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1

Measurement variation of aortic pulse wave velocity in the elderly  

Microsoft Academic Search

Accurate and reproducible measures are required to study arterial stiffness in human populations. The reproducibility of aortic pulse wave velocity was evaluated in 14 participants from a population-based study of cardiovascular disease in the elderly. Three data files were collected per participant by each of two sonographers and files were read by two readers. Seven of the 14 participants returned

Kim Sutton-Tyrrell; Rachel H. Mackey; Richard Holubkov; Peter V. Vaitkevicius; Harold A. Spurgeon; Edward G. Lakatta

2001-01-01

2

Variation of Surface - Acoustic - Wave Velocity Produced by Ion Implantation  

Microsoft Academic Search

The elastic and piezoelectric properties of substrates used in SAW devices have been changed by ion implantation. A crystalline structure is perturbed by implanted ions and an amorphous region can be obtained. The velocities of the Rayleigh waves on the implanted and unimplanted surfaces are different. The thickness of the perturbed layer depends on the kind of ion and substrate,

P. Hartemann; M. Morizot

1974-01-01

3

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

PubMed

Experimentally measured Lamb wave group velocities in composite materials with anisotropic characteristics are not the same as the theoretical group velocities which is calculated with the Lamb wave dispersion equation. This discrepancy arises from the fact that the angle between the group velocity direction and the phase velocity direction in anisotropic materials exists. Wave propagation in a composite material with anisotropic characteristics should be considered with respect to magnitude correction in addition to direction correction. In this study, S0 mode phase velocity dispersion curves are depicted with the variation of degree with respect to the fiber direction using a Lamb wave dispersion relation in the unidirectional, bidirectional, and quasi-isotropic composite plates. Slowness surface is sketched by the reciprocal value of the phase velocity curves. The magnitude and direction of the group velocity could be calculated from the slowness surface. The recalculated group velocities with consideration of the magnitude and direction from the slowness surface are compared with experimentally measured group velocities. The proposed method shows good agreements with theoretical and experimental results. PMID:17881029

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

2007-08-06

4

Short wave-length variation of seismic velocity anomalies associated with stagnant slab  

NASA Astrophysics Data System (ADS)

When mineral physicists discuss mantle properties associated with stagnant slab referring to seismological studies, they focus on long wave-length characteristics provided by seismic tomography studies. In this sense the gap between seismological studies and mineral physics is still large to explore mantle properties. On the other hand, triplicated regional body waves are highly sensitive to the transition zone structure and have ample information regarding seismic velocity anomaly and the discontinuity depth associated with stagnant cold slab. We present results of regional waveform modeling using data from deep focus earthquakes (Mw?5.5, depth?300 km) that occurred in the Kurile to Izu-Bonin subduction zones during the period of 1990 to 2005. Here the range of regional distance is considered up to 32 deg where triplication can be observed from a deep focus event due to the high velocity anomaly (HVA) and depression of the discontinuity depth. After examining the data quality, regional waveform data of about 50 events were selected for analysis. The body waves which sampled the region with apparent stagnant slab strongly, can be modeled by model M3.11 (HVA in the transition zone with depression of the discontinuity to 690 km, Tajima and Grand, 1998), model M2.0 (HVA similar to M3.11 but without broad depression of the discontinuity) or a model with their slight modifications if not by iasp91 (Kennett and Engdahl, 1991). Structural variation in the transition zone has been determined in terms of seismic model M3.11 for the Kuriles subduction zone, M2.0 for the region beneath the Japan sea and the northeastern rim of the Eurasian plate or others. The structural boundaries are sharp and distinct showing steep gradient of velocity anomaly between the regions of different structure. The variation of the discontinuity depths indicates lateral variation of temperature beneath the flattened slab. We also found anomalously broadened P waveforms that propagated through the vicinity of structural boundaries. We postulate that the broadened P waves are SV-to-P converted waves in a narrow zone of low velocity anomaly (or a high Poisson's ratio of ~ 0.32) associated with stagnant slab.

Nakagawa, T.; Tajima, F.

2006-12-01

5

Surface Wave Velocities Across Arabia  

Microsoft Academic Search

The group-velocity distribution beneath the Arabian Plate is investigated using Love and Rayleigh waves. We obtained a balanced path coverage using seismograms generated by earthquakes located along the plate boundaries. We measured Love- and Rayleigh-wave group-velocity dispersion using multiple filter analysis and then performed a tomographic inversion using these observations to estimate lateral group velocity variations in the period range

T. A. Mokhtar; C. J. Ammon; R. B. Herrmann; H. A. A. Ghalib

2001-01-01

6

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

Microsoft Academic Search

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

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

2005-01-01

7

Coseismic and postseismic elastic wave velocity variations caused by the 2008 Iwate-Miyagi Nairiku earthquake, Japan  

NASA Astrophysics Data System (ADS)

We analyze coseismic and postseismic velocity variations caused by the June 13, 2008 Iwate-Miyagi Nairiku earthquake (MW= 6.9) using Passive Image Interferometry (PII). Seismic noise is correlated in order to reconstruct the Green's function between two sensors. Shear wave velocity changes are determined by relating the coda parts of the daily Green's functions to a long-term reference Green's function. Our study extends from January 2008 to August 2010 and includes the correlations for 190 station pairs in three different frequency ranges from 0.125 to 1.0 Hz. We show that combining the 9 different component cross-correlation functions stabilizes the velocity change estimation and increases analysis resolution. The observed velocity change curves can be fitted by model time series consisting of a coseismic velocity drop followed by logarithmic postseismic recovery and seasonal velocity variations. The coseismic velocity drops are stronger at higher frequencies and are concentrated in the southern part of the fault zone. A tomography algorithm was developed to reproject the observed velocity variations of the different sensor pairs onto the single sensors. The depth distribution of coseismic changes was modeled for the three stations with the largest velocity drops. At two stations, the coseismic velocity changes are located in the upper several hundred meters. The third station shows indications for deeper changes, in the order of kilometers. Postseismic recovery takes significantly longer than the analyzed two year period. Seasonal velocity variations with periods of one year are observed at all analyzed frequencies for most station pairs.

Hobiger, M.; Wegler, U.; Shiomi, K.; Nakahara, H.

2012-09-01

8

Velocities under Water Waves  

NSDL National Science Digital Library

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

Dalrymple, Robert A.; Delaware, University O.

9

Highlighting seismic velocity variations in cratonic lithosphere from the consistent analysis of surface wave dispersion.  

NASA Astrophysics Data System (ADS)

One robust approach in assessing the variations in structure beneath different cratonic regions is through the comparison of the dispersion characteristics measured at a seismic array, or as part of a broader tomographic study. Subsequently, a consistent analysis technique can be used to model (inverse methods or forward modelling) the velocity structure that provides a good level of fit to these dispersion data. In contrast to direct comparison of pre-existing velocity models this approach minimises the effect that different parameterisations or regularisations will have on the velocity variation with depth. However, for inverse modelling a significant challenge in interpreting the resulting variations remains the dependence on the choice of starting model. We assess the variations in lithospheric structure beneath Fennoscandia, southern Africa, Slave Craton (Canada) and the Yilgarn Craton (Australia), by inverting the dispersion characteristics with respect to a starting model that is derived from experimental mineral physics. The combination of Litmod and Perplex are used to define an a priori velocity structure for the cratons assuming a slightly depleted mantle composition and a steady state geotherm with a thermally defined base of the lithosphere at 200km depth. One advantage in using this style of starting model, as opposed to a seismologically determined reference (e.g. PREM or ak135), is that the perturbations in velocity can be more meaningfully interpreted. Variations from the starting model now clearly indicate regions where the thermal, or compositional, structures are more complicated than our initial a priori choice. Our investigations focus particularly on the uppermost mantle - from the Moho to 100km depth. At this depth, many seismic models beneath cratons indicate slower velocities than would be expected. By damping back towards our physically derived a priori starting model, we significantly increase confidence that the slower velocities are a robust feature, rather than an artifact of the parameterisation and a poor choice of reference model. The most plausible explanation of these low velocities is a distinctly different composition in this region. We would therefore anticipate that with sufficient data, mantle discontinuities should also be observed in receiver functions, which would clearly indicate a compositional layering within the lithospheric mantle.

Fishwick, S.; Pedersen, H. A.; Snyder, D. B.; Fullea, J.

2012-04-01

10

Delineation of spatial variation of shear wave velocity with high-frequency Rayleigh waves in Anchorage, Alaska  

Microsoft Academic Search

High-frequency Rayleigh waves were generated in the frequency range of about 1-100Hz by an electromagnetic vibrator in co-operation with the Vibration Instrument Company, Japan, and the Ensol Corporation, North Carolina, at 36 sites in Anchorage. From phase delay times between two sensors, the phase velocity of the fundamental mode at each site was computed. These data were inverted in terms

U. Dutta; N. Biswas; A. Martirosyan; S. Nath; M. Dravinski; A. Papageorgiou; R. Combellick

2000-01-01

11

Delineation of spatial variation of shear wave velocity with high-frequency Rayleigh waves in Anchorage, Alaska  

NASA Astrophysics Data System (ADS)

High-frequency Rayleigh waves were generated in the frequency range of about 1-100Hz by an electromagnetic vibrator in co-operation with the Vibration Instrument Company, Japan, and the Ensol Corporation, North Carolina, at 36 sites in Anchorage. From phase delay times between two sensors, the phase velocity of the fundamental mode at each site was computed. These data were inverted in terms of shear wave velocity structure by a stochastic inversion scheme. Of the 36 sites, values of shear wave velocity (?) as a function of depth were available at seven sites from downhole measurements. At these sites, the comparison of the results obtained by others between surface and downhole measurements showed reasonable agreement. These results were therefore combined with those of the remaining 29 sites obtained in this study. The ? structure of the 36 sites could be subdivided into four groups. On the basis of NEHRP provision and from the time-averaged ? structures for the uppermost 30m corresponding to the four groups, it has been possible to identify the lateral extent of soil classes C and D in the Anchorage area. From statistical analysis of the time-averaged ? data, it is shown that the lithology of the area in soil class C is distinct from that in D. The same is true for the subunits, namely, glaciofluvial deposits in areas of C and D. Moreover, the areas in soil class D along the Knik Arm in west Anchorage with relatively low ?-values coincide with the areas of high ground failure susceptibility identified by others from observations following the Prince William Sound earthquake (Mw=9.2) of 1964.

Dutta, U.; Biswas, N.; Martirosyan, A.; Nath, S.; Dravinski, M.; Papageorgiou, A.; Combellick, R.

2000-11-01

12

P-wave velocity variation in the upper mantle beneath Tibetan Plateau  

NASA Astrophysics Data System (ADS)

We produced a P-wave model of the upper mantle beneath Tibeatan Plateau from a combination of International Seismological Centre (ISC) P and pP data, processed by Engdahl et al. (1998), P data of the Annual Bulletin of Chinese Earthquake (ABCE) [IG-CSB, 1990-1998], and travel times of P phases recorded at temporary arrays around Tibetan Plateau, including arrays operated by (a) MIT and the Chengdu Institute of Geology and Mineral Resources (MIT-CIGMR) - 09/2003-09/2004; (b) Lehigh university and CIGMR - 07/2003-10/2004; (c) the INDEPTH (InterNational DEep Profiling of Tibet and the Himalaya) project - 05/1994-10/1994, 07/1997-06/1999; and (d) various French and Chinese groups - 07/1991-06/1992. Incorporating the travel times of phases recorded at arrays allow us to constrain upper mantle structure with much greater resolution and confidence than before, and the preliminary models reveal intriguing variations in P-wavespeed in the upper mantle beneath Tibetan Plateau. Our images suggest that the Indian lithosphere subducts from the foreland basin and underlies only the southwestern margin of the Tibetan Plateau, implying that much of the Tibetan Plateau is not underlain by Indian but by Asian lithosphere. Some of the seismically slow structures beneath the eastern part of the plateau may connect to structures, and presumably, processes in the upper mantle beneath the South China Sea.

Li, C.; van der Hilst, R.; Chen, Z.; Anne, M.

2005-12-01

13

Elastic wave velocities in rocks  

Microsoft Academic Search

Compressional wave velocity has been measured in the laboratory by the ultrasonic pulse technique in a number of rock specimens of different geological formations collected from different parts of India. The effect of water saturation on the velocity in some of the porous samples has been investigated. The velocity in some polycrystalline aggregate crystals and in some ores has also

Satyabrata Datta; K. R. Madhwa Simha

1968-01-01

14

Shear Wave Velocity Estimation Using PS Converted-Wave  

Microsoft Academic Search

Shear (S-) wave velocity structure over the basement is one of the key elements for the estimation of strong ground motion generated by earthquakes. PS converted-wave reflection survey is superior to S-wave reflection survey in imaging the deeper structure, thus give us the deeper S-wave velocity information. But in the large Vp\\/Vs area, conventional velocity analysis and RMS velocity assumption

N. Kano; T. Yokokura; K. Yamaguichi; T. Kiguchi

2003-01-01

15

Shear Wave Velocity Estimation Using PS Converted-Wave  

NASA Astrophysics Data System (ADS)

Shear (S-) wave velocity structure over the basement is one of the key elements for the estimation of strong ground motion generated by earthquakes. PS converted-wave reflection survey is superior to S-wave reflection survey in imaging the deeper structure, thus give us the deeper S-wave velocity information. But in the large Vp/Vs area, conventional velocity analysis and RMS velocity assumption fails to give us a good estimate of the S-wave velocity. The P-wave velocity derived from the velocity analysis is relatively reliable. When we get good images in both P-wave and PS converted-wave sections, correlation of the reflectors in the two sections gives us good estimates for Vp/Vs. Using these Vp/Vs values and P-wave velocities derived from P-wave velocity analysis, we can calculate S-wave velocities. We applied this methodology to a 3-component survey at Fuchu, Tokyo in Japan. The survey line was along the river and there is a well near by which is deep enough to reach the basement, about 2000m. The source was two vibrators. Three-component geophones are set in 10m interval. Geophones are fixed in 192 locations. The source-line was 3080m long so that we can get long offset data to use in PS converted-wave processing. From the P-wave sections, we can see the strata are inclining towards east. P-S converted-wave section has a good agreement with P-wave section. By correlation of the two sections, we derived Vp/Vs map of the section. Then we calculated the S-wave velocity using Vp/Vs value and P-wave velocity. We compared the velocity structure with the well log data. The derived S-wave velocities, ranging from 570m/s to 1780m/s, are in good agreement with the well data.

Kano, N.; Yokokura, T.; Yamaguichi, K.; Kiguchi, T.

2003-12-01

16

Azimuthal velocity variations caused by borehole stress concentrations  

Microsoft Academic Search

In laboratory experiments, borehole stress concentrations caused by far-field uniaxial stress produce measurable variations in compressional wave velocities near the borehole. Uniaxial stress was applied perpendicular to the axis of a borehole drilled through a sandstone block. Inside the fluid-filled borehole, refracted compressional waves were propagated in the rock parallel to the borehole axis at discrete azimuths, producing a scan

Kenneth W. Winkler

1996-01-01

17

Eurasian surface wave tomography: Group velocities  

NASA Astrophysics Data System (ADS)

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.

Ritzwoller, Michael H.; Levshin, Anatoli L.

1998-03-01

18

Seismicity rate and wave-velocity variations as consequences of rainfall: the case of the catastrophic storm of September 2002 in the Nîmes Fault region (Gard, France)  

NASA Astrophysics Data System (ADS)

The western Provence in southern France is an intraplate low deforming region, cut by large sinistral strike-slip faults as the Nîmes Fault. The deformation rate of this fault was estimated at 0.1 mm yr-1 from geological and morphological observations. Nevertheless, some large earthquakes occurred in this area in historical times inducing well-documented partial destructions on the roman monument `Pont-du-Gard'. In order to investigate if this area is seismically active, we installed a temporary seismological network of 14 stations between the cities of Nîmes and Avignon for a 1-yr period (2002 July-2003 June). We recorded and located a total amount of 80 earthquakes of magnitude Ml smaller than 2.8, and of 153 quarry blasts. The seismic event locations are interpreted in terms of regional tectonics as well as of geometry at depth of the Nîmes Fault and of possible seismic activity of the Roquemaure Fault. At the beginning of 2002 September, a catastrophic storm occurred in the same area with cumulated precipitations at 600 mm in 28 hr, causing casualties and major inundations and damages. We identified a clear and sudden increase of the seismic activity as an immediate consequence of this exceptional meteorological phenomenon. We interpret this rainfall triggering of earthquakes as the response of the crust to an abrupt vertical loading. The geological context of this zone is characterized by the presence of sedimentary basins and of an important karstic network in a calcareous environment allowing the retention of a third of the total rainwater volume during few weeks after the catastrophic storm. Month by month inversion of the seismic wave velocities for only the first 1-km thick layer of the crust allows investigating the influence of the stored water. A clear decrease of both P- and S-velocities, and an increase of the Vp/Vs ratio are evidenced. The variations obtained are at 2, 6 and 4.5 per cent for P-, S-velocities and Vp/Vs ratio, respectively. These variations are discussed in confront of previous studies and can be directly related to the known water volume.

Rigo, Alexis; Béthoux, Nicole; Masson, Frédéric; Ritz, Jean-François

2008-05-01

19

Electromagnetic wave velocities: an experimental approach  

NASA Astrophysics Data System (ADS)

We describe experiments with coaxial transmission lines for the study of some of the velocities used to characterize the propagation of electromagnetic waves in a medium, namely phase, group and signal velocities. The experiments are suitable for undergraduates at advanced laboratory level. Their purpose is to acquaint the students with the fact that in a dispersive medium there are many possible definitions for the speed of light, and that the measurement of these different velocities is important for general understanding of wave propagation.

Santos, A. C. F.; Santos, W. S.; Aguiar, C. E.

2013-05-01

20

Mean Velocities in a Stokes Wave  

NASA Astrophysics Data System (ADS)

We prove that in a periodic travelling wave propagating at the surface of an inviscid homogenous fluid in irrotational flow over a flat bed, the horizontal mean velocity exceeds the depth-averaged velocity in the frame of reference in which the wave is stationary. The long-standing conjectural nature of this fundamental issue was due to its undecidability within the framework of linear wave theory.

Constantin, Adrian

2013-03-01

21

Propagation Velocity of Ultrasonic Waves in Solids.  

National Technical Information Service (NTIS)

The propagation velocity of ultrasonic waves was measured by the wedge method in the following materials: marble (white), iron, porcelain (white), cast iron, glass (flint glass), polystyrene, rosin, and oak (against the grain).

N. F. Otpushchennikov

1964-01-01

22

Continuous subsurface velocity measurement with coda wave interferometry  

NASA Astrophysics Data System (ADS)

A 1-month field experiment was conducted near Kunming in Yunnan Province, China, to continuously monitor subsurface velocity variations along different baselines. The experiment site is located 10 km west to the seismically very active Xiaojiang fault zone. An electric hammer was used as a source to generate highly repeatable seismic waves, which were recorded by 5 short-period seismometers deployed at ˜10 m to 1.2 km away from the source. Velocity variation was estimated by using coda wave interferometry technique. The technique measures changes in differential time between the coda and the first arrival, which is in principal insensitive to timing errors. We obtained a fractional velocity perturbation (?v/v) of 10-3 to 10-2 with a precision of 10-4. The measured velocity variation is consistent among different components and stations and appears to well correlate with deep water level. The velocity variation is featured by a long-term linear trend and well-developed daily cycles. The latter is interpreted as the velocity response to the barometric pressure. A multivariate linear regression analysis of the data indicates that the velocity change exhibits a negative correlation with barometric pressure, with a stress sensitivity of 10-6/Pa at the experimental site.

Wang, Baoshan; Zhu, Ping; Chen, Yong; Niu, Fenglin; Wang, Bin

2008-12-01

23

“Skewness” of S-wave velocity in the mantle  

NASA Astrophysics Data System (ADS)

We analyze tomographic models of the S-wave velocity in the mantle. The depth variation of laterally heterogeneous structure is parametrized in terms of the “skewness,” which yields information on mantle convection. Recent models show negative skewness in the lower half of the mantle. Assuming that the velocity anomaly is related to the temperature anomaly, this suggests that there is significant heat flow from the core.

Yanagisawa, Takatoshi; Hamano, Yozo

24

A coronary pulse wave velocity measurement system.  

PubMed

Pulse wave velocity (PWV) is a basic parameter in the dynamics of pressure and flow wave traveling in arteries. But it is difficult to measure the pulse wave transmission time between coronary arterial proximal and distal point by manual method using the graph on which pulse wave and ECG are recorded. The system that can measure PWV in real time was developed and clinical experiment was carried out for patients to validate the accuracy of the measured coronary arterial PWV. The average value of the measured coronary arterial PWV was 934.764+/-104.606 cm/sec. PMID:18002122

Nam, Taewoo; Cho, Jongman; Choi, Junghyeon; Park, Junho; Cho, Wookhyun

2007-01-01

25

Wave measurements using GPS velocity signals.  

PubMed

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

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

2011-01-18

26

Complex Shear Wave Velocity Structure Imaged Beneath Africa and Iceland.  

PubMed

A model of three-dimensional shear wave velocity variations in the mantle reveals a tilted low velocity anomaly extending from the core-mantle boundary (CMB) region beneath the southeastern Atlantic Ocean into the upper mantle beneath eastern Africa. This anomaly suggests that Cenozoic flood basalt volcanism in the Afar region and active rifting beneath the East African Rift is linked to an extensive thermal anomaly at the CMB more than 45 degrees away. In contrast, a low velocity anomaly beneath Iceland is confined to the upper mantle. PMID:10583949

Ritsema; van Heijst HJ; Woodhouse

1999-12-01

27

Latitudinal Variation of Solar Wind Velocity  

NASA Astrophysics Data System (ADS)

Single station solar wind velocity measurements using the Ooty Radio Telescope (ORT) in India (operating at 327 MHz) are reported for the period August 1992 to August 1993. Interplanetary scintillation (IPS) observations on a large number of compact radio sources covering a latitudinal range of ±80° were used to derive solar wind velocities using the method of fitting a power law model to the observed IPS spectra. The data shows a velocity versus heliographic latitude pattern which is similar to that reported by Rickett and Coles (1991) for the 1981 1982 period. However, the average of the measured equatorial velocities are higher, being about 470 km s-1 compared to their value of 400 km s-1. The distribution of electron density variations (?N e ) between 50R? and 90R? was also determined and it was found that ?N e was about 30% less at the poles as compared to the equator.

Ananthakrishnan, S.; Balasubramanian, V.; Janardhan, P.

1995-04-01

28

Soil liquefaction evaluation using shear wave velocity  

Microsoft Academic Search

A reasonably good relationship between shear wave velocity (SWV) and standard penetration resistance (SPT) of granular soils in agreement with previous studies was obtained from field tests. A similar correlation between SWV and cone penetration resistance of granular soils was also obtained. Using Seed's Standard Penetration Test (SPT)-based soil liquefaction charts, new charts of soil liquefaction evaluation based on SWV

Kamil Kayabali

1996-01-01

29

Upper mantle P-wave velocity structure beneath southern Scandinavia  

NASA Astrophysics Data System (ADS)

This study images upper mantle structure beneath different tectonic and geomorphological provinces in southern Scandinavia by P-wave travel time tomography based on teleseismic events. We present integrated results using data from several projects (CALAS, MAGNUS, SCANLIPS, CENMOVE and Tor) with a total of 202 temporary seismological stations deployed in southern Norway, southern Sweden, Denmark and the northernmost part of Germany. These stations, together with 18 permanent stations, yield a high density data coverage enabling presentation of the first high resolution 3D seismic P-wave velocity model for the upper mantle for this region, which includes areas of Baltic Shield, Scandinavian Caledonides, the entire northern part of the prominent Tornquist Zone and the Southern Scandes Mountains. P-wave arrival time residuals of up to ±1 s are observed reflecting large seismic velocity contrasts at depths. Relative regional as well as absolute global tomographic inversion is carried out and consistently show upper mantle velocity variations relative to the ak135 reference model of up to ± 2-3 % corresponding to P-wave velocity differences of about 0.4 km/s from depths of about 100 km to more than 300 km. High upper mantle velocities are observed to great depth to the east in Baltic Shield areas of southwestern Sweden. Lower velocities are found to the west and southwest beneath the Danish and North German sedimentary basins and in most of southern Norway. A well-defined, generally narrow deep boundary is observed between areas of contrasting upper mantle seismic velocity. In basin areas, low upper mantle velocities are associated with thinned lithosphere and velocity contrasts are interpreted to represent differences between deep shield lithosphere and shallow basin asthenosphere with a deep lithospheric boundary running close to the Sorgenfrei-Tornquist Zone. Differences in P-wave velocity are here likely to arise mainly from temperature differences. To the north, the boundary crosses various tectonic and geomorphologic units including shield units, the Caledonides as well as areas of high topography, and a structural and geodynamic interpretation is more complex. Reduced upper mantle velocities below southern Norway also appear to be associated with a thinner lithosphere compared to shield areas to the east. Velocity contrasts may be explained to a higher degree by both compositional and temperature differences and a geodynamic origin including both Proterozoic and Phanerozoic events. Below southern Norway, a regional contribution to buoyancy from reduced density in the upper mantle is likely to exist, but we observe no clear correlation between reduced upper mantle seismic velocity and high topography of the southern Scandes Mountains.

Medhus, A. B.; Balling, N.; Jacobsen, B. H.; England, R. W.; Kind, R.; Weidle, C.; Voss, P.; Thybo, H.

2012-04-01

30

Comet flares and velocity waves in the solar wind  

SciTech Connect

The flare activity of comets and the structure of the solar wind fluxes are compared with data of measurements of Pioneer-10, -11, Vela-3, IPM-7, and -8 at a heliocentric distance of r approx. = 1-6 AU. It is shown that velocity waves of the solar wind, which evolve into corotating shock waves beyond the orbit of the earth, may be responsible for the flare activity of comets. The work notes a correspondence between the variations of flare activity of comets as a function of heliocentric distance and the behavior of velocity waves in the solar wind, the closeness of the characteristic times of velocity waves (about 7-8 days at r = 1 AU) and the duration of comet flares, and the increase of this characteristic time with increasing r in both cases. The observed distribution of the parameters of comet flare activity in the 11-yr cycle also corresponds well to the distribution of the area of coronal holes and the rate of variation of the area of sunspots ..delta..Sp over the phase of the solar cycle.

Ptitsyna, N.G.; Breus, T.K.; Rikhter, A.K.

1986-05-01

31

Frequency Dispersion of Wave Velocity in Arterial Vessels  

Microsoft Academic Search

Pulse wave velocity in an artery is a very important indicator of the stiffness and disease of the artery. Pulse wave velocity in an artery is measured with the standard pulse delay technique. However, the precise timing of the pressure wave is difficult due to the presence of reflected waves. In this paper we propose to generate a wave of

Xiaoming Zhang; Mostafa Fatemi; James F. Greenleaf

2004-01-01

32

Temperature Dependence of Compressional and Shear Wave Velocities in Rocks  

Microsoft Academic Search

Concurrent measurements of compressional and shear wave velocities were conducted as functions of temperature on two sandstone and seven carbonate samples subjected to simulated overburden and pore fluid pressures. On the average, the compressional wave velocities decreased by 1.7 percent and the shear wave velocities by 0.9 percent for a 100°C increase in temperature.

Aytekin Timur

1977-01-01

33

Shear wave crustal velocity model of the Western Bohemian Massif from Love wave phase velocity dispersion  

NASA Astrophysics Data System (ADS)

We propose a new quantitative determination of shear wave velocities for distinct geological units in the Bohemian Massif, Czech Republic (Central Europe). The phase velocities of fundamental Love wave modes are measured along two long profiles (~200 km) crossing three major geological units and one rift-like structure of the studied region. We have developed a modified version of the classical multiple filtering technique for the frequency-time analysis and we apply it to two-station phase velocity estimation. Tests of both the analysis and inversion are provided. Seismograms of three Aegean Sea earthquakes are analyzed. One of the two profiles is further divided into four shorter sub-profiles. The long profiles yield smooth dispersion curves; while the curves of the sub-profiles have complicated shapes. Dispersion curve undulations are interpreted as period-dependent apparent velocity anomalies caused both by different backazimuths of surface wave propagation and by surface wave mode coupling. An appropriate backazimuth of propagation is found for each period, and the dispersion curves are corrected for this true propagation direction. Both the curves for the long and short profiles are inverted for a 1D shear wave velocity model of the crust. Subsurface shear wave velocities are found to be around 2.9 km/s for all four studied sub-profiles. Two of the profiles crossing the older Moldanubian and Teplá-Barrandian units are characterized by higher velocities of 3.8 km/s in the upper crust while for the Saxothuringian unit we find the velocity slightly lower, around 3.6 km/s at the same depths. We obtain an indication of a shear wave low velocity zone above Moho in the Moldanubian and Teplá-Barrandian units. The area of the Eger Rift (Teplá-Barrandian-Saxothuringian unit contact) is significantly different from all other three units. Low upper crust velocities suggest sedimentary and volcanic filling of the rift as well as fluid activity causing the earthquake swarms. Higher velocities in the lower crust together with weak or even missing Moho implies the upper mantle updoming.

