrelation (SPAC) method and from the active data using the Multichannel Analysis of Surface Waves method. These methods yielded well-defined dispersion curves for frequencies of 7 to 19 Hz and 11 to 50 Hz, respectively. We combined these dispersion curves to better resolve the Vs structure and then derived an initial velocity model of 40 1-m thick layers using the 1/3-wavelength rule. This initial velocity model varied smoothly with depth except for an abrupt change of velocity at 2 m depth corresponding to the interface between the topsoil and an underlying gravelly sand layer. Additional information on interfaces was derived from refraction tomography using the sledgehammer-generated data and from the well located 5 m north of the SPAC array center. Slight modifications of the initially modeled Vs at the top and bottom of a weathered rock layer improved the match between the observed and modeled dispersion curves. The modeled Vs for the 2-m thick topsoil, 2-m thick gravelly sand, 1-m thick layer of cobbles, 9-m thick weathered bedrock, and the underlying soft bedrock were 231, 270, 388, 477, and 827 m/s, respectively.

  7. Wave Velocities in Hydrocarbons and Hydrocarbon Saturated - Applications to Eor Monitoring.

    NASA Astrophysics Data System (ADS)

    Wang, Zhijing

    In order to effectively utilize many new seismic technologies and interpret the results, acoustic properties of both reservoir fluids and rocks must be well understood. It is the main purpose of this dissertation to investigate acoustic wave velocities in different hydrocarbons and hydrocarbon saturated rocks under various reservoir conditions. The investigation consists of six laboratory experiments, followed by a series of theoretical and application analyses. All the experiments involve acoustic velocity measurements in hydrocarbons and rocks with different hydrocarbons, using the ultrasonic pulse-transmission methods, at elevated temperatures and pressures. In the experiments, wave velocities are measured versus both temperature and pressure in 50 hydrocarbons. The relations among the acoustic velocity, temperature, pressure, API gravity, and the molecular weight of the hydrocarbons are studied, and empirical equations are established which allow one to calculate the acoustic velocities in hydrocarbons with known API gravities. Wave velocities in hydrocarbon mixtures are related to the composition and the velocities in the components. The experimental results are also analyzed in terms of various existing theories and models of the liquid state. Wave velocities are also measured in various rocks saturated with different hydrocarbons. The compressional wave velocities in rocks saturated with pure hydrocarbons increase with increasing the carbon number of the hydrocarbons. They decrease markedly in all the heavy hydrocarbon saturated rocks as temperature increases. Such velocity decreases set the petrophysical basis for in-situ seismic monitoring thermal enhanced oil recovery processes. The effects of carbon dioxide flooding and different pore fluids on wave velocities in rocks are also investigated. It is highly possible that there exist reflections of seismic waves at the light-heavy oil saturation interfaces in-situ. It is also possible to use seismic methods to monitor carbon dioxide flooding processes. Velocity dispersions are analyzed theoretically in rocks saturated with different pore fluids. The results are discussed in terms of the Biot theory and the "local flow" mechanism. Applications of the results and the applicability of using seismic methods to monitor various enhanced oil recovery and production processes are also discussed.

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

    PubMed

    Stojadinović, Bojana; Tenne, Tamar; Zikich, Dragoslav; Rajković, Nemanja; Milošević, Nebojša; Lazović, Biljana; Žikić, 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

  9. 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.

  10. Global Rayleigh wave phase-velocity maps from finite-frequency tomography

    NASA Astrophysics Data System (ADS)

    Liu, Kui; Zhou, Ying

    2016-04-01

    We report global phase-velocity maps of fundamental-mode Rayleigh waves at periods between 25 and 100 s based on finite-frequency tomography. Rayleigh wave dispersion measurements are made using a multitaper technique for both minor-arc and major-arc wave trains. The global phase-velocity maps confirm many features associated with surface tectonics including the ocean-continent dichotomy and the signature of lithospheric cooling in oceanic plates. In addition, the high-resolution phase-velocity maps reveal a major change in the distribution of small-scale anomalies in the Pacific at different wave periods. We calculate the global average of Rayleigh wave phase velocity in major tectonic regions and show that large discrepancies exist between our model and global crustal and mantle models: (1) In oceanic regions, short-period (<˜40 s) Rayleigh waves are faster than calculations based on models CRUST2.0 and S40RTS. The discrepancies could be explained by a thinner crust or faster wave speeds in the crust or upper mantle. The implementation of model CRUST1.0 significantly improves the agreement, with phase-velocity discrepancies less than 0.5 per cent on average. (2) In Archean cratons, Rayleigh wave phase velocities in our model are faster than calculations based on model S40RTS at periods longer than ˜40 s; and the global average in orogenic belts is ˜1-2 per cent slower than CRUST1.0 at periods shorter than ˜50 s.

  11. 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; Schnlieb, 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.

  12. Hurricane Directional Wave Spectrum Spatial Variation at Landfall

    NASA Technical Reports Server (NTRS)

    Walsh, Edward J.; Wright, C. Wayne; Vandemark, Douglas C.; Krabill, William B.; Garcia, Andrew W.; Houston, Samuel H.; Powell, Mark D.; Black, Peter G.; Marke, Frank D.; Busalacchi, Antonio J. (Technical Monitor)

    2000-01-01

    On 26 August 1998, hurricane Bonnie was making landfall near Wilmington, NC. The NASA airborne scanning radar altimeter (SRA) carried aboard one of the NOAA WP-3D hurricane hunter aircraft at 2.2 km height documented the sea surface directional wave spectrum in the region between Charleston, SC and Cape Hatteras, NC. The aircraft ground track included both segments along the shoreline and Pamlico Sound as well as far offshore. An animation of the directional wave spectrum spatial variation at landfall will be presented and contrasted with the spatial variation when Bonnie was in the open ocean on 24 August 1998.

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  14. 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.

  15. Low-velocity fault-zone guided waves: Numerical investigations of trapping efficiency

    USGS Publications Warehouse

    Li, Y.-G.; Vidale, J.E.

    1996-01-01

    Recent observations have shown that shear waves trapped within low-velocity fault zones may be the most sensitive measure of fault-zone structure (Li et al., 1994a, 1994b). Finite-difference simulations demonstrate the effects of several types of complexity on observations of fault-zone trapped waves. Overlying sediments with a thickness more than one or two fault-zone widths and fault-zone step-overs more than one or two fault widths disrupt the wave guide. Fault kinks and changes in fault-zone width with depth leave readily observable trapped waves. We also demonstrate the effects of decreased trapped wave excitation with increasing hypocentral offset from the fault and the effects of varying the contrast between the velocity in the fault zone and surrounding hard rock. Careful field studies may provide dramatic improvements in our knowledge of fault-zone structure.

  16. Excitation of solitons by an external resonant wave with a slowly varying phase velocity

    SciTech Connect

    Aranson, I.; Meerson, B. ); Tajima, T. Department of Physics, The University of Texas at Austin, Austin, Texas 78712 )

    1992-05-15

    A mechanism is proposed for the excitation of solitons in nonlinear dispersive media. The mechanism employs an external pumping wave with a varying phase velocity, which provides a continuous resonant excitation of a nonlinear wave in the medium. Two different schemes of a continuous resonant growth (continuous phase locking) of the induced nonlinear wave are suggested. The first of them requires a definite time dependence of the pumping-wave phase velocity and is relatively sensitive to the initial wave phase. The second employs the dynamic autoresonance effect and is insensitive to the exact time dependence of the pumping-wave phase velocity. It is demonstrated analytically and numerically, for a particular example of a driven Korteweg--de Vries (KdV) equation with periodic boundary conditions, that as the nonlinear wave grows, it transforms into a soliton, which continues growing and accelerating adiabatically. A fully nonlinear perturbation theory is developed for the driven KdV equation to follow the growing wave into the strongly nonlinear regime and describe the soliton formation.

  17. Excitation of solitons by an external resonant wave with a slowly varying phase velocity

    SciTech Connect

    Aranson, I.; Meerson, B.; Tajima, Toshiki

    1992-02-01

    A novel mechanism is proposed for the excitation of solitons in nonlinear dispersive media. The mechanism employs an external pumping wave with a varying phase velocity, which provides a continuous resonant excitation of a nonlinear wave in the medium. Two different schemes of a continuous resonant growth (continuous phase-locking) of the induced nonlinear wave are suggested. The first of them requires a definite time dependence of the pumping wave phase velocity and is relatively sensitive to the initial wave phase. The second employs the dynamic autoresonance effect and is insensitive to the exact time dependence of the pumping wave phase velocity. It is demonstrated analytically and numerically, for a particular example of a driven Korteweg-de Vries (KdV) equation with periodic boundary conditions, that as the nonlinear wave grows, it transforms into a soliton, which continues growing and accelerating adiabatically. A fully nonlinear perturbation theory is developed for the driven KdV equation to follow the growing wave into the strongly nonlinear regime and describe the soliton formation.

  18. Relationship between Elastic wave Velocity and Permeability of Rock Model with penny-shaped cracks

    NASA Astrophysics Data System (ADS)

    Yamabe, H.; Tsuji, T.; Matsuoka, T.

    2011-12-01

    Estimating underground fluid-flow is of great importance in petroleum engineering and carbon capture and storage (CCS). Permeability is one of the most important parameters which show how easily fluid passes through rock mass. It could be acquired just by measuring rock samples near borehole in lab-experiments. It means that permeability except near borehole should be estimated, considering other information. In this research, elastic wave velocity is focused as a tool of estimating permeability, because it is one of the most popular parameter which has underground information. The relationship between permeability and elastic wave velocities should be revealed, in order to establish a methodology to estimate rock permeability from elastic wave velocity. These two parameters are controlled by pore geometry of rock. Therefore, we focused on pore geometry as connecting bridge between the two parameters: permeability, elastic wave velocity. We modeled the considering rock as a solid mass containing a lot of same-sized penny-shaped cracks randomly. LBM (Lattice Boltzmann Method), which is one of the computational fluid dynamics methods, is adopted for calculating permeability in our study. This method has a storing point especially under complicated fluid-solid boundary condition. Elastic wave velocities are derived from effective elastic moduli (i.e., bulk modulus, stiffness). They are estimated by self-consistent approximation, which needs porosity of rock model, aspect ratio of penny-shaped cracks and volume fraction of each phase. In this research, we assume that solid phase is composed only by quartz and rock's pore space is filled with water. The simulated results demonstrate that aspect ratio of crack can be estimated by P- and S-wave velocity, and aspect ratio and P-wave velocity can determine porosity. Whereas, the relationship between porosity and permeability is dependent on aspect ratio, which means permeability can be estimated by aspect ratio and porosity. Therefore, this research reveals that permeability can be estimated by P-wave velocity and S-wave velocity if the rock is composed by same-sized penny cracks.

  19. 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.

  20. Analysis of non linear partially standing waves from 3D velocity measurements

    NASA Astrophysics Data System (ADS)

    Drevard, D.; Rey, V.; Svendsen, Ib; Fraunie, P.

    2003-04-01

    Surface gravity waves in the ocean exhibit an energy spectrum distributed in both frequency and direction of propagation. Wave data collection is of great importance in coastal zones for engineering and scientific studies. In particular, partially standing waves measurements near coastal structures and steep or barred beaches may be a requirement, for instance for morphodynamic studies. The aim of the present study is the analysis of partially standing surface waves icluding non-linear effects. According to 1st order Stokes theory, synchronous measurements of horizontal and vertical velocity components allow calculation of rate of standing waves (Drevard et al, 2003). In the present study, it is demonstrated that for deep water conditions, partially standing 2nd order Stokes waves induced velocity field is still represented by the 1st order solution for the velocity potential contrary to the surface elevation which exhibits harmonic components. For intermediate water depth, harmonic components appear not only in the surface elevation but also in the velocity fields, but their weight remains much smaller, because of the vertical decreasing wave induced motion. For irregular waves, the influence of the spectrum width on the non-linear effects in the analysis is discussed. Keywords: Wave measurements ; reflection ; non-linear effects Acknowledgements: This work was initiated during the stay of Prof. Ib Svendsen, as invited Professor, at LSEET in autumn 2002. This study is carried out in the framework of the Scientific French National Programmes PNEC ART7 and PATOM. Their financial supports are acknowledged References: Drevard, D., Meuret, A., Rey, V. Piazzola, J. And Dolle, A.. (2002). "Partially reflected waves measurements using Acoustic Doppler Velocimeter (ADV)", Submitted to ISOPE 03, Honolulu, Hawaii, May 2003.

  1. Spatial variation of coda wave attenuation in northwestern Colombia

    NASA Astrophysics Data System (ADS)

    Vargas, Carlos A.; Ugalde, Arantza; Pujades, Llus G.; Canas, Jos A.

    2004-08-01

    One thousand seven hundred and eighty-six vertical-component, short-period observations of microearthquake codas from regional earthquakes recorded by 17 stations belonging to the National Seismological Network of Colombia were used to estimate seismic wave attenuation in Colombia. Local magnitudes range from 2.9 to 6.0 and only events occurring at hypocentral distances up to 255 km were considered for the analysis. The frequencies of interest lay between 1 and 19 Hz and the analysis was performed for each seismic station separately. Coda-wave attenuation (Q-1c) was estimated by means of a single-scattering method whereas the separation of intrinsic absorption (Q-1i) and scattering attenuation (Q-1s) from total attenuation (Q-1t) was performed using a multiple lapse time-window analysis based on the hypothesis of multiple isotropic scattering and uniform distribution of scatterers. A regionalization of the estimated Q0 (Qc at 1 Hz) values was performed and a contour map of seismic coda attenuation in Colombia is presented, where four zones with significant variations of attenuation related to different geological and tectonic characteristics can be observed. The highest attenuation is linked to the central and western regions (Q0 around 50 and 56) whereas a lower attenuation (Q0 around 69 and 67) is assigned to the northern and eastern regions. Results show that the Q-1 values are frequency dependent in the considered frequency range, and are approximated by a least-square fit to the power law Q-1(f) =Q-10(f/f0)-?. The exponents of the frequency dependence law ranged from ?= 0.65 to 1.01 for Q-1c, ?= 0.62 to 1.78 for Q-1i, ?= 0.28 to 1.49 for Q-1s, and ?= 0.53 to 1.67 for Q-1t. On the other hand, intrinsic absorption is found to dominate over scattering in the attenuation process for most of the stations and frequency bands analysed. Some discrepancies have been observed between the theoretical model and the observations for some frequency bands which indicate that it would be necessary to consider models for depth-dependent velocity structure and/or non-isotropic scattering patterns.