Kolínský, Petr; Málek, Ji?í; Brokešová, Johana

2011-01-01

34

Upper mantle shear wave velocity structure of the Arabian Shield from teleseismic surface wave tomography  

Microsoft Academic Search

We investigate the seismic shear wave velocity structure of the shallow upper mantle beneath the Arabian Shield by inverting Rayleigh wave phase velocity measurements between 44 and 140 s together with previously published Rayleigh wave group velocity measurements between 10 and 50 s from Pasyanos. The Rayleigh wave phase velocity measurements between 44 and 140 s have been made using

A. A. Nyblade; A. J. Rodgers; A. Al-Amri

2007-01-01

35

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

Microsoft Academic Search

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

Dapeng Zhao; Akira Hasegawa; Shigeki Horiuchi

1992-01-01

36

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

NASA Astrophysics Data System (ADS)

Recent studies have suggested that uplift of the northern Tibetan plateau may be related to removal of lithospheric mantle, resulting in emplacement of hotter, less dense asthenosphere. Other studies propose that plateau uplift and crustal thickening have occurred through a process of lateral mid-crustal flow or coherent deformation between crust and lithospheric mantle. Some authors attribute the geophysical properties of upper mantle beneath the plateau to either delamination of thickened lithosphere, or asthenospheric counterflow associated with subduction of continental Indian lithosphere beneath central Tibet. In order to study the evolution and dynamics of the Tibetan plateau, we deployed 74 broadband seismic stations throughout northeastern Tibet within the scope of ASCENT/INDEPTH-IV experiment. In conjunction with Namche Barwa data, we have calculated fundamental mode Rayleigh wave phase velocities utilizing two-plane wave approach, for periods between 20-143 seconds. We also obtained preliminary phase velocities using Love waves. To invert for shear wave velocities, we use partial derivatives from Saito (1988), assuming a constant Poisson's ratio. Our azimuthal anisotropy measurements agree well with SKS splitting results; both indicate significant (>2%) average azimuthal anisotropy throughout the upper mantle down to depths exceeding 250 km, with a dominantly EW fast directions. Although we observe variations of fast directions with depth, they are generally consistent (i.e., within 15 degrees) up to ~200 km, indicative of vertically coherent deformation. Furthermore at crustal depths, azimuthal fast directions tend be sub-parallel to the strikes of major strike slip faults, suggesting that shearing is the dominant deformation mechanism in eastern Tibet. Our tomographic models show an uppermost mantle low velocity anomaly north of Bangong-Nujiang Suture (BNS) in northeastern Tibet, and a high velocity anomaly extending ~200 km centered on the BNS. We suggest that the low velocity zone is due to warmer, thinner lithosphere in the northern Qiangtang and Songpan-Ganzi terranes. At depth, we observe high velocity bodies to the south both in our phase velocity and shear wave velocity maps, indicative of an underthrusting Indian lithosphere. Our phase maps and shear wave velocity-anomaly isosurfaces strongly indicate that underthrusting of Indian plate is sub-horizontal, has variable geometry in EW direction, and does not extend north of the BNS. We propose that underthrusting is accompanied by lateral tearing along old weak zones into at least two fragments, and subsequent break-off of the western-most portion. Our models reveal low velocity zones concentrated along major strike slip faults, which we attribute to strain heating. Furthermore, the Qiadam Basin is characterized by high velocities in the mantle, and moderate to slow velocities below the Kunlun Shan and northern Qiangtang argue against continental subduction.

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

2011-12-01

37

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

NASA Astrophysics Data System (ADS)

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

Corchete, V.

2013-04-01

38

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

Microsoft Academic Search

The shear-wave (S-wave) velocity of near-surface ma- terials (soil, rocks, pavement) and its effect on seismic- wave propagation are of fundamental interest in many groundwater, engineering, and environmental studies. Rayleigh-wave phase velocity of a layered-earth model is a function of frequency and four groups of earth prop- erties: P-wave velocity, S-wave velocity, density, and thickness of layers. Analysis of the

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

1999-01-01

39

Upper mantle anisotropy and shear wave velocity structure beneath the Slave craton inferred from Rayleigh waves  

NASA Astrophysics Data System (ADS)

The seismic structure and depth extent of cratonic lithosphere is crucial to understanding the dynamics of continental evolution and stabilization, a subject that remains poorly understood. In this study, Rayleigh wave phase and amplitude data are analyzed to constrain velocity structure in the upper mantle beneath the Slave craton, in the northwestern Canadian Shield. We measure phase velocities for periods between 20-142 s (with greatest sensitivity at depths of 28-200 km, but providing resolution down to ~300 km) of crossing ray paths from events recorded by the POLARIS broadband seismic network and the Yellowknife array. To optimally resolve lateral velocity variations under this region, we employ an inversion technique that considers the multipathing and finite frequency scattering effects of surface waves. The technique recovers shear-wave (S) velocities and azimuthal anisotropy for each period, thus providing constraints on the depth of anisotropic structure that shear-wave splitting alone cannot recover. Phase velocities obtained for the Slave province are comparable to values from other cratons at shorter periods, but exceed global average by ~2% at periods above 60 s. One-dimensional inversion of phase velocities yields high S-wave velocities (4.72±0.02 km/s) representative of cratonic lithosphere between 50-200 km depths. The depth to the base of the cratonic lithosphere is estimated at ~200 km, in agreement with petrological constraints from mantle xenolith analyses. Two-dimensional phase velocity maps indicate noticeable lateral variations. In the western part of the Slave, which corresponds to the oldest portion of this craton, high velocities are consistently observed between 25-33 s. In contrast, lower velocities are observed at periods 25-50 s in the central part of the craton, a region that hosts an important cluster of kimberlite pipes. We investigate whether these anomalies are crustal signals or may extend to the deeper mantle. Inversion for anisotropic parameters reveals two distinct trends in the Slave's lithosphere. A fast direction of N59°E±20° is found at periods above 29 s, consistent with the direction of absolute plate motion. At shorter periods 20-25 s, the fast direction is N10°E±20°, corresponding mainly to crustal structure. These anisotropic characteristics are in remarkable agreement with results from shear-wave splitting analyses supporting a previously proposed two-layer model, and suggest a significant anisotropic structure in the Slave craton's lithosphere and perhaps sub-lithospheric mantle that is likely influenced by asthenospheric flow.

Chen, C.; Rondenay, S.; Weeraratne, D. S.; Yang, Y.; Snyder, D. B.

2005-12-01

40

Shear wave velocity depth profiles from dispersive waves recorded in the natural laboratory (NATLAB) in the Arkona Basin, Baltic Sea.  

NASA Astrophysics Data System (ADS)

The assessment of shear waves in the sea floor under in-situ conditions and the correlation of shear wave velocities with sediment properties can contribute significantly to the solution of geotechnical problems with respect to fluid content and cementation processes as encountered in gashydrate bearing sediments. Methodological investigations have been performed to determine the shear wave velocity depth profile using full wave field inversion of the slowness spectra of dispersive guided and interface waves. The dispersion characteristics and modal distribution of the wave field depends dominantly on the seismic properties of the sediments as well as the structure and layering of the sub surface. Seismic measurements conducted at two locations in the NATLAB area in the Arkona Basin with airgun sources, Ocean-Bottom-Seismometer (OBS)-stations and a solid-state-streamer showed distinct difference in respect to the observed wave types at each location. At the southeast rim of the study area, where a hard basement is found at shallow depth, interface waves were measured. In the central part of the Arkona Basin, where soft mud and till layers dominate, shear wave velocity information could be inverted from multi-modal acoustic guided waves for the first time, while interface waves were not observed. Interface waves, e.g. Scholte Waves, are highly sensitive to shear wave velocity variations with depth and propagate at distinct layer interfaces and are characterised by low velocity and frequency, while acoustic guided waves propagate in the water column of shallow depth with sensitivity to shear and compressional wave velocity variation with depth. The interface waves were depictable on Streamer and OBS data, yet the resolution of the Streamer data is not sufficient for stand alone inversion. A-priory information is required for the inversion procedures to produce a start model. The acoustic modes of the central Arkona Basin are of exceptional good quality resolvable in the frequency range from 10 to 140 Hz with more than 6 higher modes. The shear wave velocity profile determined by the inversion exhibits low velocities of 40-50 m/s at the sea floor with two dominant steps. Comparison with the geological setting and core samples are in good agreement. Therefore we derived an appropriate shear wave velocity depth profile from guided waves in an area, where normal dispersion analysis methods focused on interface waves would fail.

Klein, G.; Mathys, M.; Thießen, O.; Schmidt, M.; Theilen, F.; Bohlen, T.

2003-04-01

41

Shear-wave velocity structure of Antarctica from Rayleigh-wave analysis  

NASA Astrophysics Data System (ADS)

The elastic structure beneath Antarctica is shown by means of S-velocity maps for depths ranging from zero to 400 km, determined by the regionalization and inversion of Rayleigh-wave dispersion. The traces of 93 earthquakes, occurring from 1990 to 2011, have been used to obtain Rayleigh-wave dispersion data. These earthquakes were registered by 30 seismic stations located in Antarctica. The dispersion curves were obtained for periods between 5 and 250 s, by digital filtering with a combination of MFT and TVF filtering techniques. Later, all seismic events (and some stations) were grouped to obtain a dispersion curve for each source-station path. These dispersion curves were regionalized and inverted according to the generalized inversion theory, to obtain shear-wave velocity models for a rectangular grid of 20 × 20 points. The shear-velocity structure obtained through this procedure is shown in the S-velocity maps plotted for several depths. These results agree well with the geology and other geophysical results previously obtained. The obtained S-velocity models suggest the existence of lateral and vertical heterogeneities. The zones with consolidated and old structures present greater S-velocity values than the other zones, although this difference can be very little or negligible in some case. Nevertheless, in the depth range of 10 to 45 km, the different Moho depths present in the study area generate the principal variation of S-velocity. A similar behaviour is found for the depth range from 80 to 230 km, in which the lithosphere-asthenosphere boundary generates the principal variations of S-velocity. Finally, a new and interesting feature obtained in this study should be highlighted: the definition of the LAB and the base of the asthenosphere (for the whole study area), for depths ranging from 80 to 230 km and from 180 to 280 km, respectively.

Corchete, V.

2013-01-01

42

S wave velocity structure of the Arabian Shield upper mantle from Rayleigh wave tomography  

Microsoft Academic Search

The shear wave velocity structure of the shallow upper mantle beneath the Arabian Shield was modeled by inverting Rayleigh wave phase velocity measurements between 45 and 140 s together with previously published Rayleigh wave group velocity measurements between 10 and 45 s. For measuring phase velocities, we applied a modified array method to data from several regional networks that minimizes

Andrew A. Nyblade; Arthur J. Rodgers; Abdullah Al-Amri

2008-01-01

43

Depth resolution of earthquakes in Central Asia by moment tensor inversion of long-period Rayleigh waves: Effects of phase velocity variations across eurasia and their calibration  

Microsoft Academic Search

The moment tensor inversion method for long-period Rayleigh waves is discussed from the point of view of event-depth resolution. In this method, depth is usually determined by finding the minima in appropriate least squares residuals versus depth curves. We show that depth cannot be resolved if the data are sampled only at one frequency and a choice of frequencies spanning

Barbara Romanowicz

1981-01-01

44

Orbital velocity and breaking in steep random gravity waves  

NASA Astrophysics Data System (ADS)

Laboratory measurements by PIV of strongly nonlinear irregular waves are compared to orbital velocity calculations of directional field waves. Nondimensional fluid velocities are obtained dividing by a local wave phase speed which is evaluated from a local wave number and wave slope. 30 laboratory waves have slope in the range 0.14-0.4. Nine among the waves have a slope of about 0.3, and breaking is measured in four among the waves. A backward breaking wave has local wave slope as small as 0.22. Wave induced acceleration is measured. Orbital velocity of two samples of directional field waves in storm conditions are calculated by nonlinear method and compared to the laboratory kinematics. The effect of the ocean surface current is accounted for. The field data include wave groups of local elevation gradient up to 0.3. The sample with the longest fetch exhibits nondimensional orbital velocities that are similar to the laboratory waves including levels up to breaking. In the other field sample, nondimensional fluid velocities are proportional to the local wave slope (up to 0.3), and velocities are well below breaking level.

Grue, John; Jensen, Atle

2012-07-01

45

Structure of the upper mantle in Asia from phase and group velocities of Rayleigh waves  

NASA Astrophysics Data System (ADS)

Dispersion curves of phase velocities of Rayleigh waves are determined by the method of frequency-time analysis in a range of periods of 10 200 s from data of 43 interstation traces in Central Asia. Because the joint use of phase and group velocities significantly decreases the uncertainty in the determination of S wave velocity structures, the same traces were used for calculating group velocities from tomographic reconstructions obtained in [Yanovskaya and Kozhevnikov, 2003, 2006] and determining average velocity structures along these traces. The velocity structures were calculated by the Monte Carlo and linear inversion methods, which gave consistent results. Using velocity values obtained at fixed depths by the 2-D tomography method, lateral variations in velocities at these depths were estimated, which allowed us to construct smoothed vertical velocity structures at some points in the region. The resulting structures were used as initial approximations for constructing local velocity structures solely from previously obtained local dispersion curves of group velocities in the area (32° 56°N, 80° 120°E). Based on these structures, we mapped the lateral distribution of velocity variations at upper mantle depths of 75 400 km and along three vertical profiles. The inferred velocity variations are in good agreement with data on the tectonics of the region.

Yanovskaya, T. B.; Kozhevnikov, V. M.; Solovei, O. A.; Akchurin, K. R.

2008-08-01

46

Mass sensitivity of acoustic wave devices from group and phase velocity measurements  

NASA Astrophysics Data System (ADS)

The effect of dispersion on acoustic wave sensors is considered. The discussion is focused upon layer guided surface acoustic waves (Love waves), which obtain their high mass sensitivity for the first Love wave mode by optimizing the guiding layer thickness, d, such that dapprox][lambdal/4; the wavelength in the layer is given by lambdal=f/vl where f is the operating frequency and vl is the shear acoustic speed of the guiding layer. We show that this optimization of guiding layer thickness corresponds to strong dispersion so that the phase and group velocities can be quite different. From the definition of the phase velocity mass sensitivity, we show that it can be determined from either the slope of the curve of phase velocity with normalized guiding layer thickness, z=d/lambdal, or from the phase and group velocities measured for a given guiding layer thickness. Experimental data for a poly(methylmethacrylate) polymer guiding layer on 36deg XY Lithium Tantalate is presented. Measurements of phase velocity and group velocity determined by a network analyzer were obtained for systematically increasing guiding layer thicknesses; a pulse transit experiment was also used to provide independent confirmation of the group velocity data. Two independent estimates of the mass sensitivity are obtained for z=d/lambdal<0.22 from (i) the slope of the phase velocity curve and (ii) the measurements of the group and phase velocity. These two estimates are shown to be consistent and we, therefore, conclude that it is possible to determine the mass sensitivity for a Love wave device with a given guiding layer thickness from measurements of the phase and group velocities. Moreover, we argue that the formula using group velocity to determine phase velocity mass sensitivity can be extended to a wide range of other acoustic wave sensors. In addition, we suggest that variations in the group velocity due to deposited mass may be a more sensitive parameter than variations in the phase velocity.

McHale, G.; Martin, F.; Newton, M. I.

2002-09-01

47

P-wave Velocity Structures near the Inner Core Boundary in the Eastern and Western Hemispheres  

NASA Astrophysics Data System (ADS)

It is well known that the P-wave velocity structures near the inner core boundary are different in the eastern and western hemispheres. However, the detailed variations in velocity structure in each hemisphere are not well constrained yet. We examined seismic waveforms recorded at about 850 stations in Japan from 279 events occurred in and around South America and the Southern Atlantic Ocean between 2004 and 2009. The differential travel-times of PKP(BC) and PKP(DF) at epicentral distance ranges between 145° and 153° were measured by waveform cross-correlation method. To construct the P wave velocity model, we used the grid-search technique to match observed and theoretical differential travel times for selected events. As we expected, the best-fitting P wave velocity models for the eastern hemisphere are systematically different from those for the western hemisphere. Moreover, we found that there are significant variations of the P wave velocity structures in each hemisphere, especially for the western hemisphere. The one dimensional P-wave velocity models constructed for different paths can provide more constraints on the detailed P-wave velocity structures near the inner core boundary.

Yee, T.; Rhie, J.

2009-12-01

48

S-wave velocity structure beneath the South Pacific Superswell derived from passive seismic experiments  

NASA Astrophysics Data System (ADS)

Three-dimensional S-wave velocity structure beneath the South Pacific Superswell is obtained from joint broadband seismic experiments on the ocean floor and islands. As the noise level is significantly high in the horizontal components, we collected only approximately 800 relative times of long-period teleseismic SH- waves (T = 13 to 33 s) by using a waveform cross-correlation from 76 events occurring from Jan. 2003 to May 2005. We conducted relative time tomography with TOMOG3D2 (Zhao et al., 1992) to depths of 2000 km. The velocity perturbations are assigned to grid nodes with horizontal intervals of 5 and 6 degrees for latitudes and longitudes, respectively, and vertical interval of 400 km. The rms residual of 1.2 s is improved to 0.54 s after three time iterations. In the resultant image, we find an elongated large low velocity region beneath the Society to Pitcairn hotspots at 1200km depth. Such a low velocity region can be identified in the some global S-wave velocity models, for example SAW24B16 (Megnin and Romanowicz, 2002). At 800 km depth, two linear low velocity regions are located beneath Tuamotu and Austral islands. These S-wave low velocity regions in the lower mantle are qualitatively similar to those of P-wave by Tanaka et al. (2008). However, unlike the P-wave tomographic image, the S-wave low velocity region at 1200 km depth seems to be isolated from the deeper low velocity region as seen in the global models. Furthermore low velocity regions beneath major hotspots are unclear at 400 km depth. Only a relatively low velocity channel is found in the eastern neighbor of the Society hotspot between 400 and 800 km depth. These features are not consistent with the P-wave velocity structure, suggesting the depth variation of dlnVs/dlnVp.

Tanaka, S.; Suetsugu, D.; Shiobara, H.; Sugioka, H.; Kanazawa, T.; Fukao, Y.; Barruol, G.; Raymond, D.

2008-12-01

49

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

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

50

Arterial Pulse Wave Velocity and Cognition with Advancing Age  

PubMed Central

We hypothesized that carotid-femoral pulse wave velocity, a marker of arterial stiffness, interacts with age such that the magnitude of associations between pulse wave velocity and cognitive performance are greater with increasing age, and that this interaction is observed despite adjustments for demographic variables, mean arterial pressure, and cardiovascular risk factors. Pulse wave velocity was estimated using applanation tonometry in 409 dementia- and stroke-free participants of the Maine-Syracuse Longitudinal Study (24 to 92 years of age, 62.3% women). Using linear regression analyses in a cross-sectional design, associations between pulse wave velocity, age, and the interaction of pulse wave velocity and age were examined in relation to a Global composite score, the Wechsler Adult Intelligence Scale Similarities test (abstract reasoning) and four cognitive domains indexed by multiple cognitive measures. Adjusting for age, gender, education, height, weight, heart rate, mean arterial pressure, and antihypertensive treatment, pulse wave velocity by age interactions were obtained for the Global, Visual-Spatial Organization and Memory, Scanning and Tracking, and Verbal Episodic Memory composites, and Similarities. The combination of higher pulse wave velocity and age resulted in progressively lower cognitive performance. This finding was the same with an extended model which also included adjustment for cardiovascular risk factors and other confounds. Pulse wave velocity interacts with age in a multiplicative way to exert a negative influence on cognitive performance level. Early interventions to prevent an increase in arterial stiffness could possibly play an important role in preservation of cognitive ability.

Elias, Merrill F.; Robbins, Michael A.; Budge, Marc M.; Abhayaratna, Walter P.; Dore, Gregory A.; Elias, Penelope K.

2009-01-01

51

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

USGS Publications Warehouse

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.

Swain, E. D.

1992-01-01

52

Nontriggered MRI quantification of aortic pulse-wave velocity.  

PubMed

Pulse-wave velocity is an index of arterial stiffness, which is a strong indicator of cardiovascular risk. We present a high-speed technique that generates time-resolved complex difference signal intensity simultaneously in the ascending and descending aorta from velocity-encoded projections without gating, allowing quantification of pulse-wave velocity. The velocity-time curve was approximated with a time-resolved complex difference signal intensity to estimate the propagation time of the pulse wave in the aortic arch. The path length of the pulse wave is measured from an oblique sagittal image in a plane encompassing thoracic ascending and descending aorta, and pulse-wave velocity is computed from the ratio between the path length and pulse-wave propagation time. The method was implemented at 1.5 T and 3 T, and pulse-wave velocity was quantified in healthy subjects (ages 20-70 years, N=23) without symptoms or prior history of cardiovascular events. In addition, the method was compared against retrospectively EKG-gated PC-MRI. The overall results were found to be in good agreement with literature data showing age-related increase in aortic stiffness. The RMS differences between the projection and gated PC-MRI methods were less than 4%. Key benefits of the proposed method are simplicity in both data acquisition and processing requiring only computation of the complex difference between the velocity-encoded projections rather than absolute velocity. PMID:20882637

Langham, Michael C; Li, Cheng; Magland, Jeremy F; Wehrli, Felix W

2010-09-29

53

Numeric implementation of wave-equation migration velocity analysis operators  

Microsoft Academic Search

Wave-equation migration velocity analysis (MVA) is a technique similar to wave- equation tomography because it is designed to update velocity models using infor- mation derived from full seismic wavefields. On the other hand, wave-equation MVA is similar to conventional, traveltime-based MVA because it derives the information used for model updates from properties of migrated images, e.g. focusing and moveout. The

Paul Sava; Ioan Vlad

2008-01-01

54

Determination of the material damping ratio and the shear wave velocity with the Seismic Cone Penetration Test  

Microsoft Academic Search

The Seismic Cone Penetration Test (SCPT) is used to determine the variation with depth of the shear (and longitudinal) wave velocity at various sites in Belgium. The cross correlation technique together with a posteriori increase of the sampling frequency proves to be a reliable method to determine wave velocities by the SCPT. Additionally, the Spectral Ratio Slope (SRS) method is

L. Karl; W. Haegeman; G. Degrande

2006-01-01

55

Variations in seismic velocity and attenuation associated with seismogenesis: A numerical verification using ambient noise  

NASA Astrophysics Data System (ADS)

Seismic velocity variations associated with the seismogenic process have been studied worldwide for almost half a century since the dilatancy hypothesis proposed in early 1970s. However, the reports in seismogenesis-associated variations in attenuation are rare. Reports on simultaneous variation of velocity and attenuation are even rarer. The conventional way to obtain the seismogenic temporal variation in velocity and attenuation is through the observation of travel time and amplitude variations of microseismicity in a seismogenic zone. Anyhow, for some major earthquakes there may not always be microseismicity prior to the mainshock. Thus, obtaining a complete record of seismic velocity and attenuation variation from microseismicity is severely limited if pre-mainshock microseismicity exists. In contrast, seismic ambient noise is an ideal source for crustal stimulation for monitoring temporal variations in velocity and attenuation in a seismogenic zone.In this paper the seismogenesis-associated seismic velocity and attenuation variations shown as some observable parameters in ambient noise measurements are verified using a numerical simulation approach. First, based on the temporal variation in seismic velocity observed along the Longmenshan fault associated with the 2008 Wenchuan earthquake, we divided the seismogenic process into six phases upon velocity drop stages in an elliptic area in the crust. Second, using finite difference time domain method we generated 30-minute low frequency ambient noise over a vertical profile of 200 × 45 km and recorded it with a 90-station array on the surface. Next, we processed the synthetic ambient noise records to get the auto-correlation function (ACF), cross-correlation function (CCF), Rayleigh wave dispersion curve, and horizontal-to-vertical spectral ratio (H/V). Finally, we examined the temporal variation of these parameters versus the phases of the seismogenic process and found the most pronounced changes occur in the phase with the largest velocity drop and the recovery phase directly before the mainshock.

Rohrbach, Eric; Liu, Lanbo; Wang, Linying

2013-01-01

56

Crustal P and Pn Wave Velocity Perturbations Beneath Caucasus Region  

NASA Astrophysics Data System (ADS)

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.

Mumladze, T.; Wu, Y. M.

2012-04-01

57

Variation in ejecta size with ejection velocity  

Microsoft Academic Search

A knowledge of the size-velocity distribution of ejecta from impact craters is important for a number of processes that occur or may have occurred in the solar system, such as planetary accretion, collisional evolution of asteroids, the ejection of meteorites from parent bodies larger than asteroids (such as the lunar meteorites and the SNC meteorites, which may be from Mars),

Ann M. Vickery

1987-01-01

58

Wave orbital velocity, fade, and SAR response to azimuth waves  

Microsoft Academic Search

Orbital motion of azimuth waves imposes differential Doppler shifts on wave imagery as seen by a SAR. This paper shows that these Doppler shifts are a function only of the wave and sensor geometry, and are not a function of SAR parameters. The azimuth wave reflectivity so modulated is equivalent to a redistributed scatterer density which can be used as

R. Raney

1981-01-01

59

The Height Variation of Granular and Oscillatory Velocities.  

National Technical Information Service (NTIS)

Previous observations of spatially-resolved vertical velocity variations in ten lines of Fe I spanning the height range 0 < or = h < or = 1000 km are re-analyzed using velocity weighting functions. The amplitudes and scale heights of granular and oscillat...

R. C. Canfield

1976-01-01

60

Velocity matched spectrum analysis: a new method for suppressing velocity ambiguity in pulsed-wave Doppler.  

PubMed

A new approach to spectrum analysis, which is capable of suppressing velocity ambiguity in pulsed-wave ultrasonic Doppler, is presented. By simultaneous processing of several data samples from a range in depth, the movement of the scatterers along the ultrasonic beam can be tracked from pulse to pulse for each velocity component in the spectrum. In this way the correlation length of the signal component arising from a specific velocity increases when that velocity matches the expected velocity. The resulting velocity/time spectral display shows a more clearly defined spectral envelope of the maximum velocity than with conventional methods based on the discrete Fourier transform of the Doppler signal. This makes it possible to delineate velocity waveforms with peak velocity up to several times the Nyquist limit. Experimental data from human subclavian and aortic arteries are presented, where the new method is compared to conventional spectrum analysis. PMID:7491748

Torp, H; Kristoffersen, K

1995-01-01

61

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

SciTech Connect

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).

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

1997-07-15

62

Tracer vs. pressure wave velocities through unsaturated saprolite  

SciTech Connect

Saprolite is a form of weathered bedrock that is commonly used as the host material at waste disposal sites in the Southeastern Piedmont. However, estimating the unsaturated hydraulic and transport properties of saprolite is difficult due to saprolite's low permeability. The authors demonstrate the use of short-duration fluid irrigation pulses for maintaining unsaturated conditions in intact saprolite columns. Concomitant Cl{sup {minus}} tracer experiments demonstrate that irrigated waters moved through an effective volumetric porosity substantially less than the ambient water-filled porosity. The authors observed the unexpected result that irrigation-induced pressure wave velocities were {approx}1,000 times faster than tracer velocities. The relationship between pressure wave velocities and fluid velocities is described using kinematic wave theory, presented for four parametric representations (Brooks-Corey, van Genuchten-Mualen, Broadbridge-White, and the Galileo Number), that predicts fluid pressure velocities to be from approximately two to fifteen times faster than saprolite tracer velocities. None of the kinematic models was able to reproduce observed rapid pressure wave velocities. A hydraulic form of the advection-diffusion equation based on Richards' equation is presented that favorably predicts the shape of pressure response curves only when the kinematic velocity is ignored and the hydraulic diffusivity of the unsaturated saprolite is considered. Based on the advection-diffusion equation, diffusion-dominated soil water pressure wave velocities should decrease with depth, eventually conforming with kinematic wave theory. Pressure pulse velocity monitoring may be an additional tool for estimating unsaturated hydraulic properties in low permeability media.

Rasmussen, T.C.; Baldwin, R.H. Jr.; Dowd, J.F.; Williams, A.G.

2000-02-01

63

Molecular Velocity Distribution Function Measurements in a Normal Shock Wave  

Microsoft Academic Search

Molecular velocity distribution functions have been measured throughout a normal, M = 1.59 helium shock wave that was formed in a low-density wind tunnel. The measurements were obtained by using the electron beam fluorescence technique. Throughout the shock transition, distributions of random velocities were observed from directions both parallel and perpendicular to the flow. Also, direct measurements were made of

E. P. Muntz; L. N. Harnett

1969-01-01

64

Piezoelectric sensor determination of arterial pulse wave velocity  

Microsoft Academic Search

Arterial pulse wave velocity (APWV) is a measure of the elasticity (or stiffness) of peripheral arterial blood vessels. The pulse referred to here will be the pressure pulse as opposed to the flow pulse measured by ultrasound Doppler. The pressure pulse velocity varies over the range from about 12 m s?1 to 15 m s?1 in stiff peripheral arteries, whereas

J McLaughlin; M McNeill; B Braun; P D McCormack

2003-01-01

65

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

NASA Astrophysics Data System (ADS)

A model of upper-mantle S-wave velocity and transverse anisotropy beneath northwestern Europe is presented, based on regional surface wave observations. Group velocities for both Love and Rayleigh surface waves are measured on waveform data from international and regional data archives (including temporary deployments) and then inverted for group velocity maps, using a method accounting for Fresnel zone sensitivity. The group velocity variations are larger than in global reference maps, and we are able to resolve unprecedented details. We then apply a linear inversion scheme to invert for local 1-D shear wave velocity profiles which are consequently assembled to a 3-D model. By choosing conservative regularization parameters in the 2-D inversion, we ensure the smoothness of the group velocity maps and hence of the resulting 3-D shear wave speed model. To account for the different tectonic regimes in the study region and investigate the sensitivity of the 1-D inversions to inaccuracies in crustal parameters, we analyse inversions with different reference models of increasing complexity (pure 1-D, 3-D crust/1-D mantle and pure 3-D). We find that all inverted models are very consistent at depths below 70 km. At shallower depths, the constraints put by the reference models, primarily Moho depth which we do not invert for, remain the main cause for uncertainty in our inversion. The final 3-D model shows large variations in S-wave velocity of up to +/-12 per cent. We image an intriguing low-velocity anomaly in the depth range 70-150 km that extends from the Iceland plume beneath the North Atlantic and in a more than 400 km wide channel under Southern Scandinavia. Beneath Southern Norway, the negative perturbations are around 10 per cent with respect to ak135, and a shallowing of the anomaly is indicated which could be related to the sustained uplift of Southern Scandinavia in Neogene times. Furthermore, our upper-mantle model reveals good alignment to ancient plate boundaries and first-order crustal fronts around the triple junction of the Baltica-Avalonia-Laurentia collision in the North Sea.

Weidle, Christian; Maupin, Valérie

2008-12-01

66

Effect of crack aperture on P-wave velocity and dispersion  

NASA Astrophysics Data System (ADS)

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.

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

2013-06-01

67

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

SciTech Connect

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)

Spence, W.L.

1985-04-01

68

Longitudinal variation and waves in Jupiter's south equatorial wind jet  

NASA Astrophysics Data System (ADS)

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 increasing with distance from the disturbance. The chevrons move with velocities near the maximum wind jet velocity of ˜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 = 75-100) 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 ˜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°N and 7.5°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.

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

2012-04-01

69

Seasonal variation of gravity wave activity in the lower atmosphere observed with the MU radar  

Microsoft Academic Search

In this paper we analyzed the seasonal variation of gravity wave activity in the troposphere and lower stratosphere (5-25 km) as revealed by monthly observations with the MU radar between December 1985 and December 1989. In the lower stratosphere, wind velocity variance due to gravity waves with periods of 5 min-21 hours showed a clear annual variation with a maximum

Y. Murayama; T. Tsuda; S. Fukao

1994-01-01

70

Nonlinear group velocity of an electron plasma wave  

SciTech Connect

The nonlinear group velocity of an electron plasma wave is investigated numerically using a Vlasov code, and is found to assume values which agree very well with those predicted by a recently published theory [D. Benisti et al., Phys. Rev. Lett. 103, 155002 (2009)], which we further detail here. In particular we show that, once Landau damping has been substantially reduced due to trapping, the group velocity of an electron plasma wave is not the derivative of its frequency with respect to its wave number. This result is moreover discussed physically, together with its implications in the saturation of stimulated Raman scattering.

Benisti, Didier; Morice, Olivier; Gremillet, Laurent; Siminos, Evangelos [CEA, DAM, DIF, F-91297 Arpajon (France); Strozzi, David J. [AX Division, Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)

2010-08-15

71

Mean drift velocity in the Stokes interfacial edge wave  

NASA Astrophysics Data System (ADS)

The Stokes interfacial edge wave in a viscous rotating two-layer system is studied theoretically. The mean wave-induced Lagrangian drift velocity is obtained from the vertically integrated Eulerian equations of momentum and mass, correct to second order in wave steepness. The analysis is valid for shallow-water waves in the case when the upper layer is much thicker than the lower layer. In the lower layer the effect of viscosity is confined to a frictional boundary layer at the bottom. The waves are trapped by the bottom slope and can propagate in either direction along the bottom contours (in the y direction). Assuming that the waves attenuate in space as they propagate, this yields a Stokes drift velocity and a mean energy density E that decay exponentially in y. In this problem -?E/?y is the relevant radiation stress forcing in the wave propagation direction. It is explained why this differs from the radiation-stress forcing of -??E/?y for plane waves in an unbounded nonrotating shallow ocean. The bottom stress acting on the mean Eulerian wave-induced flow is modeled by a turbulent friction coefficient. The results show that the maximum mean Eulerian drift current is considerably larger than the maximum Stokes drift velocity. Since the Eulerian current becomes negative at larger seaward distances, the total mean Lagrangian drift current is confined to a rather narrow wedge in the lower layer.

Weber, Jan Erik H.; StøYlen, Eivind

2011-04-01

72

Radial velocity variations in pulsating Ap stars. V. 10 Aquilae  

NASA Astrophysics Data System (ADS)

We have used precise stellar radial velocities to study the pulsational motion of the rapidly oscillating Ap star 10 Aql. Observations were made on three separate nights using the high resolution spectrograph of the Harlan J. Smith 2.7 m telescope at McDonald Observatory. A high radial velocity precision was achieved by using an iodine gas absorption cell. The integrated radial velocity measurements using the full wavelength region covered by iodine absorption lines (5000-6300 Å) failed to detect any coherent pulsational velocity variations to a level of 2.5-5 m s-1. An analysis over a much narrower wavelength range revealed that pulsational radial velocity variations are indeed present in 10 Aql, but only in 5 spectral lines. The amplitude of these variations ranged from about 100 m s-1 to as high as 398 m s-1 for an unidentified feature at ?5471.40 Å. Other spectral features showing pulsational radial velocity variations are tentatively identified as Sm II and Tm II. Based on observations collected at McDonald Observatory.

Hatzes, A. P.; Mkrtichian, D. E.

2005-01-01

73

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

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

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

74

Adjoint wave-equation velocity analysis  

Microsoft Academic Search

Summary A methodology for velocity updating using one-way wavefield extrapolation is described. The method is based on iterative optimization of two different objective functions; one that minimizes an image difference, and a second that optimizes focusing in the offset-at-depth domain, or equivalently, gather flatness in the angle domain. Various aspects of the method are illustrated with a 4D data example

U. Albertin; P. Sava; J. Etgen; M. Maharramov

2006-01-01

75

THE VALIATION OF WATER LEVEL AND FLOW VELOCITY IN SEMI-CLOSED WATER AERA BY WIND AND BOAT WAVE  

NASA Astrophysics Data System (ADS)

In this study, to clarify the relationship between water level variation and turbulence of flow, field observations were carried out in Omaehama beach, Nishinomiya City, Hyogo Prefecture, JAPAN. In each observation, wind speed and its direction, water level, wave height, flow velocity and its direction were measured in the vicinity of shoreline. The data of wave height was transformed to the velocity by using a liner filter theory and examined the effect of boat wave and wind one on turbulence of flow. The transferred velocity from wind wave was coincided with the turbulence of flow, however, that from boat wave was not so good. From the results of this study, we can see both boat wave and wind one are the significant factors of water level variation in urban semi-closed water area.

Uno, Kohji; Tsujimoto, Gozo; Kakinoki, Tetsuya

76

Group-Velocity-Matched Three Wave Mixing in Birefringent Crystals  

SciTech Connect

We show that the combination of pulse-front slant, k-vector tilt, and crystal birefringence often permits exact matching of both phase and group velocities in three wave mixing in birefringent crystals. This makes possible more efficient mixing of short light pulses, and it permits efficient mixing of chirped or broad bandwidth light. We analyze this process and present examples. Differences in the group velocities of the three interacting waves in a nonlinear crystal often limits the effective interaction length. For example, in mixing very short pulses, temporal walk off can stretch the pulses in time unless the crystal is very short. Efficient mixing with such short crystals requires high irradiances, but the irradiances are limited by higher order nonlinear effects such as intensity-dependent refractive index and two-photon absorption. Improved matching of the group velocities can alleviate this problem, allowing longer crystal and lower irradiances. Similarly, for high energy pulses, practical limits on crystal apertures mandate temporally stretching the pulses to reduce irradiances. For the resulting chirped pulses, temporal walk off restricts the chirp range unless the group velocities are well matched. In addition to perfectly matching the group velocities of all three waves, it is sometimes useful to match two velocities, such as the signal and idler in parametric amplification, permitting broadband parametric amplification, or to arrange the velocities of two inputs to bracket the generated sum frequency pulse, giving pulse compression under suitable circumstances.

SMITH,ARLEE V.

2000-12-12

77

Optical determination of the phase velocity of short gravity waves  

NASA Astrophysics Data System (ADS)

Images of short wind-driven gravity waves were taken from an offshore platform, using a charge coupled device television camera recording diffuse sky radiance reflected from the ocean surface. A two-dimensional power spectrum was calculated from nine statistically independent images. The resultant ensemble-averaged spectrum exhibited good statistical stability and provided information on the angular spread and direction of the wave components present. One-dimensional sampling of each image in a sequence allowed a space-time image to be constructed which clearly shows the effects of wave dispersion as well as the modulation of the phase velocities of the short wavelength waves by the long wavelength components. An ensemble-averaged space-time spectrum, when combined with the directional parameters, is compared with the predictions of linear gravity wave dispersion theory. Two distinct wave systems were present: the local wind driven system showed a space-time spectrum in agreement with linear theory out to ˜1 cyc/m, but with excess phase velocity at higher spatial frequencies. The second wave system, which was presumably generated by a distant wind field, showed a deficiency in phase velocity when compared to linear theory.

Gotwols, B. L.; Irani, G. B.

1980-07-01

78

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

NASA Astrophysics Data System (ADS)

We present a new transversely isotropic shear wave velocity model of the upper mantle in the European and Mediterranean region, obtained by analysis of surface wave group speed. Our data set consists of fundamental mode Love and Rayleigh wave group speed measurements, taken by multi-filter analysis on wave groups isolated by phase matched filtering on seismograms recorded at regional distance. Group velocity maps for periods ranging from 35 to 150s are then obtained by linear inversion. Data coverage in this region is not uniform, as it is highly influenced by the uneven distribution of stations and events. We therefore stabilize the inversion using a priori information in the form of a smooth global reference model we previously derived by inverting a phase velocity dataset (Ekstrom et al. 1997) on a global grid, where our regional grid is embedded. This greatly improves the coverage near the borders of our region. In each pixel - approximately 120 km in size - the set of group velocities are then used to find the best-fitting vertical shear velocity profile by nonlinear inversion. In this step, we make use of a priori knowledge from PREM and CRUST2.0. We present results in terms of Voigt average velocity variations, and radial anisotropy, and compare them with other results from the literature. The resulting model confirms the larger-scale deep geological features known for the region, and add great detail due to the inclusion of measurements on shorter paths.

Schivardi, R.; Morelli, A.

2007-12-01

79

Preliminary investigation on apparent seismic velocity variations caused by microseism noise source variability  

NASA Astrophysics Data System (ADS)

Currently there is strong interest in monitoring temporal changes in seismic wave velocity in various geological settings. These settings can range from volcano monitoring to reservoir monitoring amongst others. Green's functions are often used to monitor temporal variations in seismic velocity as their arrival times contain information about velocity changes. The velocities can be measured through the cross correlation of Green's functions for a given pair of stations. Correlation of ambient noise is typically used for Green's function retrieval. The great advantage of using noise is that noise is continuous in time and there are no natural explosive or repeatable sources required. However temporal and spatial variations of non-uniformly distributed noise sources may lead to apparent changes in Green's functions which are related to the source not the path. This could lead to a misinterpretation of temporal changes in wave velocity. Ireland is a good location in which to study these effects, as it is tectonically very quiet and is relatively close to large noise sources in the North Atlantic. The spatial and temporal distribution of noise sources are being tracked using seismic arrays deployed in Ireland under a sister project (called WaveObs). Concurrently, in this project, we are searching for temporal variations in wave velocity using noise correlation and comparing them to the temporal and spatial distribution of the noise sources as determined under the WaveObs project. The aims of this project are to find out how the waveform and the arrival time of the Green's functions correlate with spatial and temporal variability of the noise sources and what minimum trace length of noise is required for the Green's functions to converge. The expected outcome of the project is therefore an assessment of the degree to which velocity variations are caused by changes in the sources. Hence, these lemiting conditions can be considered when this method is used in a different setting where we expect velocities to change rapidly e.g. on a volcano or in a reservoir.

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

2013-04-01

80

S wave velocity structure of the Northern Cascadia subduction zone  

Microsoft Academic Search

Teleseismic receiver functions from an array of portable broadband seismograph stations located in southwestern British Columbia are interpreted to estimate the S wave velocity structure to upper mantle depths across the northern Cascadia subduction zone. At our westernmost station on central Vancouver Island, a prominent low-velocity zone (DeltaVs=-1 km s-1) with a high Poisson's ratio is estimated at 36-41 km

John F. Cassidy; Robert M. Ellis

1993-01-01

81

Measurement of shock wave velocity using the Doppler principle  

Microsoft Academic Search

The combination of a schlieren system with a laser Doppler arrangement enables one to measure the velocity of moving phase\\u000a objects. The combined system is applied to determine the velocities of air shock waves in a shock tube. The method is described\\u000a independently in terms of the Doppler principle and in terms of optical interferometry. The two descriptions are found

W. Merzkirch; W. Erdmann

1974-01-01

82

Nearshore wave height variation in unsaturated surf  

NASA Astrophysics Data System (ADS)

The nearshore evolution of wave height is presented from field observations during unsaturated surf conditions from 10 different beaches characterized by microtidal conditions and predominantly swell-dominated wave climates. Wave evolution is presented in terms of wave height to water depth ratio (?) for comparison with previous data from saturated surf. Both conventional time-averaged (?rms) and a new wave-by-wave analysis (?w) are performed. Values of ? increase with increasing offshore wave height, indicating unsaturated surf. The observations show a variation in ? values from near constant values in the mid surf zone to rapidly and asymptotically increasing ? values in the inner surf zone. In contrast to previous data from saturated surf, ? shows no dependence on either the absolute beach slope or the relative beach slope ?/k?. The skewness of the distributions of ?w is consistent with waves that are not depth limited. The inner surf zone wave heights are approximately equally dependent on the water depth and offshore wave height. The previous observations of ? from saturated surf are shown to be consistent with a terminal bore height at the shoreline which is in excellent agreement with a previously derived value for the Miche parameter. In contrast, for the present unsaturated surf conditions, the terminal bore height at the shoreline can be approximated by Hb ? 0.12Ho, which is consistent with recent laboratory data sets.

Power, H. E.; Hughes, M. G.; Aagaard, T.; Baldock, T. E.

2010-08-01

83

Impact of Phase Transitions on P Wave Velocities  

SciTech Connect

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.

D Weidner; L Li

2011-12-31

84

Impact of Phase Transitions on P Wave Velocities  

SciTech Connect

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.

Weidner, D.; Li, L

2010-01-01

85

Anisotropic parameter estimation using velocity variation with offset analysis  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

86

Miniaturised ultrasonic-wave velocity and attenuation sensors for liquid  

Microsoft Academic Search

The development of miniaturized ultrasonic-wave velocity and attenuation sensors for liquids is described. The sensors employ ZnO-film\\/Pyrex-glass composite diaphragm transducers. The transducers efficiently launch spurious-free ultrasonic-waves into liquids over a wide bandwidth in VHF\\/UHF ranges. Emphasis is placed on the development of sensors used for online monitoring of industrial production processes. The sensor is made by uniting the transducer with

K.-Y. Hashimoto; Yoshihisa Yamada; Takuya Ienaka; Masatsune Yamaguchi

1992-01-01

87

On electromagnetic waves with a negative group velocity  

SciTech Connect

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.

Makarov, V. P.; Rukhadze, A. A.; Samokhin, A. A. [Russian Academy of Sciences, Prokhorov Institute of General Physics (Russian Federation)

2010-12-15

88

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

NASA Astrophysics Data System (ADS)

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.

Krupi?ski, Adam

2012-10-01

89

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

Microsoft Academic Search

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

Jonathan M. Lees; Robert S. Crosson

1990-01-01

90

Teleseismic P-wave Velocity Tomography Beneath The Arabian Peninsula  

Microsoft Academic Search

We have imaged tomographically the three-dimensional velocity structure of the upper mantle beneath the Arabian Peninsula using teleseismic P-waves. The data came from the Saudi Arabian National Digital Seismic Network (SANDSN) operated by King Abdulaziz City for Science and Technology (KACST) and three permanent stations (RAYN, EIL and MRNI). The KACST network consists of 38 stations (27 broadband and 11

A. A. Nyblade; A. Rodgers; A. Al-Amri

2004-01-01

91

Liquefaction Resistance of Soils from Shear-Wave Velocity  

Microsoft Academic Search

A simplified procedure using shear-wave velocity measurements for evaluating the liquefaction resistance of soils is presented. The procedure was developed in cooperation with industry, researchers, and practitioners and evolved from workshops in 1996 and 1998. It follows the general format of the Seed-Idriss simplified procedure based on standard penetration test blow count and was developed using case history data from

Ronald D. Andrus; Kenneth H. Stokoe II

2000-01-01

92

Studies on the determination of shear wave velocity in sands  

Microsoft Academic Search

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

P. P. Bartake; D. N. Singh

2007-01-01

93

Magnetically accelerated, ultrahigh velocity flyer plates for shock wave experiments  

Microsoft Academic Search

The intense magnetic field produced by the 20 MA Z accelerator is used as an impulsive pressure source to accelerate metal flyer plates to high velocity for the purpose of performing plate impact, shock wave experiments. This capability has been significantly enhanced by the recently developed pulse shaping capability of Z, which enables tailoring the rise time to peak current

R. W. Lemke; M. D. Knudson; D. E. Bliss; K. Cochrane; J.-P. Davis; A. A. Giunta; H. C. Harjes; S. A. Slutz

2005-01-01

94

A New Dual Channel Pulse Wave Velocity Measurement System  

Microsoft Academic Search

Pulse wave velocity (PWV) is the most popular index to assessment the arterial stiffness. Currently, several non-invasive examination methods with single channel for PWV are announced. This paper proposes a non-invasive digital volume pulse (DVP) measuring system using a dual channel simultaneous measurement method try to meet the demands for home healthcare equipment which is easy to operate. Through synchronal

Yung-kang Chen; Hsien-tsai Wu; Chih-kai Chi; Wei-chuan Tsai; Ju-yi Chen; Ming-chun Wang

2004-01-01

95

Electromagnetic wave propagation in dispersive negative group velocity media  

Microsoft Academic Search

We study theoretically the propagation of electromagnetic waves in an infinite, isotropic, and homogenous, medium with both temporal and spatial dispersion included. We derive a partial differential equation connecting temporal and spacial dispersion to achieve negative group velocity. An exact solution of the equation is found and is shown to lead to negative-refraction media even when both isin and mu

Said M. Mikki; A. A. Kishky

2008-01-01

96

Blast Waves Generated by Constant Velocity Flames: A Simplified Approach.  

National Technical Information Service (NTIS)

The self-similar solution to the blast waves generated by a constant velocity flame can be calculated easily if one assumes that the pressure and density between the flame and shock are constant, irrespective of geometry. The technique of calculation is d...

R. A. Strehlow

1974-01-01

97

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

NASA Astrophysics Data System (ADS)

Recent studies have revealed that uplift of the Tibetan plateau may be related to removal of lithospheric mantle and resulting emplacement of hotter, less dense asthenospheric material. In addition to these modes of deformation, other studies have proposed that plateau uplift and crustal thickening have occurred through a process of lateral crustal flow. In order to study the evolution and continental dynamics of the Tibetan plateau, we deployed 74 broadband seismic stations throughout northern Tibet. We have measured the fundamental mode Rayleigh wave phase velocities using the two plane wave approach for periods between 20-143 seconds and verified our results utilizing a two station method. Similar to the fast directions obtained from teleseismic shear wave splitting, our measurements indicate significant (>2%) azimuthal anisotropy throughout the upper mantle down to depths exceeding 250 km, with a dominantly east-west fast direction. Although we observe some variations in fast directions with depth, they are generally consistent (i.e., within 15 degrees). Furthermore, we observe a correlation between fast directions and strikes of major fault zones that may be indicative of vertically coherent deformation within the mantle. Our 3D tomographic models show an uppermost mantle low velocity zone north of Bangong-Nujiang Suture (BNS) in northern Tibet, and a high velocity anomaly extending ~200 km centered on BNS. We suspect that the low velocity zone is due to warmer and thinner lithosphere in the northern Qiangtang and Songpan-Gonzi terranes. At depth, we observe high velocity bodies to the south both in our phase velocity and shear wave velocity maps, possibly indicative of underthrusting Indian lithosphere. Further, high velocity bodies weaken with decreasing depth, which could be alternatively interpreted as delaminating Asian lithosphere. Shear-wave velocities and dispersion curves for northern Tibet are lower than those of Southern Tibet at depths ~80-190 km, indicating warmer, thinner lithosphere. Phase velocity tomography results are coherent with those of body waves. Comparison of dispersion curves obtained from northern and southern portions of the study region reveal lower phase velocities, implying that underthrusting does not extend beneath the entire region. In our models, a high velocity body outlines the geometry of Qaidam Basin clearly, indicating a thicker lithosphere. We do not see any indication of continental subduction along the southern boundary of the basin.

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

2010-12-01

98

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

Microsoft Academic Search

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

Chong Zeng; Jianghai Xia; Richard D. Miller; Georgios P. Tsoflias

2011-01-01

99

Traveling waves in an optimal velocity model of freeway traffic  

NASA Astrophysics Data System (ADS)

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].

Berg, Peter; Woods, Andrew

2001-03-01

100

Traveling waves in an optimal velocity model of freeway traffic.  

PubMed

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

Berg, P; Woods, A

2001-02-21

101

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

NASA Astrophysics Data System (ADS)

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

Bosch, Miguel

1997-03-01

102

Wave induced velocities inside and outside a riparian seagrass bed.  

NASA Astrophysics Data System (ADS)

Coastal wetlands landscapes, such as salt marshes and mangroves, form and evolve by dynamic feedbacks between vegetation establishment, flow hydrodynamics, and landforms changes. The vegetation-flow feedbacks make coastal vegetation very useful for coastal defense against storms and erosion, therefore importance of conservation of both aquatic and riparian vegetation is today commonly recognized. Experiments were carried out in order to study the flow structure within and outside a riparian seagrass bed in a laboratory flume subject to propagating waves. Different canopy densities, vegetation heights and wave frequencies were studied. Experiments were conducted in a 5m-long, 50cm-wide and 50 cm-deep flume equipped with a wave maker. Flow velocity measurements were undertaken with a microADV (Sontek, Inc) in two different points situated in the transversal section of the flume, one within the canopy and the other outside (in the centre of the flume). A mean return current was found in both regions studied (outside and within the vegetation) only for emergent vegetation. The mean current induced within the emergent vegetation was found larger for lower densities and found at the bottom layer of the flume (from the flume bottom to the half of the depth of the water). In contrast, this current was shifted to shallower depths for larger densities (from the half of the flume water up to 4 cm depth). On the other hand, induced current velocities outside the vegetation were found higher for emergent vegetation patterns than for submerged, decreasing the differences when the canopy density increases. For submerged vegetation of different densities similar values of the mean current velocity were found outside the canopy. Within the meadow horizontal wave velocity behavior is independent on both the vegetation density and height, but above the vegetation it appears a clear differentiation, becoming higher the wave velocity in the submerged vegetation case.

El-Allaoui, N.; Serra, T.; Soler, M.

2012-04-01

103

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

PubMed Central

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.

Varghese, Tomy; Madsen, Ernest L.

2011-01-01

104

Lateral Variation of Velocity Discontinuities in the Lowermost Mantle Under the Cocos Plate  

NASA Astrophysics Data System (ADS)

A double Array Method (DAM) and Migration method have been used to delineate the lateral variation of the discontinuities in the lowermost mantle under the Cocos Plate. We used P and S waves from deep and intermediate earthquakes in South America recorded at Californian broadband network stations. For the DAM, the data were deconvolved by the P and S beams for each event to get rid of the source time function so that all events can be stacked simultaneously. Subsequently, a band-pass filter of 1-10 s was applied for P waves and a low-pass filter at 0.3 Hz for S waves. We set bins to cover the PcP and ScS reflection points and the sizes of bins are 4 degrees of latitude for P waves and 2 degrees for S waves. The bins are shifted by 1 degree overlapping from the south to the north. We detect P wave velocity anomalies in this region where up to now mainly S wave observations have been reported. The topography observed in P wave essentially follows the one reported in S wave using the migration method.The P and S wave velocity discontinuties detected by the DAM are essentially consistent, although the form of the discontinuities depends on the frequency bands. The discontinuities in the southern part of our study area tend to be deeper than those in the northern part undulating from 2550 km to 2700 km depths both in P and S waves. This may indicate the top of the dense subducted slab or the recently discovered post-perovskite structure deep mantle phase change.

Kito, T.; Rost, S.; Thomas, C.; Garnero, E. J.

2005-12-01

105

Calculation of Rayleigh-wave phase velocities due to models with a high-velocity surface layer  

NASA Astrophysics Data System (ADS)

Rayleigh-wave phase velocities have been utilized to determine shear (S)-wave velocities in near-surface geophysics since early 1980s. One of the key steps is to calculate theoretical dispersion curves of an earth model. When the S-wave velocity of the surface layer is higher than some of the layers below, however, the Rayleigh-wave phase velocity in a high-frequency range calculated by existing algorithms approaches the lowest S-wave velocity among the layers above the half-space, rather than a value related to the S-wave velocity of the surface layer. According to our numerical modeling results based on wave equation, trends of the Rayleigh-wave dispersive energy approach about a 91% of the S-wave velocity of the surface layer at a high-frequency range when its wavelength is much shorter than the thickness of the surface layer, which cannot be fitted by a dispersion curve calculated by existing algorithms. We propose a method to calculate Rayleigh-wave phase velocities of models with a high-velocity surface layer by considering its penetration depth. We build a substituted model that only contains the layer with the lowest S-wave velocity among the layers above the half-space and the layers above it. We use the substituted model to replace the original model to calculate phase velocities when the Rayleigh-wave wavelength is not long enough to penetrate the lowest S-wave velocity layer. Several synthetic models are used to verify fitness between the dispersion curve calculated by our proposed method and the trend of the highest dispersive energy. Examples of inversion also demonstrate high accuracy of using our method as the forward calculation method during the inversions.

Pan, Yudi; Xia, Jianghai; Gao, Lingli; Shen, Chao; Zeng, Chong

2013-09-01

106

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

NASA Astrophysics Data System (ADS)

Shear (S)-wave velocity is a key property of near-surface materials and is the fundamental parameter for many environmental and engineering geophysical studies. Directly acquiring accurate S-wave velocities from a seismic shot gather is usually difficult due to the poor signal-to-noise ratio. The relationship between Rayleigh-wave phase velocity and frequency has been widely utilized to estimate the S-wave velocities in shallow layers using the multichannel analysis of surface waves (MASW) technique. Hence, Rayleigh wave is a main focus of most near-surface seismic studies. Conventional dispersion analysis of Rayleigh waves assumes that the earth is laterally homogeneous and the free surface is horizontally flat, which limits the application of surface-wave methods to only 1D earth models or very smooth 2D models. In this study I extend the analysis of Rayleigh waves to a 2D domain by employing the 2D full elastic wave equation so as to address the lateral heterogeneity problem. I first discuss the accurate simulation of Rayleigh waves through finite-difference method and the boundary absorbing problems in the numerical modeling with a high Poisson's ratio (> 0.4), which is a unique near-surface problem. Then I develop an improved vacuum formulation to generate accurate synthetic seismograms focusing on Rayleigh waves in presence of surface topography and internal discontinuities. With these solutions to forward modeling of Rayleigh waves, I evaluate the influence of surface topography to conventional dispersion analysis in 2D and 3D domains by numerical investigations. At last I examine the feasibility of inverting waveforms of Rayleigh waves for shallow S-wave velocities using a genetic algorithm. Results of the study show that Rayleigh waves can be accurately simulated in near surface using the improved vacuum formulation. Spurious reflections during the numerical modeling can be efficiently suppressed by the simplified multiaxial perfectly matched layers. The conventional MASW method can tolerate gentle topography changes with insignificant errors. Finally, many near-surface features with strong lateral heterogeneity such as dipping interfaces, faults, and tunnels can be imaged by the waveform inversion of Rayleigh waves for shallow S-wave velocities. This thesis consists of four papers that are either published (chapter 1) or in review (chapter 2, 3, and 4) for consideration of publication to peer-refereed journals. Each chapter represents a paper, and therefore inadvertently there will be a certain degree of overlap between chapters (particularly for the introduction parts, where references to many common papers occur).