  2. Atmospheric Coupling Through Gravity Waves During Stratospheric Sudden Warmings: Gravity Wave Variations, Generation Mechanisms, and Impacts

    NASA Astrophysics Data System (ADS)

    Yamashita, Chihoko

    2011-12-01

    Full understanding of gravity wave influences on the middle and upper atmosphere remains an unresolved research topic. The goals of this work are two-fold. First, gravity wave sources and propagation characteristics are explored using assimilated meteorological analyses from the European Centre for Medium-Range Weather Forecasting (ECMWF) during the 2009 stratospheric sudden warming (SSW). Second, gravity wave impacts on polar temperatures in the middle and upper atmosphere are examined by modulating the gravity wave parameterization scheme in the Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM). Gravity waves that are resolved in ECMWFT799 are validated with satellite and lidar observations. ECMWF gravity wave potential energy density (GW-Ep) shows two enhancements, on January 5 and 15--22, prior to the peak 2009 SSW on January 23--24. The two gravity wave enhancements are associated with the amplifications of planetary wave 1 and wave 2, respectively, and there is a sudden decay of GW-Ep after the peak 2009 SSW. GW-Ep enhancements prior to the SSW correspond well with the positive vertical gradients of total perturbation energy flux (FE), indicating an in-situ energy source. The spatial and temporal distributions of gravity wave activities correlate with those of the residual tendencies introduced by Snyder et al. [2009]. These results suggest that the two peaks of GW-Ep are caused by the enhancements of the wave excitation in the stratosphere due to the residual tendency forcings. The sudden decay of gravity wave amplitudes correlates well with the suppressions of gravity wave propagation from the troposphere to the stratosphere obtained from the ray-tracing model. In addition, the vertical derivatives of FE decay after January 22. These results indicate that the sudden decay of gravity waves after the wind reversal is likely due to suppressions of gravity wave propagation from the troposphere along with the reductions of in-situ gravity wave excitation by the polar night jet. The responses of the mesosphere and lower thermosphere (MLT) temperatures to gravity waves during SSWs are investigated using TIME-GCM through modifying gravity wave parameters. This study confirms that the height of gravity wave forcing region is mainly determined by gravity wave amplitude and wavelength, and the vertical depth is closely tied to the spectral width of gravity wave phase speed. The gravity wave forcings control the pattern and strength of residual circulation and thereby the characteristics of MLT cooling and warming regions. The planetary wave forcings in the MLT also affect the vertical depth and magnitude of MLT temperature anomalies through further modifying the residual circulation. These planetary wave forcings are likely generated in-situ by the gravity wave forcings at high latitudes. Therefore, the mechanisms of gravity wave controlling the MLT temperature during a SSW are directly through gravity wave forcing and indirectly through generating planetary waves in-situ. Realistic gravity wave variations during the 2009 SSW obtained from ECMWF-T799 are implemented in TIME-GCM. The following two simulations are examined. Case 1 includes the enhanced gravity waves with longitudinal variations. Case 2 suppresses gravity waves with horizontal wavelength longer than 150 km. Both cases improve the TIME-GCM simulations of the MLT temperature responses to the 2009 SSW, indicating that realistic gravity wave variations have impacts on the MLT thermal structure.

  3. Comparison of P- and S-wave velocities and Q's from VSP and sonic log data

    SciTech Connect

    De, G.S.; Winterstein, D.F.; Meadows, M.A. )

    1994-10-01

    The authors compared P- and S-wave velocities and quality factors (Q's) from vertical seismic profiling (VSP) and sonic log measurements in five wells, three from the southwest San Joaquin Basin of California, one from near Laredo, Texas, and one from northern Alberta. Their purpose was to investigate the bias between sonic log and VSP velocities and to examine to what degree this bias might be a consequence of dispersion. VSPs and sonic logs were recorded in the same well in every case. Subsurface formations were predominantly clastic. The bias found was that VSP transit times were greater than sonic log times, consistent with normal dispersion. For the San Joaquin wells, differences in S-wave transit times averaged 1--2 percent, while differences in P-wave transit times averaged 6--7 percent. For the Alberta well, the situation was reversed, with differences in S-wave transit times being about 6 percent, while those for P-waves were 2.5 percent. For the Texas well, the differences averaged about 4 percent for both P- and S-waves. The authors calculated (Q's) from a velocity dispersion formula and from spectral ratios. When the two Q's agreed, they concluded that velocity dispersion resulted solely from absorption. These Q estimation methods were reliable only for Q values smaller than 20. They found that, even with data of generally outstanding quality, Q values determined by standard methods can have large uncertainties, and negative Q's may be common.

  4. 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.

  5. 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 513MHz 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, 49.83.1 years) and 45 matched healthy subjects (25 male, 49.33.0 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 (6.291.04m/s vs. 5.310.72m/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

  6. 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 -2C and 13C).

  7. 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

  8. Sound velocity variation as function of polarization state in Lead Zirconate Titanate (PZT) Ceramics

    NASA Astrophysics Data System (ADS)

    Essolaani, W.; Farhat, N.

    2012-02-01

    There are several ultrasonic techniques to measure the sound velocity, for example, the pulse-echo method. In such method, the size of transducer used to measure the sound velocity must be in the same order of the sample size. If not, the incompatibility of sizes becomes an error source of the sound velocity measurement. In this work, the Laser Induced Pressure Pulse (LIPP) method is used as ultrasonic method. This method has been very useful for studying the spatial distribution of charges and polarization in dielectrics. We take advantage of the fact that the method allows the sound velocity measurement, to study its variation as function of polarization state in (PZT) ceramics. In a sample with a known thickness e, the sound velocity ν is deduced from the measurement of the transit time T. The sound velocity depends on the elastic constants which in turn they depend on poling conditions. Thus, the variation of the sound velocity is related to the direction and the amplitude of the polarization.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

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

  11. 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.

  12. 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.

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

    SciTech Connect

    Lemar, E.R.; Forbes, J.W.; Sutherland, G.T.

    1996-05-01

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

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

    SciTech Connect

    Harvey, R.W.; Jaeger, F.; Berry, L.A.; Batchelor, D.B.; D'Azevedo, E.; Carter, M.D.; Ershov, N.M.; Smirnov, A.P.; Bonoli, P.; Wright, J.C.; Smithe, D.N.

    2005-09-26

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

  15. Variants of the strain-amplitude dependence of elastic wave velocities in rocks under pressure

    NASA Astrophysics Data System (ADS)

    Mashinskii, E. I.

    2004-12-01

    The dependence of the compressional and shear wave velocities on strain amplitude in the Madra dolomites is studied. The experiments were performed using an ultrasonic pulse transmission technique (f = 1 MHz) with a uniaxial pressure of P = 1-60 MPa. An amplitude dependence of wave velocity in the range ɛd ~ (1-3) × 10-6 under a pressure of 5-20 MPa is found. The compressional velocity depends on strain amplitude but the shear velocity does not depend on amplitude change. Determined by the first arrival time, the compressional velocity increases with amplitude. However, if the compressional velocity is determined by the measurement of peak time, the velocity decreases with amplitude. For the upward and downward pressure, the curve Vp(Pax) exhibits open hysteresis, yielding a residual component of velocity. An intersection of the branches of the hysteretic loop is observed in more porous dolomites in comparison with less porous dolomite. This intersection is manifested most in the residual components of the dynamic bulk modulus and Poisson's ratio. The dynamic parameters can be used as is supposed as additional criteria in a geological interpretation.

  16. Effects of stress on magnetically induced velocity changes for ultrasonic longitudinal waves in steels

    NASA Astrophysics Data System (ADS)

    Kwun, H.

    1985-03-01

    Effects of both uniaxial tensile and compressive stresses on the magnetically induced velocity changes for 10-MHz ultrasonic longitudinal waves were investigated in specimens of ASTM A-36, SAE 4340, and HY-80 steels. The magnetically induced ultrasonic velocity changes were found to exhibit characteristically different stress effects depending on the magnitude and sign, i.e., tensile or compressive, of the stress and the relative orientation between the stress and applied magnetic field . The effects of a compressive stress were particularly distinctive producing a prominent minimum in the velocity changes as a function of the applied magnetic field. The observed stress dependence of the magnetically induced velocity changes is qualitatively explained considering the effect of the stress and the magnetic field on the rotational motion of the domain magnetization caused by the propagating ultrasonic waves due to the magnetoelastic coupling.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  18. Short-term velocity variations at 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.

    2016-01-01

    In recent years, strong variations in the speed of rock glaciers have been detected, raising questions about their stability under changing climatic conditions. In this study, we present continuous time series of surface velocities over 3 years of six GPS stations located on three rock glaciers in Switzerland. Intra-annual velocity variations are analysed in relation to local meteorological factors, such as precipitation, snow(melt), and air and ground surface temperatures. The main focus of this study lies on the abrupt velocity peaks, which have been detected at two steep and fast-moving rock glacier tongues ( ≥ 5 m a-1), and relationships to external meteorological forcing are statistically tested.The continuous measurements with high temporal resolution allowed us to detect short-term velocity peaks, which occur outside cold winter conditions, at these two rock glacier tongues. Our measurements further revealed that all rock glaciers experience clear intra-annual variations in movement in which the timing and the amplitude is reasonably similar in individual years. The seasonal decrease in velocity was typically smooth, starting 1-3 months after the seasonal decrease in temperatures, and was stronger in years with colder temperatures in mid winter. Seasonal acceleration was mostly abrupt and rapid compared to the winter deceleration, always starting during the zero curtain period. We found a statistically significant relationship between the occurrence of short-term velocity peaks and water input from heavy precipitation or snowmelt, while no velocity peak could be attributed solely to high temperatures. The findings of this study further suggest that, in addition to the short-term velocity peaks, the seasonal acceleration is also influenced by water infiltration, causing thermal advection and an increase in pore water pressure. In contrast, the amount of deceleration in winter seems to be mainly controlled by winter temperatures.

  19. 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

  20. 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.

  1. Effects of plastic deformation on magnetically induced ultrasonic wave velocity changes in steel

    NASA Astrophysics Data System (ADS)

    Kwun, H.

    1985-02-01

    Effects of a uniaxial tensile plastic deformation on magnetically induced velocity changes for 10-MHz ultrasonic longitudinal waves in a specimen of SAE 4340 steel were investigated. The velocity change as a function of the applied magnetic field, measured after plastic deformation under uniaxial tension, was found to be similar to that obtained under uniaxial compression before deformation, suggesting the presence of a residual compressive stress in the plastically deformed specimen. This finding agrees with other reported results.

  2. 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.

  3. 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.

  4. Velocity-curvature relationship of colliding spherical calcium waves in rat cardiac myocytes.

    PubMed Central

    Wussling, M H; Scheufler, K; Schmerling, S; Drygalla, V

    1997-01-01

    Colliding spherical calcium waves in enzymatically isolated rat cardiac myocytes develop new wavefronts propagating perpendicular to the original direction. When investigated by confocal laser scanning microscopy (CLSM), using the fluorescent Ca2+ indicator fluo-3 AM, "cusp"-like structures become visible that are favorably approximated by double parabolae. The time-dependent position of the vertices is used to determine propagation velocity and negative curvature of the wavefront in the region of collision. It is evident that negatively curved waves propagate faster than positively curved, single waves. Considering two perfectly equal expanding circular waves, we demonstrated that the collision of calcium waves is due to an autocatalytic process (calcium-induced calcium release), and not to a simple phenomenon of interference. Following the spatiotemporal organization in simpler chemical systems maintained under conditions far from the thermodynamic equilibrium (Belousov-Zhabotinskii reaction), the dependence of the normal velocity on the curvature of the spreading wavefront is given by a linear relation. The so-called velocity-curvature relationship makes clear that the velocity is enhanced by curvature toward the direction of forward propagation and decreased by curvature away from the direction of forward propagation (with an influence of the diffusion coefficient). Experimentally obtained velocity data of both negatively and positively curved calcium waves were approximated by orthogonal weighted regression. The negative slope of the straight line resulted in an effective diffusion coefficient of 1.2 x 10(-4) mm2/s. From the so-called critical radius, which must be exceeded to initiate a traveling calcium wave, a critical volume (with enhanced [Ca2+]i) of approximately 12 microm3 was calculated. This is almost identical to the volume that is occupied by a single calcium spark. Images FIGURE 2 FIGURE 4 FIGURE 5 FIGURE 6 PMID:9284291

  5. 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.

  6. 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.

  7. Nonlinear pulse propagation and phase velocity of laser-driven plasma waves

    SciTech Connect

    Schroeder, Carl B.; Benedetti, Carlo; Esarey, Eric; Leemans, Wim

    2011-03-25

    Laser evolution and plasma wave excitation by a relativistically-intense short-pulse laser in underdense plasma are investigated in the broad pulse limit, including the effects of pulse steepening, frequency red-shifting, and energy depletion. The nonlinear plasma wave phase velocity is shown to be significantly lower than the laser group velocity and further decreases as the pulse propagates owing to laser evolution. This lowers the thresholds for trapping and wavebreaking, and reduces the energy gain and efficiency of laser-plasma accelerators that use a uniform plasma profile.

  8. Predicting Ground Motions In Seattle Using A New Shear Wave Velocity Model

    NASA Astrophysics Data System (ADS)

    Delorey, A. A.; Vidale, J. E.

    2010-12-01

    Much of Seattle lies atop a deep sedimentary basin. The Seattle Basin amplifies and distorts seismic waves in ways that modulate the hazard from earthquakes. Seismic hazard assessments heavily depend upon upper crustal and near-surface S-wave velocity models. Improving the accuracy and resolution of basin S-wave models is key to improving predictions of ground shaking. Tomography, with short-period Rayleigh waves extracted using noise interferometry, can refine S-wave velocity models in urban areas with dense arrays of short period and broadband instruments. We applied this technique to develop a new S-wave velocity model encompassing the upper 3-4 km and covering Seattle and several neighboring cities. We then embed this updated model into the regional velocity model that was used in the development of the USGS seismic hazard maps for Seattle. We collected data from two local earthquakes, one crustal and one Benioff Zone event, which were recorded on many strong motion stations operated by the Pacific Northwest Seismic Network and the USGS Earthquake Hazards program. For the two local earthquakes, we compared amplitudes and waveforms predicted by our new velocity model to predictions made using the older velocity model at stiff soil sites. For the crustal event, the amplitudes predicted by simulations with our new model are closer to the data than those predicted by the previous model. At periods between 1.25-5 seconds our new model makes considerably better predictions, while at periods between 1-1.25 seconds our new model makes better predictions, but the difference is smaller. For the Benioff zone event, the two models’ predictions are both good, but also favor our model. At periods between 1.6-3.3, the previous model makes better predictions while our model makes better predictions at periods between 1-1.6 and 3.3-5 seconds. Our simulations confirm that amplitudes are determined by a complex set of variables including basin velocity structure, wave-guides, and soil type. We are working to improve predicted amplifications to improve seismic hazard assessments. Many new strong motion instruments have been installed within the last year, including Netquakes seismographs operated by the USGS, providing us with a valuable data set for improving our predictions. Shear wave velocities in the Seattle Basin

  9. 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.

  10. Are There Optical Solitary Wave Solutions in Linear Media with Group Velocity Dispersion?

    NASA Technical Reports Server (NTRS)

    Li, Zhonghao; Zhou, Guosheng

    1996-01-01

    A generalized exact optical bright solitary wave solution in a three dimensional dispersive linear medium is presented. The most interesting property of the solution is that it can exist in the normal group-velocity-dispersion (GVD) region. In addition, another peculiar feature is that it may achieve a condition of 'zero-dispersion' to the media so that a solitary wave of arbitrarily small amplitude may be propagated with no dependence on is pulse width.