Zeng, Chong

107

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

PubMed

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

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

2010-05-19

108

A P wave velocity model of Earth's core  

NASA Astrophysics Data System (ADS)

Present Earth core models derived from the retrieval of global Earth structure are based on absolute travel times, mostly from the International Seismological Centre (ISC), and/or free-oscillation eigenfrequencies. Many core phase data are left out of these constructions, e.g., PKP differential travel times, amplitude ratios, and waveforms. This study is an attempt to utilize this additional information to construct a model of core P wave velocity which is consistent with the different types of core phase data available. In conjunction with our waveform modeling we used 150 differential time measurements and 87 amplitude ratio measurements, which were the highest-quality observations chosen from a large population of Global Digital Seismograph Network (GDSN) records. As a result of fitting these various data sets, a one-dimensional P wave velocity model of the core, PREM2, is proposed. This model, modified from the Preliminary Reference Earth Model (PREM) (Dziewonski and Anderson, 1981), shows a better fit to the combined data set than any of the existing core models. Major features of the model include a sharp velocity discontinuity at the inner core boundary (ICB), with a large jump (0.78 km/s), and a low velocity gradient at the base of the fluid core. The velocity is nearly constant over the lower 100 km of the outer core. The model features a depth-dependent Q? structure in the inner core such that a constant t* for the inner core fits the amplitude ratios and waveforms of short-period waves moderately well. This means the top of the inner core is more attenuating than the deeper part of the inner core. In addition, the P velocity in the lowermost mantle is reduced from that of PREM as a baseline adjustment for the observed separations of the DF and AB branches of PKP at large distances.

Song, Xiaodong; Helmberger, Don V.

1995-06-01

109

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

SciTech Connect

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.

Artley, C.T.

1992-12-01

110

Measurements of parallel electron velocity distributions using whistler wave absorption  

SciTech Connect

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.

Thuecks, D. J.; Skiff, F.; Kletzing, C. A. [Department of Physics and Astronomy, University of Iowa, 203 Van Allen Hall, Iowa City, Iowa 52242 (United States)

2012-08-15

111

Measurements of parallel electron velocity distributions using whistler wave absorption.  

PubMed

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

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

2012-08-01

112

Measurements of parallel electron velocity distributions using whistler wave absorption  

NASA Astrophysics Data System (ADS)

We describe a diagnostic to measure the parallel electron velocity distribution in a magnetized plasma that is overdense (?pe > ?ce). This technique utilizes resonant absorption of whistler waves by electrons with velocities parallel to a background magnetic field. The whistler waves were launched and received by a pair of dipole antennas immersed in a cylindrical discharge plasma at two positions along an axial background magnetic field. The whistler wave frequency was swept from somewhat below and up to the electron cyclotron frequency ?ce. As the frequency was swept, the wave was resonantly absorbed by the part of the electron phase space density which was Doppler shifted into resonance according to the relation ? - k||v|| = ?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.

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

2012-08-01

113

Joint inversion of Rayleigh wave phase velocity and ellipticity using USArray: Constraining velocity and density structure in the upper crust  

NASA Astrophysics Data System (ADS)

Rayleigh wave ellipticity, or H/V ratio, observed on the surface is particularly sensitive to shallow earth structure. In this study, we jointly invert measurements of Rayleigh wave H/V ratio and phase velocity between 24-100 and 8-100 sec period, respectively, for crust and upper mantle structure beneath more than 1000 USArray stations covering the western United States. Upper crustal structure, in particular, is better constrained by the joint inversion compared to inversions based on phase velocities alone. In addition to imaging Vs structure, we show that the joint inversion can be used to constrain Vp/Vs and density in the upper crust. New images of uppermost crustal structure (<3 km depth) are in excellent agreement with known surface features, with pronounced low Vs, low density, and high Vp/Vs anomalies imaged in the locations of several major sedimentary basins including the Williston, Powder River, Green River, Denver, and San Juan basins. These results demonstrate not only the consistency of broadband H/V ratios and phase velocity measurements, but also that their complementary sensitivities have the potential to resolve density and Vp/Vs variations.

Lin, Fan-Chi; Schmandt, Brandon; Tsai, Victor C.

2012-06-01

114

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

SciTech Connect

Relativistic optical guiding allows two colinear short pulse radiation beams, provided they are of sufficiently high power, to propagate through a plasma without diffracting. By further accounting for finite radial beam geometry, it is possible for the phase velocity of the radiation beat (ponderomotive) wave to equal the speed of light. Provided the plasma wave phase velocity remains equal to the beat wave phase velocity, then phase detuning between the accelerated electrons and the plasma wave is no longer a limiting factor in determining the maximum energy gain in the plasma heat wave accelerator. As the plasma wave grows to sufficiently large amplitudes, however, it strongly affects the diffractive properties of the radiation beams. In particular, a large amplitude plasma wave will break up an initially uniform radiation beam into periodic beamlet segments, of length less than or equal to half a plasma wavelength, which remain optically guided as they propagate. In the plasma beat wave accelerator, for an optimal choice of the mismatch between the radiation beat frequency and the ambient plasma frequency, then the resonantly driven plasma wave may lead to enhanced focusing of the radiation beams. {copyright} 1989 American Institute of Physics

Esarey, E.; Ting, A.; Sprangle, P. (Plasma Theory Branch, Plasma Physics Division, Naval Research Laboratory, Washington, DC 20375-5000 (US))

1989-10-15

115

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

SciTech Connect

Tomographic inversion is applied to delay times from local earthquakes to image three dimensional velocity variations in the Puget Sound region of western Washington. The 37,500 square km region is represented by nearly cubic blocks of 5 km per side. P-wave arrival time observations from 4,387 crustal earthquakes, with depths of 0 to 40 km, were used as sources producing 36,865 rays covering the target region. A conjugate gradient method (LSQR) is used to invert the large, sparse system of equations. To diminish the effects of noisy data, the Laplacian is constrained to be zero within horizontal layers, providing smoothing of the model. The resolution is estimated by calculating impulse responses at blocks of interest and estimates of standard errors are calculated by the jackknife statistical procedure. Results of the inversion are correlated with some known geologic features and independent geophysical measurements. High P-wave velocities along the eastern flank of the Olympic Peninsula are interpreted to reflect the subsurface extension of Crescent terrane. Low velocities beneath the Puget Sound further to the east are inferred to reflect thick sediment accumulations. The Crescent terrane appears to extend beneath Puget Sound, consistent with its interpretation as a major accretionary unit. In the southern Puget Sound basin, high velocity anomalies at depths of 10-20 km are interpreted as Crescent terrane and are correlated with a region of low seismicity. Near Mt. Ranier, high velocity anomalies may reflect buried plutons.

Lees, J.M.; Crosson, R.S. (Univ. of Washington, Seattle (United States))

1990-04-10

116

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

117

Shear Wave Velocity Models for Southeasthern Europe from Inversion of Surface Wave Data  

NASA Astrophysics Data System (ADS)

Digital seismograms from more than 100 earthquakes located in the southeastern part of Europe, recorded by 3-component very broadband seismometers at 9 stations, were processed to obtain the dispersion properties of Rayleigh and Love surface waves. Regionalized group-velocity patterns for periods in range 8 40 seconds were determined using 2D-tomography method. Local group-velocity curves were constructed in a grid of 1x1 degree. Some phase velocity data were collected from the literature. Both phase and group dispersion data were processed by linear inversion method based on Backus-Gilbert inversion theory. S-wave velocity models were constructed for each local dispersion curve. Comparison between the models obtained by Rayleigh wave inversion and Love wave inversion was done. Models obtained show good correlation with well known geological zones in the studied region. Maps of S-wave velocities at different depths were constructed. The discrepancies between Love and Rayleigh Vs models are considered as an evidence for existence of anisotropic layers in the lithosphere.

Raykova, R.; Nikolova, S. B.

2003-04-01

118

Velocities of Compressional and Shear Waves in Marine Sediments Determined In Situ from a Research Submersible  

Microsoft Academic Search

In situ measurements of the velocity and attenuation of compressional waves, and velocities of Stoneley waves from which shear-wave velocities were computed, were made at three stations in the sea floor off San Diego, California, from a research submersible; a fourth station was occupied by divers. Sediment types and water depths ranged from medium sand at 20 meters to clayey

E. L. Hamilton; H. P. Bucker; D. L. Keir; J. A. Whitney

1970-01-01

119

Constraints on the seismic wave velocity structure beneath the Tibetan plateau and their tectonic implications  

Microsoft Academic Search

We combine observations of group and phase velocity dispersion of Rayleigh waves, of the waveform of a long-period PL phase, of Pn and Sn velocities from unreversed refraction profiles using earthquakes, and of teleseismic S-P travel time residuals to place bounds on the seismic wave velocity structure of the crust and upper mantle under Tibet. From surface wave measurements alone,

Wang-Ping Chen; Peter Molnar

1981-01-01

120

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

Microsoft Academic Search

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

H. Kwun

1985-01-01

121

Near surface shear wave velocity in Bucharest, Romania  

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

122

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

PubMed

Knowledge of the seismic velocity structure at the top of the Earth's inner core is important for deciphering the physical processes responsible for inner-core growth. Previous global seismic studies have focused on structures found 100 km or deeper within the inner core, with results for the uppermost 100 km available for only isolated regions. Here we present constraints on seismic velocity variations just beneath the inner-core boundary, determined from the difference in travel time between waves reflected at the inner-core boundary and those transmitted through the inner core. We found that these travel-time residuals-observed on both global seismograph stations and several regional seismic networks-are systematically larger, by about 0.8 s, for waves that sample the 'eastern hemisphere' of the inner core (40 degrees E to 180 degrees E) compared to those that sample the 'western hemisphere' (180 degrees W to 40 degrees E). These residuals show no correlation with the angle at which the waves traverse the inner core; this indicates that seismic anisotropy is not strong in this region and that the isotropic seismic velocity of the eastern hemisphere is about 0.8% higher than that of the western hemisphere. PMID:11323668

Niu, F; Wen, L

2001-04-26

123

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

NASA Astrophysics Data System (ADS)

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.

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

2011-12-01

124

Tomographic reconstruction of upper crustal velocity variations in the Arunta Block, central Australia  

NASA Astrophysics Data System (ADS)

A Seismic refraction/reflection programme of crustal/upper-mantle investigations was recently undertaken by the Australian Bureau of Mineral Resources within the Proterozoic Arunta Block, central Australia. One experiment involved the successive deployment of sixteen portable Seismic recorders on two approximately orthogonal, intersecting traverses. Shots detonated on one traverse were recorded on the other traverse to give three-dimensional coverage. Shot-receiver distances varied from 1 to 39 km.P-wave first-arrival times were processed using an OCSIRT (overlapping-cell simultaneous iterative reconstruction tomography) technique to produce a map of upper crustal velocity inhomogeneity. Synthetic data, using the same shooting geometry, were also processed as an aid to interpretation.The final tomograms exhibit a velocity variation from 5.5 to 6.4 km s-1. The higher velocities (> 5.9 km s-1) are associated with mafic and felsic granulites of the Central Arunta Province that have been thrust over amphibolite facies gneisses and migmatites of the Southern Arunta Province. The lower velocities (< 5.9 km s-1) are generally associated with wave paths through the mylonites of the Redbank Thrust Zone and migmatitic gneisses of the Southern Arunta Province.

Greenhalgh, S. A.; Sugiharto, S.; Wright, C.; Goleby, B. R.

1990-02-01

125

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

NASA Astrophysics Data System (ADS)

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.

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

2003-12-01

126

Effects of crustal thickness variations on surface wave phase delays  

NASA Astrophysics Data System (ADS)

Surface waves are very sensitive to crustal thickness perturbations and can be potentially used to constrain crustal structure at a global scale. In this study, we investigate finite-frequency effects of surface wave phase delays upon variations in crustal thickness as well as non-linear dependence of phase delays upon Moho depth variations. We simulate wave propagation in global crustal models using spectral element method (SEM) and compare SEM delay-time measurements with calculations based upon ray theory and finite-frequency theory. Our calculations confirm that finite-frequency effects can be significant when the dominant length scale of Moho depth perturbations is comparable to seismic wavelengths. In regional studies where Moho depth perturbations are less than ˜10 km, boundary sensitivity kernels based on linear perturbation theory can be applied to model finite-frequency effects; in global inversions where perturbations in crustal thickness are large, non-linearity and finite-frequency effects can be accounted for by using 2-D phase-velocity kernels for boundary perturbations. Finally, we calculate boundary sensitivity kernels in 3-D reference earth models for iterative inversions of global crustal structure.

Liu, Kui; Zhou, Ying

2013-02-01

127

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

128

Blood pulse wave velocity measured by photoacoustic microscopy  

NASA Astrophysics Data System (ADS)

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.

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

2013-03-01

129

In Vitro Validation of Rapid MR Measurement of Wave Velocity  

PubMed

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

Kraft; Fatouros; Corwin; Fei

1997-05-01

130

The bound weighted average method (BWAM) for predicting S-wave velocity  

NASA Astrophysics Data System (ADS)

The shear-wave velocity is a very important parameter in oil and gas seismic exploration, and vital in prestack elastic-parameters inversion and seismic attribute analysis. However, shearing-velocity logging is seldom carried out because it is expensive. This paper presents a simple method for predicting S-wave velocity which covers the basic factors that influence seismic wave propagation velocity in rocks. The elastic modulus of a rock is expressed here as a weighted arithmetic average between Voigt and Reuss bounds, where the weighting factor, w, is a measurement of the geometric details of the pore space and mineral grains. The S-wave velocity can be estimated from w, which is derived from the P-wave modulus. The method is applied to process well-logging data for a carbonate reservoir in Sichuan Basin, and shows the predicted S-wave velocities agree well with the measured S-wave velocities.

Liu, Ling; Geng, Jian-Hua; Guo, Tong-Lou

2012-12-01

131

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

NASA Astrophysics Data System (ADS)

The principal tool by which we learn about the upper part of the mantle (the top 1000 km say) is through the study of surface waves and, importantly, surface wave overtones. In this study we combine a variety of existing databases of surface wave phase velocity measurements into a very large data set consisting of more than 9,500,000 dispersion measurements of fundamental and higher mode (up to the 4th overtone) Rayleigh and Love waves with wave periods between T=35s and T=200s (Visser et al., GRL, 2007; van Heijst and Woodhouse, GJI, 1999; Ekström et al., JGR, 1997). We carry out inversions of this large data set for perturbations in the isotropic S-velocity structure and the anisotropic parameter ? s=\\frac{v2SH-v2SV}{2v2S} in the top 1000 km of the Earth's mantle. The models are parameterised using spherical harmonic basis functions up to degree 20 for the lateral variations and using 21 spline functions for the depth dependence. We carry out a large number of inversions using a variety of damping schemes and we choose the optimal model using the Akaike Bayesian Information Criterion (ABIC) together with a priori information. In a first step, we invert separately the Rayleigh and Love wave data sets for perturbations in the isotropic SV-velocity and SH-velocity structures, respectively. Our 3D isotropic models share the large scale features of previous global tomographic studies. Furthermore, these isotropic models fit well the various existing subsets of dispersion measurements we use, showing that they are quite compatible with each other. We then invert the complete data set of surface wave dispersion measurements for perturbations in purely isotropic S- velocity structure. The estimated model shows well known large scale anomalies and provides a reasonable fit to the data. In a second step, we address the distribution of radial anisotropy, using fully anisotropic sensitivity kernels. Overall, allowing for radial anisotropy improves the data fit by about 2% compared to a purely isotropic inversion. Nevertheless, for certain surface wave modes, the data fit is improved by more than 10% when allowing for radial anisotropy. We investigate what is the smallest significant amount of anisotropy required by the different subsets of data. Finally, we compare our prefered 3D anisotropic model with previous tomographic studies and discuss possible relationships between flow and anisotropy.

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

2007-12-01

132

Latitudinal Variations Observed in Gravity Waves with Short Vertical Wavelengths  

Microsoft Academic Search

Knowledge of the latitudinal variations in the occurrence of gravity waves is important for their parameter- ization in global models. Observations of gravity waves with short vertical scales have shown a pronounced peak in wave activity at tropical latitudes. In this paper, it is shown that such a peak may be a natural consequence of the latitudinal variation in the

M. Joan Alexander; Toshitaka Tsuda; Robert A. Vincent

2002-01-01

133

The local amplification of surface waves: A new observable to constrain elastic velocities, density, and anelastic attenuation  

NASA Astrophysics Data System (ADS)

The deployment of USArray across the continental U.S. has prompted developments within surface wave tomography to exploit this unprecedented data set. Here, we present a method to measure a new surface wave observable: broadband surface wave amplification that provides new and unique constraints on elastic velocities and density within the crust and upper mantle. The method, similar to its phase velocity counterpart referred to as Helmholtz tomography, initiates by constructing phase travel time and amplitude maps across the array for each period and earthquake. Spatial differential operators are then applied to evaluate the amplitude variation, as well as the effect of focusing/defocusing. Based on the 2-D damped wave equation, the amplitude variation corrected for focusing/defocusing is linked directly to both local amplification and intrinsic attenuation, which are separated by examining waves propagating in opposite directions. We apply the method to teleseismic Rayleigh waves observed across USArray between periods of 24 and 100 s and show that the observed amplification maps are strongly correlated with known geological features. Small-scale attenuation measurements are contaminated by wavefield complexities, but larger-scale anelastic attenuation is estimated reliably. The observed amplification maps compare well with predictions based on recent 3-D shear velocity models of the western U.S. that were produced from ambient noise and earthquake data. Notably, predictions based on models with different prescribed density structures demonstrate the potential for using estimates of local amplification to constrain not only 3-D velocity structure but also density.

Lin, Fan-Chi; Tsai, Victor C.; Ritzwoller, Michael H.

2012-06-01

134

Two Energy Types in Wave Motion and Their Relation to Group and Wave Velocity  

Microsoft Academic Search

The energy of an element in a wave motion can be of two kinds: first, non-interactive like the energy of a set of independent pendulum bobs, and second, interactive like the potential energy of an element of a stretched string which is dependent only on the relative position of the neighboring elements. In the former case the group velocity is

Lewi Tonks

1929-01-01

135

Shear-wave velocity estimation using multiple logs and multicomponent seismic AVO interpretation: Gulf of Thailand  

NASA Astrophysics Data System (ADS)

Shear-wave velocity (Vs) is very important to seismic interpretation. Shear-wave logs, however, are often missing. Existing Vs estimation methods either require detailed rock volumetric and fluid prediction first or give large errors in the study area: a gas field in the Gulf of Thailand where sediments consist of sand-shale mixtures and coals. Two petrophysical characteristics of the sand-shale mixtures are worth noting. First, when the clay content increases, their compressional-wave velocity (Vp) and Vs increase when the clay content is low and decrease when the clay content is high. This velocity behavior separates the sand-shale mixtures into two groups: the porous sand with low clay content and the low porosity sand-shale with high clay content. Second, the porous sands usually have higher velocities but lower density than the low porosity sand-shale. Based on these and other petrophysical characteristics, two methods of Vs estimation are given for the three groups of sediments: the porous sand, the low porosity sand-shale, and the coal. P-wave AVO technique, as a powerful hydrocarbon prospecting too], is applied almost routinely in practice now. However, current AVO analyses assume a generalized Gardner's equation for the density-Vp relationship across the interface, which is not true in some areas including the study gas field. Therefore, I derived an AVO analysis technique without a predefined density-Vp relationship. Multicomponent seismic data are becoming popular. Information extracted from converted-wave AVO should significantly enhance that obtained from P-wave AVO. Unfortunately, there is not much literature available. Therefore, I analyzed the characteristics of converted-wave AVO under different shear-wave acoustic-impedance contrasts and Vp/ Vs ratios, and derived a method for converted-wave AVO crossplotting to detect hydrocarbon and lithologic variations. Finally, it has always been difficult to discriminate low and high gas saturations theoretically and practically prior to drilling. Consequently, drilling into non-commercial gas reservoirs has been called a "technical success." However, I found very good partial gas indicators (PGIs) using multicomponent seismic AVO data. Theoretical results show that the proposed PGIs can separate regions of high gas saturation from low saturation areas and distinguish water saturation changes from porosity or clay content changes.

Zhu, Fuping

2000-10-01

136

The velocity structure of the upper mantle of europe from the ambient noise surface wave tomography  

NASA Astrophysics Data System (ADS)

The method for surface wave tomography based on the records of ambient seismic noise (Ambient Noise Tomography, ANT) is applied to the data from the East European and West European stations. In order to reduce the effects of the earthquakes at long periods, the cross correlation functions were calculated for the time interval of 2001-2003, when distinct clusters of the earthquakes were absent. Using the local dispersion curves in the range of 10-100 s, we reconstructed the vertical velocity sections at the nodes of the 3° × 3° grid. On the basis on these curves, we calculated the horizontal distributions of S-velocity variations in the upper mantle in the depth interval of 75-275 km and the vertical velocity sections along the profiles across the Vrancea zone and the region of the Baltic and Ukrainian shields. The velocity distribution in the Vrancea zone confirms the subduction of the ancient oceanic plate from the east westwards and the detachment of its bottom part, as hypothesized by some authors. Beneath the Baltic Shield lithosphere, there is a low-velocity zone, which can be interpreted as the asthenospheric layer. It is noted that the velocity distributions beneath the Baltic and Ukrainian shields are similar, which probably points to the genetic relationship between these two structures.

Yanovskaya, T. B.; Lyskova, E. L.

2013-09-01

137

Magnetospheric electron-velocity-distribution function information from wave observations  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

138

Coseismic velocity variations caused by static stress changes associated with the 2001 Mw = 4.3 Agios Ioanis earthquake in the Gulf of Corinth, Greece  

Microsoft Academic Search

The analysis of temporal variations in the seismic velocity across faults can be used to estimate in situ stress changes. Seismic velocity of propagation depends on the fault stiffness, which is a function of stress. The coda wave interferometry technique is applied to seven families of repeating earthquakes (multiplets) recorded on the southern shore of the Gulf of Corinth, Greece,

L. Cociani; C. J. Bean; H. Lyon-Caen; F. Pacchiani; A. Deschamps

2010-01-01

139

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)

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.

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

2010-12-01

140

Global Shear Wave Velocity Database for Probabilistic Assessment of the Initiation of Seismic-Soil Liquefaction  

Microsoft Academic Search

Engineering practitioners commonly use penetration-based methods (SPT & CPT) for assessment of seismic liquefaction triggering hazard. On the horizon, shear wave velocity (Vs) may offer engineers a third tool that is lower cost and provides more physically meaningful measurements. Development of the shear wave velocity liquefaction method has been hampered by a paucity of published velocity profiles; particularly in deeper

Robert Kayen; Raymond B. Seed; Robb E. S. Moss; Onder K. Cetin; Y. Tanaka; Kohji Tokimatsu

2004-01-01

141

Surface-Wave Phase-Velocity Maps of the Western US From USArray Data  

NASA Astrophysics Data System (ADS)

Taking advantage of the exceptional quality and spatial sampling of the data from USArray, we present phase-velocity maps of the western US obtained by inversion of a large data set of inter-station surface-wave phase delays. Single-station phase anomalies are measured using the method of Ekström, Tromp and Larson (1997) for Love and Rayleigh waves in the period range 25-100 seconds. Two-station phase delays are then derived by differencing phase anomalies for those station pairs that lie within 2.5° azimuth of the great-circle path. The initial data set, consisting of up to 385,000 two-station phase delays at a given period, is reduced by assigning a single median measurement with an associated uncertainty to each unique station pair. The phase-velocity maps are parameterized in terms of 0.5° by 0.5° pixels, and a smoothness constraint is applied to regularize the inversions. Results in the 25-75 s period range for Rayleigh waves and 25-60 s period range for Love waves are robust, based on comparisons of multiple inversions derived using distinct subsets of the data, grouped on the basis of inter-station distance or azimuth. The phase-velocity maps correlate well with variations in crustal thickness, elevation, and known tectonic features, with the Yellowstone hotspot being notable for its prominence in the intermediate-period Rayleigh wave maps. We address the potential limitations of our analysis caused by the application of simple ray theory to interpret the phase delays, and investigate our ability to resolve azimuthal anisotropy from these data.

Foster, A. E.; Ekström, G.

2008-12-01

142

Wave velocity dispersion and attenuation in media exhibiting internal oscillations  

NASA Astrophysics Data System (ADS)

Understanding the dynamical and acoustical behavior of porous and heterogeneous rocks is of great importance in geophysics, e.g. earthquakes, and for various seismic engineering applications, e.g. hydrocarbon exploration. Within a heterogeneous medium oscillations with a characteristic resonance frequency, depending on the mass and internal length of the heterogeneity, can occur. When excited, heterogeneities can self-oscillate with their natural frequency. Another example of internal oscillations is the dynamical behavior of non-wetting fluid blobs or fluid patches in residually saturated pore spaces. Surface tension forces or capillary forces act as the restoring force that drives the oscillation. Whatever mechanism is involved, an oscillatory phenomena within a heterogeneous medium will have an effect on acoustic or seismic waves propagating through such a medium, i.e. wave velocity dispersion and frequency-dependent attenuation. We present two models for media exhibiting internal oscillations and discuss the frequency-dependent wave propagation mechanism. Both models give similar results: (1) The low-frequency (i.e. quasi-static) limit for the phase velocity is identical with the Gassmann-Wood limit and the high-frequency limit is larger than this value and (2) Around the resonance frequency a very strong phase velocity change and the largest attenuation occurs. (1) Model for a homogeneous medium exhibiting internal oscillations We present a continuum model for an acoustic medium exhibiting internal damped oscillations. The obvious application of this model is water containing oscillating gas bubbles, providing the material and model parameters for this study. Two physically based momentum interaction terms between the two inherent constituents are used: (1) A purely elastic term of oscillatory nature that scales with the volume of the bubbles and (2) A viscous term that scales with the specific surface of the bubble. The model is capable of taking into account an arbitrary number of oscillators with different resonance frequencies. Exemplarily, we show a log-normal distribution of resonance frequencies. Such a distribution changes the acoustic properties significantly compared to the case with only one resonance frequency. The dispersion and attenuation resulting from our model agree well with the dispersion and attenuation (1) derived with a more exact mathematical treatment and (2) measured in laboratory experiments. (2) Three-phase model for residually saturated porous media We present a three-phase model describing wave propagation phenomena in residually saturated porous media. The model consists of a continuous non-wetting phase and a discontinuous wetting phase and is an extension of classical biphasic (Biot-type) models. The model includes resonance effects of single liquid bridges or liquid clusters with miscellaneous eigenfrequencies taking into account a visco-elastic restoring force (pinned oscillations and/or sliding motion of the contact line). In the present investigation, our aim is to study attenuation due to fluid oscillations and due to wave-induced flow with a macroscopic three-phase continuum model, i.e. a mixture consisting of one solid constituent building the elastic skeleton and two immiscible fluid constituents. Furthermore, we study monochromatic waves in transversal and longitudinal direction and discuss the resulting dispersion relations for a typical reservoir sandstone equivalent (Berea sandstone).

Frehner, Marcel; Steeb, Holger; Schmalholz, Stefan M.

2010-05-01

143

Variational wave functions for homogenous Bose systems  

SciTech Connect

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

Sueto, Andras [Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences, P. O. Box 49, H-1525 Budapest (Hungary); Szepfalusy, Peter [Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences, P. O. Box 49, H-1525 Budapest (Hungary); Department of Physics of Complex Systems, Eoetvoes University, H-1117 Budapest (Hungary)

2008-02-15

144

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

SciTech Connect

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.

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

1982-04-10

145

Resolving temporal and spatial variations in seismic velocity using similar event clusters (Invited)  

NASA Astrophysics Data System (ADS)

Recent developments in ambient noise seismology have resolved very small changes in seismic velocity and have increased interest in detecting possible temporal variations in seismic velocity associated with earthquakes and volcanoes. Another approach to monitoring velocity changes uses repeatable sources from similar event clusters. Hundreds of these clusters have been detected in southern California as part of a large-scale project to relocate the entire Southern California Seismic Network (SCSN) catalog using precise differential times obtained using waveform cross-correlation. In particular, we focus on 494 similar event clusters recorded by 166 SCSN stations, which span the time period from 1984 to 2002. We compute absolute arrival-time residuals from the differential residuals obtained following event relocation and compute time-varying station terms from all events recorded at each station. We observe nine stations with abrupt offsets in timing of 20 to 70 ms, which are likely caused by equipment changes during our study period. For other stations, we generally do not see systematic temporal variations greater than about 10 ms. These results limit large-scale, long-lasting temporal variation in P and S velocities to less than about ±0.2%. However, there is an increased fraction of individual travel-time residuals exceeding 20 ms immediately following major earthquakes from source regions near the mainshock ruptures. P- and S-wave differential times from waveform cross-correlation can be used to estimate in situ Vp/Vs estimates within similar event clusters, at much better spatial resolution than standard tomographic methods. For southern California, we obtain a median Vp/Vs ratio of 1.67 for 142 of the best-resolved clusters. This low value is hard to explain with known rock types and suggests the presence of water-filled cracks with several percent porosity within these earthquake source regions.

Shearer, P. M.; Lin, G.; Hauksson, E.

2010-12-01

146

Evidence for anisotropy in north east Africa, from geographical and azimuthal distribution of Rayleigh wave velocities, and average upper mantle structure  

NASA Astrophysics Data System (ADS)

Long period surface waves from WWSSN, GDSN, SRO and GEOSCOPE stations are analysed to obtain the dispersion of surface waves in the North-East of Africa. Lateral variations of Rayleigh wave velocities are retrieved simultaneously with the average azimuthal anisotropy. As a first result, the low velocity anomaly under the Red Sea is apparent at all periods. A second result is a nearly North-South direction of maximum group and phase velocities. This azimuthal anisotropy direction is in agreement with the direction of absolute plate motion in this region. Anisotropy is also evidenced by simultaneous inversion of Love and Rayleigh wave dispersion along the path TAM-AGD. In the resulting models, isotropic and anisotropic, very low mantle SV-wave velocities extend up to the Moho. For SH waves, we find a strong discrepancy with SV waves, SH-wave velocities being higher by 5% down to 200 km under the crust. This is characteristic of lithospheric polarization anisotropy. The S-wave anisotropy (polarization and azimuthal) found in this region, including the Red Sea, is compatible with the absolute motion of the African plate: it can be interpreted, considering the low lithospheric S-velocities, as a consequence of plastic flow in the weak lithosphere of an anomalous mantle. This anisotropy, evidenced here on S waves, may be due, as Pn and lithospheric S-wave anisotropy found in other continental areas, to dynamical processes related to plate motion.

Hadiouche, Ouiza; Jobert, Nelly

1988-04-01

147

Mineralization, crystallography, and longitudinal seismic wave velocity of speleothems  

SciTech Connect

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.

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

1993-03-01

148

Temporal pattern of pulse wave velocity during brachial hyperemia reactivity  

NASA Astrophysics Data System (ADS)

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

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

2011-09-01

149

Nearshore wave height variation in unsaturated surf  

Microsoft Academic Search

The nearshore evolution of wave height is presented from field observations during unsaturated surf conditions from 10 different beaches characterized by microtidal conditions and predominantly swell-dominated wave climates. Wave evolution is presented in terms of wave height to water depth ratio (gamma) for comparison with previous data from saturated surf. Both conventional time-averaged (gammarms) and a new wave-by-wave analysis (gammaw)

H. E. Power; M. G. Hughes; T. Aagaard; T. E. Baldock

2010-01-01

150

A wave propagation model for the high velocity impact response of a composite sandwich panel  

Microsoft Academic Search

A solution methodology to predict the residual velocity of a hemispherical-nose cylindrical projectile impacting a composite sandwich panel at high velocity is presented. The term high velocity impact is used to describe impact scenarios where the projectile perforates the panel and exits with a residual velocity. The solution is derived from a wave propagation model involving deformation and failure of

Michelle S. Hoo Fatt; Dushyanth Sirivolu

2010-01-01

151

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

ERIC Educational Resources Information Center

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

Russell, David

1997-01-01

152

Accuracy of Velocity Estimation Using Global Variational Methods  

NASA Astrophysics Data System (ADS)

In this work a method of processing digital images, such as those from PIV, MTV, or LIF, for flow velocities using Global Variational Method (GVM) is investigated. This technique is based on principles of Frobenius-Perron (FP) operator theory in which image sequences can be related to the infinitesimal generator of the FP operator to motivate a flow-recovery constraint. A regularization method is then used to minimize this constraint along with an additional constraint required to stabilize a solution. Synthetic images, with typical MTV tagging patterns, and variable noise levels were first created and then displaced using analytically derived flow fields. Displacements were calculated from pairs of images and the error was determined by comparing the measured displacements to those of the analytical flow field. A direct correlation technique (DCT) was also used to process the synthetically derived images for comparison. Results show that the GVM error levels are nominally 5-10 times higher than for the DCT. While the error is higher for GVM compared to DCT the results show potential for using this technique to provide quantitative flow measurements in cases where DCT cannot be applied.

Bohl, Doug; Santitissadeekorn, Naratip; Bollt, Erik

2008-11-01

153

Horizontal Partical Velocity Profiles Beneath the Crests of Waves Breaking on a Submarine Bar.  

National Technical Information Service (NTIS)

The horizontal particle velocity profiles beneath the crests of breaking waves have been measured and evaluated for waves breaking on a submarine bar. A breaking wave classification system based upon the cross-sectional symmetry of the wave was used to is...

W. L. Wood

1970-01-01

154

Advantages of using multichannel analysis of Love waves (MALW) in determining near-surface shear-wave velocity  

NASA Astrophysics Data System (ADS)

Surface-wave techniques have been given increasingly more attention by the near-surface community with applications to a variety of problems. Studies on high-frequency surface-wave techniques have been focused primarily on Rayleigh waves. There is much less attention on utilizing Love waves than Rayleigh waves in the near-surface community. Recent improvements in data-acquisition techniques and development of software make SH-wave data acquisition and processing easier. In addition, Love-wave analysis only results in SH-wave velocities, which suggests that we may benefit from analyzing SH-wave data using Love-wave inversion. Numerical results of SH waves and data from Kansas, Wyoming, Arizona, Washington, and Wuhan, China demonstrated three advantages of analyzing SH-wave data using multichannel analysis of Love waves (MALW). 1) Generally images of Love-wave energy are cleaner and sharper than those generated from Rayleigh waves. Owing to a long geophone spread commonly used in an SH-wave refraction survey, images of Love-wave energy are even much cleaner and sharper, which makes picking phase velocities of Love waves easier and more accurate. 2) Numerical results showed that because Love waves are independent of P-wave velocity, dispersion curves of Love waves are simpler than Rayleigh waves. "Mode kissing" (suggested by Robert Stewart) is an undesired and frequently occurred phenomenon in Rayleigh-wave analysis that causes mode misidentification. Fortunately, this phenomenon is less common in images of Love-wave energy than Rayleigh waves. 3) Real-world examples showed that inversion of Love-wave dispersion curves is less dependent on initial models and more stable than Rayleigh waves. This is because of being independent of P-wave velocity fewer unknowns in the MALW method not only make dispersion curves of Love waves simpler also reduces the degree of nonuniqueness, which leads to more stable inversion of Love-wave dispersion curves. Results also demonstrated that a more accurate model can be obtained by simultaneous inversion of the fundamental and the first-higher mode data. Our experimental study shows that the MALW method is a useful tool to analyzin high-frequency SH-wave data. It may become a common practice in the near-surface community and the oil industry because it provides SH-wave velocities that are critical for analysis of S-wave anisotropy of a near-surface velocity model. Furthermore, we realize two benefits of utilizing the MALW method in the near-surface applications. 1) Abundant SH-wave refraction data containing non-utilized strong Love-wave energy have been acquired for various environmental and engineering applications. Revisiting these data with the MALW method can enhance our knowledge of existing velocity models. 2) Acquiring Love-wave data by simply increasing a record length during future SH-wave refraction surveys and analyzing these data with the MALW method can provide accurate SH-wave velocities without additional cost in field.

Xia, J.; Xu, Y.; Luo, Y.; Miller, R. D.; Cakir, R.

2011-12-01

155

Estimation of shear wave velocity in gelatin phantoms utilizing PhS-SSOCT  

NASA Astrophysics Data System (ADS)

We report a method for measuring shear wave velocity in soft materials using phase stabilized swept source optical coherence tomography (PhS-SSOCT). Wave velocity was measured in phantoms with various concentrations of gelatin and therefore different stiffness. Mechanical waves of small amplitudes (˜10 ?m) were induced by applying local mechanical excitation at the surface of the phantom. Using the phase-resolved method for displacement measurement described here, the wave velocity was measured at various spatially distributed points on the surface of the tissue-mimicking gelatin-based phantom. The measurements confirmed an anticipated increase in the shear wave velocity with an increase in the gelatin concentrations. Therefore, by combining the velocity measurements with previously reported measurements of the wave amplitude, viscoelastic mechanical properties of the tissue such as cornea and lens could potentially be measured.

Manapuram, Ravi Kiran; Aglyamov, S.; Menodiado, F. M.; Mashiatulla, M.; Wang, Shang; Baranov, S. A.; Li, Jiasong; Emelianov, S.; Larin, K. V.

2012-09-01

156

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

NASA Astrophysics Data System (ADS)

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.

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

2012-05-01

157

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

SciTech Connect

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.

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

2012-05-17

158

Shear-Wave Velocity Structure of the New Madrid Seismic Zone From Rayleigh Wave Group Velocity Dispersion Using Regional and Local Earthquake Data  

Microsoft Academic Search

Regional and local Rayeligh-wave group velocity dispersion data were used to extract shear-wave velocity structure of several propagation paths from earthquakes into the New Madrid Seismic Zone. The dispersion data are limited at high frequency by the mid-crustal depth of the earthquakes and at low frequency because of the relatively short propagation paths involved. Inferred dispersion curves also show irregularities

A. L. Jemberie; C. A. Langston

2005-01-01

159

Improved variational wave functions for simple quantum liquids  

Microsoft Academic Search

We review variational calculations with a Jastrow wave function and show they are inadequate to calculate the zero-temperature equation of state E(rho) for liquid helium. The importance of the Feynman-Cohen backflow around a moving particle is then discussed, and a variational wave function incorporating backflow is proposed. Results with this wave function are discussed for 3He, 4He and the v2

K. E. Schmidt; V. R. Pandharipande

1979-01-01

160

Rayleigh wave phase-velocity heterogeneity and multilayered azimuthal anisotropy of the Superior Craton, Ontario  

NASA Astrophysics Data System (ADS)

We study the azimuthally anisotropic upper-mantle structure of the Superior Craton and Grenville Province in Ontario, Canada, using Rayleigh wave phase-velocity data in the period range 40-160s. 152 two-station dispersion measurements are combined in a tomographic inversion that solves simultaneously for isotropic and anisotropic terms using a least-squares technique. We perform a series of tests to derive optimal regularization (smoothing and damping) and to assess the resolution of, and trade-offs between, isotropic and anisotropic anomalies. The tomographic inversion is able to resolve isotropic phase-velocity anomalies on a scale of 200-300km and to distinguish between different anisotropic regimes on a 500-km scale across the study region. Isotropic phase-velocity anomalies in the tomographic model span a range of up to +/-2 per cent around a regional average which is similar to the Canadian Shield dispersion curve of Brune & Dorman (1963), with phase velocities up to 3 per cent above global reference models. The amplitude of azimuthal phase-velocity anisotropy reaches a maximum of ~1.2 per cent. A clear east-west division of the study area, based on both isotropic phase-velocity anomalies and azimuthal anisotropy, is apparent. In the western Superior, isotropic phase velocities are generally higher than the regional average. Anisotropy is observed at all periods, with ENE-WSW to NE-SW fast-propagation directions. At periods <=120s, the anisotropy likely results from frozen lithospheric fabric aligned with tectonic boundaries, whereas the anisotropy at longer periods is interpreted to arise from present-day sublithospheric flow. The fast directions from published SKS measurements are close to the fast Rayleigh wave propagation directions throughout the period range sampled, and the large SKS splitting times may be accounted for by this near-coincidence of fast-propagation directions. Across most of eastern Ontario, phase velocities are lower than the regional average. Fast-propagation directions rotate from ~NW-SE at 40-130s period to WNW-ESE at periods 140-160s. The results suggest a difference in fast-propagation directions between the anisotropic fabric frozen into the lithosphere and the fabric due to current and recent sublithospheric flow. The Superior Craton and Grenville Province are characterized by large-scale structural variations that reflect the complex tectonic history of the region. This study highlights differences between the characteristics of eastern and western Ontario and indicates the occurrence of multiple layers of anisotropy in the subcratonic upper mantle.

Darbyshire, Fiona A.; Lebedev, Sergei

2009-01-01

161

Crustal and mantle shear velocity structure of Costa Rica and Nicaragua from ambient noise and teleseismic Rayleigh wave tomography  

NASA Astrophysics Data System (ADS)

The Costa Rica-Nicaragua subduction zone shows systematic along strike variation in arc chemistry, geology, tectonics and seismic velocity and attenuation, presenting global extremes within a few hundred kilometres. In this study, we use teleseismic and ambient noise derived surface wave tomography to produce a 3-D shear velocity model of the region. We use the 48 stations of the TUCAN array, and up to 94 events for the teleseismic Rayleigh wave inversion, and 18 months of continuous data for cross correlation to estimate Green's functions from ambient noise. In the shallow crust (0-15 km) we observe low-shear velocities directly beneath the arc volcanoes (<3 km s-1) and higher velocities in the backarc of Nicaragua. The anomalies below the volcanoes are likely caused by heated crust, intruded by magma. We estimate crustal thickness by picking the depth to the 4 km s-1 velocity contour. We infer >40-km-thick crust beneath the Costa Rican arc and the Nicaraguan Highlands, thinned crust (˜20 km) beneath the Nicaraguan Depression, and increasing crustal thickness in the backarc region, consistent with receiver function studies. The region of thinned, seismically slow and likely weakened crust beneath the arc in Nicaragua is not localizing deformation associated with oblique subduction. At mantle depths (55-120 km depth) we observe lower shear velocities (up to 3 per cent) beneath the Nicaraguan arc and backarc than beneath Costa Rica. Our low-shear velocity anomaly beneath Nicaragua is in the same location as a low-shear velocity anomaly and displaced towards the backarc from the high VP/VS anomaly observed in body wave tomography. The lower shear velocity beneath Nicaragua may indicate higher melt content in the mantle perhaps due to higher volatile flux from the slab or higher temperature. Finally, we observe a linear high-velocity region at depths >120 km parallel to the trench, which is consistent with the subducting slab.

Harmon, Nicholas; Cruz, Mariela Salas De La; Rychert, Catherine Ann; Abers, Geoffrey; Fischer, Karen

2013-08-01

162

Crustal and mantle shear velocity structure of Costa Rica and Nicaragua from ambient noise and teleseismic Rayleigh wave tomography  

NASA Astrophysics Data System (ADS)

The Costa Rica-Nicaragua subduction zone shows systematic along strike variation in arc chemistry, geology, tectonics and seismic velocity and attenuation, presenting global extremes within a few hundred kilometres. In this study, we use teleseismic and ambient noise derived surface wave tomography to produce a 3-D shear velocity model of the region. We use the 48 stations of the TUCAN array, and up to 94 events for the teleseismic Rayleigh wave inversion, and 18 months of continuous data for cross correlation to estimate Green's functions from ambient noise. In the shallow crust (0-15 km) we observe low-shear velocities directly beneath the arc volcanoes (<3 km s-1) and higher velocities in the backarc of Nicaragua. The anomalies below the volcanoes are likely caused by heated crust, intruded by magma. We estimate crustal thickness by picking the depth to the 4 km s-1 velocity contour. We infer >40-km-thick crust beneath the Costa Rican arc and the Nicaraguan Highlands, thinned crust (˜20 km) beneath the Nicaraguan Depression, and increasing crustal thickness in the backarc region, consistent with receiver function studies. The region of thinned, seismically slow and likely weakened crust beneath the arc in Nicaragua is not localizing deformation associated with oblique subduction. At mantle depths (55-120 km depth) we observe lower shear velocities (up to 3 per cent) beneath the Nicaraguan arc and backarc than beneath Costa Rica. Our low-shear velocity anomaly beneath Nicaragua is in the same location as a low-shear velocity anomaly and displaced towards the backarc from the high VP/VS anomaly observed in body wave tomography. The lower shear velocity beneath Nicaragua may indicate higher melt content in the mantle perhaps due to higher volatile flux from the slab or higher temperature. Finally, we observe a linear high-velocity region at depths >120 km parallel to the trench, which is consistent with the subducting slab.

Harmon, Nicholas; Cruz, Mariela Salas De La; Rychert, Catherine Ann; Abers, Geoffrey; Fischer, Karen

2013-11-01

163

THE EFFECT OF SOUND VELOCITY VARIATIONS ON SYNTHETIC APERTURE SONAR  

Microsoft Academic Search

Near-field acoustic imaging requires that the geometry and the sound velocity between observation system (sonar) and scene (seafloor) to be known. An incorrect sound velocity leads to degradation imagery and poor image quality. In synthetic aperture sonar (SAS) imaging, the scene is almost always in the near-field. This means accurate estimation of sound-velocity is vitally important for high-quality imagery. We

Roy Edgar Hansen; Hayden John Callow; Torstein Olsmo Sæbø

164

MR Measurement of Cerebrospinal Fluid Velocity Wave Speed in the Spinal Canal  

Microsoft Academic Search

Noninvasive measurement of the speed with which the cerebrospinal fluid (CSF) velocity wave travels through the spinal canal is of interest as a potential indicator of CSF system pressure and compliance, both of which may play a role in the development of craniospinal diseases. However, measurement of CSF velocity wave speed (VWS) has eluded researchers primarily due to either a

Wojciech Kalata; Bryn A. Martin; John N. Oshinski; Michael Jerosch-Herold; Thomas J. Royston; Francis Loth

2009-01-01

165

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

NASA Astrophysics Data System (ADS)

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

Kimura, Masao

2005-11-01

166

Optical method of measuring velocity of shear waves  

NASA Astrophysics Data System (ADS)

Optical excitation and recording of ultrasonic vibrations for measuring the velocity of shear waves includes a ruby pulse laser as the light source. A light splitter plate deflects one part of the laser radiation through a focusing lens to an FD9E111 photodiode which triggers a recording oscillograph. The other part of the laser radiation, transmitted through the glass plate, is focused through a lens onto the specimen, typically a disk. Radiation pulses reflected by the lateral surface of the specimen proceed to a coaxially oriented laser interferometer with a 250 MHz reproducibility bandwidth. The interferometer output signal, proportional to the displacement in the ultrasonic pulse in the disk, passes through a low-pass filter and then a wideband amplifier to an S8-12 oscillograph with memory and a G5-48 pulse generator-shaper. Output signals from the latter proceed to a CH3-34A frequency meter operating in the mode of time interval measurement.

Arkhipov, V. I.; Bondarenko, A. N.; Kondratyev, A. I.

1984-09-01

167

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

USGS Publications Warehouse

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. ?? 2006 Elsevier B.V. All rights reserved.

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

2006-01-01

168

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

NASA Astrophysics Data System (ADS)

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 ([Bésuelle, 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 [Guéguen 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.

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

2004-05-01

169

Interannual variations of Atlantic tropical instability waves  

NASA Astrophysics Data System (ADS)

Observations are used to develop metrics for interannual tropical instability wave (TIW) variability in the Atlantic and to relate that variability to larger scale processes. The analysis is partitioned into different latitude bands to distinguish between off-equatorial (5°S, 2°N, and 5°N) and near-equatorial (2°S and 0°) TIWs. TIW metrics based on sea surface temperature (SST) and sea level anomaly (SLA) fluctuations are compared against interannual anomalies of SST in the cold tongue region. To examine the role of barotropic shear instabilities in modulating the intensity of a TIW season, wind stress and near-surface current indices are developed in regions where the shear between the Equatorial Undercurrent (EUC) and the northern branch of the South Equatorial Current (nSEC) and between the nSEC and the North Equatorial Countercurrent (NECC) are expected to be largest. Good agreement is found between the SST and SLA TIW metrics along the off-equatorial latitude bands, and interannual variations of both metrics can largely be attributed to barotropic shear instabilities. In particular, years with low (high) TIW variance along the off-equatorial latitude bands are associated with anomalously warm (cold) SSTs in the cold tongue region, weak (strong) wind stress divergence and curl in the EUC-nSEC region, and weak (strong) zonal current shear in the nSEC-NECC region. In contrast, in the near-equatorial latitude bands, poor agreement is found between interannual TIW activity based on the SST and SLA metrics, and near-equatorial TIW variability cannot be explained by the large-scale SST, wind stress divergence and curl, and current shear indices.

Perez, Renellys C.; Lumpkin, Rick; Johns, William E.; Foltz, Gregory R.; Hormann, Verena

2012-03-01

170

Sonic logging of compressional-wave velocities in a very slow formation  

SciTech Connect

Borehole sonic waveforms are commonly acquired to produce logs of subsurface compressional and shear wave velocities. To this purpose, modern borehole sonic tools are usually equipped with various types of acoustic sources, i.e., monopole and dipole sources. While the dipole source has been specifically developed for measuring shear wave velocities, the authors found that the dipole source has an advantage over the monopole source when determining compressional wave velocities in a very slow formation consisting of unconsolidated sands with a porosity of about 35% and a shear wave velocity of about 465 m/s. In this formation, the recorded compressional refracted waves suffer from interference with another wavefield component identified as a leaky P-wave, which hampers the determination of compressional wave velocities in the sands. For the dipole source, separation of the compressional refracted wave from the recorded waveforms is accomplished through bandpass filtering since the wavefield components appear as two distinctly separate contributions to the frequency spectrum: a compressional refracted wave centered at a frequency of 6.5 kHz and a leaky P-wave centered at 1.3 kHz. For the monopole source, the frequency spectra of the various waveform components have considerable overlap. It is therefore not obvious what passband to choose to separate the compressional refracted wave from the monopole waveforms.

Tichelaar, B.W. [Shell Research B.V., Rijswijk (Netherlands); Luik, K.W. van [Nederlandse Aardolie Maatschappij B.V., Assen (Netherlands)

1995-11-01

171

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)

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.

Bhattacharya, S. N.; Mitra, Supriyo; Suresh, G.

2013-06-01

172

Quantifying Damage, Saturation and Anisotropy in Cracked Rocks by Inverting Elastic Wave Velocities  

NASA Astrophysics Data System (ADS)

Crack damage results in a decrease of elastic wave velocities and in the development of anisotropy. Using non-interactive crack effective medium theory as a fundamental tool, we calculate dry and wet elastic properties of cracked rocks in terms of a crack density tensor, average crack aspect ratio and mean crack fabric orientation from the solid grains and fluid elastic properties. Using this same tool, we show that both the anisotropy and shear-wave splitting of elastic waves can be derived. Two simple crack distributions are considered for which the predicted anisotropy depends strongly on the saturation, reaching up to 60% in the dry case. Comparison with experimental data on two granites, a basalt and a marble, shows that the range of validity of the non-interactive effective medium theory model extends to a total crack density of approximately 0.5, considering symmetries up to orthorhombic. In the isotropic case, Kachanov's (1994) non-interactive effective medium model was used in order to invert elastic wave velocities and infer both crack density and aspect ratio evolutions. Inversions are stable and give coherent results in terms of crack density and aperture evolution. Crack density variations can be interpreted in terms of crack growth and/or changes of the crack surface contact areas as cracks are being closed or opened respectively. More importantly, the recovered evolution of aspect ratio shows an exponentially decreasing aspect ratio (and therefore aperture) with pressure, which has broader geophysical implications, in particular on fluid flow. The recovered evolution of aspect ratio is also consistent with current mechanical theories of crack closure. In the anisotropic cases—both transverse isotropic and orthorhombic symmetries were considered—anisotropy and saturation patterns were well reproduced by the modelling, and mean crack fabric orientations we recovered are consistent with in situ geophysical imaging.

Schubnel, Alexandre; Benson, Philip M.; Thompson, Ben D.; Hazzard, Jim F.; Young, R. Paul

2006-06-01

173

Non-linear surface wave phase velocity inversion based on ray theory  

Microsoft Academic Search

The development of temporary and permanent broad-band seismic arrays reinforces the need for advanced interpretation techniques in surface-wave analysis. We present a new method based on 2-D paraxial ray theory of inverting teleseismic surface-wave phase information and constructing phase velocity maps on a regional scale. Measurements of local phase velocities and propagation directions of Rayleigh waves taken from full waveform

Marianne Bruneton; Véronique Farra; Helle Anette Pedersen

2002-01-01

174

Estimations of formation velocity, permeability, and shear-wave anisotropy using acoustic logs  

SciTech Connect

Field data sets collected by an array monopole acoustic logging tool and a shear wave logging tool are processed and interpreted. The P- and S-wave velocities of the formation are determined by threshold detection with cross-correlation correction from the full waveform and the shear-wave log, respectively. The array monopole acoustic logging data are also processed using the extended Prony`s method to estimate the borehole Stoneley wave phase velocity and attenuation as a function of frequency. The well formation between depths of 2,950 and 3,150 ft (899 and 960 m) can be described as an isotropic elastic medium. The inverted V{sub S} from the Stoneley wave phase velocity is in excellent agreement with the shear-wave log results in this section. The well formation between the depths of 3,715 and 3,780 ft (1,132 and 1,152 m) can be described as a porous medium with shear-wave velocity anisotropy about 10% to 20% and with the symmetry axis perpendicular to the borehole axis. The disagreement between the shear-wave velocity from the Stoneley wave inversion and the direct shear-wave log velocity in this section is beyond the errors in the measurements. Estimated permeabilities from low-frequency Stoneley wave velocity and attenuation data are in good agreement with the core measurements. Also it is proven that the formation permeability is not the cause of the discrepancy. From the estimated ``shear/pseudo-Rayleigh`` phase velocities in the array monopole log and the 3-D finite-difference synthetics in the anisotropic formation, the discrepancy can best be explained as shear-wave anisotropy.

Cheng, N.; Cheng, C.H. [Massachusetts Inst. of Technology, Cambridge, MA (United States)

1996-03-01

175

Velocity and attenuation of seismic waves in random media: A spectral function approach  

NASA Astrophysics Data System (ADS)

This contribution investigates the scattering of scalar and elastic waves in two-phase materials and single-mineral-cubic, hexagonal, orthorhombic-polycrystalline aggregates with randomly oriented grains. Based on the Dyson equation for the mean field, explicit expressions for the imaginary part of Green's function in the frequency-wavenumber domain (?,p), also known as the spectral function, are derived. This approach allows the identification of propagating modes with their relative contribution, and the computation of both attenuation and phase velocity for each mode. The results should be valid from the Rayleigh (low-frequency) to the geometrical optics (high-frequency) regime. Applications of the proposed theory to the structure of the inner core of the Earth will be presented. In particular, it will be shown that our scattering theory can explain the striking correlation between velocity and attenuation and the associated hemispherical variations revealed by PKP waves propagating through the inner core of the Earth. The implications for inner core dynamics will be summarized.

Margerin, Ludovic; Calvet, Marie; Monnereau, Marc; Souriau, Annie

2013-04-01

176

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

Microsoft Academic Search

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

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

2007-01-01

177

Measurement of velocity and attenuation of shear waves in bovine compact bone using ultrasonic spectroscopy  

Microsoft Academic Search

The ultrasonic spectroscopy (broadband pulse) technique was applied to simultaneously measure phase velocity and attenuation coefficient of shear waves in bovine compact bone at frequencies ranging from 4.0–10.0 MHz. It was found that the ratio of attenuation coefficient of shear waves to that of longitudinal waves at a particular frequency for bovine compact bone was smaller than that of other

Junru Wu; Frances Cubberley

1997-01-01

178

Radial-velocity and light variations of IR Cephei  

Microsoft Academic Search

Radial-velocity observations of the short-period Cepheid, IR Cephei, have been used to derive a complete radial-velocity versus phase curve for the variable, to investigate the presence of a possible binary companion, and to address the question of its membership in the Cepheus OB2 association. The observations are consistent with the absence of a close binary companion and shed doubt on

Laurence A. Marschall; Michael A. Seeds; Robert J. Davis

1993-01-01

179

Pulse Wave Velocity in Korean American Men and Women  

PubMed Central

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.

Logan, Jeongok G.; Barksdale, Debra J.

2013-01-01

180

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

NASA Astrophysics Data System (ADS)

We utilize two-and-three-quarter years of vertical-component recordings made by the Transportable Array (TA) component of Earthscope to constrain three-dimensional (3-D) seismic shear wave velocity structure in the upper 200 km of the western United States. Single-taper spectral estimation is used to compile measurements of complex spectral amplitudes from 44317 seismograms generated by 123 teleseismic events. In the first step employed to determine the Rayleigh-wave phase-velocity structure, we implement a new tomographic method, which is simpler and more robust than scattering-based methods (e.g. multi-plane surface wave tomography). The TA is effectively implemented as a large number of local arrays by defining a horizontal Gaussian smoothing distance that weights observations near a given target point. The complex spectral-amplitude measurements are interpreted with the spherical Helmholtz equation using local observations about a succession of target points, resulting in Rayleigh-wave phase-velocity maps at periods over the range of 18-125 s. The derived maps depend on the form of local fits to the Helmholtz equation, which generally involve the non-plane-wave solutions of Friederich et al. In a second step, the phase-velocity maps are used to derive 3-D shear velocity structure. The 3-D velocity images confirm details witnessed in prior body-wave and surface-wave studies and reveal new structures, including a deep (>100 km deep) high-velocity lineament, of width ~200 km, stretching from the southern Great Valley to northern Utah that may be a relic of plate subduction or, alternatively, either a remnant of the Mojave Precambrian Province or a mantle downwelling. Mantle seismic velocity is highly correlated with heat flow, Holocene volcanism, elastic plate thickness and seismicity. This suggests that shallow mantle structure provides the heat source for associated magmatism, as well as thinning of the thermal lithosphere, leading to relatively high stress concentration. Our images also confirm the presence of high-velocity mantle at >~100 km depth beneath areas of suspected mantle delamination (southern Sierra Nevada; Grande Ronde uplift), low velocity mantle underlying active rift zones, and high velocity mantle associated with the subducting Juan de Fuca plate. Structure established during the Proterozoic appears to exert a lasting influence on subsequent volcanism and tectonism up to the Present.