  11. Relative velocity of seagrass blades: Implications for wave attenuation in low-energy environments

    NASA Astrophysics Data System (ADS)

    Bradley, Kevin; Houser, Chris

    2009-03-01

    While the ability of subaquatic vegetation to attenuate wave energy is well recognized in general, there is a paucity of data from the field to describe the rate and mechanisms of wave decay, particularly with respect to the relative motion of the vegetation. The purpose of this study was to quantify the attenuation of incident wave height through a seagrass meadow and characterize the blade movement under oscillatory flow under the low-energy conditions characteristic of fetch-limited and sheltered environments. The horizontal motion of the seagrass blades and the velocity just above the seagrass canopy were measured using a digital video camera and an acoustic Doppler velicometer (ADV) respectively in order to refine the estimates of the drag coefficient based on the relative velocity. Significant wave heights (Hs) were observed to increase by ˜0.02 m (˜20%) through the first 5 m of the seagrass bed but subsequently decrease exponentially over the remainder of the bed. The exponential decay coefficient varied in response to the Reynolds number calculated using blade width (as the length scale) and the oscillatory velocity measured immediately above the canopy. The ability of the seagrass to attenuate wave energy decreases as incident wave heights increase and conditions become more turbulent. Estimates of the time-averaged canopy height and the calculated hydraulic roughness suggest that, as the oscillatory velocity increases, the seagrass becomes fully extended and leans in the direction of flow for a longer part of the wave cycle. The relationship between the drag coefficient and the Reynolds number further suggests that the vegetation is swaying (going with the flow) at low-energy conditions but becomes increasingly rigid as oscillatory velocities increase over the limited range of the conditions observed (200 < Re < 800). In addition to the changing behavior of the seagrass motion, the attenuation was not uniform with wave frequency, and waves at a secondary frequency of 0.38 Hz (2.6 s) appeared to be unaffected by the seagrass. Cospectral analysis between the oscillatory and blade velocity suggests that the seagrass was moving in phase with the current at the (lower) secondary frequency and out of phase at the (higher) peak frequency. In this respect, seagrass is not only an attenuator of wave energy but also serves as a low-pass filter; higher frequencies in the spectra tend to be more attenuated.

  12. Retrospective Tests of an Earthquake Forecasting Model in Japan Based on P-Wave Velocity Anomalies

    NASA Astrophysics Data System (ADS)

    Imoto, M.; Matsubara, M.; Yamamoto, N.

    2010-12-01

    We constructed an earthquake forecasting model of long-term probability based on P-wave velocity perturbations from a standard layered model for Japan. We considered the perturbations as a predictive parameter that may be useful for assessing regional seismogenesis. We evaluated the distance between two distributions of parameters, the background distribution (parameters over the entire space domain), and the conditional distribution (parameters at earthquake epicenters) then used this distance to measure the reliability of the predictive parameters. We selected 198 epicenters of earthquakes with magnitudes of 5.0 and larger for 1961 to 2008 to estimate the conditional distribution. More than 3000 points were selected at every point on a 0.1 x 0.1 grid for the background distribution. P-wave variations were considered at four different depths (10, 15, 20, and 25km at each point) for both distributions. Both distributions were approximated by normal distributions with four variables. The distance between two distributions could be analytically estimated to be 0.3, which suggests that an average probability of the proposed model (VP4L model) over the 198 earthquakes is 1.35 times higher than that of a stationary uniform Poisson (SUP) model. To confirm this assessment, we conducted N-, L- and R-tests of the VP4L model, where the SUP model was adopted for comparisons. The retrospective test demonstrated that the observed scores of N- and L-tests are consistent with those expected from the VP4L model. However, the average probability gain calculated from the R-score is about 1.19, which is less than the assessed value. We will start the prospective test to see how the model would perform in a truly prospective test.

  13. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

  15. 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.

  16. 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.

  17. 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 90W 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.

  18. Electric field variations due to resonance between ground velocity and ions motion in the Earth's magnetic field

    NASA Astrophysics Data System (ADS)

    Matsushima, M.; Honkura, Y.; Kuriki, M.; Ogawa, Y.

    2011-12-01

    We have so far observed clear electric field variations coincident with the passage of seismic waves. Circular polarization of electric field is the distinguishing feature in this phenomenon which can be interpreted in terms of the so-called seismic dynamo effect proposed by Honkura et al. (2009). That is, circularly polarized electric field is caused by resonance-like motion of ion in groundwater under the Earth's magnetic field. Therefore, left-handed and right-handed circular polarizations, if seen towards the direction of the magnetic field, are associated with anions with negative charge and cations with positive charge, respectively. Such polarization may be inconsistent with seismoelectric signals due to the electrokinetic mechanism, because they are mainly found in the direction of transmission of seismic compressional waves, as pointed out by Strahser et al. (2007) who examined polarization of seismoelectric signals by recording the three components of electric field. However, even such circular polarization of electric field is somehow interpreted in terms of the electrokinetic mechanism. Therefore, further convincing evidence is required to support the seismic dynamo effect. On 25-26 July 2011, an experiment for studies of crustal seismic structure was made in central Japan. We carried out simultaneous observations of ground velocity and electric field on this occasion at three sites near a blasting point using 50 kg of dynamite; about 280 m east-southeast, about 190 m east, and about 360 m northwest from the blasting point. Taking into account typical frequencies of ground velocity for artificial earthquakes by blasting higher than those for natural earthquakes, we used data loggers with sampling rate of 1 kHz and could obtain the waveforms of ground velocity and electric field very clearly. We show characteristics of electric field variations, their dependence of azimuth angle with respect to the blasting point, and frequency response functions.

  19. Temperature dependence of elastic P- and S-wave velocities in porous Mt. Unzen dacite

    NASA Astrophysics Data System (ADS)

    Scheu, B.; Kern, H.; Spieler, O.; Dingwell, D. B.

    2006-05-01

    Laboratory measurements of elastic properties of volcanic rocks are crucial for the modelling of volcano seismic activity. Compared to the large database reported in the literature for sedimentary, igneous and metamorphic rocks, the data set for volcanic rocks is limited and mostly restricted to basalts. Data for more silica-rich rocks are sparse. In particular, velocity data for silica-rich volcanic rocks measured at elevated temperature are lacking. We measured the elastic P- and S-wave velocities and the velocity anisotropy of porous dacitic rocks from Unzen Volcano, Japan, exhibiting an open porosity of 3.3 to 24.3 vol.%. The measurements were done at temperatures of up to 600 °C and confining pressures of 100 MPa, corresponding to depths of ˜ 3000-4000 m. Samples with even higher porosities failed at the required pressures. The measurements were carried out in a cubic multi-anvil pressure apparatus, using the pulse transmission technique. In contrast to low-porosity magmatic and metamorphic rocks, the seismic velocities of the investigated volcanic rocks increased and the velocity anisotropies decreased with increasing temperature, due to further sample compaction. There is a close relationship between velocity, density and porosity. The higher the density (and the lower the porosity) the higher are the P- and S-wave velocities. These results can contribute to a better understanding of the propagation of seismic energy through the volcanic edifice.

  20. 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.

  1. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

  3. 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

  4. 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

  5. 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.; Grtner-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.

  6. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

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

  8. 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).

  9. Along-strike variations in the shallow seismic velocity structure of the Seattle fault zone: Evidence for fault segmentation beneath Puget Sound

    NASA Astrophysics Data System (ADS)

    Calvert, Andrew J.; Fisher, Michael A.; Johnson, Samuel Y.

    2003-01-01

    Around 1100 years ago, the Seattle fault, which trends east-west beneath Puget Sound and the greater Seattle metropolitan area, experienced a M > 7 earthquake. We present high-resolution images of the shallow P wave velocity variation across the fault zone. These images were obtained by tomographic inversion of the first arrivals recorded along two north-south oriented seismic reflection lines shot within Puget Sound near Seattle. Just beneath the seafloor, the fault zone includes uplifted Tertiary rocks with seismic velocities in the range of 2300 to 2600 m s-1. These velocities contrast markedly with values of ˜1600 m s-1 in shallow Holocene sediments. South of the Seattle fault zone volcanic rocks of the Crescent Formation, which exhibit velocities >3700 m s-1, are identified at depths of only 900 m. Seismic velocities of around 2600 m s-1, which represent Oligocene rocks, are found in the hanging wall of the Seattle fault beneath eastern Puget Sound. In the west, lower, 2300 m s-1 seismic velocities occur, probably due to the presence of Miocene rocks, which are not found in the east. Along-strike velocity variations arise from the folding of Tertiary rocks and the presence of distinct fault splays, including a north striking tear fault characterized by depressed seismic velocities that was intersected by the eastern seismic line. Along-strike differences in the uplift of Tertiary rocks beneath Puget Sound are likely associated with the existence of a segment boundary of the Seattle fault system.

  10. 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. __________________________________________________

  11. CELEBRATION 2000: P-wave velocity models of the Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Hrubcova, P.

    2003-04-01

    Deep structure of the Bohemian Massif (BM), the largest stable outcrop of Variscan rocks in Central Europe, was studied along two refraction profiles, CEL09 that traverses the whole massif in the NW-SE direction, and CEL10 that extends along its eastern edge almost perpendicularly to CEL09. Good quality recordings with clear first arrivals of crustal and upper mantle phases show apparent velocity 5.9 km/s for the upper crust with slightly higher gradient in NW part of the BM and app. velocity 8.0 to 8.1 km/s for the upper mantle. Decrease of amplitudes of crustal phases visible in some sections may be connected with a specific upper crustal structure (zero to negative velocity gradient zone). Pronounced Moho reflections in central part of the BM suggest well-defined Moho in that part and not so clear Moho with smaller velocity contrast in other parts of the BM. For interpretation, the tomographic inversion routine of Hole (1992) was used as an efficient tool to determine seismic P-wave velocity distribution in the crust using first arrivals. Tomographic models were verified by forward ray tracing modelling based on well-established algorithm developed by Cerveny et al. (1983), where apart from first arrivals also further phases were included. 2-D velocity models of first arrivals and reflected phases show high P-wave velocity gradient zone reaching the depth of 5-7 km followed by small gradient and laterally homogeneous P-wave velocity distribution in the middle crust. Differences in velocity distribution in the lower crust delimit central part of the BM (sharp Moho discontinuity) from other tectonic units within the BM (lower crust high gradient transition zone). Position of Moho discontinuity ranging from 32 km to 40 km and reflectors within the crust complement the P-wave velocity distribution. Presented models also show the contact of the BM with its neighbouring units - Carpathians, Paleozoic Platform, Vienna Basin and the Alps. References: Cerveny, V., Psencik, I., 1983. Program SEIS83, Numerical Modelling of Seismic Wave Fields in 2-D Laterally Varying Layered Structures by the Ray Method, Charles University, Prague. Hole, J.A. 1992: Non-linear high-resolution three-dimensional seismic travel time tomography, J. Geophys. Res. 97, 6553-6562.

  12. Variations in melt inputs and basal sliding velocity on the Kennicott Glacier, Alaska, USA

    NASA Astrophysics Data System (ADS)

    Armstrong, W. H.; Barnhart, K. R.; Anderson, R. S.; Rajaram, H.

    2012-12-01

    We present glacier surface motion, meteorologic, and hydrologic observations from the 2012 melt season on the Kennicott Glacier near McCarthy, Alaska. We record 15-second global positioning system (GPS) data from five monuments along the glacier centerline, 10-minute water level data from pressure sensors in four ice-marginal basins and one on the glacier outlet river, 10-minute air temperature and ablation rates, and one-hour time-lapse photography on two ice-marginal basins and the outlet stream. We use these data to investigate linkages between subglacial hydrology and glacier basal sliding velocity. Time-lapse imagery and pressure sensor time series capture a complicated early season fill-and-drain sequence on an ice-marginal lake, likely reflecting the interplay between melt supply and development of a hydrologic link between the basin and a presumed nearby low-pressure subglacial conduit. We also capture a midsummer jkulhlaup in which 20-30 x 10^6 cubic meters of water drain from the ice-dammed Hidden Creek Lake over the course of 60 hours. The flood wave propagates down-glacier, reaching the glacier terminus 15 kilometers away about 30 hours after the initiation of lake drainage. The flood wave raises stage by many tens of meters in ice-marginal basins and doubles discharge on the outlet stream. We compare water level records to differential GPS time series to monitor the glacier sliding response to seasonal, daily, and event-based variations in water inputs. This study builds on our 2006 research in the area by increasing GPS monument density, extending the monitoring season, and including time-lapse photography. These improvements allow us to resolve in greater temporal and spatial detail the glacier's response to hydrologic conditions throughout the melt season. Although the 2012 summer was generally cooler than summer 2006, we find remarkable similarity between the outburst flood hydrographs for the two years, indicating similarities in the evolution of the subglacial drainage network despite differences in the temporal pattern of melt inputs. These data will serve as a foundation for future modeling of the temporal and spatial evolution of the glacier hydrologic system and its linkages with the associated patterns of sliding.

  13. 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.

  14. Regional P wave velocity structure of the Northern Cascadia Subduction Zone

    USGS Publications Warehouse

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

    2006-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1998-01-01

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

  16. 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.

  17. Effect of slope variation and skating technique on velocity in cross-country skiing.

    PubMed

    Boulay, M R; Rundell, K W; King, D L

    1995-02-01

    The purpose of the present study was to investigate the effect of slope variations upon the maximal velocity attainable by cross-country ski racers using three skating techniques (V-1, V-2, and Gunde). Nine (2 females, 7 males) junior ski racers (16.0 +/- 0.4 yr of age, mean +/- SEM) exhibiting strong technical skills participated in the study. The subjects were required to skate at maximal velocity over five different courses (length 120-200 m) with mean slopes of -1, 0, 6, 9, and 12%. Video analysis was used to determine skiing velocity, cycle length, and cycle rate. Heart rate was monitored to verify intensity of exertion. Results indicated that intensities were similar to those observed while racing. Velocities for the three techniques were not different for -1, 0, and 6% slopes. However V-1 was significantly faster (P < 0.01) at 9% and 12% inclines. Velocity was highly correlated to cycle length (P < 0.01) but unrelated to cycle rate. Cycle length was significantly different between techniques (P < 0.01) and varied across slopes. Cycle rate was significantly different between techniques (P < 0.01) but did not vary across slopes. Thus, our results indicate that any of the three techniques is adequate on flat and rolling terrain, but V-1 should be used at slopes of 9% and above. It is also concluded that during short trials skied at maximal velocity, skiing velocity is highly dependent on cycle length and independent of cycle rate. PMID:7723654

  18. Velocity Dispersion and Attenuation of Acoustic Waves in Granular Sedimentary Media.

    NASA Astrophysics Data System (ADS)

    Tutuncu, Azra Nur

    An experimental and theoretical investigation of the effects of stress, frequency, and clay content on compressional and shear wave velocities and attenuations has been conducted using tight gas sandstone samples. The ultrasonic pulse transmission technique (~ 1 MHz) was used to measure velocities and attenuations and calculate dynamic moduli of fully brine saturated samples with porosities from 3 to 11.9 percent and clay contents from 1 to 38 percent. Simultaneous measurements were carried out to record axial and radial deformation under a biaxial stress state in order to calculate the static elastic moduli. The static moduli were found to be 1 to 6 times smaller than the dynamic moduli under the stress state. The velocities measured at ultrasonic frequency were also compared to the sonic log velocities (~20 KHz) in order to investigate dispersion effects. The trend observed in P and S wave velocities in homogeneous intervals shows that clean sandstone velocities measured in the ultrasonic frequency range deviate systematically from the log derived velocities. Compressional and shear wave amplitude data exhibited a shift in peak frequency toward lower frequencies for clay rich samples as compared to clean samples showing the important role clays play in the dissipative behavior of sandstones. The deviations from the log derived velocities are correlatable in most cases to the clay content and dispersion. The presence of clay softens the rock grain contacts and causes larger contact area values compared to the values for nearly clean rock under the same applied load. The frame moduli of sedimentary rocks are strongly influenced by the properties of the grain contacts. A modified Hertz contact theory is presented for the self consistent calculation of contact deformation, equilibrium separation distance (film thickness) and contact area for two spherical asperities in contact and subjected to an external load. It is shown that surface forces, i.e. electrostatic repulsion, Born, structural, and Van der Waals forces can be incorporated into the contact deformation problem. These forces play an important role in determining seismic wave velocities and attenuations at low confining stresses. The computed equilibrium separation distances and contact radii were used to calculate velocities and attenuations as a function of frequency and compared with measured values for glass beads, Navajo, Berea, Obernkirchner and Fort Union sandstones. The velocities and attenuations calculated as functions of stress, frequency, fluid type and saturation are all in good agreement with reported experimental data.