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

2010-03-01

181

Rupture Directivity Analysis for the 2008 Wenchuan (China) Earthquake Inferred from the Rayleigh-Wave Phase Velocity  

NASA Astrophysics Data System (ADS)

The rupture directivity for the 2008 Wehchuan (China) earthquake is analyzed by examining travel-time differences of 100-s Rayleigh-waves between the main shock and the reference earthquake. The Rayleigh-wave travel times for the reference earthquake are calculated from a known global Rayleigh-wave phase-velocity map. Variations of travel-time differences with station azimuths demonstrate apparently the rupture directivity for the 2008 Wehchuan (China) earthquake. The maximum travel-time difference (~125 s) appears in an azimuth of about 130 degree; whereas the minimum one (~20 s) locates in an azimuth of about 33degree. By the rupture directivity analysis, the optimal rupture azimuth is about 48 degree, and then we obtain the average source duration of ~83.3 sec and the propagation time, ~50.9 sec, with which the 100-s Rayleigh-wave passed through the fault. Providing the phase-velocity of 4.15 km/sec in the source area, we estimate the rupture length from the propagation time to be about 211.2 km, and then the rupture velocity estimated from the entire source duration is about 2.54 km/sec. Because the entire source duration includes the rupture time and rise time of source, we analyze the spectral-node periods of Rayleigh waves to judge the reasonable rupture time. The estimated rise time is about 18 sec. Thus, the rupture velocity is estimated afresh to be 3.23 km/sec, probably approaching to the S-wave velocity in the upper crust.

Chang, W.; Hwang, R.; Chang, J.; Wu, J.

2009-12-01

182

Shear Wave Velocities in the Pampean Flat Slab Region from Rayleigh Wave Tomography: Implications for Crustal Composition and Upper Mantle Hydration  

NASA Astrophysics Data System (ADS)

The Pampean flat slab region, located in Chile and western Argentina between 29° and 34° S, is characterized by the subducting Nazca plate assuming a sub-horizontal geometry for ~300 km laterally before resuming a more "normal" angle of subduction. The onset of flat slab subduction is associated with the cessation of regional arc related volcanism and the migration of deformation inboard from the high Andes into the thin-skinned Precordillera and thick-skinned Sierras Pampeanas. Developing a better understanding of this region's geology is of particular importance, as it is an ideal area to study flat slab subduction and serves as a modern analogue to Laramide flat slab subduction in the western US. To study the crustal and mantle structure in the region, we combine ambient noise tomography and ballistic surface wave tomography to produce a regional 3D shear wave velocity model that encompasses flat slab subduction in the north and normal subduction geometry in the south, allowing for a comparison of the two. Results from this work show that shear velocities within the upper crust are largely determined by composition, with sedimentary basins and areas with active volcanism exhibiting slower velocities than basement cored uplifts and other bedrock exposures. Though surface waves are not particularly sensitive to the depth of sharp velocity contrasts, we observe an eastward increase in shear velocity at depth that correlates with an eastward decrease in crustal thickness. In both the slab and overlying mantle, we observe significant variations in shear wave velocity. North of 32° S, where flat slab subduction is occurring, the Nazca plate contains low-velocity zones (LVZs) beneath the high Andes and Precordillera that are not present in the east beneath the Sierras Pampeanas. An opposite transition is observed in the overlying mantle, which changes from fast in the west to slow in the east. Both of these observations are consistent with an initially hydrated slab dehydrating and releasing water into the overlying mantle. Within this region we also observe a LVZ immediately above the slab as the subduction angle steepens. This zone potentially represents asthenosphere or hydrated lithospheric mantle. South of 32° S, where subduction is occurring at a more normal angle, the slab is visible as a high-velocity body with a low-velocity mantle wedge present beneath the arc and back arc. The variations in slab and upper mantle shear velocities are consistent with a hydrated flat slab and the presence of a LVZ above the flat slab as it steepens suggests that water is being transported to a significant depth or that an asthenospheric wedge is present between the slab and cratonic lithosphere.

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

2011-12-01

183

Shear-Wave Velocity Structure of the New Madrid Seismic Zone From Rayleigh Wave Group Velocity Dispersion Using Regional and Local Earthquake Data  

NASA Astrophysics Data System (ADS)

Regional and local Rayeligh-wave group velocity dispersion data were used to extract shear-wave velocity structure of several propagation paths from earthquakes into the New Madrid Seismic Zone. The dispersion data are limited at high frequency by the mid-crustal depth of the earthquakes and at low frequency because of the relatively short propagation paths involved. Inferred dispersion curves also show irregularities possibly due to velocity heterogeneity along the path. The working passband occurs between frequencies of 0.05 and 0.5Hz. The dispersion data were inverted for shear-wave velocity structures. Our starting model for the inversion was a crustal model obtained from a seismic refraction experiment performed in the Eastern Tennessee Seismic zone. Preliminary results indicate a high shear-wave velocity layer at a depth of about 12-15km within the crust. The high velocity layer is seen to occur at a shallower depth compared to the result of the refraction data anlaysis of Catchings (1999) and the resolution is relatively poor for deeper parts of the crustal model.

Jemberie, A. L.; Langston, C. A.

2005-12-01

184

Earthquake Prediction: Variation of Seismic Velocities before the San Francisco Earthquake  

Microsoft Academic Search

A large precursory change in seismic body-wave velocities occurred before the earthquake in San Fernando, California. The discovery that this change is mainly in the P-wave velocity clearly relates the effect to the phenomenon of dilatancy in fluid-filled rocks. This interpretation is supported by the time-volume relation obtained by combining the present data with the data from previous studies. The

James H. Whitcomb; Jan D. Garmany; Don L. Anderson

1973-01-01

185

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)

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

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

2012-11-01

186

Rayleigh wave phase velocities, small-scale convection, and azimuthal anisotropy beneath southern California  

Microsoft Academic Search

We use Rayleigh waves to invert for shear velocities in the upper mantle beneath southern California. A one-dimensional shear velocity model reveals a pronounced low-velocity zone (LVZ) from 90 to 210 km. The pattern of velocity anomalies indicates that there is active small-scale convection in the asthenosphere and that the dominant form of convection is three-dimensional (3-D) lithospheric drips and

Yingjie Yang; Donald W. Forsyth

2006-01-01

187

Measurement of velocity distribution of Laser-generated Rayleigh wave on welded structure  

NASA Astrophysics Data System (ADS)

A new method based on laser-generated ultrasound and piezoelectric transducer (PZT) is proposed to measure the velocity distribution on welded metal structure. High-frequency Rayleigh waves are excited by the Nd: YAG pulsed laser and probed by self-made transducer. A serial of ultrasonic pulses can be detected on the surface of the sample by the transducer through the scan of the line source with translation stage. The waveform cross-correlation technique is applied to compute the propagation velocity of Rayleigh waves. Then analogically, a series of wave velocities at different positions are detected, by which the distribution of velocities is obtained. It is found that high frequency wave signals excited by laser line pulse can be probed effectively using the PZT, and results indicate that this method can provide the basis for precision detection with quick scanning and the reliable measurement of velocity distribution.

Dong, Li-Ming; Ni, Chenyin; Shen, Zhong-Hua; Ni, Xiao-Wu

2010-08-01

188

Shear-wave velocity estimation in porous rocks; Theoretical formulation, preliminary verification and applications  

SciTech Connect

This paper discusses heat-wave velocity logs, useful for various seismic interpretation applications, including bright spot analyses, amplitude-versus-offset analyses and multicomponent seismic interpretations. Measured shear-wave velocity logs are, however, often unavailable. The authors developed a general method to predict shear-wave velocity in porous rocks. If reliable compressional-wave velocity, lithology, porosity and water saturation data are available, the precision and accuracy of shear-wave velocity prediction are 9% and 3%, respectively. The success of the authors' method depends on: robust relationships between compressional- and shear-wave velocities for water-saturated, pure, porous lithologies; nearly linear mixing laws for solid rock constituents; first-order applicability of the Biot-Gassmann theory to real rocks. The authors verified these concepts with laboratory measurements and full waveform sonic logs. Shear-wave velocities estimated by the authors' method can improve formation evaluation. The authors' method has been successfully tested with data from several locations.

Greenberg, M.L. (Atlantic Richfield Corp., Plano, TX (US)); Castagna, J.P. (ARCO Oil and Gas Co., Houston, TX (US))

1992-02-01

189

Variations in Compressional Waves at Teleseismic Distances.  

National Technical Information Service (NTIS)

Short-period seismic waves from three underground explosions at the Nevada test site were recorded at comparable distances by University of Michigan field crews located at various sites between Minnesota and Georgia. The signal levels measured on the seis...

D. E. Willis

1965-01-01

190

High resolution 3D P wave velocity structure beneath Tenerife Island (Canary Islands, Spain) based on tomographic inversion of active-source data  

NASA Astrophysics Data System (ADS)

We present a high resolution 3 dimensional (3D) P wave velocity model for Tenerife Island, Canaries, covering the top of Teide volcano (3,718 m a.s.l.) down to around 8 km below sea level (b.s.l). The tomographic inversion is based on a large data set of travel times obtained from a 3D active seismic experiment using offshore shots (air guns) recorded at more than 100 onshore seismic stations. The obtained seismic velocity structure is strongly heterogeneous with significant (up to 40%) lateral variations. The main volcanic structure of the Las Cañadas-Teide-Pico Viejo Complex (CTPVC) is characterized by a high P wave velocity body, similar to many other stratovolcanoes. The presence of different high P wave velocity regions inside the CTPVC may be related to the geological and volcanological evolution of the system. The presence of high P wave velocities at the center of the island is interpreted as evidence for a single central volcanic source for the formation of Tenerife. Furthermore, reduced P wave velocities are found in a small confined region in CTPVC and are more likely related to hydrothermal alteration, as indicated by the existence of fumaroles, than to the presence of a magma chamber beneath the system. In the external regions, surrounding CTPVC a few lower P wave velocity regions can be interpreted as fractured zones, hydrothermal alterations, porous materials and thick volcaniclastic deposits.

GarcíA-Yeguas, Araceli; Koulakov, Ivan; IbáñEz, Jesús M.; Rietbrock, A.

2012-09-01

191

Rayleigh wave phase velocities in old oceanic seafloor from the PLATE experiment  

NASA Astrophysics Data System (ADS)

The process of formation and growth of the oceanic lithosphere is of fundamental importance to our understanding of plate tectonics. Measurements and physical properties of the oceanic lithosphere and their variation with age, however, are sparse due to difficult access in ocean waters. Observations of seafloor subsidence and heat flow are inconsistent with the classic, conductive, cooling-half-space model for lithospheric growth and thickening at seafloor ages greater than ~80 Ma and are better fit by cooling plate models with thickness 90 to 125 km. However, global seismic tomography using surface waves that propagate great distances across the seafloor indicate that the plates continue to thicken after 80 Ma, more like the cooling half-space models, but lateral resolution from these long ray paths is relatively poor. Here we present Rayleigh wave phase velocities obtained from a recent marine seismic experiment conducted in the northwest Pacific ocean on old seafloor (150-160 Ma) in an area that has not been significantly affected by later intraplate volcanism. The PLATE project (Pacific Lithosphere Anisotropy and Thickness Experiment) was designed to deploy an array of ocean bottom seismometers on each arm of a magnetic bight to exploit the contrast in remnant lithospheric anisotropy expected in each region. We present phase velocity results in this old oceanic lithosphere at periods from 18s to 100s. Azimuthal anisotropy averaged over the study area at different periods will distinguish mineral alignment in the lithosphere and the asthenosphere indicating the depth of transition of this boundary. Estimates of lithospheric depth inferred from seismic velocity and anisotropy will provide direct measurements needed to address discrepancies in lithospheric formation, growth, and cooling evolution with time.

Sotirov, T. A.; Brimm, J.; Weeraratne, D. S.; Ramirez, C.; Forsyth, D. W.

2011-12-01

192

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

SciTech Connect

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.

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

2006-03-20

193

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

NASA Astrophysics Data System (ADS)

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-Forêts Enhanced Geothermal System (EGS) records of induced seismicity during hydraulic injection.

Shalev, Eyal; Calò, Marco; Lyakhovsky, Vladimir

2013-11-01

194

Temperature variation of sound velocity in liquid He II  

NASA Astrophysics Data System (ADS)

The temperature dependences of the sound velocity in liquid helium II in bulk and in film are evaluated explicitly for low temperatures. In the bulk case, our theory yields results which agree with experiment better than the previous theories of Andreev and Khalatnikov and of Singh and Prakash. The film case is shown to be somewhat different from the bulk case.

Um, Chung-In; Kahng, Woo-Hyung; Yeon, Kyu-Hwang; Choh, Soon-Tahk; Isihara, A.

1984-05-01

195

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

NASA Astrophysics Data System (ADS)

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

Huang, H.; Hsu, C.

2009-12-01

196

Traveling waves in an optimal velocity model of freeway traffic  

Microsoft Academic Search

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

Peter Berg; Andrew Woods

2001-01-01

197

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

PubMed

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

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

2012-09-12

198

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

NASA Astrophysics Data System (ADS)

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.

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

2013-09-01

199

Solitary Waves of the MRLW Equation by Variational Iteration Method  

SciTech Connect

In a recent publication, Soliman solved numerically the modified regularized long wave (MRLW) equation by using the variational iteration method (VIM). In this paper, corrected numerical results have been computed, plotted, tabulated, and compared with not only the exact analytical solutions but also the Adomian decomposition method results. Solitary wave solutions of the MRLW equation are exactly obtained as a convergent series with easily computable components. Propagation of single solitary wave, interaction of two and three waves, and also birth of solitons have been discussed. Three invariants of motion have been evaluated to determine the conservation properties of the problem.

Hassan, Saleh M. [Department of Mathematics, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Department of Mathematics, College of Science, Ain Shams University, Abbassia 11566, Cairo (Egypt); Alamery, D. G. [Department of Mathematics, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia)

2009-09-09

200

Solitary Waves of the MRLW Equation by Variational Iteration Method  

NASA Astrophysics Data System (ADS)

In a recent publication [1], Soliman solved numerically the modified regularized long wave (MRLW) equation by using the variational iteration method (VIM). In this paper, corrected numerical results have been computed, plotted, tabulated, and compared with not only the exact analytical solutions but also the Adomian decomposition method results. Solitary wave solutions of the MRLW equation are exactly obtained as a convergent series with easily computable components. Propagation of single solitary wave, interaction of two and three waves, and also birth of solitons have been discussed. Three invariants of motion have been evaluated to determine the conservation properties of the problem.

Hassan, Saleh M.; Alamery, D. G.

2009-09-01

201

Effects of soil moisture variations on deposition velocities above vegetation.  

SciTech Connect

The parameterized subgrid-scale surface flux (PASS) model provides a simplified means of using remote sensing data from satellites and limited surface meteorological information to estimate the influence of soil moisture on bulk canopy stomatal resistances to the uptake of gases over extended areas. PASS-generated estimates of bulk canopy stomatal resistance were used in a dry deposition module to compute gas deposition velocities with a horizontal resolution of 200 m for approximately 5000 km{sup 2} of agricultural crops and rangeland. Results were compared with measurements of O{sub 3} flux and concentrations made during April and May 1997 at two surface stations and from an aircraft. The trend in simulated O{sub 3} deposition velocity during soil moisture drydown over a period of a few days matched the trend observed at the two surface stations. For areas under the aircraft flight paths, the variability in simulated O{sub 3} deposition velocity was substantially smaller than the observed variability, while the averages over tens of kilometers were usually in agreement within 0.1 cm s{sup -1}. Model results indicated that soil moisture can have a major role in deposition of O{sub 3} and other substances strongly affected by canopy stomatal resistance.

Wesely, M. L.; Song, J.; McMillen, R. T.; Meyers, T. P.; Environmental Research; Northern Illinois Univ.; National Oceanic and Atmospheric Administration

2001-01-01

202

Estimating shear wave velocity of soil deposits using polynomial neural networks: Application to liquefaction  

NASA Astrophysics Data System (ADS)

Geophysical and geotechnical field investigations have introduced several techniques to measure in-situ shear wave velocity of soils. However, there are some difficulties for the easy and economical use of these techniques in the routine geotechnical engineering works. For the soil deposits, researchers have developed correlations between shear wave velocity and SPT-N values. In the present study, a new database containing the measured shear wave velocity of soil deposits have been compiled from the previously published studies. Using polynomial neural network (PNN), a new correlation has been subsequently developed for the prediction of shear wave velocity. The developed relationship shows an acceptable performance compared with the available relationships. Three examples are then presented to confirm accuracy and applicability of the proposed equation in the field of liquefaction potential assessment.

Ghorbani, Ali; Jafarian, Yaser; Maghsoudi, Mohammad S.

2012-07-01

203

Velocity dispersion of P and Stoneley waves: an insight into permeability of porous rocks  

NASA Astrophysics Data System (ADS)

Permeability is a key parameter in hydrocarbon exploration and reservoir analysis. It is usually expensive to obtain in situ permeability well logs. Pride (2005) indicates that a higher permeability in a porous rock results in greater P-wave velocity dispersion. We utilize uncorrelated vibrator VSP data and broadband full-waveform sonic data to study the relation of permeability and velocity dispersion of P and Stoneley waves. Both the vibrator and the sonic datasets were acquired from the Mallik gashydrate research wells in Mackenzie Delta, Northwest Territory, Canada. For the vibrator data, P wave velocity is extracted continuously in the entire frequency band of the signal using a moving-window crosscorrelation procedure, so that velocity dispersion is obtained as a function of frequency. For the sonic data, velocities of P and Stoneley waves are measured respectively by means of semblance analysis on low and high pass components, and the velocity difference is therefore velocity dispersion between the two frequency components. Well logs from the same boreholes are then investigated to produce cross plots of velocity dispersion, permeability, and porosity. The measurements from both datasets show positive correlation between significant velocity dispersion and elevated permeability. For P wave, this observation is consistent with Pride's theory, showing that velocity dispersion is a potential indicator of in situ permeability. It is very common that Stoneley wave is much stronger and easier to identify than P wave in borehole sonic surveys. Although there are a limited number of observations on Stoneley wave dispersion, most of the existing theories linking velocity dispersion and petrophysical properties are for P and S waves. Our effort demonstrates that by investigating its velocity dispersion, Stoneley wave can contribute to a better insight into permeability of porous rocks. ACKNOWLEDGMENTS: This project is supported by a starting grant by China University of Petroleum (Beijing) to L. Sun. The Mallik uncorrelated vibrator VSP, full-waveform sonic, and NMR-derived permeability data were acquired as part of the JAPEX/JNOC/GSC el al Mallik gashydrate research wells. W. Pun was supported by NSERC. REFERENCE: Pride, S.R., 2005: Relations between seismic and hydrological properties, in Y. Rubin and S.S. Hubbards, eds., Hydrogeophysics. Springer, 253-290.

Sun, L. F.; Pun, W.; Milkereit, B.

2011-12-01

204

Lateral Variations in Mantle P Velocity for a Tectonically Regionalized Earth.  

National Technical Information Service (NTIS)

Estimates of tau functions for a tectonically regionalized earth are obtained from over 1.25 million seismic ray paths of ISC Bulletin data to study the correlation of lateral variations in mantle P velocity with surface heterogeneity. Statistical regular...

D. M. Tralli

1986-01-01

205

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

SciTech Connect

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.

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

2010-05-15

206

Correlating Wave Velocities with Physical, Mechanical Properties and Petrographic Characteristics of Peridotites from the Central Greece  

Microsoft Academic Search

Knowledge of compressional and shear wave velocities is necessary to estimate the physical, dynamic and mechanical properties\\u000a of rocks with an indirect, but easy, fast and economical way. Although, many attempts have been made to correlate the wave\\u000a velocities with the rock characteristics, only few studies have been concentrated on ultrabasic rocks and especially on peridotites.\\u000a The aim of this

K. Diamantis; S. Bellas; G. Migiros; E. Gartzos

207

Nanga Parbat crustal anisotropy: Implications for interpretation of crustal velocity structure and shear-wave splitting  

Microsoft Academic Search

The Nanga Parbat-Haramosh massif represents a unique exposure of mid-lower continental crust from beneath the Himalayan orogen. Seismic velocity measurements on a suite of quartzofeldspathic gneisses show up to 12.5% velocity anisotropy for compressional waves and up to 21% for shear waves. The degree of anisotropy is a function of mica content and rock fabric strength. Over 30% of the

Anne Meltzer; Nikolas Christensen

2001-01-01

208

Study on estimate method of wave velocity and quality factor to fault seals  

Microsoft Academic Search

Based on ultrasonic test of fault rocks, the responses for wave velocity and quality factor (Q value) to lithology, porosity and permeability of fault rocks and mechanical property of faults are studied. In this paper,\\u000a a new quantitative estimate method of fault seals is originally offered. The conclusions are as follows: (1) Wave velocity\\u000a andQ value increase and porosity decreases

Zhensheng Li; Deliang Liu; Bo Liu; Qiang Yang; Jingming Li

2005-01-01

209

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

210

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

ERIC Educational Resources Information Center

|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…

Siboni, S.

2009-01-01

211

Lateral variations in mantle P velocity for a tectonically regionalized earth  

SciTech Connect

Estimates of tau functions for a tectonically regionalized earth are obtained from over 1.25 million seismic ray paths of ISC Bulletin data to study the correlation of lateral variations in mantle P velocity with surface heterogeneity. Statistical regularity criteria check the consistency of the regionalization. Tau perturbations attributed to crustal and shallow-mantle velocity variations are also estimated. ''Single region'' tau functions are constructed and inverted to obtain velocity-depth functions and extremal bounds at the 99.9% confidence level for seven different types of tectonic regions. Deviations from a regionally weighted reference mean velocity function indicate significant differences, particularly between oceanic and continental tectonic regions, extending to a depth of 700 km. Increased shallow-mantle velocities are observed from young to old oceans and from active to stable continents. Evidence for a velocity anomaly between 700 and 950 km is indicated. Significant negative residuals are observed centered at about 780 km depth below young oceans and about 880 km below active continents. The level of variations decreases below 950 km. Lateral velocity variations are also suggested within 250 km of the core boundary. Tau perturbations are indicative of negative shallow-mantle velocity anomalies beneath oceanic regions and positive anomalies beneath continental regions and oceanic trenches. A less than average crustal thickness in oceans and greater thickness in stable continents are also indicated.

Tralli, D.M.

1986-04-01

212

S wave velocity structure of the northern Cascadia subduction zone  

Microsoft Academic Search

The shear velocity structure across the northern Cascadia subduction zone is examined using three-component broadband digital seismographs. Locally generated P-to-S conversions are analyzed to estimate the S velocity structure to upper mantle depths and to constrain the subduction geometry of the Juan de Fuca plate. The oceanic crust is at 47-53 km beneath central Vancouver Island, 60-65 km beneath Georgia

John F. Cassidy; Robert M. Ellis

1993-01-01

213

Observation of an extrinsic critical velocity using matter wave interferometry  

SciTech Connect

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

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

2007-08-01

214

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

PubMed

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(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 ~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. PMID:22462936

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

2012-03-01

215

Minimizers with discontinuous velocities for the electromagnetic variational method  

Microsoft Academic Search

The electromagnetic two-body problem has neutral differential delay equations of motion that, for generic boundary data, can have solutions with discontinuous derivatives. If one wants to use these neutral differential delay equations with arbitrary boundary data, solutions with discontinuous derivatives must be expected and allowed. Surprisingly, Wheeler-Feynman electrodynamics has a boundary value variational method for which minimizer trajectories with discontinuous

Jayme de Luca

2010-01-01

216

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

SciTech Connect

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.

Hollweg, J.V.; Yang, G.; Cadez, V.M.; Gakovic, B. (New Hampshire Univ., Durham (USA) Institut za Fiziku, Belgrade (Yugoslavia) Sarajevo Univerzitet (Yugoslavia))

1990-01-01

217

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

Microsoft Academic Search

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

KEVIN D. LEAMANAND; Thomas B. Sanford

1975-01-01

218

Thermal structure of continental upper mantle inferred from S-wave velocity and surface heat flow  

Microsoft Academic Search

Results from seismic tomography provide information on the thermal structure of the continental upper mantle. This is borne out by the good agreement between tectonic age, surface heat flow and a tomographic S-wave velocity model for depths less than 180 km. The velocity anomalies of tomographic layers deeper than 230 km have relatively small amplitudes and show little correlation with

Axel H. E Röhm; Roel Snieder; Saskia Goes; Jeannot Trampert

2000-01-01

219

Surface wave higher-mode phase velocity measurements using a roller-coaster-type algorithm  

Microsoft Academic Search

In order to solve a highly non-linear problem by introducing the smallest a priori information, we present a new inverse technique called the `roller coaster' technique and apply it to measure surface wave mode-branch phase velocities. The fundamental mode and the first six overtone parameter vectors, defined over their own significant frequency ranges, are smoothed average phase velocity perturbations along

Éric Beucler; Éléonore Stutzmann; Jean-Paul Montagner

2003-01-01

220

Eurasian fundamental mode surface wave phase velocities and their relationship with tectonic structures  

Microsoft Academic Search

We automatically analyzed 32,000 fundamental mode Love and Rayleigh wave signals with earthquake-station paths traversing Eurasia and Indonesia and obtained robust average phase velocity measurements between 20 s and 170 s periods along 4389 Love and 4020 Rayleigh paths. These were inverted to give phase velocity maps at 14 fixed periods. Resolution tests suggest that features with diameter >750 km

Andrew Curtis; Jeannot Trampert; Roel Snieder; Bernard Dost

1998-01-01

221

Effect of temperature on wave velocities in sands and sandstones with heavy hydrocarbons  

Microsoft Academic Search

A laboratory investigation was made of the effects of temperature on wave velocities in well cemented Massillon and Boise sandstones and unconsolidated Ottawa sand saturated with heavy hydrocarbons, as well as the dependence of compressional velocities in the hydrocarbons themselves as a function of temperature. The hydrocarbons selected as pore saturants were a commercial paraffin wax, 1-Eicosene, natural heavy crude,

Z. Wang; A. M. Nur

1986-01-01

222

Geodynamical Interpretation of Crustal and Mantle Shear-Wave Velocity Structures Beneath the Carpathian-Pannonian Region  

NASA Astrophysics Data System (ADS)

The Carpathian-Pannonian system of Eastern and Central Europe represents a unique opportunity to study the interaction between surface tectonic processes involving convergence and extension, and convective processes in the upper mantle. The South Carpathian Project (SCP), a major temporary deployment (2009-2011) of seismic broadband systems extending across the eastern Pannonian Basin and the South Carpathian Mountains was set up with the purpose of bringing constraints on the geodynamical processes that have shaped the region. Imaging the seismic velocity structure of the crust and the upper mantle helps us to understand the structure and geodynamical evolution of this part of central Europe. Here, we present high-resolution images of both crustal and upper mantle shear-wave velocity structures beneath the Carpathian-Pannonian region using surface waves obtained from ambient noise tomography, and finite-frequency teleseismic tomography using S-wave arrivals, from 54 stations of the South Carpathian Project (SCP, 2009-2011), 56 stations of the Carpathian Basins Project (CBP, 2005-2007) and 131 national network broadband stations. For ambient noise tomography, we computed cross-correlations of vertical component continuous ambient seismic noise recordings for all possible pairs of stations and stacked the correlated waveforms over 1-2 years for the temporary stations and up to 5 years for permanent stations to estimate Rayleigh wave empirical Green's functions. Over 5700 final Rayleigh wave Green's functions were selected for the measurement of group velocity dispersion curves between 4s and 40s using the multiple-filter analysis technique. Group velocity maps are first computed on a grid discretized with 0.2°x0.2° steps from a non-linear 2-D tomographic inversion of measured group velocity dispersion curves. We then inverted the Rayleigh wave group velocity at each location to obtain the 3-D shear-wave velocity structure of the crust and uppermost mantle beneath the Carpathian-Pannonian region. In the finite-frequency teleseismic tomography of S waves, we have selected earthquakes with magnitude greater than 5.5 in the distance range 30°-95°, which occurred between 2006 and 2011. Using multi-channel cross-correlation technique, over 29661 and 41875 relative S arrival times were measured in high and intermediate frequency bands (0.1-0.5 Hz and 0.05-0.1 Hz) respectively. The relative arrival times are inverted for S-wave velocity distribution in the upper mantle according to the 3-D finite frequency kernel formulation. Our shear-wave velocity models provide a uniquely complete and relatively high-resolution view of the crustal and upper mantle structures in the region. We will discuss the interpretations of these velocity variations for the formation and geodynamical evolution of the lithosphere and upper mantle of the Carpathian-Pannonian region.

Ren, Yong; Stuart, Graham; Houseman, Gregory; Grecu, Bogdan; Ionescu, Constantin; Hegedüs, Endre; Radovanovi?, Slavica; Shen, Yang; South Carpathian Project working group

2013-04-01

223

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

NASA Astrophysics Data System (ADS)

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.

Priestley, Keith; McKenzie, Dan

2013-11-01

224

Hyperbolicity of Velocity-Stress Equations for Waves in Anisotropic Elastic Solids  

Microsoft Academic Search

This paper reports mathematical properties of the three-dimensional, first-order, velocity-stress equations for propagating\\u000a waves in anisotropic, linear elastic solids. The velocity-stress equations are useful for numerical solution. The original\\u000a equations include the equation of motion and the elasticity relation differentiated by time. The result is a set of nine,\\u000a first-order partial differential equations (PDEs) of which the velocity and stress

Yung-Yu Chen; Lixiang Yang; Sheng-Tao John Yu

225

The effect of wind velocity on the amplitude scintillations of millimetre radio waves  

Microsoft Academic Search

The effect of transverse wind velocity on the amplitude scintillations of millimeter radio waves is studied. Scintillation data obtained on two line-of-sight microwave links at 36 GHz and 110 GHz on a common 4.1 km path are used to estimate the wind velocity perpendicular to the propagation path. The estimated wind velocity is within 20% of the value obtained from

K. L. Ho; R. S. Cole; N. D. Mavrokoukoulakis

1978-01-01

226

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)

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.

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

2013-09-01

227

Shear Wave Velocity, Seismic Attenuation, and Thermal Structure of the Continental Lithosphere  

NASA Astrophysics Data System (ADS)

Theoretical models based on laboratory studies of dissipation of energy in the crystalline rocks typical for the Earth's mantle suggest a temperature dependence of attenuation through the activation energy. We therefore compare global maps of the thermal structure of the continental lithosphere with the inverse attenuation of seismic shear waves Qs and seismic velocity Vs as determined from surface wave dispersion and amplitudes. Our study is based on recently available global databases. We compare the values of Qs, Vs, and temperature T at the depths of 50, 100, and 150 km in the continental lithosphere. We find that qualitatively (by the sign of the anomaly) the maps of Qs closely correlate with lithospheric temperatures. The best correlation is observed for the depth of 100 km, where the resolution of the attenuation model is the highest. At this depth, the contour of zero attenuation anomaly approximately corresponds to the 1000°C contour of lithospheric temperature, in agreement with laboratory data on a sharp change in seismic attenuation and shear velocities in upper mantle rocks at 900-1000°C. The correlation between Vs and two other parameters (T and Qs), though present, is less distinct. We find that most cratonic regions (the Siberian Craton, the East European Platform and the Baltic Shield, the North American Craton, West Africa, western Australia) show high lithospheric Vs, Qs and low T. In contrast, the South African craton has neither high Qs, nor low temperatures. Several prominent low Qs regions correlate with high lithospheric temperatures; this includes the Paleozoic West Siberian Basin, the Cenozoic-Paleozoic structures of the Western Europe, and western North America. We calculate correlation coefficients between Vs, Qs and T and find that at any depth, for any pair of the parameters the correlation is less than 0.42. It implies that even if temperature variations in the lithosphere are the main cause of seismic velocity and attenuation variations, the relation between temperature and seismic properties is non-linear and the concept of the compositionally homogeneous lithospheric roots is not true.

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

2002-12-01

228

Radial anatomic variation of ultrasonic velocity in human cortical bone.  

PubMed

Quantitative ultrasound techniques can be used to retrieve cortical bone quality. The aim of this study was to investigate the anatomic variations in speed of sound (SOS) in the radial direction of cortical bone tissue. SOS measurements were realized in 17 human cortical bone samples with a 3.5-MHz transverse transmission device. The radial dependence of SOS was investigated in a direction perpendicular to the periosteum. For each sample, bone porosity was measured using an X-ray micro-computed tomography device. The mean SOS was 3586 ± 255 m/s. For 16 of 17 specimens, similar radial variations in SOS were observed. In the periosteal region, SOS first decreased in the direction of the endosteum and reached a minimum value approximately in the middle of the cortical bone. SOS then increased, moving to the endosteal region. A significant negative correlation was obtained between SOS and porosity (R = -0.54, p = 0.02). PMID:23969161

Mathieu, Vincent; Chappard, Christine; Vayron, Romain; Michel, Adrien; Haïat, Guillaume

2013-08-19

229

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

PubMed

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

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

2004-04-01

230

Velocity renormalization of nodal quasiparticles in d-wave superconductors  

NASA Astrophysics Data System (ADS)

Gapless nodal quasiparticles emerge at a low-energy regime of high-Tc cuprate superconductors due to the dx2-y2 gap symmetry. We study the unusual renormalizations of the Fermi velocity vF and gap velocity v? of these quasiparticles close to various quantum critical points in a superconducting dome. Special attention is paid to the behavior of the velocity ratio, v?/vF, since it determines a number of observable quantities. We perform a renormalization-group analysis and show that the velocity ratio may vanish, approach unity, or diverge at different quantum critical points. The corresponding superfluid densities and critical temperatures are suppressed, slightly increased, or significantly enhanced. The effects of three types of static disorders, namely, random mass, random gauge potential, and random chemical potential, on the stability of the system are also addressed. An analogous analysis reveals that both random mass and random gauge potential are irrelevant. This implies that these fixed points of the velocity ratio are stable, and hence observable effects ignited by them are unchanged. However, the random chemical potential is marginal. As a result, these fixed points are broken, and thus, the instabilities of quantum phase transitions are triggered.

Wang, Jing

2013-02-01

231

Shear Wave Velocity, Seismic Attenuation, and Thermal Structure of the Continental Lithosphere  

Microsoft Academic Search

Theoretical models based on laboratory studies of dissipation of energy in the crystalline rocks typical for the Earth's mantle suggest a temperature dependence of attenuation through the activation energy. We therefore compare global maps of the thermal structure of the continental lithosphere with the inverse attenuation of seismic shear waves Qs and seismic velocity Vs as determined from surface wave

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

2002-01-01

232

Velocity measurements in the field of an internal gravity wave by means of speckle photography  

Microsoft Academic Search

Speckle velocimetry with forward scattering has been applied to measure and visualize the two-dimensional velocity field in an internal gravity wave. The wave was produced by towing a cylinder in vertical direction, normal to its axis, through stratified salt water. Neutrally buoyant tracer particles whose density was matched with the density distribution of the stratification were uniformly distributed in the

U. Gärtner; U. Wernekinck; W. Merzkirch

1986-01-01

233

Three-Dimensional P-Wave Velocity Image under the Carpathian Arc.  

National Technical Information Service (NTIS)

An inversion of P-wave travel time residuals from selected earthquakes in the distance range 30 deg to 98 deg to 2 seismic station networks was used to model P-wave velocity anomalies down to 250 Km depth. In the first inversion experiment a region betwee...

M. C. Oncescu V. Burlacu M. Anghel V. Smalbergher

1982-01-01

234

The statistics of particle velocities and accelerations under waves with directional spread  

Microsoft Academic Search

The statistics of the horizontal component of the water particle velocity vector under random waves are considered. A spread in the directions of travel of the component wave trains does not affect the rms value of the modulus r but it affects the shape of its probability distribution in such a way that the probability of extreme values is reduced.

M. J Tucker

1998-01-01

235

Assessment Of The True Pulse-wave Velocity Over The Physiological Pressure Range  

Microsoft Academic Search

The pulse-wave velocity (PWV) is measd to assess the arterial wall elasticity. The PWV is commonly estimated by taking some characteristic features of the arterial pulse wave and by deterrnining the time interval between its appearance at two points, a known distance apart along the artery. However due to the nonlinear pulse propagation in the arterial tree, this method provides

Y. Tardy; P. P. Vicyres; J. J. Meister

1990-01-01

236

Shear-Wave Velocity Structure in the Northern Basin and Range Province from the Combined Analysis of Receiver Functions and Surface Waves  

Microsoft Academic Search

A new method based on the joint inversion of receiver functions and surface-wave phase velocities results in well-determined shear-velocity structures that are consistent with the compressional-wave structure, gravity, heat flow, and elevation data in the northern Basin and Range. This new inversion method takes advantage of average-velocity information present in the surface-wave method and differential velocity information contained in the

Serdar Ozalaybey; Martha K. Savage; Anne F. Sheehan; John N. Louie; James N. Brune

1997-01-01

237

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

USGS Publications Warehouse

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.

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

2004-01-01

238

S-wave velocity as an indicator of solid-liquid transition in clay  

NASA Astrophysics Data System (ADS)

Clayey landslides, which are widely spread all over the world, pose specific problems to territorial planners, owing to dramatic variations in kinematics. Indeed, the analysis of landslide movements in a clay-rich area like the Trièves plateau (French Western Alps) indicates that slow slope movements can suddenly accelerate or fluidize as a result of heavy and/or long-lasting rainfalls or loading. Previous rheometric tests performed on the Trièves clay revealed a thixotropic behavior of the clay with a highly pronounced viscosity bifurcation at a yield stress ?c. Below that stress, the material behaves like a solid, while it abruptly starts flowing when this yield stress is reached. This solid-liquid transition was investigated by measuring the variations of the shear wave velocity (Vs) in the Trièves clay during rheometric tests and flume tests. First, rheometric parallel-plate tests were performed at 3 different clay water contents (52%, 66% and 78%). Oscillatory stress tests were conducted during the experiments, allowing the shear modulus and Vs to be measured as a function of the shear stress level. Results revealed a dramatic Vs change at the same yield stress as for the viscosity bifurcation. When the stress is lower than the yield stress, Vs regularly increases with time up to a limit value. As soon as the yield stress is reached, Vs abruptly decreases to reach values of a few m/s in the fluidized clay. In order to investigate at a larger scale (approximately 1 m) the evolution of the shear wave velocity during the clay fluidization, flume tests were performed for two clay water contents (57 % and 68%). These experiments consist in progressively tilting a flume filled with a saturated clay layer (35cm wide, 60cm long and 10cm deep) until reaching the fluidization at a given slope. The Rayleigh wave velocity (VR), which is related to Vs, was continuously monitored using a piezometric source and 4 vertical component accelerometers placed at the surface of the clay layer. The Rayleigh wave propagation was reconstructed by cross correlating the source signal (50-700 Hz sweep) and the 4 recorded signals. The clay mass motion was measured, using 3 height sensors (vertical displacement) and a digital camera to follow the displacement of three superficial markers (colored pins). The tilt angle, which increased by 1 degree per minute, was given by an inclinometer placed on the flume. Signals were generated every 30 seconds. Results showed no variation of VR during the flume tilting. Just before that the mass moved at a critical angle, a rapid decrease in VR (between 4 and 7%) was observed on all the signals, evidencing a change in Vs at the base of the layer. Both experiments showed that Vs could be a valuable good indicator for rheological changes in clay. The seismic measurements during flume tests are in agreement with passive seismic monitoring results at the Pont Bourquin landslide (Switzerland), where a drop of 7% in VR was measured 4 days before a earth-slide earth-flow in 2010, which mobilized about 4,500 m3 of clay material.

Mainsant, Guénolé; Jongmans, Denis; Chambon, Guillaume; Larose, Eric; Baillet, Laurent

2013-04-01

239

Carbonate reservoir characterization using seismic velocity and amplitude variation with offset analysis: Hardeman basin, Texas, test case  

SciTech Connect

Mississippian bioherms in the Hardeman basin, Texas, produce from dolomitized mud cores with porosities that can vary from 10 to 40%. These carbonate buildups, though often similar in seismic reflector boundary configuration, can vary remarkably in reservoir quality (e.g., porosity) owing to diagenesis. However, imaging these lateral variations of porosity and determining the reservoir pressure is possible with detailed seismic velocity control and amplitude variation with offset (AVO) analysis. The investigated 24-fold seismic profile was acquired by four Vibroseis trucks in the Hardeman basin across two bioherms, one oil-productive and other tight and water-filled. Detailed stacking velocity analyses on the relative amplitude processed line directly delineate areas of increasing and decreasing gross porosity and dramatically differentiate the two mounds. Moreover, the detailed velocity analyses help provide a more accurate stacked section with resultant better definition of the external mound configuration. Analysis of available laboratory compressional and shear wave velocity data for carbonate rocks reveal that Young's modulus in carbonates is a function of porosity and differential pressure. Comparison of the derived Young's modulus from an inversion of the AVO data for the unstacked line with the experimental laboratory data yield porosity and differential pressure estimates over the productive bioherm which are within 18% and 15%, respectively, of those observed in the borehole.

Pigott, J.D.; Shrestha, R.K. (Univ. of Oklahoma, Norman (United States)); Warwick, R.A. (Oryx Energy Co., Dallas, TX (United States))

1991-03-01

240

Variational formulation of covariant eikonal theory for vector waves  

SciTech Connect

The eikonal theory of wave propagation is developed by means of a Lorentz-covariant variational principle, involving functions defined on the natural eight-dimensional phase space of rays. The wave field is a four-vector representing the electromagnetic potential, while the medium is represented by an anisotropic, dispersive nonuniform dielectric tensor D/sup ..mu nu../(k,x). The eikonal expansion yields, to lowest order, the Hamiltonian ray equations, which define the Lagrangian manifold k(x), and the wave-action conservation law, which determines the wave-amplitude transport along the rays. The first-order contribution to the variational principle yields a concise expression for the transport of the polarization phase. The symmetry between k-space and x-space allows for a simple implementation of the Maslov transform, which avoids the difficulties of caustic singularities.

Kaufman, A.N.; Ye, H.; Hui, Y.

1986-10-01

241

Phase velocities of rayleigh waves in the MELT experiment on the east pacific rise  

PubMed

The phase velocities of Rayleigh waves increase more rapidly with distance from the East Pacific Rise (EPR) axis than is predicted by models of conductive cooling of the lithosphere. Low velocities near the axis are probably caused by partial melt at depths of 20 to 70 kilometers in a zone several hundred kilometers wide. The lowest velocities are offset to the west of the EPR. Wave propagation is anisotropic; the fast direction is approximately perpendicular to the ridge, parallel to the spreading direction. Anisotropy increases from a minimum near the axis to 3 percent or more on the flanks. PMID:9596571

Forsyth; Webb; Dorman; Shen

1998-05-22

242

Converted PS-Wave Velocity Structure Of Post-Rift Sediments In the Eastern Black Sea  

Microsoft Academic Search

The combined analysis of P- and S-waves can be used successfully to characterize lithology and pore fluids, resolving ambiguities that would result from the analysis of P-wave data alone. Knowledge of S-wave velocity may also contribute to pore pressure estimation using either empirical relationships or rock physics models. Using wide-angle seismic data collected from the Eastern Black Sea Basin (EBSB)

Georgios N. Moukos; Timothy A. Minshull; Rosemary A. Edwards

2010-01-01

243

Precise P and S wave velocity structures in the Kitakami massif, Northern Honshu, Japan, from a seismic refraction experiment  

NASA Astrophysics Data System (ADS)

The Kitakami massif, which is located in the eastern part of Northern Honshu, Japan, is composed of two geological units. The northern Kitakami terrane is characterized as a Jurassic accretionary complex, while the southern Kitakami terrane consists of pre-Silurian basement and Silurian-lower Cretaceous marine sediments. The boundary region of these two units, called the Hayachine tectonic belt (HTB), is composed of mafic to ultramafic rocks. The Kitakami massif experienced intense granitic intrusions in the Cretaceous. We present a detailed crustal structure model for the eastern part of the massif derived from an extensive seismic refraction experiment conducted on a 194-km N-S line. The uppermost crust is covered with a very thin (0.5-1 km) surface layer with a velocity of 3.1-5.4 km/s. The velocity structure below this layer shows remarkable lateral variation. In the northern Kitakami terrane the P wave velocity and V(sub p)/V(sub s) at the top of the basement are 5.85-5.95 km/s and 1.68-1.70, respectively. The seismic attenuation in this region is high (Q(sub p) = 150-200 and Q(sub s) = 70-100). In contrast, the uppermost crust in the southern Kitakami terrane is characterized by a high P wave velocity (6.05-6.15 km/s) and V(sub p)/V(sub s) (1.74-1.77). The Q(sub p) and Q(sub s) also show high values of 300-400 and 150-200, respectively. Such a structural difference persists to 14- to 16-km depth, at which the P wave velocity increases to 6.45 km/s. The low velocity and high attenuation in the northern Kitakami terrane represent a highly deformed structure of the accretionary complex. The high P wave velocity and V(sub p)/V(sub s) in the southern Kitakami terrane indicate the relatively mafic crustal composition, which may result from the fragment of the oceanic crust incorporated by the accretion process or the uplifting in the latest Jurassic-early Cretaceous. A midcrustal interface determined from wide-angle reflections shows an abrupt southward depth decrease from 25 to 20 km under the HTB. The P wave velocity and V(sub p)/V(sub s) between 14- and 16-km depth and the midcrustal interface are 6.45-6.55 km/s and 1.74-1.78, respectively. The Moho depth under the northern Kitakami terrane decreases southward from 34 to 32 km. In the southern Kitakami terrane the Moho dips slightly southward. wave velocity and the V(sub p)/V(sub s) ratio in the lower crust are 6.9-7.0 km/s and 1.75-1.76, respectively. &The P wave velocity in the uppermost mantle is not well resolved but is probably less than 7.7 km/s. The S wave velocity derived from relatively clear S(sub n) is 4.35-4.40 km/s. Our results show that the HTB is a prominent structural boundary extending to the Moho. *The crust of Kitakami massif was not homogenized by the Cretaceous granitic intrusions, and the original structural difference remains in the upper crust.

Iwasaki, Takaya; Yoshii, Toshikatsu; Moriya, Takeo; Kobayashi, Akio; Nishiwaki, Makoto; Tsutsui, Tomoki; Iidaka, Takashi; Ikami, Akira; Masuda, Tetsu

1994-11-01

244

Simultaneous bimodal surface acoustic-wave velocity measurement by scanning acoustic force microscopy  

NASA Astrophysics Data System (ADS)

We present scanning acoustic force microscopy (SAFM) mixing experiments of differently polarized surface acoustic waves (SAW) with noncollinear propagation directions. The phase velocities of the SAWs are measured at a submicron lateral scale, employing a multimode SAFM that is capable of detecting the wave's normal and in-plane oscillation components. Hereby, the down conversion of the surface oscillations into cantilever vibrations due to the nonlinearity of the tip-sample interaction is utilized. The simultaneous determination of the phase velocities within a microscopic sample area is demonstrated for the mixing of Rayleigh and Love waves on the layered system SiO2/ST-cut quartz.

Behme, G.; Hesjedal, T.

2000-07-01

245

Minimizers with discontinuous velocities for the electromagnetic variational method  

Microsoft Academic Search

The electromagnetic two-body problem has \\\\emph{neutral differential delay}\\u000aequations of motion that, for generic boundary data, can have solutions with\\u000a\\\\emph{discontinuous} derivatives. If one wants to use these neutral\\u000adifferential delay equations with \\\\emph{arbitrary} boundary data, solutions\\u000awith discontinuous derivatives must be expected and allowed. Surprisingly,\\u000aWheeler-Feynman electrodynamics has a boundary value variational method for\\u000awhich minimizer trajectories with discontinuous

Jayme De Luca; Rodovia Washington Luis

2010-01-01

246

Influence of scattering on seismic waves: Velocity and attenuation of the upper crust in southeast Maine  

NASA Astrophysics Data System (ADS)

Rg and Pg velocities and Rg attenuation have been examined for the Central Merrimack Synclinorium and nearby regions in southeastern Maine using digital records from a seismic refraction experiment. Determination of Rg group velocities and Pg travel times indicates that both lateral variations and azimuthal anisotropy are present in the study area. The axes of the azimuthal velocity anisotropy appear to lie along and perpendicular to the Appalachian structural strike in the region, with Rg group velocities along strike up to 20 percent faster than cross strike velocities. Measurement of Rg attenuation gives Q values of 25 to 80, varying with frequency. Inversion of the Rg group velocity for velocity structure shows that both the compressional and shear velocities increase rapidly with depth in the upper 1 km in the region.

Reister, Edmund; Dainty, Anton M.; Toksoez, M. N.

1988-03-01

247

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

National Technical Information Service (NTIS)

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 ...

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

2010-01-01

248

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

NASA Astrophysics Data System (ADS)

We estimate shear wave velocities in the shallow subsurface throughout Japan by applying seismic interferometry to the data recorded with KiK-net, a strong motion network in Japan. Each KiK-net station has two receivers; one receiver on the surface and the other in a borehole. By using seismic interferometry, we extract the shear wave that propagates between these two receivers. Applying this method to earthquake-recorded data at all KiK-net stations from 2000 to 2010 and measuring the arrival time of these shear waves, we analyze monthly and annual averages of the near-surface shear wave velocity all over Japan. Shear wave velocities estimated by seismic interferometry agree well with the velocities obtained from logging data. The estimated shear wave velocities of each year are stable. For the Niigata region, we observe a velocity reduction caused by major earthquakes. For stations on soft rock, the measured shear wave velocity varies with the seasons, and we show negative correlation between the shear wave velocities and precipitation. We also analyze shear wave splitting by rotating the horizontal components of the surface sensors and borehole sensors and measuring the dependence on the shear wave polarization. This allows us to estimate the polarization with the fast shear wave velocity throughout Japan. For the data recorded at the stations built on hard rock sites, the fast shear wave polarization directions correlate with the direction of the plate motion.

Nakata, N.; Snieder, R.

2012-01-01

249

S-velocity upper mantle structure beneath the NW Pacific from surface-wave tomography  

NASA Astrophysics Data System (ADS)

The three-dimensional lithospheric structure in the north-western Pacific region is investigated by multimode surface wave tomography, incorporating finite frequency effects. The data are collected from the IRIS (Incorporated Research Institutions for Seismology) network in the north-western Pacific region. Three- component broad-band seismograms of FARM (Fast Archive Recovery Method) data recorded from seismic events with magnitudes greater than 6.0 from 1990 to 2005 are used in this study. The initial data set is composed of 23 stations and 271 events. The recorded waveforms are processed by the three-stage inversion technique of Yoshizawa & Kennett (2004), which comprises three independent steps: (1) to estimate a path-specific multi-mode phase dispersion from a fully non-linear waveform inversion, (2) to construct phase velocity maps as a function of frequency and mode, incorporating effects of finite frequency as well as off-great-circle propagation, and (3) to combine the phase velocity maps for a model of 3-D shear wave velocity. The 3-D shear wave velocity maps are obtained down to 200 km, using 740 paths. The subducting Pacific plate is clearly imaged as a high velocity anomaly up to 6 percents. A low velocity anomaly beneath Japan Sea and Okhotsk Sea is associated to the mantle wedge. The absolute S wave velocities in the mantle wedge are approximately 4 km/s, probably indicating the presence of partial melt in this area. A small-scale high velocity anomaly is located in the northern part of the Okhotsk Sea. The position of this anomaly correlates well with the high velocity anomaly found in the P-wave tomography of Gorbatov et al. (2000), which may be interpreted as a relict of the subducted Okhotsk plate.

Litvina, E.; Yoshizawa, K.; Yomogida, K.

2006-12-01

250

Guided Waves in Moving Dispersive Media Part II: Relativistic Velocities  

Microsoft Academic Search

The detailed modal field structure has been determined for electromagnetic waves propagating in a uniform cylindrical lossIess waveguide of arbitrary cross section filled with a moving medium. The medium is assumed to be homogeneous, isotropic, and nondissipative, but may be dispersive. It moves uniformly, with a constant speed v, parllel to the axis of the waveguide. The solutions obtained are

H. Berger; J. W. E. Griemsmann

1968-01-01

251

S wave velocity structure of the northern Cascadia subduction zone  

NASA Astrophysics Data System (ADS)

The shear velocity structure across the northern Cascadia subduction zone is examined using three-component broadband digital seismographs. Locally generated P-to-S conversions are analyzed to estimate the S velocity structure to upper mantle depths and to constrain the subduction geometry of the Juan de Fuca plate. The oceanic crust is at 47-53 km beneath central Vancouver Island, 60-65 km beneath Georgia Strait, and 70-75 km beneath EGM station on the Sechelt Peninsula. The dip direction of the plate at each site provides new evidence that the Juan de Fuca plate is arched upward in the Puget Sound region. The dip angle increases from 15 deg +/- 5 deg to 22 deg +/- 5 deg near LAS station, where a concentration of seismicity occurs near 60 km depth. This study provides the first definitive evidence that the reflective zones imaged beneath Vancouver Island are regions of low S velocity and that they extend into the lower crust and upper mantle beneath the British Columbia mainland.

Cassidy, John F.; Ellis, Robert M.

1993-03-01

252

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

SciTech Connect

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

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

2002-06-17

253

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

SciTech Connect

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.

Aranson, I.; Meerson, B. [Hebrew Univ., Jerusalem (Israel). Racah Inst. of Physics; Tajima, Toshiki [Texas Univ., Austin, TX (United States)

1992-02-01

254

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

NASA Astrophysics Data System (ADS)

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.

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

2011-12-01

255

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

NASA Astrophysics Data System (ADS)

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.

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

2003-04-01

256

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

NASA Astrophysics Data System (ADS)

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

Wu, C.; Huang, H.

2009-12-01

257

Search for Variations in Pluto's Millimeter-Wave Emission  

Microsoft Academic Search

We report on repeated bolometric observations of the Pluto–Charon system at 1.2 mm with the IRAM 30-m telescope. These observations indicate at most small (?1–2 mJy) variations of the millimeter-wave emission of Pluto with orbital longitude, suggesting that the dark regions of Pluto have a millimeter emissivity of ?0.6–0.7.

E. Lellouch; G. Paubert; R. Moreno; B. Schmitt

2000-01-01

258

Lateral variation of Lg wave propagation in southern Mexico  

Microsoft Academic Search

In this study we investigated lateral variation of Lg wave propagation in southern Mexico from recordings of 92 crustal earthquakes along 591 travel paths. The efficiency of Lg propagation was measured in terms of Lgto Pn spectral ratio. It was found that Lgpropagation is inefficient for travel paths through the Gulf of Mexico coastal plains and the Gulf of Tehuantepec,

Lars Ottemöller; Nikolai M. Shapiro; Shri Krishna Singh; Javier F. Pacheco

2002-01-01

259

Density variation due to wave heating in Tokamak plasmas  

Microsoft Academic Search

The Tokamak plasma density was observed to drop during electron cyclotron resonance heating (ECRH), and to increase during ion cyclotron resonance frequency heating (ICRF) and LHH. A mechanism is proposed herein to explain these density variations. Depending on the nature of the specific wave heating, electrons or ions tend to pile up toward the weak field side. A poloidally varying

J. Y. Hsu; V. S. Chan; R. W. Harvey; F. L. Hinton; R. Prater; S. K. Wong

1984-01-01

260

Barometric Pressure Variations Associated with Eastern Pacific Tropical Instability Waves  

Microsoft Academic Search

Barometric pressure, surface temperature, and wind time series in the eastern equatorial Pacific are analyzed to determine if oceanic tropical instability wave (TIW) sea surface temperature variations cause barometric pressure gradients large enough to influence the atmospheric boundary layer. During the study period from April 2001 to September 2002, 11 TIWs propagated westward past 110°W, causing a spectral peak at

Meghan F. Cronin; Shang-Ping Xie; Hiroshi Hashizume

2003-01-01

261

P-wave velocities of alkaline olivine basalt at high pressure and temperature and its controlling factors  

Microsoft Academic Search

SEISMIC wave inversion is one of the most important means for us to recognize the composition and structure of the Earth's interior. Although the experimental techniques of elastic wave velocity measurement at in situ high pressure and temperature develop very fast in recent years and the elastic wave velocities of the Earth's interior material can be measured at pressure up

Maoshuang Song; Hongsen Xie; Yueming Zhang; Wei Hou; Jian Xu; Yousheng Xu

1997-01-01

262

Effect of the perforation of the pipeline wall on the velocity of propagation of long compression waves in a fluid  

NASA Astrophysics Data System (ADS)

A model for predicting the velocity of a weak compression wave propagating over a fluid in a tube with perforated holes is suggested. The fluid is retained in the perforations by surface tension. The wave velocity weakly decreases with an increase in the pressure drop over the wave. Examples of particular predictions are given.

Kuznetsov, N. M.; Timofeev, E. I.

1993-01-01

263

Seismic waves converted from velocity gradient anomalies in the Earth's upper mantle  

NASA Astrophysics Data System (ADS)

Modelling of elastic wave propagation in 1-D structures is frequently performed using reflectivity techniques in which the Earth's velocity profile is approximated by stacks of homogeneous layers. The complete reflection/transmission (R/T) response of a zone with arbitrary 1-D depth variation (including both gradients and discontinuities in material properties) can, however, be calculated using invariant embedding techniques. Results from earlier studies are here extended to derive exact expressions for R/T matrices in arbitrary, 1-D anisotropic media using a form of Born approxi-mation valid for thin scatterers and which does not assume small perturbations in material properties. The R/T matrices are solutions to a system of non-linear, ordinary differential equations of Ricatti type and may be manipulated using standard R/T matrix algebra. In an equivalent description, the wavefield within the heterogeneous zone is considered in terms of depth-dependent contributions from up- and downgoing waves propagating within the embedding reference medium. This leads to efficient calculation of the internal wavefield using R/T matrices of the heterogeneous stratification and portions thereof at minor additional expense. Mode conversion of teleseismic P and S phases from velocity gradients is examined by way of examples and comparison with three-component data from broad-band stations of the Yellowknife seismic array. The frequency dependence of such wave interactions depends on the differences in vertical slowness between incident and scattered modes. It is shown that significant energy is converted from transition zones with extent L

Bostock, M. G.