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

    NASA Astrophysics Data System (ADS)

    Çınar, 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.

  20. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

    Broadband waveforms recorded at stations in Europe and surrounding regions were inverted for shear-wave velocity of the European upper mantle. For events between 1995 and 2007 seismograms were collected from all permanent stations for which data are available via the data centers ORFEUS, GEOFON, ReNaSs and IRIS. In addition, we incorporated data from temporary experiments, including SVEKALAPKO, TOR, Eifel Plume, EGELADOS and other projects. Automated Multimode Inversion of surface and S-wave forms was applied to extract structural information from the seismograms, in the form of linear equations with uncorrelated uncertainties. Successful waveform fits for about 70,000 seismograms yielded over 300,000 independent linear equations that were solved together for a three-dimensional tomographic model. Resolution of the imaging is particularly high in the mantle lithosphere and asthenosphere. The highest velocities in the mantle lithosphere of the East European Craton are found at about 150 km depth. There are no indications for a large scale deep cratonic root below about 330 km depth. Lateral variations within the cratonic mantle lithosphere are resolved by our model as well. The locations of diamond bearing kimberlites correlate with reduced S-wave velocities in the cratonic mantle lithosphere. This anomaly is present in regions of both Proterozoic and Archean crust, pointing to an alteration of the mantle lithosphere after the formation of the craton. Strong lateral changes in S-wave velocity are found at the western margin of the East European Craton and hint to erosion of cratonic mantle lithosphere beneath the Scandes by hot asthenosphere. The mantle lithosphere beneath Western Europe and between the Tornquist-Teyissere Zone and the Elbe Line shows moderately high velocities and is of an intermediate character, between cratonic lithosphere and the thin lithosphere of central Europe. In central Europe, Caledonian and Variscian sutures are not associated with strong lateral changes in the lithosphere-asthenosphere system. Cenozoic anorogenic intraplate volcanism in central Europe and the Circum Mediterranean is found in regions of shallow asthenosphere and close to sharp gradients in the depth of the lithosphere-asthenosphere boundary. Low-velocity anomalies extending vertically from shallow upper mantle down to the transition zone are found beneath the Massive Central, Sinai, Canary Islands and Iceland.

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  3. 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.

  4. ACE stimulated neural network for shear wave velocity determination from well logs

    NASA Astrophysics Data System (ADS)

    Asoodeh, Mojtaba; Bagheripour, Parisa

    2014-08-01

    Shear wave velocity provides invaluable information for geomechanical, geophysical, and reservoir characterization studies. However, measurement of shear wave velocity is time, cost and labor intensive. This study proposes a swift and exact methodology, called ACE stimulated neural network, for prediction of shear wave velocity from available well logs such that it will be able to surpass previous models. The proposed method is composed of two major parts: 1) transforming input/output data space to a higher correlated space using alternative condition expectation (ACE), and 2) making a neural network formulation in transformed data space. Transforming in the first step makes it easier for neural network to find the complicated underlying dependency of input/output data. Therefore, neural network will be able to develop an accurate and strong formulation between conventional well logs and shear wave velocity. The Propounded approach was successfully applied in one of the carbonate gas fields of Iran. A comparison between proposed model and previous models showed superiority of ACE stimulated neural network.

  5. RELATIONS BETWEEN DAIRY FOOD INTAKE AND ARTERIAL STIFFNESS: PULSE WAVE VELOCITY AND PULSE PRESSURE

    PubMed Central

    Crichton, Georgina E.; Elias, Merrrill F.; Dore, Gregory A.; Abhayaratna, Walter P.; Robbins, Michael A.

    2012-01-01

    Modifiable risk factors, such as diet, are becomingly increasingly important in the management of cardiovascular disease, one of the greatest major causes of death and disease burden. Few studies have examined the role of diet as a possible means of reducing arterial stiffness, as measured by pulse wave velocity, an independent predictor of cardiovascular events and all-cause mortality. The aim of this study was to investigate whether dairy food intake is associated with measures of arterial stiffness including carotid-femoral pulse wave velocity and pulse pressure. A cross-sectional analysis of a subset of the Maine Syracuse Longitudinal Study sample was performed. A linear decrease in pulse wave velocity was observed across increasing intakes of dairy food consumption (ranging from never/rarely to daily dairy food intake). The negative linear relationship between pulse wave velocity and intake of dairy food was independent of demographic variables, other cardiovascular disease risk factors and nutrition variables. The pattern of results was very similar for pulse pressure, while no association between dairy food intake and lipid levels was found. Further intervention studies are needed to ascertain whether dairy food intake may be an appropriate dietary intervention for the attenuation of age-related arterial stiffening and reduction of cardiovascular disease risk. PMID:22431583

  6. Relations between dairy food intake and arterial stiffness: pulse wave velocity and pulse pressure.

    PubMed

    Crichton, Georgina E; Elias, Merrrill F; Dore, Gregory A; Abhayaratna, Walter P; Robbins, Michael A

    2012-05-01

    Modifiable risk factors, such as diet, are becomingly increasingly important in the management of cardiovascular disease, one of the greatest major causes of death and disease burden. Few studies have examined the role of diet as a possible means of reducing arterial stiffness, as measured by pulse wave velocity, an independent predictor of cardiovascular events and all-cause mortality. The aim of this study was to investigate whether dairy food intake is associated with measures of arterial stiffness, including carotid-femoral pulse wave velocity and pulse pressure. A cross-sectional analysis of a subset of the Maine-Syracuse Longitudinal Study sample was performed. A linear decrease in pulse wave velocity was observed across increasing intakes of dairy food consumption (ranging from never/rarely to daily dairy food intake). The negative linear relationship between pulse wave velocity and intake of dairy food was independent of demographic variables, other cardiovascular disease risk factors, and nutrition variables. The pattern of results was very similar for pulse pressure, whereas no association between dairy food intake and lipid levels was found. Further intervention studies are needed to ascertain whether dairy food intake may be an appropriate dietary intervention for the attenuation of age-related arterial stiffening and reduction of cardiovascular disease risk. PMID:22431583

  7. 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.

  8. 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/ω{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.

  9. 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.

  10. Field observations of linear transition ripple migration and wave orbital velocity skewness

    NASA Astrophysics Data System (ADS)

    Crawford, Anna Morwenna

    A new laser illuminated underwater video system has been developed for simultaneously imaging sediment suspension and monitoring bedforms under waves in the nearshore. The system consists of a video camera and diode laser- generated light plane which illuminates suspended material in section and profiles the bed where it intersects the bottom. The system was deployed in the field along with acoustic devices for measurement of nearbed flow velocities and independent bedform observation at Queensland Beach, Nova Scotia. Observations were made in 3 to 4 m water depth of linear transition ripple geometry and migration using the laser- video system and acoustic scanning sensors during both the growth and decay phases of an autumn storm event. Linear transition ripples are long crested, low steepness bedforms in the anorbital ripple class. The transition ripples occurred under relatively high energy waves, just below the flatbed threshold, and had wavelengths of 8.5 +/- 0.5 cm and heights of 0.3 +/- 0.1 cm. The maximum observed migration rate was 0.7 cm/min. Migration was offshore during storm growth, and onshore during storm decay. The observed ripple migration rates were highly correlated with nearbed wave orbital velocity skewness (r2 > 0.7). During storm growth, the incident wave spectrum was bimodal and the orbital velocity skewness was negative. During storm decay, the wave spectrum was unimodal and the velocity skewness was positive. Bispectral analysis shows that the main contribution to negative velocity skewness during storm growth arose from a difference interaction between the two principal components (sea and swell) of the bimodal wave spectrum. Positive velocity skewness during storm decay was due to self-self interaction of the narrowband swell. These observations are shown to be consistent with a second-order wave theory. These observations support a skewness, or u3 , dependence of transition ripple migration on nearbed orbital velocity in a field setting and provide a demonstration of storm modulated off- and on-shore directed ripple migration, thus suggesting a mechanism for the reversible sediment transport cycle during storms.

  11. An experimental study on the correlation between the elastic wave velocity and microfractures in coal rock from the Qingshui basin

    NASA Astrophysics Data System (ADS)

    Feng, Zhou; Mingjie, Xu; Zhonggao, Ma; Liang, Cai; Zhu, Zhu; Juan, Li

    2012-12-01

    In order to study the impact of microfractures on the elastic wave velocity, multi-azimuth elastic wave velocity experiments were performed with coal rock samples under a confining pressure similar to the one in the buried coal strata of the Qinshui basin. The results indicate that (1) the microfractures in coal rock reduce the elastic wave velocity. In the experiments, the velocity was increased with a confining pressure. However, when the confining pressure was increased to 10 MPa, the velocity became stable because most of the microfractures in the coal rock samples were closed. (2) The elastic wave velocity is sensitive to the microfracture orientation in coal rock. The elastic wave propagates rapidly along the microfracture direction, while it propagates slowly perpendicular to the microfracture direction. This research provides the basic data to predict microfractures in coal rock.

  12. Seasonal and spatial variations in ice velocity, South-West Greenland

    NASA Astrophysics Data System (ADS)

    Sundal, A. V.; Shepherd, A.; Nienow, P.; Palmer, S. J.; Hanna, E.

    2009-12-01

    We used satellite offset tracking and synthetic aperture radar interferometry (InSAR) to investigate seasonal and spatial variations in ice velocity in South-West Greenland. The study area covers approximately 10 000 km2 of the south-western ice sheet margin and includes 6 land-terminating glaciers. We processed about 50 pairs of European Remote Sensing (ERS) synthetic aperture radar (SAR) images using offset tracking and 7 image pairs using SAR interferometry. The offset tracking technique was applied to 35-day repeat-track pairs from 1992-1998, while the InSAR image pairs (1-day repeat) were acquired during 1995 and 1996. The results reveal a clear seasonal pattern of velocity variation for all the 6 glaciers, with significantly higher ice velocities occurring from May to September compared to the rest of the year. The summer speed-ups vary between 50 and 200 % and are believed to be caused by routing of surface meltwater to the glacier base, leading to enhanced glacial sliding. Altitudinal variations in ice velocities were also observed, with summer speed-ups generally starting earlier at locations close to the ice sheet margin compared to the colder higher elevation areas.

  13. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  15. New look at wave analogy for prediction of bubble terminal velocities

    SciTech Connect

    Maneri, C.C.

    1995-03-01

    The analogy between waves on the surface of an infinite fluid and bubbles rising in low-viscosity fluids of infinite extent, originally proposed by Mendelson for 3-D bubbles, has been used to predict the terminal velocity, of plane bubbles. In terms of its terminal velocity, a plane bubble rising in a rectangular duct of small aspect (spacing-to-width) ratio behaves as if it were a 3-D bubble rising in an infinite medium as long as the end walls (the walls in the width wise direction) are sufficiently far apart. As the end walls are moved toward each other, a wall effect is found to exist. A general expression for the terminal velocity of a bubble of any size rising in a rectangular duct including this wall effect is also developed based on the wave analogy and shown to compare well with existing data.

  16. 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.

  17. Evolution of microstructure and elastic wave velocities in dehydrated gypsum samples

    NASA Astrophysics Data System (ADS)

    Milsch, H.; Priegnitz, M.

    2012-04-01

    This study aims at contributing to the experimental database of changes in rock physical properties, particularly elastic wave velocities, induced by devolatilization reactions. Cylindrical samples of natural gypsum were dehydrated in air for up to 800 h at ambient pressure and temperatures between 378 and 423 K. Subsequently, the transformation kinetics, reaction induced changes in microstructure and porosity and the concurrent evolution of the sample P and S-wave velocities were constrained. Weighing the heated samples in predefined time intervals yielded the reaction progress where the stoichiometric mass balance indicated an ultimate dehydration to anhydrite regardless of temperature. Porosity was observed to continuously increase with reaction progress from approximately 2 % for fully hydrated samples to 30 % for completely dehydrated ones, whilst the initial bulk volume was preserved. In a first set, P-wave velocity was measured at ambient conditions with ultrasonic transducers indicating a linear decrease with porosity from 5.2 km/s at 2 % to 1.0 km/s at 30 %. Results of a second set of ultrasonic measurements for both P and S-waves will be presented as well aiming at a spatially resolved wave velocity dependence on microstructure. For P-waves three different effective medium models - Voigt, Wyllie (Reuss), and Nur - were compared to the data. The linear dependence of P-wave velocity on porosity observed is best represented by the Voigt bound. The Voigt bound, however, overestimates the measured values significantly. The Wyllie-Equation (the Reuss bound) does not replicate the linear decrease in P-wave velocity with porosity and generally underestimates the data. However, at porosities above approximately 25 % the agreement with measured values is excellent. The Nur-Model yields a nonlinear dependence but replicates the data best for model-inherent critical porosities between 0.25 and 0.3. Thin section micrographs taken on selected samples reveal a sharp reaction front progressively migrating sample inwards. SEM imaging confirmed this observation, additionally showing (1) that the cylindrical outer rim consists of a highly porous network within an anhydrite matrix and (2) that the remaining inner cylinder appears unaltered at 388 K whereas bassanite needles progressively turning into anhydrite can be found at 398 K.

  18. 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.

  19. 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

  20. Pulse Wave Velocity Testing in the Baltimore Longitudinal Study of Aging

    PubMed Central

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

    2014-01-01

    Carotid-femoral pulse wave velocity is considered the gold standard for measurements of central arterial stiffness obtained through noninvasive methods1.Subjects are placed in the supine position and allowed to rest quietly for at least 10 min prior to the start of the exam. The proper cuff size is selected and a blood pressure is obtained using an oscillometric device. Once a resting blood pressure has been obtained, pressure waveforms are acquired from the right femoral and right common carotid arteries. The system then automatically calculates the pulse transit time between these two sites (using the carotid artery as a surrogate for the descending aorta). Body surface measurements are used to determine the distance traveled by the pulse wave between the two sampling sites. This distance is then divided by the pulse transit time resulting in the pulse wave velocity. The measurements are performed in triplicate and the average is used for analysis. PMID:24561745

  1. 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

  2. Development a polymer-based electronic pulse diagnosis instrument for measuring and analyzing pulse wave velocity.

    PubMed

    Chou, Hsi-Chiang; Lin, Kai-Jie; Fang, Yun-Xiang; Liou, Jia-Fu

    2015-01-01

    A novel pulse-diagnosis system was proposed in this study for measuring pulse wave velocities. In contrast with most conventional mechanical, rigid-type pulse diagnosis instruments such as pressure transducers and microactuators, a conductive elastic polymer was adopted as the sensor material. The soft and formability properties of such material enabled fabricating a flexible pulse diagnosis instrument. In addition, the flexible design was integrated with a contemporary, wrist-type pulse-wave acquisition system to ensure stable measurements. Closely related to the incidence of cardiovascular diseases, pulse wave velocity was analyzed in applications to verify the feasibility of this system. Regarding signal processing, the cun, guan, and chi pulse signals obtained through the data acquisition device were sent to the LabVIEW platform for reconstructing the pulse waveforms. Finally, the results of 20 measured samples were compared and analyzed to evaluate the level of system performance. PMID:26684574

  3. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2004-06-01

    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.

  6. 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.

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

    SciTech Connect

    Fusco, A.C. . Center for Atmospheric Theory and Analysis); Salby, M.L. )

    1999-06-01

    Interannual variations of total ozone at midlatitudes of the Northern Hemisphere are shown to operate coherently wit h variations of upwelling planetary wave activity from the troposphere. Variations of upwelling wave activity, which modulate ozone transport and chemical production by the diabatic mean circulation of the stratosphere, account for much of the interannual variance of total ozone, including its systematic decline during the 1980s. Chemical depletion, enhanced by increasing halocarbon levels, accounts for the remainder of the midlatitude trend, consistent with values widely reported by chemical models that do not account for observed changes in upwelling planetary wave activity. Much of the chemical contribution comes from sharply enhanced depletion following the eruption of Mt. Pinatubo, during the final years of the satellite record. Incomplete representation of the 3--5-yr recovery toward normal aerosol and ozone after Pinatubo appears to distort the trend inferred from the overall satellite record to values that are unrepresentative of the rest of the record. The impact on ozone of interannual changes of upwelling planetary wave activity is evaluated in calculations with a three-dimensional model of stratospheric dynamics and photochemistry, which reproduce the magnitude and structure of observed interannual variations.

  8. 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.

  9. Long-term radial-velocity variations of the Sun as a star: The HARPS view

    NASA Astrophysics Data System (ADS)

    Lanza, A. F.; Molaro, P.; Monaco, L.; Haywood, R. D.

    2016-03-01

    Context. Stellar radial velocities play a fundamental role in the discovery of extrasolar planets and the measurement of their physical parameters as well as in the study of stellar physical properties. Aims: We investigate the impact of the solar activity on the radial velocity of the Sun using the HARPS spectrograph to obtain measurements that can be directly compared with those acquired in the extrasolar planet search programmes. Methods: We used the Moon, the Galilean satellites, and several asteroids as reflectors to measure the radial velocity of the Sun as a star and correlated this velocity with disc-integrated chromospheric and magnetic indexes of solar activity that are similar to stellar activity indexes. We discuss in detail the systematic effects that affect our measurements and the methods to account for them. Results: We find that the radial velocity of the Sun as a star is positively correlated with the level of its chromospheric activity at ~95 percent significance level. The amplitude of the long-term variation measured in the 2006-2014 period is 4.98 ± 1.44 m/s, which is in good agreement with model predictions. The standard deviation of the residuals obtained by subtracting a linear best fit is 2.82 m/s and is due to the rotation of the reflecting bodies and the intrinsic variability of the Sun on timescales shorter than the activity cycle. A correlation with a lower significance is detected between the radial velocity and the mean absolute value of the line-of-sight photospheric magnetic field flux density. Conclusions: Our results confirm similar correlations found in other late-type main-sequence stars and provide support to the predictions of radial velocity variations induced by stellar activity based on current models.

  10. Inversion of Surface Wave Phase Velocities for Radial Anisotropy to an Depth of 1200 km

    NASA Astrophysics Data System (ADS)

    Xing, Z.; Beghein, C.; Yuan, K.

    2012-12-01

    This study aims to evaluate three dimensional radial anisotropy to an depth of 1200 km. Radial anisotropy describes the difference in velocity between horizontally polarized Rayleigh waves and vertically polarized Love waves. Its presence in the uppermost 200 km mantle has well been documented by different groups, and has been regarded as an indicator of mantle convection which aligns the intrinsically anisotropic minerals, largely olivine, to form large scale anisotropy. However, there is no global agreement on whether anisotropy exists in the region below 200 km. Recent models also associate a fast vertically polarized shear wave with vertical upwelling mantle flow. The data used in this study is the globally isotropic phase velocity models of fundamental and higher mode Love and Rayleigh waves (Visser, 2008). The inclusion of higher mode surface wave phase velocity provides sensitivities to structure at depth that extends to below the transition zone. While the data is the same as used by Visser (2008), a quite different parameterization is applied. All the six parameters - five elastic parameters A, C, F, L, N and density - are now regarded as independent, which rules out possible biased conclusions induced by scaling relation method used in several previous studies to reduce the number of parameters partly due to limited computing resources. The data need to be modified by crustal corrections (Crust2.0) as we want to look at the mantle structure only. We do this by eliminating the perturbation in surface wave phase velocity caused by the difference in crustal structure with respect to the referent model PREM. Sambridge's Neighborhood Algorithm is used to search the parameter space. The introduction of such a direct search technique pales the traditional inversion method, which requires regularization or some unnecessary priori restriction on the model space. On the contrary, the new method will search the full model space, providing probability density function of each anisotropic parameter and the corresponding resolution.

  11. 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.

  12. Velocity Variations of the Kaskawulsh Glacier, Yukon Territory, 2009-2011

    NASA Astrophysics Data System (ADS)

    Darling, Samantha

    Laser altimetry and satellite gravity surveys indicate that the St Elias Icefields are currently losing mass and are among the largest non-polar sea level contributors in the world. However, a poor understanding of glacier dynamics in the region is a major hurdle in evaluating regional variations in ice motion and the relationship between changing surface conditions and ice flux. This study combines in-situ dGPS measurements and advanced Radarsat-2 (RS-2) processing techniques to determine daily and seasonal ice velocities for the Kaskawulsh Glacier from summer 2009 to summer 2011. Three permanent dGPS stations were installed along the centreline of the glacier in 2009, with an additional permanent station on the South Arm in 2010. The Precise Point Positioning (PPP) method is used to process the dGPS data using high accuracy orbital reconstruction. RS-2 imagery was acquired on a 24-day cycle from January to March 2010, and from October to March 2010-2011 in a combination of ultra-fine and fine beam modes. Seasonal velocity regimes are readily identifiable in the dGPS results, with distinct variations in both horizontal velocity and vertical motion. The Spring Regime consists of an annual peak in horizontal velocity that corresponds closely with the onset of the melt season and progresses up-glacier, following the onset of melt at each station. The Summer Regime sees variable horizontal velocity and vertical uplift, superimposed on a long-term decline in motion. The Fall Regime sees a gradual slowing at all stations with little variation in horizontal velocity or vertical position. Rapid but short accelerations lasting up to 10 days were seen in the Winter regimes in both 2010 and 2011, occurring at various times throughout each regime. These events initiated at the Upper Station and progress down-glacier at propagation speeds up to 16,380 m day-1 and were accompanied by vertical uplift lasting for similar periods. Three velocity maps, one from the winter of 2010 and two from the fall/winter of 2011, produced from speckle tracking were validated by comparison with dGPS velocity, surface flow direction, and bedrock areas of zero motion, with an average velocity error of 2.0% and average difference in orientation of 4.3.

  13. Mesoscale variations in acoustic signals induced by atmospheric gravity waves.

    PubMed

    Chunchuzov, Igor; Kulichkov, Sergey; Perepelkin, Vitaly; Ziemann, Astrid; Arnold, Klaus; Kniffka, Anke

    2009-02-01

    The results of acoustic tomographic monitoring of the coherent structures in the lower atmosphere and the effects of these structures on acoustic signal parameters are analyzed in the present study. From the measurements of acoustic travel time fluctuations (periods 1 min-1 h) with distant receivers, the temporal fluctuations of the effective sound speed and wind speed are retrieved along different ray paths connecting an acoustic pulse source and several receivers. By using a coherence analysis of the fluctuations near spatially distanced ray turning points, the internal wave-associated fluctuations are filtered and their spatial characteristics (coherences, horizontal phase velocities, and spatial scales) are estimated. The capability of acoustic tomography in estimating wind shear near ground is shown. A possible mechanism describing the temporal modulation of the near-ground wind field by ducted internal waves in the troposphere is proposed. PMID:19206843

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Shear wave velocity and radial anisotropy along the Rio Grande rift

    NASA Astrophysics Data System (ADS)

    Li, A.; Fu, Y. V.

    2011-12-01

    We have determined shear wave velocity and radial anisotropy beneath the Rio Grande rift by analyzing ambient seismic noise recorded at the USArray Transportable Array in New Mexico. The results reveal a variable degree of lithosphere extension along the rift. Magma chambers are imaged as significant low velocity anomalies under the Albuquerque volcano in the shallow crust and beneath Socorro in the mid-crust. The central and southern rift is characterized by high velocity anomaly in the lower crust and uppermost mantle, reflecting residual materials after the extraction of melt, and by strong radial anisotropy with VSH > VSV in the mid to lower crust, implying horizontal alignment of crustal minerals due to the vigorous extensional deformation. However, low velocity anomaly and small radial anisotropy are observed in the rift in northern New Mexico, suggesting the presence of partial melt in the lower crust and uppermost mantle and a weak lithosphere extension.

  1. 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.

  2. Surface wave tomography of the western United States from ambient seismic noise: Rayleigh wave group velocity maps

    NASA Astrophysics Data System (ADS)

    Moschetti, M. P.; Ritzwoller, M. H.; Shapiro, N. M.

    2007-08-01

    We have applied ambient noise surface wave tomography to data that have emerged continuously from the EarthScope USArray Transportable Array (TA) between October 2004 and January 2007. Estimated Green's functions result by cross-correlating noise records between every station-pair in the network. The 340 stations yield a total of more than 55,000 interstation paths. Within the 5- to 50-s period band, we measure the dispersion characteristics of Rayleigh waves using frequency-time analysis. High-resolution group velocity maps at 8-, 16-, 24-, 30-, and 40-s periods are presented for the western United States. The footprint of the TA encloses a region with a resolution of about the average interstation spacing (70 km). Velocity anomalies in the group velocity maps correlate well with the dominant geological features of the western United States. Coherent velocity anomalies are associated with the Sierra Nevada, Peninsular, and Cascade Ranges, Great Valley, Salton Trough, and Columbia basins, the Columbia River flood basalts, the Snake River Plain and Yellowstone, and mantle wedge features associated with the subducting Juan de Fuca plate.

  3. Variations of the pole motion velocity and their correlation with variations of the E.A.M. function in the period 1985 - 1987.

    NASA Astrophysics Data System (ADS)

    Nastula, J.

    The variations of the pole motion velocity in the years 1085 - 87 have been analysed. The velocity of pole motion was computed from x, y of CSR and of IRIS data as well as from the atmospheric equatorial effective angular momentum (E.A.M.) function ? data. The correlation between the variations of pole motion velocity and the E.A.M. function has been investigated.

  4. 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 Ekstrm 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.

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

    NASA Astrophysics Data System (ADS)

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

    2000-04-01

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

  6. Laboratory measurement of elastic-wave velocity, associated dispersion, attenuation and particle resonance

    NASA Astrophysics Data System (ADS)

    Molyneux, Joseph Benedict

    Laboratory velocity measurements are an integral component of solid earth seismic investigations. Typically, ultrasonic measurements from centimeter scale plug samples are used to model large sections of the crust, core and mantle. By using the laboratory determined velocities, the seismic arrival time can more accurately calibrate spatial physical properties of the solid-earth. A semi-automated picking procedure is presented which determines the velocity measured from recorded ultrasonic pulses propagated through laboratory samples. This procedure is quicker and more consistent than the standard hand picking method, allowing larger data sets to be accurately investigated. Furthermore, a series of common velocity analyses are compared to the physical properties of phase and group velocity in an attenuating medium of glycerol saturated glass bead packs (Q ˜ 3). It is found that the velocity determined from the first break of the waveform (signal velocity) is up to 13% different from group and phase velocities. This illustrates that signal velocity is unsuitable to determine rock properties in highly attenuating media. Also, greater than 81% velocity dispersion is observed when the dominant propagating wavelength is comparable to the bead size. More surprisingly, on propagation of the broad band input signal a bimodal amplitude spectrum becomes apparent. The low frequency peak is consistent with standard attenuation, whereas the high frequency peak is related to resonance of either the constituent beads or the interbead fluid cavity. Such resonance partitions energy of the main incoming signal. This phenomenon represents a new and fundamental attenuation mechanism that should be considered in many wave-propagation experiments.

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

    NASA Astrophysics Data System (ADS)

    Svitek, Tom; Vavry?uk, Vclav; Lokaj?ek, Tom; Petrulek, Mat?j

    2014-12-01

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

  9. 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

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  11. 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

  12. Crustal P-wave velocity model for the central-western region of Mexico

    NASA Astrophysics Data System (ADS)

    Ochoa, J.; Escudero, C. R.; Perez, O. G.; Nunez-Cornu, F. J.

    2012-12-01

    Several studies require a p-wave velocity model to obtain accurate results moreover such models could provide an insight of the tectonic structure of the study area. Accordingly, in this study we estimate the crustal 3D p-wave velocity model for the Jalisco Block located at the central-western region of Mexico. The Jalisco Block is limited on its eastern side by the Colima and Tepic-Zacoalcos Rifts, and the Trans-Mexican Volcanic Belt; while on its western side it is limited by the Mesoamerican Trench. Cocos and Rivera plates are subducting beneath the Jalisco Block conforming a tectonically complex region. We used earthquakes occurring within the limits of lithosphere volume from which we want to estimate the velocity model. Such events were registered by the Mapping the Rivera Subduction Zone experiment (MARS) and the Seismic and Acelerometric Network of Jalisco (RESAJ). During MARS experiment 51broadband stations active from January 2006 to June 2007 were deployed while RESAJ by July of 2012consists of nine active stations however more stations will be deployed until reach 30 stations. The velocity model is estimated using the Fast Marching Tomography (FMTOMO) software. FMTOMO uses the Fast Marching Method (FMM) in order to solve the forward problem; the FMM is a numerical algorithm that tracks the interfaces evolution along a nodes narrow band, and travel times are updated solving the eikonal equation. Finally , the inverse problem is about adjusting the model parameters (interface depth, velocity, hypocenter location) in order to try to satisfy the observed data (travel times). We perform a resolution test using several events that show good resolution results up to a 60 km depth. We present a 3D p-wave velocity model, we compare our results within the MARS data with previous results for greater depths, approximately the upper mantle, finally we also present studies towards the northern portion of the Jalisco Block using the RESAJ data.

  13. 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.

  14. Temporal and spatial variations in density and velocity fields of the waters of Gareloch, Scotland

    NASA Astrophysics Data System (ADS)

    Lindsay, P.

    1996-12-01

    Spatial variations in the density and velocity fields have been observed in the Gareloch (Scotland) during surveys in 1987 1988 and 1993 1994. The variation of the density field has been analyzed on a variety of time scales from semidiurnal to seasonal in order to quantify effects caused by the forcing factors of tidal mixing, freshwater input, and wind. Initial results indicate that water density in the loch is controlled (to a major degree) by the freshwater input from runoff from the local catchment area and from freshwater entering on the flood tide from the Clyde Estuary. It is estimated that during winter periods the high freshwater flows from the rivers Leven and Clyde into the Clyde Estuary account for up to 75% of the freshwater creating the density structure in the loch. Analysis of long-term dissolved oxygen data reveals that major bottom water renewals occurred between July and January in the years 1987 1994. Major bottom water dissolved oxygen renewals have a general trend but during the year sporadic renewals can take place due to abnormal dry spells increasing the density of the water entering from the Clyde, or consistently strong winds from the north reducing stratification in the loch and producing better mixed conditions. Velocities vary spatially, with the highest velocities of up to 0.6 m s 1 being associated with the velocity jet effect at the constriction at the sill of the loch. Observed near-surface mid-loch velocities increased as the vertical density gradients in the upper layers increased. This indicates for the observed conditions that increased stratification in the upper layers inhibits the entrainment rate and hence rate of gain of thickness of the wind-driven surface layer, resulting in increased surface velocities for a given wind speed and direction. The main flow is concentrated in the upper 10 m and velocities below 10 m are low. Observed mean spring tide surface velocities are on average 30% greater than mean neap tide surface velocities.

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

    NASA Astrophysics Data System (ADS)

    Tataru, Dragos; Grecu, Bogdan; Zaharia, Bogdan

    2014-05-01

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

  16. Discovery of a surface wave velocity anomaly in the West Sea of South Korea

    NASA Astrophysics Data System (ADS)

    Cho, Kwang Hyun

    2014-01-01

    Imaging of Rayleigh- and Love-wave velocities is very important in detecting geophysical anomalies within the earth. Surface wave velocity imaging studies using ambient noise have provided enhanced and detailed images of velocity anomalies for sedimentary basins, hotspots, and volcanoes in various regions of the Earth (Yang et al., 2008). Cross-correlations of ambient noises observed from the Korea Meteorological Administration (KMA) seismic network provide the short-period Rayleigh-and Love-wave dispersion characteristics of the Korean Peninsula (Cho et al., 2007). Signal whitening and multiple-filter analysis are used to equalise power in signals from different times before noise processing, such as cross-correlation and stacking to extract group velocities from the estimated Green's functions, which are then used to image the spatially varying dispersion at periods between 1 and 5 s. The analysis method and data used in this paper are the same as those of Cho et al. (2007) except for the addition of the dataset of a new station, HUK. However, this paper notes that Rayleigh- and Love-wave velocity images in short periods show a very different group velocity image for the north-eastern area of the HUK station because additional data was analysed. This velocity anomaly corresponds with the residual anomaly of gravity tomography obtained in prior studies (Yu and Min, 2005; Kim and Oh, 2007). Our results show that a fracture zone concerning the Permo-Triassic collision (Choi et al., 2006; Kwon et al., 2009) exists below the north-eastern sea of the HUK station. In addition, recent studies (de Ridder and Dellinger, 2011; de Ridder and Biondi, 2013; Mordret et al., 2011, 2013a, 2013b, 2013c; Bussat and Kugler, 2011) regarding ambient noise tomography in hydro-carbon fields show that the anomaly might have resulted from the hydro-carbon reservoir. In the near future, the ambient noise tomography (ANT) method can replace seismic survey dominantly using body waves to find oil and gas reservoirs.

  17. 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 LambRayleigh 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 LambRayleigh velocity and that the shear wave attenuation is about 20% lower than the LambRayleigh attenuation. Results of numerical simulations in the frequency range 0500?Hz are presented. PMID:22225009

  18. Shear-wave velocity structure of the south-eastern part of the Iberian Peninsula from Rayleigh wave analysis

    NASA Astrophysics Data System (ADS)

    Corchete, V.; Chourak, M.

    2011-10-01

    In this study, we present the lithospheric structure of the south-eastern part of the Iberian Peninsula by means of a set of 2D images of shear velocity, for depths ranging from 0 to 50 km. This goal will be attained by means of the inversion of the Rayleigh wave dispersion. For it, the traces of 25 earthquakes occurred on the neighbouring of the study area, from 2001 to 2003, will be considered. These earthquakes have been registered by 11 broadband stations located on Iberia. All seismic events have been grouped in source zones to get an average dispersion curve for each source-station path. The dispersion curves have been measured for periods between 2 and 45 s, by combination of two digital filtering techniques: Multiple Filter Technique and Time Variable Filtering. The resulting set of source-station averaged dispersion curves has been inverted according to the generalized inversion theory, to get S-wave velocity models for each source-station path. Later, these models have been interpolated using the method of kriging, to obtain a 2D mapping of the S-wave velocity structure for the south-eastern part of Iberia. The results presented in this paper show that the techniques used here are a powerful tool to investigate the crust and upper mantle structure, through the dispersion analysis and its inversion to obtain shear velocity distributions with depth. By means of this analysis, principal structural features of the south-eastern part of Iberia, such as the existence of lateral and vertical heterogeneity in the whole study area, or the location of the Moho discontinuity at 30 km of depth (with an average S-velocity of uppermost mantle of 4.7 km/s), have been revealed. Other important structural features revealed by this analysis have been that the uppermost of Iberian massif shows higher velocity values than the uppermost of the Alpine domain, indicating that the massif is old and tectonically stable. The average velocity of the crust in Betic cordillera is of 3.5 km/s, while in the Iberian massif is 3.7 km/s. All these features are in agreement with the geology and other previous geophysical studies.

  19. 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

  20. On-line noninvasive one-point measurements of pulse wave velocity.

    PubMed

    Harada, Akimitsu; Okada, Takashi; Niki, Kiyomi; Chang, Dehua; Sugawara, Motoaki

    2002-12-01

    Pulse wave velocity (PWV) is a basic parameter in the dynamics of pressure and flow waves traveling in arteries. Conventional on-line methods of measuring PWV have mainly been based on "two-point" measurements, i.e., measurements of the time of travel of the wave over a known distance. This paper describes two methods by which on-line "one-point" measurements can be made, and compares the results obtained by the two methods. The principle of one method is to measure blood pressure and velocity at a point, and use the water-hammer equation for forward traveling waves. The principle of the other method is to derive PWV from the stiffness parameter of the artery. Both methods were realized by using an ultrasonic system which we specially developed for noninvasive measurements of wave intensity. We applied the methods to the common carotid artery in 13 normal humans. The regression line of the PWV (m/s) obtained by the former method on the PWV (m/s) obtained by the latter method was y = 1.03x - 0.899 (R(2) = 0.83). Although regional PWV in the human carotid artery has not been reported so far, the correlation between the PWVs obtained by the present two methods was so high that we are convinced of the validity of these methods. PMID:12541096

  1. The effect of superluminal phase velocity on electron acceleration in a powerful electromagnetic wave

    NASA Astrophysics Data System (ADS)

    Robinson, A. P. L.; Arefiev, A. V.; Khudik, V. N.

    2015-08-01

    In this paper, we examine the effect that electromagnetic dispersion has on the motion of an electron in a relativistically strong plane wave. We obtain an analytic solution for the electron momentum and check this solution against direct numerical integration of the equations of motion. The solution shows that even a relatively small difference between the phase velocity of the wave, vp, and the speed of light, c, can significantly alter the electron dynamics if the normalized wave amplitude a0 exceeds ?{2 c /(vp-c ) } . At this amplitude, the maximum longitudinal electron momentum scales only linearly with a0, as opposed to a02 . We also show that at this amplitude the impact of an accelerating longitudinal electric field and electron pre-acceleration is negated by the superluminous phase velocity of the wave. This has implications for the potential of Direct Laser Acceleration of electrons. We point out that electromagnetic dispersion can arise from both propagation in a plasma and from propagating the laser in what is effectively a wave-guiding structure, and that this latter source of dispersion is likely to be more significant.

  2. Circumferential-wave phase velocities for empty, fluid-immersed spherical metal shells.

    PubMed

    Uberall, Herbert; Ahyi, A Claude; Raju, P K; Bjrn, Irina K; Bjrn, Leif

    2002-12-01

    In earlier studies of acoustic scattering resonances and of the dispersive phase velocities of surface waves that generate them [see, e.g., Talmant et al., J. Acoust. Soc. Am. 86, 278-289 (1989) for spherical aluminum shells] we have demonstrated the effectiveness and accuracy of obtaining phase velocity dispersion curves from the known acoustic resonance frequencies. This possibility is offered through the condition of phase matching after each complete circumnavigation of these waves [Uberall et al., J. Acoust. Soc. Am. 61, 711-715 (1977)], which leads to a very close agreement of resonance results with those calculated from three-dimensional elasticity theory whenever the latter are available. The present investigation is based on the mentioned resonance frequency/elasticity theory connection, and we obtain comparative circumferential-wave dispersion-curve results for water-loaded, evacuated spherical metal shells of aluminum, stainless steel, and tungsten carbide. In particular, the characteristic upturn of the dispersion curves of low-order shell-borne circumferential waves (A or A0 waves) which takes place on spherical shells when the frequency tends towards very low values, is demonstrated here for all cases of the metals under consideration. PMID:12508991

  3. Solar cycle variation of gravity waves observed in OH airglow

    NASA Astrophysics Data System (ADS)

    Gelinas, L. J.; Hecht, J. H.; Walterscheid, R. L.; Reid, I. M.; Woithe, J.; Vincent, R. A.

    2013-12-01

    Airglow imaging provides a unique means by which to study many wave-related phenomena in the 80 to 100 km altitude regime. Two-dimensional image observations reveal quasi-monochromatic disturbances associated with atmospheric gravity waves (AGWs) as well as small-scale instabilities, often called ripples. Image-averaged temperature and intensity measurements can be used to study the response of the airglow layer to tides and planetary waves, as well as monitor longer-term climatological variations. Here we present results of low and mid-latitude OH airglow observations beginning near solar max of solar cycle 23 and continuing through solar max of cycle 24. Aerospace imagers deployed at Alice Springs (23o42'S, 133o53'E) and Adelaide (34o55'S, 138o36'E) have been operating nearly continuously since ~2001. The imagers employ filters measuring OH Meinel (6, 2) and O2 Atmospheric (0, 1) band emission intensities and temperatures, as well as atmospheric gravity wave parameters. The Aerospace Corporation's Infrared Camera deployed at Maui, HI (20.7N,156.3W), collected more than 700 nights of airglow images from 2002-2005. The camera measures the OH Meinel (4,2) emission at 1.6 um using a 1 second exposure at a 3 second cadence, which allows the study of AGW and ripple features over very short temporal and spatial scales. The camera was relocated to Cerro Pachon, Chile (30.1 S, 70.8 W) and has been operating continuously since 2010. Temperature, intensity and gravity wave climatologies derived from the two Australian airglow imagers span a full solar cycle (solar max to solar max). Emission intensities have been calibrated using background stars, and temperatures have been calibrated with respect to TIMED/SABER temperatures, reducing the influence of instrument degradation on the solar cycle climatology. An automated wave detection algorithm is used to identify quasi monochromatic wave features in the airglow data, including wavelength, wave period and propagation direction. Supplemental observations of OH emission brightness and gravity waves (including ripple climatology) at Maui (2002-2005) and Chile (2010-present) will be compared to the Australian observations.

  4. Seasonal variation of solitary wave properties in Lake Constance

    NASA Astrophysics Data System (ADS)

    Preusse, M.; Freisthler, H.; Peeters, F.

    2012-04-01

    The properties of internal solitary waves (ISWs) depend on the stratification of the water body. In most climatic regions the stratification in lakes and oceans varies during the year, and hence the properties of the ISWs can also be expected to change over the seasons. On the basis of a long-term temperature time series recorded over 6 years, this paper investigates seasonal changes in the characteristic properties of ISWs in Lake berlingen, a subbasin of Lake Constance. A large number of ISWs with amplitudes ranging from 3 m to 30 m were identified. More than 15% of the leading ISWs of a wave train were associated with density inversions, often indicating shear instabilities or trapped cores. For all waves the propagation depth and the value of a nonlinearity index nlp providing the degree of nonlinearity were determined, propagation depth being the rest height of the isotherm undergoing maximum displacement and nlp the ratio between wave amplitude and propagation depth. The index nlp was found to be a good parameter for predicting the occurrence of inversions. The statistical analysis of the wave properties derived from the observations revealed that the degree of nonlinearity of the ISWs changes with season. Complementary to the statistical analysis, the seasonally averaged ISW properties were compared with wave prototypes obtained numerically from the Dubreil-Jacotin-Long (DJL) and the stratified Korteweg-deVries (KdV) models. The simulations indicate that the typical stratification and its seasonal variation are responsible for the degree and the seasonality of nonlinearity of the ISWs.

  5. 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

  6. 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.

  7. Inversion of surface wave data for shear wave velocity profiles: Case studies of thick buried low-velocity layers in Malta

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    The islands composing the Maltese archipelago (Central Mediterranean) are characterised by a four layer sequence of limestones and clays, with the Lower Coralline Limestone being the oldest exposed layer. The hard Globigerina Limestone (GL) overlies this layer and is found outcropping in the eastern part of Malta and western part of Gozo. The rest of the islands are characterised by Upper Coralline Limestone (UCL) plateaus and hillcaps covering a soft Blue Clay (BC) layer which can be up to 75 m thick. Thus the BC layer introduces a velocity inversion in the stratigraphy, and makes the Vs30 parameter not always suitable for seismic microzonation purposes. Such a layer may still produce amplification effects, however would not contribute to the numerical mean of Vs in the upper 30m. Moreover, buildings are being increasingly constructed on this type of geological foundation. Obtaining the shear wave (Vs) profiles of the different layers around the islands is the first step needed for a detailed study of local seismic site response. A survey of Vs in each type of lithology and around the islands has never been undertaken. Array measurements of ambient noise using vertical geophones were carried out at six sites in Malta and one in Gozo, characterised by the buried low-velocity layer. The array was set up in an L-shaped configuration and the Extended Spatial Autocorrelation (ESAC) technique was used to extract Rayleigh wave dispersion curves. The effective dispersion curve obtained at all the sites exhibited a 'normal' dispersive trend (i.e. velocity decreases with increasing frequency) at low frequencies, followed by an inverse dispersive trend at high frequencies. Such a shape can be tentatively explained in terms of the presence of higher mode Rayleigh waves, which are generally present when a stiff layer overlies a softer layer. Additionally a series of three-component ambient noise measurements were taken at each of the sites and H/V curves obtained. The lithological sequence gives rise to a ubiquitous peak between 1 and 2 Hz which is observed in all the studied sites and is in agreement with studies previously done on the islands. The H/V curve and the Rayleigh wave dispersion curve were then jointly inverted using a genetic algorithm, considering higher modes, so that the Vs profiles are obtained. All the curves were well fitted and the 10 final profiles extracted in each process show a good agreement especially in the velocity and thickness of the BC layer, emphasizing the sensitivity of the curves to this layer. Regional differences were observed for the velocities in the UCL and BC, e.g. highly fractured UCL demonstrates a lower Vs. The Vs in the clay also varied according to the depth of burial of the clay, clearly increasing from a surface outcrop of BC to a deeply buried layer. This could essentially be linked to the effective pressure caused by the UCL overburden which makes the BC more compact and having a higher Vs. Comparisons are also done with one particular site in Malta where the BC layer is not present in the geological sequence.

  8. 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.; Ekstrm, 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.

  9. Robust angle-independent blood velocity estimation based on dual-angle plane wave imaging.

    PubMed

    Fadnes, Solveig; Ekroll, Ingvild Kinn; Nyrnes, Siri Ann; Torp, Hans; Lovstakken, Lasse

    2015-10-01

    Two-dimensional blood velocity estimation has shown potential to solve the angle-dependency of conventional ultrasound flow imaging. Clutter filtering, however, remains a major challenge for large beam-to-flow angles, leading to signal drop-outs and corrupted velocity estimates. This work presents and evaluates a compounding speckle tracking (ST) algorithm to obtain robust angle-independent 2-D blood velocity estimates for all beam-to-flow angles. A dual-angle plane wave imaging setup with full parallel receive beamforming is utilized to achieve high-frame-rate speckle tracking estimates from two scan angles, which may be compounded to obtain velocity estimates of increased robustness. The acquisition also allows direct comparison with vector Doppler (VD) imaging. Absolute velocity bias and root-mean-square (RMS) error of the compounding ST estimations were investigated using simulations of a rotating flow phantom with low velocities ranging from 0 to 20 cm/s. In a challenging region where the estimates were influenced by clutter filtering, the bias and RMS error for the compounding ST estimates were 11% and 2 cm/s, a significant reduction compared with conventional single-angle ST (22% and 4 cm/s) and VD (36% and 6 cm/s). The method was also tested in vivo for vascular and neonatal cardiac imaging. In a carotid artery bifurcation, the obtained blood velocity estimates showed that the compounded ST method was less influenced by clutter filtering than conventional ST and VD methods. In the cardiac case, it was observed that ST velocity estimation is more affected by low signal-to-noise (SNR) than VD. However, with sufficient SNR the in vivo results indicated that a more robust angle-independent blood velocity estimator is obtained using compounded speckle tracking compared with conventional ST and VD methods. PMID:26470038

  10. 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.

  11. Variational stereo imaging of oceanic waves with statistical constraints.

    PubMed

    Gallego, Guillermo; Yezzi, Anthony; Fedele, Francesco; Benetazzo, Alvise

    2013-11-01

    An image processing observational technique for the stereoscopic reconstruction of the waveform of oceanic sea states is developed. The technique incorporates the enforcement of any given statistical wave law modeling the quasi-Gaussianity of oceanic waves observed in nature. The problem is posed in a variational optimization framework, where the desired waveform is obtained as the minimizer of a cost functional that combines image observations, smoothness priors and a weak statistical constraint. The minimizer is obtained by combining gradient descent and multigrid methods on the necessary optimality equations of the cost functional. Robust photometric error criteria and a spatial intensity compensation model are also developed to improve the performance of the presented image matching strategy. The weak statistical constraint is thoroughly evaluated in combination with other elements presented to reconstruct and enforce constraints on experimental stereo data, demonstrating the improvement in the estimation of the observed ocean surface. PMID:23807444

  12. Age-specific nomogram of brachial-ankle pulse wave velocity in Japanese adolescents.

    PubMed

    Miyai, Nobuyuki; Utsumi, Miyoko; Gowa, Yoshiaki; Igarashi, Yuko; Miyashita, Kazuhisa; Takeda, Shintaro; Arita, Mikio

    2013-01-01

    To obtain data on the brachial-ankle pulse wave velocity (baPWV) distribution during adolescence, a total of 3215 Japanese adolescents ranging from 12 to 18 years of age were studied. The brachial-ankle pulse wave velocity increased substantially with age and was significantly higher in males than in females. Multivariate regression analysis revealed that age, weight, and systolic and diastolic blood pressures were the major determinants of baPWV for both genders. Age-specific centile curves of baPWV were constructed for males and females by regression curve analysis. The proposed distribution curves of baPWV and its derived cutoff values may allow the atherosclerotic risk profile among adolescents of different ages to be more precisely estimated. PMID:22680041

  13. Correlations between ultrasonic guided wave velocities and bone properties in bovine tibia in vitro.

    PubMed

    Lee, Kang Il; Yoon, Suk Wang

    2012-05-01

    Correlations between ultrasonic guided wave velocities and bone properties were investigated in bovine tibia in vitro. The velocities of the first arriving signal and the slow guided wave, termed V(FAS) and V(SGW), along the long axis of the tibia were measured at 200 kHz in 20 bovine tibiae using the axial transmission technique. V(FAS) yielded significant negative correlation coefficients of -0.54 to -0.66 with the bone properties. In contrast, V(SGW) yielded strong positive correlation coefficients of 0.68-0.84. The best univariate predictor of V(FAS) and V(SGW) was the cortical thickness yielding adjusted squared correlation coefficients of 0.41 and 0.69, respectively. PMID:22559455

  14. Influence of pressure on permeability and elastic wave velocities in macro- and micro-fractured rock

    NASA Astrophysics Data System (ADS)

    Meredith, Philip; Nara, Yoshitaka; Yoneda, Tetsuro; Kaneko, Katsuhiko

    2010-05-01

    Long-term integrity is required for many sub-surface structures excavated in the rock mass; such as repositories for radioactive wastes and caverns for the storage of liquid petroleum gas and natural gas. An essential requirement for long-term integrity is to retard the migration of fluids into and through these structures. In crustal rocks, fracture and pore networks provide the principal pathways for fluid flow. However, if fractures and pores are closed or sealed, the migration of fluids can be retarded. Thus it is important to study the process of fracture and pore closure. Here, we report changes in the fluid permeability and P- and S-wave velocities of intact, macro-fractured, and micro-fractured rock sample subjected to elevated effective pressures. In order to investigate the influence of pressure on the closure of macro-fractures and micro-fractures, we used a rock sample with no visible pre-existing cracks and very low initial permeability. For this reason, Seljadur basalt (SB) from Iceland was chosen as the sample material. SB is a fresh, columnar-jointed, intrusive basalt with a porosity of 4 % and no visible microcracks. Permeability was measured in a servo-controlled permeameter using the steady-state flow method. The permeameter is equipped with transducers that allow the simultaneous measurement of P- and S-wave velocities. The wave velocities were measured by the ultrasonic transmission method. Measurements of permeability and elastic wave velocities were first made on intact samples. The Brazil test technique was then used to split the samples in half to provide macro-fractured sample for further testing. Measurments of permeability and elastic wave velocities were then made on the macro-fractured sample in order to investigate the effect of fracture closure. Then, we heated the macro-fractured sample at 800 degree Celsius in order to produce micro-fractures in the sample and conducted further measurements of permeability and wave velocities. It was shown that the permeability of intact SB was low and remains essentially constant over the whole effective pressure range. By contrast, the permeability of the macro-fractured SB was initially much higher, but decreased clearly as effective pressure was increased and the fracture became closed. The permeability of the macro- and micro-fractured SB also decreased with increasing the pressure. The permeability of the macro- and micro-fractured SB was similar to that of the macro-fractured SB under low pressure. This result indicates that the open macro-fractures dominate the permeability under low pressure. On the other hand, the permeability of the macro-and micro-fractured SB was higher than that of the macro-fractured SB under high pressure. This indicates that the macro-fractures with low aspect ratio close easily and open micro-fractures with high aspect ratio become dominant to the permeability with increasing the pressure. The difference in the wave velocities between intact, macro-fractured, and macro- and micro-fractured samples decreased with increasing effective pressure, tracking the closure of the fractures. Specifically, the increase of S-wave velocity vibrating nornal to the macro-fractures was clear with increasing the pressure, which indicates the closure of fracture. Overall, results in this study demonstrate the importance of the closure of fractures to increase the shielding ability of rock and to retard the migration of fluids into and through structres in a rock mass.

  15. Three-dimensional P and S wave velocity structures of southern Peru and their tectonic implications

    NASA Technical Reports Server (NTRS)

    Cunningham, Paul S.; Roecker, Steven W.; Hatzfeld, Denis

    1986-01-01

    Arrival times of compressional and shear (S) waves from microearthquakes recorded in 1981 by an 18-station regional array are used to study the three-dimensional velocity structure of the crust and upper mantle of the central Andes. The data suggest a crustal thickness of about 40 km beneath the coast, increasing to about 70 km beneath the Cordillera Occidental. The inverse correlation between the dip in the Moho and the dip of the slab may indicate a broad-scale causal relation between the two. S wave velocities in the mantle between 70 and 130 km depth above the 30-degree dipping slab are low, possibly indicating the presence of a partially melted asthenosphere that may be responsible for the magmatic activity recorded in southern Peru.

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

    NASA Astrophysics Data System (ADS)

    Cals, 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.

  17. P wave seismic velocity and Vp/Vs ratio beneath the Italian peninsula from local earthquake tomography

    NASA Astrophysics Data System (ADS)

    Scafidi, Davide; Solarino, Stefano; Eva, Claudio

    2009-02-01

    We investigate the P wave velocity structure and the Vp/Vs ratio beneath the Italian peninsula down to 100 and 60 km depth respectively by seismic travel time tomography. We invert data provided by the International Seismological Centre (ISC) (1997-2005), making use of some alternative strategies for the travel time approach in a well constrained and worldwide adopted code (SIMULPS). Resolution for the different layers is discussed and sensitivity analyses are performed through test inversions to explore the resolution characteristics of the model at different spatial scales. The resulting tomographic images provide a detailed sketch of the P wave anomalies, clearly showing, among the other features, the shape of the Ivrea body in the Western Alps, the upwelling of the oceanic crust in the Ligurian Sea and the slab under the Calabrian arc. They are less informative for the Vp/Vs ratio. Nevertheless, some features are very interesting and deserve further investigation like the anomalous decrease of the Vp/Vs ratio under the Ligurian Sea or the variations of the Vp/Vs ratio calculated in the first 10 km depth of the Apenninic region with respect to the lower values of the Alpine region at the same depth. The tomographic cross sections reveal a continuous superposition of two kinds of crusts (transitional over Adriatic) all along the peninsula but do not show any slab, intended as a clear, vertical downgoing high velocity material in either the northern or central Apennines.

  18. Correlation between arterial stiffness and coronary flow velocity reserve in subjects with pulse wave velocity >1400?cm/s.

    PubMed

    Liu, Jinbo; Wang, Ying; An, Huijie; Liu, Jia; Wei, Jinru; Wang, Hongyu; Wang, Guang

    2016-01-01

    Brachial-ankle pulse wave velocity (ba-PWV) is an independent predictor for cardiovascular events. Coronary flow velocity reserve (CFVR) provides important information for coronary endothelial function. In the present study, we investigated the possible relationship between PWV and CFVR, especially in subjects with PWV?>?1400?cm/s. Seventy five subjects were divided into two groups based on baPWV value (baPWV?>?1400?cm/s versus baPWV??1400?cm/s than in patients with baPWV??1400?cm/s (r?=?-0.42, p??1400?cm/s, and baPWV was independently associated with CFVR. PMID:26362523

  19. 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.

  20. Elastic Wave Velocity Measurements on Mantle Peridotite at High Pressure and Temperature

    NASA Astrophysics Data System (ADS)

    Mistler, G. W.; Ishikawa, M.; Li, B.

    2002-12-01

    With the success of conducting ultrasonic measurements at high pressure and high temperature in large volume high pressure apparatus with in-situ measurement of the sample length by X-ray imaging, it is now possible to measure elastic wave velocities on aggregate samples with candidate compositions of the mantle to the conditions of the Earth's transition zone in the laboratory. These data can be directly compared with seismic data to distinguish the compositional models in debate. In this work, we carried out velocity measurements on natural peridotite KLB-1 at the conditions of the Earth's upper mantle. Fine powered sample of natural KLB-1 was used as starting material. Specimens for ultrasonic measurements were hot-pressed and equilibrated at various pressure and temperature conditions along geotherm up to the transition zone. The recovered samples were characterized with density measurement, X-ray diffraction and microprobe analysis. Bench top P and S wave velocities of KLB-1 sample sintered at 3-4 GPa and 1400 degree centigrade showed a very good agreement with the VRH average of pyrolite. High pressure and high temperature measurements was conducted up to 7 GPa and 800 degree centigrade using ultrasonic interferometric method in a DIA-type high pressure apparatus in conjunction with X-ray diffraction and X-ray imaging. The utilization of X-ray imaging technique provides direct measurements of sample lengths at high pressure and high temperature, ensuring a precise determination of velocities. The results of P and S wave velocities at high pressure and high temperature as well as their comparison with calculated pyrolite model will be presented.

  1. Phenomenological model of propagation of the elastic waves in a fluid-saturated porous solid with nonzero boundary slip velocity.

    PubMed

    Tsiklauri, David

    2002-09-01

    It is known that a boundary slip velocity starts to play an important role when the length scale over which the fluid velocity changes approaches the slip length, i.e., when the fluid is highly confined, for example, fluid flow through porous rock or blood vessel capillaries. Zhu and Granick [Phys. Rev. Lett. 87, 096105 (2001)] have recently experimentally established the existence of a boundary slip in a Newtonian liquid. They reported typical values of the slip length of the order of few micrometers. In this light, the effect of introduction of the boundary slip into the theory of propagation of elastic waves in a fluid-saturated porous medium formulated by Biot [J. Acoust. Soc. Am. 28, 179-191 (1956)] is investigated. Namely, the effect of introduction of boundary slip upon the function F(kappa) that measures the deviation from Poiseuille flow friction as a function of frequency parameter kappa is studied. By postulating phenomenological dependence of the slip velocity upon frequency, notable deviations in the domain of intermediate frequencies in the behavior of F(kappa) are introduced with the incorporation of the boundary slip into the model. It is known that F(kappa) crucially enters Biot's equations, which describe dynamics of fluid-saturated porous solid. Thus, consequences of the nonzero boundary slip by calculating the phase velocities and attenuation coefficients of both rotational and dilatational waves with the variation of frequency are investigated. The new model should allow one to fit the experimental seismic data in circumstances when Biot's theory fails, as the introduction of phenomenological dependence of the slip velocity upon frequency, which is based on robust physical arguments, adds an additional degree of freedom to the model. In fact, it predicts higher than the Biot's theory values of attenuation coefficients of the both rotational and dilatational waves in the intermediate frequency domain, which is in qualitative agreement with the experimental data. Therefore, the introduction of the boundary slip yields threefold benefits: (1) better agreement of theory with experimental data since the parametric space of the model is larger (includes effects of boundary slip); (2) the possibility to identify types of porous medium and physical situations where boundary slip is important; and (3) constrain model parameters that are related to the boundary slip. PMID:12243170

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

    NASA Astrophysics Data System (ADS)

    Farra, Vronique; Wittlinger, Grard

    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.

  3. 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.

  4. Estimation of local pulse wave velocity using arterial diameter waveforms: Experimental validation in sheep

    NASA Astrophysics Data System (ADS)

    Graf, S.; Craiem, D.; Barra, J. G.; Armentano, R. L.

    2011-12-01

    Increased arterial stiffness is associated with an increased risk of cardiovascular events. Estimation of arterial stiffness using local pulse wave velocity (PWV) promises to be very useful for noninvasive diagnosis of arteriosclerosis. In this work we estimated in an instrumented sheep, the local aortic pulse wave velocity using two sonomicrometry diameter sensors (separated 7.5 cm) according to the transit time method (PWVTT) with a sampling rate of 4 KHz. We simultaneously measured aortic pressure in order to determine from pressure-diameter loops (PWVPDLoop), the "true" local aortic pulse wave velocity. A pneumatic cuff occluder was implanted in the aorta in order to compare both methods under a wide range of pressure levels. Mean pressure values ranged from 47 to 101 mmHg and mean proximal diameter values from 12.5. to 15.2 mm. There were no significant differences between PWVTT and PWVPDLoop values (45143 vs. 44748 cm/s, p = ns, paired t-test). Both methods correlated significantly (R = 0.81, p<0.05). The mean difference between both methods was only -429 cm/s, whereas the range of the limits of agreement (mean 2 standard deviation) was -61 to +53 cm/s, showing no trend. In conclusion, the diameter waveforms transit time method was found to allow an accurate and precise estimation of the local aortic PWV.

  5. Variational structure of inverse problems in wave propagation and vibration

    SciTech Connect

    Berryman, J.G.

    1995-03-01

    Practical algorithms for solving realistic inverse problems may often be viewed as problems in nonlinear programming with the data serving as constraints. Such problems are most easily analyzed when it is possible to segment the solution space into regions that are feasible (satisfying all the known constraints) and infeasible (violating some of the constraints). Then, if the feasible set is convex or at least compact, the solution to the problem will normally lie on the boundary of the feasible set. A nonlinear program may seek the solution by systematically exploring the boundary while satisfying progressively more constraints. Examples of inverse problems in wave propagation (traveltime tomography) and vibration (modal analysis) will be presented to illustrate how the variational structure of these problems may be used to create nonlinear programs using implicit variational constraints.

  6. 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.

  7. Intracycle velocity variation of the body centre of mass in front crawl.

    PubMed

    Figueiredo, P; Kjendlie, P L; Vilas-Boas, J P; Fernandes, R J

    2012-04-01

    Our aim was to determine the 3-dimensional intracycle velocity variation (IVV) of the body centre of mass during a 200-m front crawl event, and to analyse its relation with the segmental hand kinematics and the velocity (v) changes. 10 high-level male swimmers performed a 200-m front crawl swim at maximal intensity. 2 above- and 4 underwater cameras were used to record one complete non-breathing cycle for each 50-m lap, and APASystem was used for imaging processing. The coefficient of variation was calculated to assess the IVV in the horizontal (x), vertical (y), and lateral (z) axes; hand kinematics was also computed. IVV remained stable across the 200 m, and significant correlations were found between vx and vmaxx (r=0.55), vminx (r = 0.68), IVVx (r = -0.45), and IVVz (r = -0.45) (all p?0.01). In addition, IVVx was correlated with the backward horizontal amplitude normalized to stroke length (r = 0.54), IVVy with hand angular velocity (r = -0.40), and IVVz with the elbow angle range in the pull phase (r = - 0.37) (all p<0.05). This study shows the stability of the IVV (x,y,z), the inverse relation of the IVV (x, z) with v, the direct relation of the vmaxx and vminx with v, and the influence of the hand kinematics in the IVV. PMID:22318557

  8. 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.

  9. 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.

  10. On-chip laser Doppler vibrometer for arterial pulse wave velocity measurement

    PubMed Central

    Li, Yanlu; Segers, Patrick; Dirckx, Joris; Baets, Roel

    2013-01-01

    Pulse wave velocity (PWV) is an important marker for cardiovascular risk. The Laser Doppler vibrometry has been suggested as a potential technique to measure the local carotid PWV by measuring the transit time of the pulse wave between two locations along the common carotid artery (CCA) from skin surface vibrations. However, the present LDV setups are still bulky and difficult to handle. We present in this paper a more compact LDV system integrated on a CMOS-compatible silicon-on-insulator substrate. In this system, a chip with two homodyne LDVs is utilized to simultaneously measure the pulse wave at two different locations along the CCA. Measurement results show that the dual-LDV chip can successfully conduct the PWV measurement. PMID:23847745

  11. Verification of correctness of using real part of complex root as Rayleigh-wave phase velocity with synthetic data

    NASA Astrophysics Data System (ADS)

    Pan, Yudi; Xia, Jianghai; Zeng, Chong

    2013-01-01

    High-frequency (? 2 Hz) Rayleigh-wave phase velocities have been utilized to determine shear-wave velocities in near-surface geophysics since the early 1980s. One of the key steps is to calculate theoretical dispersion curves of an earth model. When the earth model contains a low-velocity half-space, however, some roots of the dispersion equation turn out to be complex numbers, which makes phase velocities disappear at some frequencies. When encountering this situation, the common practice is to append an additional high velocity layer as the half-space to the model to make the roots real or use the real parts of complex roots as Rayleigh-wave phase velocities. The correctness of the first method has been verified. The correctness of the second method, however, remains to be unproved. We use synthetic data generated by numerical modeling of the wave equation to verify the correctness of the second method. In this paper, we firstly discuss the reasons that only complex numbers of the dispersion equation exist at some frequencies when an earth model contains a low velocity half-space. Then we discuss how the nearest offset affects a synthetic model and recommend an optimal nearest offset in generating synthetic data that are close to real-world situations. Several synthetic models are used to verify correctness of using real parts of complex roots as Rayleigh-wave phase velocities when an earth model contains a low velocity layer as the half-space.

  12. Shear Wave Velocity Imaging over Quick Clays Using Multiple Seismic Methods

    NASA Astrophysics Data System (ADS)

    Comina, C.; Krawczyk, C. M.; Polom, U.; Socco, L. V.

    2014-12-01

    Quick-clays are characterized by an highly unstable particle structure. This structure is usually caused by freshwater leaching of the original high salinity pore water generated by the former marine deposition environment. Given this instability, the clay structure can easily collapse leading to landslides of varying destructiveness. It is, therefore, of major importance to detect the presence of quick-clays. While resistivity based methodologies are commonly used to detect them (lower conductivity of the leached interstitial fluid in respect to the original one) there are also some evidences that leaching can result in a reduction of the undisturbed shear strength of these clays. Multiple integrated shear wave velocity based seismic methods (mainly SH seismic reflection and Love wave dispersion data) have been therefore applied in a case study to evaluate the potential of shear wave velocity imaging for detecting quick clays. An area near the Göta River in southwest Sweden, which was the scene of a quick clay landslide about 40 years ago, was chosen as experimental site. High-resolution SH reflection data were acquired in the area, as part of a joint project studying clay-related landslides. Seismic reflection processing has evidenced several geologically interesting interfaces related to the presence of quick clays (locally confirmed by boreholes), and sand-gravelly layers strongly contributing to water circulation within them. Dispersion data have been extracted along one of the reflection arrays with a Gaussian windowing approach, and data have been inverted with a Laterally Constrained Inversion using a priori information coming from the seismic reflection imaging. The inversion of dispersion curves has evidenced, in some portion of the seismic line, the presence of a low velocity layer most probably correlatable with quick clays. Even given the limited dispersion information extracted from the dataset, and the not yet completely understood shear wave velocity properties of quick clays, our work has evidenced the potential of the proposed approach for a more comprehensive imaging of the shear wave velocity distribution. This could be a valuable approach in quick clay identification in general.

  13. Seasonal and interannual variations in geostrophic velocity in the Middle Atlantic Bight

    NASA Astrophysics Data System (ADS)

    Dong, Shenfu; Kelly, Kathryn A.

    2003-06-01

    More than 6 years of measurements from the TOPEX/POSEIDON (T/P) altimeter are used to study the seasonal and interannual variations of the geostrophic velocity anomalies in the Middle Atlantic Bight region. Geostrophic velocities from T/P data are compared with the simultaneous low-pass filtered current meter data. The correlations are all above 95% significance for the three current meter observations at the 1000-m, 2210-m, and 2990-m isobaths. The seasonal mean geostrophic currents from 63-75W show coherent variations along isobaths, with seasonal reversals: toward the southwest during the winter and toward the northeast during the summer. The EOF analysis indicates that the seasonal reversals disappeared during 1996. This disruption is part of the intensification of the slope sea gyre and is related to the southward shift of the Gulf Stream, which acts as the boundary between the subpolar and subtropical gyres. The Gulf Stream moved farther south during 1996-1998. The variations in the Gulf Stream position may be caused by the wind stress/wind stress curl change.

  14. Brachial artery peak velocity variation to predict fluid responsiveness in mechanically ventilated patients

    PubMed Central

    2009-01-01

    Introduction Although several parameters have been proposed to predict the hemodynamic response to fluid expansion in critically ill patients, most of them are invasive or require the use of special monitoring devices. The aim of this study is to determine whether noninvasive evaluation of respiratory variation of brachial artery peak velocity flow measured using Doppler ultrasound could predict fluid responsiveness in mechanically ventilated patients. Methods We conducted a prospective clinical research in a 17-bed multidisciplinary ICU and included 38 mechanically ventilated patients for whom fluid administration was planned due to the presence of acute circulatory failure. Volume expansion (VE) was performed with 500 mL of a synthetic colloid. Patients were classified as responders if stroke volume index (SVi) increased ? 15% after VE. The respiratory variation in Vpeakbrach (?Vpeakbrach) was calculated as the difference between maximum and minimum values of Vpeakbrach over a single respiratory cycle, divided by the mean of the two values and expressed as a percentage. Radial arterial pressure variation (?PPrad) and stroke volume variation measured using the FloTrac/Vigileo system (?SVVigileo), were also calculated. Results VE increased SVi by ? 15% in 19 patients (responders). At baseline, ?Vpeakbrach, ?PPrad and ?SVVigileo were significantly higher in responder than nonresponder patients [14 vs 8%; 18 vs. 5%; 13 vs 8%; P < 0.0001, respectively). A ?Vpeakbrach value >10% predicted fluid responsiveness with a sensitivity of 74% and a specificity of 95%. A ?PPrad value >10% and a ?SVVigileo >11% predicted volume responsiveness with a sensitivity of 95% and 79%, and a specificity of 95% and 89%, respectively. Conclusions Respiratory variations in brachial artery peak velocity could be a feasible tool for the noninvasive assessment of fluid responsiveness in patients with mechanical ventilatory support and acute circulatory failure. Trial Registration ClinicalTrials.gov ID: NCT00890071 PMID:19728876

  15. On the velocity variation in atmospheric pressure plasma plumes driven by positive and negative pulses

    SciTech Connect

    Xiong, Z.; Lu, X.; Xian, Y.; Jiang, Z.; Pan, Y

    2010-11-15

    To better understand the variation in the ''plasma bullet'' velocity, the dynamics of an atmospheric pressure plasma plume driven by positive and negative pulses are investigated in detail. It is found that, before the plasma exits the nozzle, the plasma propagates at a speed of about 30 km/s for both positive and negative pulses. As soon as the plasma exits the nozzle, the plasma propagation speed increases dramatically for both cases. The peak velocity for the case of the positive pulse is much higher than that of the negative pulse, it is approximately 150 km/s and 70 km/s, respectively. According to the optical emission spectra, the acceleration behavior of the plasma bullet when it exits the nozzle is due to the increase in the N{sub 2}{sup +} concentration.

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

    NASA Astrophysics Data System (ADS)

    Barkalova, T.; Kuzikov, S.

    2009-04-01

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

  17. Anisotropic Love and Rayleigh wave phase velocity maps for central to northern Europe

    NASA Astrophysics Data System (ADS)

    Soomro, R. A.; Weidle, C.; Lebedev, S.; Cristiano, L.; Behrmann, J. H.; Meier, T. M.

    2014-12-01

    We processed all freely available data in Europe, from 1990 to October 2013, obtained through theEuropean Integrated data archive (EIDA) to calculate surface wave phase velocity maps. With anautomated inter-station method, we have obtained highly consistent, high quality, very broad band(10 s ->200 s), phase velocity measurements for both Love and Rayleigh waves. We performedmore than 8 million cross correlations to obtain around 1.5 million individual phase velocitymeasurements. Path-wise averaging resulted in more than 22,000 average dispersion curves fordifferent inter-station paths, with an average standard deviation of less than 1.5%. These averagephase velocity dispersion curves are then used to obtain Love and Rayleigh wave phase velocitymaps. We carried out number of resolutions tests to check the reliability of the isotropic and anisotropiccomponents of the maps. A quasi checkerboard test shows the areas of the best sampling, while thereliability of azimuthal anisotropy is tested using a synthetic model with fast directions at 90 tothose in the actual phase velocity maps. The results of the tests show that we obtain a lateralresolution from 100 to 200 km. At shortest periods (10 s) the isotropic maps clearly image the Central European basin system(CEBS) extending from north German basin in the north towards the Polish basin further southeast.In southern Central Europe low velocities are associated with thick sedimentary cover in the Pobasin and in the Pannonian basin. At these periods, there is a N-S trend of the anisotropy in thenorth, and E-W trend in the Alpine region in south, and in the Pannonian basin. Remarkably,isotropic velocities of the central European mantle lithosphere show no imprint of the Caledonianand Variscan sutures. In the uppermost mantle, a sharp lateral gradient at the Teisseyre-Tornquist-Zone (TTZ) is observed as compared to a more gradual lateral transition across the Sorgenfrei-Tornquist-Zone (STZ). We denote the shallow asthenosphere south west of the TTZ as Tornquist-Teisseyre-Asthenosphere (TTA), analogous to the TTZ. A pronounced high velocity anomaly in thewestern Alps is interpreted as subducting European lithosphere. At 200 s period, a high velocityanomaly beneath the Pannonian basin, may be due to a slab subducting into the Mantle TransitionZone (MTZ).

  18. 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.

  19. Multi-channel analysis of surface waves MASW of models with high shear-wave velocity contrast

    USGS Publications Warehouse

    Ivanov, J.; Miller, R.D.; Peterie, S.; Zeng, C.; Xia, J.; Schwenk, T.

    2011-01-01

    We use the multi-channel analysis of surface waves MASW method to analyze synthetic seismic data calculated using models with high shear-wave velocity Vs contrast. The MASW dispersion-curve images of the Rayleigh wave are obtained using various sets of source-offset and spread-size configurations from the synthetic seismic data and compared with the theoretically calculated fundamental- and higher-mode dispersion-curves. Such tests showed that most of the dispersion-curve images are dominated by higher-mode energy at the low frequencies, especially when analyzing data from long receiver offsets and thus significantly divert from numerically expected dispersion-curve trends, which can lead to significant Vs overestimation. Further analysis showed that using data with relatively short spread lengths and source offsets can image the desired fundamental-mode of the Rayleigh wave that matches the numerically expected dispersion-curve pattern. As a result, it was concluded that it might be possible to avoid higher-mode contamination at low frequencies at sites with high Vs contrast by appropriate selection of spread size and seismic source offset. ?? 2011 Society of Exploration Geophysicists.

  20. Lateral Variations of Coda Wave Attenuation in the Alps

    NASA Astrophysics Data System (ADS)

    Mayor, J.; Margerin, L.; Calvet, M.; Traversa, P.

    2014-12-01

    We explore lateral variations of coda wave attenuation in the French Alps and surrounding regions. The area of investigation extends from the Rhine Graben in the north, to the northern Apennine Range in the south, and includes the Eastern and Western Alps. Following the classical work of Aki and Chouet (1975), coda wave attenuation has been characterized by measuring the coda quality factor of short-period S waves (Qc). We have selected about 2000 weak to moderate earthquakes, with magnitudes ranging from 3 to 5. Waveform data recorded by permanent seismic networks have been collected at the ORFEUS data center through the ArcLink protocol. Qc has been measured in five frequency bands [1-2], [2-4], [4-8], [8-16], [16-32] Hz, by applying a simple linear regression to the smooth energy envelopes of seismograms in the time domain. Various choices of coda window length (Lw), and coda onset time (tw, as measured from the origin time) have been tested to ensure that our measurements are free from any systematic effects of lapse-time dependence in the range of epicentral distance considered. The optimal choice, which simultaneously maximizes the geographical coverage and minimizes the measurement biases, is obtained for Lw=50s and tw=70s, for epicentral distances smaller than 180 km. The map of Qc is obtained by discretizing the Alpine region into pixels of dimension (20km x 20km). For each source/receiver pair, the estimated value of Qc is distributed along the direct ray path. An average over all paths that cross an individual pixel is performed to obtain the local value of Qc. A spatial smoothing over an area covering a square of 9 pixels is subsequently applied. The maps of Qc display strong lateral variations of attenuation in the Alpine area. At all frequencies, the ratio between the lowest and largest value of Qc is typically larger than 2. The attenuation pattern is complex but relatively independent of frequency. Some geological formations such as the Upper Rhine Graben and the eastern Alps show up clearly on the maps and systematically exhibit lower attenuation than the Po Valley and the Apennines. The typical scale of the spatial variations of the coda quality factor is of the order of 100km, which suggests rapid lateral variation of attenuation properties in the crust.

  1. ConsoliTest - Using Surface Waves for Estimating Shear-Wave Velocities in the Dutch Subsurface

    NASA Astrophysics Data System (ADS)

    Westerhoff, Rogier; van Hoegaerden, Vincent; Brouwer, Jan; Rijkers, Richard

    ConsoliTest is a geophysical method for estimating geomechanical parameters of the shallow subsurface. The procedure is based on the MASW method (Park et al, 1999) and has additional verification and validation modules. The Dutch subsurface can consist of an alternation of very stiff layers and weak layers. In these types of soils many non-standard waveforms are generated, which cannot be inverted properly by using only the MASW algorithm. By describing two case-studies we explain the developments at TNO-NITG for creating a surface wave method designed for the Dutch subsurface.

  2. 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)

  3. 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.

  4. 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 ɛ = 0.07-0.09, superposed on a background exponential PSDF (a = 3 km, ɛ = 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.

  5. 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-sh