1999-09-01

264

S-Wave Velocity Structure and Seismic Anisotropy beneath Tibetan Plateau  

NASA Astrophysics Data System (ADS)

Recent studies on Tibet have proposed that the uplift of the plateau is related to the removal of lithospheric mantle and its replacement by the hotter and less dense asthenospheric material. Conversely, other studies have proposed that the Tibetan plateau has been uplifted and the crust thickened through a process of lateral crustal flow. Some authors have attributed the geophysical properties of upper mantle beneath the Tibetan Plateau either to a delamination of the thickened lithosphere or an asthenospheric counterflow associated with subduction of Indian continental lithosphere. In order to test these models and determine the crustal and upper mantle shear wave velocity structure of lithosphere beneath the Tibetan plateau, our research focuses on investigating the dispersion of surface waves across the region. To determine the shear wave velocities and seismic anisotropy, we have deployed 74 broadband seismic stations throughout the northeastern Tibetan plateau, and we obtained Rayleigh wave phase velocities for the anisotropic media using dispersion data. Our preliminary tomographic models show an uppermost mantle low velocity zone north of the Bangong-Nujiang Suture (BNS) in northern Tibet, and a high velocity anomaly that extends at least to 200 km centered on the BNS. We suspect that the low velocity zone north of the BNS is due to a warm and possibly thin lithosphere. Our measurements indicate that there is significant azimuthal anisotropy (>2%) throughout the upper mantle to depths greater than 250 km. We also find evidence for north-south fast directions. On the northeastern Tibet (GanSu Providence) margin, we observe a velocity boundary between the low-velocity Tibet and the high-velocity Ordos and Sichuan blocks, with NNW-SSE fast directions. The north-south fast directions in the northern Tibet might be pointing to a more complex flow beneath the region considering east-west anisotropy which is generally dominant in central Tibet.

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

2009-12-01

265

Variation of Seismic Velocity Structure around the Mantle Transition Zone and Conjecture of Deep Water Transport by Subducted Slabs  

NASA Astrophysics Data System (ADS)

Seismic tomography models published in the past two decades determined common long-wavelength features of subducting plates as high velocity anomalies and upwelling plumes as low velocity anomalies, and have led to a new class of high-resolution three-dimensional (3D) modeling of global mantle convection with a link to tomography models [e.g., Becker and Boschi, 2002; Ritsema et al., 2007; Schuberth et al., 2009a,b]. However, even such high resolution numerical models do not account for the variation associated with different behaviors of subducting plates as they enter the mantle transition zone (MTZ), i.e., some flatten to form stagnant slabs with a large lateral extent and others descend further into the lower mantle. There are conventional interpretations applied for the cause of variation of the subducted slab behaviors, i.e., temperature difference due to different plate age, different geochemical compositions, different water content and subsequent possible reduction of viscosity etc., which could be taken as non-unique and somewhat equivocal. These parameters and conditions have been tested in two-dimensional numerical simulations, while the water content in the MTZ or the mechanisms of hydration and dehydration through subduction process are still in the realm of conjecture. Recent models of seismic P- and SH-wave velocities derived for the mantle structure beneath northeast China [Wang and Niu, 2010; Ye et al., 2011] using reflectivity synthetics with data from the dense Chinese networks of broadband seismic instruments, show a broader 660 km discontinuity (by about 30 to 70 km) and slower shear velocities above the MTZ than a global standard model iasp91 (Kennett and Engdahl, 1991). These features were interpreted with a mixture of different chemical properties which show delayed phase transformation, and effects of water above the flattened slab. Nonetheless, the SH-wave model has a structure similar to model TNA above the MTZ, which was derived for the structure beneath tectonic North America [Grand and Helmberger, 1984] and has a sharp discontinuity. Tajima and Nakagawa [2006] have already shown that SH waveforms which sampled the stagnant slab in the northwestern Pacific subduction zone could be modeled with TNA well. The reflectivity synthetic approaches attempted to model a large number of waveform data obtained from an array with a layered structure, and tend to average the discontinuity depth variation and other features. Our 3D finite difference waveform modeling clearly suggests variation of relatively sharp phase transformation depths beneath stagnant slabs. The results were interpreted with variation of geochemical properties under wet condition at the base of MTZ. Accordingly we explore how well the hydrous and dry conditions can be delineated for varying chemical properties from seismic waveform analysis.

Tajima, F. C.; Stahler, S. C.; Ohtani, E.; Yoshida, M.; Sigloch, K.

2011-12-01

266

Relationships between Existence of Negative Group Velocity and Physical Parameters of Materials for Lamb-Type Waves in Solid\\/Liquid\\/Solid Structure  

Microsoft Academic Search

We considered the negative group velocity of plate-mode waves. Lamb waves are a typical example of existence of negative group velocity. However, if we try to apply the negative group velocity of Lamb waves to some applications such as acoustical flat lenses, there is a problem about the existence of negative group velocity of Lamb waves. Its existence depends only

Kojiro Nishimiya; Koichi Mizutani; Naoto Wakatsuki; Ken Yamamoto

2008-01-01

267

Abnormalities of T waves in effort angina pectoris patients at rest evaluated by spatial velocity electrocardiogram.  

PubMed

The normal shape of the T wave on the standard 12-lead electrocardiogram (ECG) is asymmetrical. The spatial velocity electrocardiogram (SVECG) is a method of recording the slope of the wave of the ECG and makes it possible to quantify the symmetry of the ECG-T wave. The aim of this study was to diagnose resting effort angina pectoris not detectable by conventional resting ECG using SVECG. We studied SVECG-T waves in effort angina pectoris patients with significant coronary artery stenosis but with normal resting ECG (AP group: 50 subjects) and in an age- and sex-matched normal controls (N group: 30 subjects). The SVECG is depicted as a simple differential wave, and all SVECG-T waves had two peaks. The first peak of the SVECG-T wave was designated as the 'a' wave and the second peak as the 'c' wave. The heights (a wave-mag, c wave-mag) and c wave-mag/a wave-mag ratio (c/a ratio) were calculated. The c/a ratio was significantly decreased in the AP group (1.52 +/- 0.29 vs 1.87 +/- 0.27, p < 0.0001). In cases below the cut off c/a ratio of 1.7, the diagnostic sensitivity, specificity and accuracy for effort angina pectoris were retrospectively evaluated to be 82%, 70% and 78%, respectively. The heights of the 'a' and 'c' waves correspond to the maximum slope of the ascending and descending limbs of the T wave on ECG. The symmetrization of the T wave on ECG is considered to occur when the c/a ratio decreases and approaches 1.0. In conclusion, the c/a ratio of the SVECG-T wave is a useful index to diagnose effort angina pectoris at rest when the resting ECG is normal. PMID:9057682

Sasaki, A; Takimiya, A; Arai, T; Song, Y; Nakajima, S; Muto, K; Ibukiyama, C

1996-11-01

268

Progressive inversion for hypocenters and P wave and S wave velocity structure: Application to the Geysers, California, geothermal field  

Microsoft Academic Search

Seismicity at The Geysers is induced by some aspect of steam production. Accurate earthquake locations, particularly hypocentral depth, are needed to determine the relationship between geothermal energy production and seismicity. Progressive P and S wave velocity-hypocenter inversions were done using data from 39 microearthquakes at The Geysers to estimate microearthquake locations and determine if the geothermal field has a distinctive

Daniel R. H. O'Connell

1991-01-01

269

Progressive inversion for hypocenters and P wave and S wave velocity structure: Application to The Geysers, California, geothermal field  

Microsoft Academic Search

Seismicity at The Geysers is induced by some aspect of steam production. Accurate earthquake locations, particularly hypocentral depth, are needed to determine the relationship between geothermal energy production and seismicity. Progressive P and S wave velocity-hypocenter inversions were done using data from 39 microearthquakes at The Geysers to estimate microearthquake locations and determine if the geothermal field has a distinctive

D. R. H. OConnell

1991-01-01

270

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

NASA Astrophysics Data System (ADS)

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 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 -17% beneath the Toledo embayment and the Valle Grande, (2) midcrustal low velocities of -23% in an ellipsoidal volume underneath the northwest quadrant of the caldera, and (3) a broad zone of low velocities (-15%) 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%. 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.

Steck, Lee K.; Thurber, Clifford H.; Fehler, Michael C.; Lutter, William J.; Roberts, Peter M.; Baldridge, W. Scott; Stafford, Darrik G.; Sessions, Robert

1998-10-01

271

Joint Inversion of Multimode Love Wave Dispersion Curves for Accurately Appraising of Shear Wave Velocity Reversal Profile  

NASA Astrophysics Data System (ADS)

The use of multimode dispersion curves (DCs) in surface wave inversion to derive shear wave velocity (VS) profiles has increased in the past decade as the inclusion of higher mode data can improve the accuracy of the inversion results. This paper presents a joint inversion codes to invert multimode Love wave (fundamental plus higher modes) DCs and focuses on the attempt to improve the accurate appraisal of the VS reversal profile. The multimode Love wave DCs were synthesized using full SH (Shear Horizontal) waveform reflectivity as the true model. In this study, we used a frequency-slowness (f-p) transform to extract DC from full SH waveform reflectivity. DCs overlain in the dispersion images were picked manually. The DCs were then inverted using modified genetic algorithm (GA). Our numerical modeling showed that, the joint inversion of multimode Love wave DCs can significantly improve the accurate assessment of VS reversal profiles.

Hamimu, La; Nordin, M. Nawawi M.; Safani, Jamhir

2010-07-01

272

Velocity of sound behind strong shock waves in 2024 A1  

SciTech Connect

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

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

1983-01-01

273

Transient velocity measurement in dusty boundary layyr developed behind a shock wave  

NASA Astrophysics Data System (ADS)

The results of recent particle velocity measurements at the 4 x 4 inch shock tube at TRW are presented. The measurements were made in a dusty boundary layer induced by the passage of a normal shock wave over a dust bed. The dust particle velocity was measured using a single component laser velocimeter. The measurement of the transient flow was made with a fast digitizer, at a sample rate of 100 MHz. Processing of the signal was achieved through software. A number of routines for detection of acceptable signal and discrimination against background noise was developed and evaluated. The velocity time history of the dust particles behind the moving shock waves at a number of heights above the dust level were measured. Simultaneous measurement of the laser light beam extinction was used to evaluate the dust density profile behind the shock wave.

Modarress, D.

274

Fragmentation Speed, Elastic Wave Velocity and Fracture Velocity In Dome Magma  

Microsoft Academic Search

One of the most important parameters for the modeling of explosive eruptions is the fragmentation speed. In combination with the gas expansion, the fragmentation speed influences the effusion rate during an explosive eruption. We determined the statis- tically relevant variation of the density from pyroclastic depostits in the field (e.g. Kueppers et al, EGS 2002). This allows us to investigate

B. Scheu; O. Spieler; D. B. Dingwell

2002-01-01

275

Differential Semblance Velocity Analysis by Wave Equation Migration, Applications to High Resolution HAFB Dataset  

NASA Astrophysics Data System (ADS)

In pre-stack migrated seismic reflection data, common image gathers in angle are flat at correct velocity, and gathers in offset are concentrated at zero offset. Differential semblance measures the deviation from flatness or concentration. The objective function of differential semblance optimization (DSO) responds smoothly to velocity changes. Therefore gradient descent methods are attractive for DSO velocity updates. Because of their kinematic fidelity, wave equation (depth extrapolation) migration methods are a natural means for velocity analysis in complex structure. We demonstrate the computation of the differential semblance gradient formulated through the adjoint of the linearized wave equation migration and its use in constructing velocity updates by optimization. A synthetic example with a low velocity lens has been tested and shows satisfactory velocity reconstruction by differential semblance optimization. We apply this algorithm to the high resolution land surface data collected at Hill Air Force Base. Images and velocity reconstruction are compared with results of waveform type of analysis, and with more conventional data processing results.

Shen, P.; Symes, W. W.; Morton, S.; Gao, F.; Levander, A.

2003-12-01

276

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

USGS Publications Warehouse

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

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

2010-01-01

277

Effect of laminar velocity profile variation on mixing in microfluidic devices: The sigma micromixer  

NASA Astrophysics Data System (ADS)

The effect of the laminar velocity profile and its variation on mixing phenomena at the reduced scale is studied. It is shown that the diffusive mass flux between two miscible streams, flowing laminar in a microchannel, is enhanced if the velocity at their diffusion interface is increased. Based on this idea, an in-plane passive micromixing concept is proposed and implemented in a working device (sigma micromixer). This mixer shows considerable mixing performance by periodically varying the flow velocity profile, such that the maximum of the profile coincides with the transversely progressing diffusion fronts repeatedly throughout the mixing channel.

Yakhshi Tafti, Ehsan; Kumar, Ranganathan; Cho, Hyoung J.

2008-10-01

278

Referential ZMP Trajectory for Minimizing Variation of COG Velocity in Single Support Phase of Biped Robot  

NASA Astrophysics Data System (ADS)

The referential ZMP (Zero-Moment Point) trajectory that minimizes the variation of COG (Center of Gravity) velocity in the single support phase of a biped robot is shown. Two advantages of using this ZMP trajectory are discussed. The first advantage is that the variation of COG velocity is gradual. The second advantage is that the biped robot enables the heel-contact motion and the toe-off motion in the single support phase. The trajectory planning based on this ZMP trajectory is proposed. In simulation and experiment, the validity of the proposed method was confirmed.

Sato, Tomoya; Ohnishi, Kouhei

279

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

280

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

NASA Astrophysics Data System (ADS)

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 ? 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.

Essolaani, W.; Farhat, N.

2012-02-01

281

Velocity of Compressional Waves in Various Minerals at Pressures to 10 Kilobars  

Microsoft Academic Search

The velocity of compressional waves in several minerals, as a function of pres- sure to 10 kb, has been measured. Data for single-crystal microcline suggest that measurements of elastic constants should be made under hydrostatic pressure for all material not of gem quality. Velocities for some rocks with high calcium content suggest a correction to the ve- locity-density-mean atomic weight

Gene Simmons

1964-01-01

282

Rayleigh Wave Phase Velocity Structure of the Mariana Mantle Wedge From an Ocean Bottom Seismograph Deployment  

NASA Astrophysics Data System (ADS)

We study the shear velocity structure of the Mariana mantle wedge using Rayleigh wave phase velocities. We use vertical component Rayleigh waves recorded by a combined deployment of 20 broadband land stations and 58 semi-broadband ocean bottom seismographs, which ran from June 2003 to May 2004. 14 teleseismic events with magnitudes ranging from 6.0 to 7.8 provide good signal-to-noise ratio from 20-80 s period even on the ocean bottom seismographs and a wide azimuthal distribution. Instrument responses are corrected according to each of the four instrument types (including STS-2s and 40Ts on land and OBS instruments with 2 different gains) and in some cases empirical corrections are performed using nearby stations with known instrument responses. Phase velocities are determined using the Forsyth and Li (2005) method of decomposing the incoming waveform as two interfering plane waves and matching the amplitude as well as phase of the observed waveforms. The phase velocity inversion can incorporate both lateral heterogeneity and anisotropy, and incorporates finite frequency kernels. Surface wave velocities at periods of 20-25 seconds range from 3.62 to 3.82 km/s, with the lowest velocities beneath the arc and forearc, probably due to crust that is thicker than the surrounding oceanic crust. Between about 30-60 s we observe a pronounced low velocity region ranging between 3.70-3.90 km/s beneath the backarc spreading center and faster velocities ranging from 3.82-4.0 km/s in the forearc. Preliminary results for seismic anisotropy suggest about 3% peak to peak anisotropy from 20-78 s. The fast azimuth is roughly ENE for 22-40 s and shifts to a more trench parallel NNE for 55-78 s, suggesting a change in average anisotropic direction with depth.

Pyle, M. L.; Wiens, D. A.; Weeraratne, D.; Shore, P. J.; Shiobara, H.; Sugioka, H.

2006-12-01

283

Electromagnetic wave propagation with negative phase velocity in regular black holes  

SciTech Connect

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.

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

2012-12-15

284

Characteristics of Light Reflected from a Dense Ionization Wave with a Tunable Velocity  

Microsoft Academic Search

An optically dense ionization wave (IW) produced by two femtosecond (approx10\\/30 fs) laser pulses focused cylindrically and crossing each other may become an efficient coherent x-ray converter in accordance with the Semenova-Lampe theory. The resulting velocity of a quasiplane IW in the vicinity of pulse intersection changes with the angle between the pulses from the group velocity of ionizing pulses

A. Zhidkov; T. Fujii; K. Nemoto; T. Esirkepov; J. Koga; S. V. Bulanov

2009-01-01

285

Characteristics of Light Reflected from a Dense Ionization Wave with a Tunable Velocity  

Microsoft Academic Search

An optically dense ionization wave (IW) produced by two femtosecond (˜10\\/30fs) laser pulses focused cylindrically and crossing each other may become an efficient coherent x-ray converter in accordance with the Semenova-Lampe theory. The resulting velocity of a quasiplane IW in the vicinity of pulse intersection changes with the angle between the pulses from the group velocity of ionizing pulses to

A. Zhidkov; T. Esirkepov; T. Fujii; K. Nemoto; J. Koga; S. V. Bulanov

2009-01-01

286

A Simple Nondestructive Evaluation of an Adhesive Layer Using Elastic Wave Velocities  

NASA Astrophysics Data System (ADS)

A curing process of epoxy adhesive layers has been investigated by an ultrasonic pulse spectroscopy and a Brillouin scattering technique. Observed longitudinal elastic wave velocities in the curing layer depended on the velocity in the prepolymer used. From this result, we suggest a simple nondestructive method for the estimation of sample Tg (glass transition temperature) during cure. The estimated Tg values were in good accordance with the Tg values measured by differential scanning calorimetry.

Matsukawa, Mami; Nakayama, Shuhei; Ohtori, Norikazu

2000-05-01

287

Active control of lithium niobate single crystals for classification by the velocities of acoustic surface wave  

SciTech Connect

For the industrial manufacture of crystals, the technique of measuring the angle of the scalar synchronism of second optical harmonic generation (SHG) is suggested. A correlation has been found between the scalar synchronism angle of SHG in a layer of a crystal and the velocity of acoustic surface wave (ASW) in a plate cut from that layer. The derived relationship makes it possible to predict the ASW velocity on a free surface prior to a single-crystal boule cut into plates.

Musikhin, L.A.; Osintsev, V.V.; Chernyak, R.V. [Research and Development Technological Institute of Materials for Radioelectronics, Apatity (Russian Federation)

1994-07-01

288

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

Microsoft Academic Search

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

H. Kwun

1985-01-01

289

Group velocity measurement from the propagation of the ionization front in a surface-wave-produced plasma  

SciTech Connect

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

Cotrino, J.; Gamero, A.; Sola, A.; Lao, C. (Departamento de Fisica Aplicada, Universidad de Cordoba, San Alberto Magno, s/n. 14071 Cordoba (ES))

1989-05-01

290

Stiffness matrix determination of composite materials using lamb wave group velocity measurements  

NASA Astrophysics Data System (ADS)

The use of Lamb waves in Non-Destructive Evaluation (NDE) and Structural Health Monitoring (SHM) is gaining popularity due to their ability to travel long distances without significant attenuation, therefore offering large area inspections with a small number of sensors. The design of a Lamb-wave-based NDE/SHM system for composite materials is more complicated than for metallic materials due to the directional dependence of Lamb wave propagation characteristics such as dispersion and group velocity. Propagation parameters can be theoretically predicted from known material properties, specifically the stiffness matrix and density. However, in practice it is difficult to obtain the stiffness matrix of a particular material or structure with high accuracy, hence introducing errors in theoretical predictions and inaccuracies in the resulting propagation parameters. Measured Lamb wave phase velocities can be used to infer the stiffness matrix, but the measurements are limited to the principal directions due to the steering effect (different propagation directions of phase and corresponding group velocities). This paper proposes determination of the stiffness matrix from the measured group velocities, which can be unambiguously measured in any direction. A highly anisotropic carbon-fibre-reinforced polymer plate is chosen for the study. The influence of different stiffness matrix elements on the directional group velocity profile is investigated. Thermodynamic Simulated Annealing (TSA) is used as a tool for inverse, multi variable inference of the stiffness matrix. A good estimation is achieved for particular matrix elements.

Putkis, O.; Croxford, A. J.

2013-04-01

291

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

292

Modeling the permeability evolution of microcracked rocks from elastic wave velocity inversion at elevated isostatic pressure  

NASA Astrophysics Data System (ADS)

A key consequence of the presence of microcracks within rock is their significant influence upon elastic anisotropy and transport properties. Here two rock types (a basalt and a granite) with contrasting microstructures, dominated by microcracks, have been investigated using an advanced experimental arrangement capable of measuring porosity, P wave velocity, S wave velocity, and permeability contemporaneously at effective pressures up to 100 MPa. Using the Kachanov (1994) noninteractive effective medium theory, the measured elastic wave velocities are inverted using a least squares fit, permitting the recovery of the evolution of crack density and aspect ratio with increasing isostatic pressure. Overall, the agreement between measured and predicted velocities is good, with average error less than 0.05 km/s. At larger scales and above the percolation threshold, macroscopic fluid flow also depends on the crack density and aspect ratio. Using the permeability model of Guéguen and Dienes (1989) and the crack density and aspect ratio recovered from the elastic wave velocity inversion, we successfully predict the evolution of permeability with pressure for direct comparison with the laboratory measurements. We also calculate the evolution of the crack porosity with increasing isostatic pressure, on the basis of the calculated crack density, and compare this directly with the experimentally measured porosity. These combined experimental and modeling results illustrate the importance of understanding the details of how rock microstructures change in response to an external stimulus when predicting the simultaneous evolution of rock physical properties.

Benson, Philip; Schubnel, Alexandre; Vinciguerra, Sergio; Trovato, Concetta; Meredith, Philip; Young, R. Paul

2006-04-01

293

Effect of temperature on wave velocities in sands and sandstones with heavy hydrocarbons  

SciTech Connect

A laboratory investigation was made of the effects of temperature on wave velocities in well cemented Massillon and Boise sandstones and unconsolidated Ottawa sand saturated with heavy hydrocarbons, as well as the dependence of compressional velocities in the hydrocarbons themselves as a function of temperature. The hydrocarbons selected as pore saturants were a commercial paraffin wax, 1-Eicosene, natural heavy crude, and natural tar. The experimental results show that the compressional wave velocities in the hydrocarbons decrease markedly with increasing temperature. In contrast wave velocities in the Massillon and Boise sandstones and unconsolidated Ottawa sand saturated with air or water decrease only little with increasing temperatures. The main reason for the large decreases in rocks with hydrocarbons is the melting of solid hydrocarbons, and high pore pressure. Thermal expansion of the saturants, and possibly thermal cracking of the heavy fractions and vaporization of the light fractions of the hydrocarbons may also contribute. The large decreases of the compressional and shear wave velocities in the hydrocarbon-saturated rocks and sands with temperature, suggest that seismic measurements such as used in seismology or borehole tomography may be very useful in detecting steam fronts in heavy hydrocarbon reservoirs undergoing steam flooding.

Wang, Z.; Nur, A.M.

1986-01-01

294

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

295

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

SciTech Connect

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.

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

2011-03-25

296

Phase and group velocities of fast and slow compressional waves in trabecular bone.  

PubMed

This Letter is an extension to a multilayer model of porous bone first proposed by Hughes et al. [Ultrasound Med. Biol. 25, 811-821 (1999)]. Both slow and fast compressional waves propagate when the acoustic wave propagation is parallel to the trabecular alignment. However, a slow wave disappears at high refraction angles. To explain this phenomenon, the multilayer model is extended to compute group velocity surface and arrival times with an angle. Two major effects are highlighted as the refraction angle increases. First, the energy of the slow wave is refracted from the phase propagation direction. Second, the signals of fast and slow waves overlap. As a consequence, the slow wave may not be observed for a refraction angle greater than 40 degrees, which is in agreement with previous experimental data published by Hughes et al. and others. PMID:11051523

Padilla, F; Laugier, P

2000-10-01

297

The Nature of Magnetospheric Electron Velocity Distribution Functions from Wave Observations  

Microsoft Academic Search

It is often assumed, as a first approximation, that the electron velocity distribution function is Maxwellian when calculating the dispersion of magnetospheric plasma waves. Data from the relaxation sounder on the GEOS-1 satellite were used to relate natural emissions between the harmonics of the electron cyclotron frequency fce, often referred to as ``(n+1\\/2)fce'' waves, to sounder-stimulated plasma resonances (known as

R. F. Benson; A. F. Vinas; V. A. Osherovich; J. Fainberg; C. M. Purser

2010-01-01

298

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

Microsoft Academic Search

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

M. K. Schreba

1972-01-01

299

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

Microsoft Academic Search

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

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

2002-01-01

300

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

NASA Astrophysics Data System (ADS)

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.

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

2010-12-01

301

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

Microsoft Academic Search

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

Harley M. Benz; Robert B. Smith

1984-01-01

302

Compressional- and shear-wave velocities and attenuation in deep-sea sediment during laboratory compaction  

NASA Astrophysics Data System (ADS)

Velocities and attenuation of compressional (50 kHz) and shear waves (100 kHz) in two deep-sea sediment samples are investigated as a function of effective pressure up to 20 MPa with simultaneous measurement of porosity, density, and permeability. In both samples, the compressional-wave velocities show a strong increase with pressure, ranging from 1683 m/s at 1 MPa to 2128 m/s at 20 MPa in a silty clay and from 1840 m/s to 2462 m/s in a foraminiferal mud. Shear wave propagation is strongly restricted at pressures below 4 and 9 MPa in the respective sample, indicating a structural change in the sediment material at critical porosity values of 0.430 and 0.397, respectively. The compressional-wave attenuation, in terms of 1/QP, varies between 0.03 and 0.08, and 0.04 and 0.07, respectively. A result previously not reported in laboratory studies is a maximum in 1/QP as a function of effective pressure observed in both samples. The shear-wave attenuation is nearly constant as a function of pressure, having average values of about 0.07. The maximum of compressional-wave attenuation occurs at the respective critical porosity for each sample. Velocities and attenuation from this experiment exhibit a systematic pattern in a QP/QS vs (VP/VS)2 representation. .

Leurer, Klaus C.

2004-10-01

303

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

SciTech Connect

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

Martin, Richard W.; Reibel, Richard S.; Sathish, Shamachary [University of Dayton Research Institute, 300 College Park, Dayton, OH 45469-0127 (United States); Blodgett, Mark P. [Air Force Research Laboratory, Metals, Ceramics and NDE Division, 2230 Tenth St., Wright Patterson Air Force Base, Dayton, OH 45433-7817 (United States)

2004-02-26

304

Collisional and wave-particle interactions in critical-velocity ionization  

SciTech Connect

Alfven's critical ionization velocity (CIV) process involves collective and collisional interactions of a magnetoplasma streaming through a neutral gas. Numerical simulations of CIV are reported using particle-in-cell plasma codes including various collisional interactions. Fast electron heating is observed. The interplay between collisional and collective interactions renders the hot electron tail shorter than in non-CIV situations with collisionless wave-particle interactions without a neutral gas. Metastable states serve in the role of energy pooling and foster rapid ionization near the critical velocity. Line excitation is a severe energy loss mechanism. Charge exchange replenishes ion energy and is important during tight energy budget situations near the critical velocity.

McNeil, W.J.; Lai, S.T.; Murad, E.

1989-01-01

305

The Vertical Propagation of Tropospheric Rossby Waves and its Variation with Climate  

Microsoft Academic Search

Rossby wave propagation is theoretically affected by zonal wind gradients, in particular the second derivative of the zonal wind shear in the vertical and meridional directions. Vertical propagation is hindered by the strong winds in the upper troposphere, particularly for short wavelength waves, or by critical levels where the background wind velocity equals the wave phase velocity. In practice, tropospheric

D. H. Rind; J. Perlwitz

2002-01-01

306

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

USGS Publications Warehouse

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.

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

1998-01-01

307

Phase and group velocity matching for cumulative harmonic generation in Lamb waves  

NASA Astrophysics Data System (ADS)

Owing to the enhanced sensitivity of nonlinear acoustic methods to material damage, the nonlinear Lamb wave propagation is pertinent to the nondestructive evaluation of platelike structures, and it is typically manifested as generation of higher harmonics. For dispersive waves such as Lamb waves, however, the cumulative growth of harmonics requires that the primary mode and the generated higher harmonic modes possess identical phase and group velocities. In this paper, this issue of the phase and group velocity matching in Lamb waves is explored based on a systematic analysis of the Rayleigh-Lamb frequency equations. The analysis shows that for certain values of the phase velocity, the Rayleigh-Lamb frequency equations are satisfied at equi-spaced frequencies which are multiples of the smallest. Such frequencies, together with the corresponding phase velocities and the Lamb modes, are determined analytically. Four such types of Lamb modes are identified: (i) Lamé modes, (ii) symmetric modes with dominant longitudinal displacements, (iii) intersections of symmetric and antisymmetric modes and (iv) extra Rayleigh modes. For the first three types, it is also established that the primary and the harmonic modes have the same group velocity, and that the surface motion of the plate is featured with vanishing vertical or horizontal displacements. In contrast to these three types, the fourth type only exists for a special range of the transverse to longitudinal wave speeds of the solid. This type is not featured with a common group velocity, and neither of the vertical or horizontal displacement vanishes on the plate surfaces. The obtained results are summarized as tables, and demonstrated graphically on the dispersion curves for aluminum as well as iron plates.

Matsuda, Naoki; Biwa, Shiro

2011-05-01

308

Damage Evolution, Acoustic Emissions and Elastic Wave Velocities in Porous Carbonate Rocks  

NASA Astrophysics Data System (ADS)

We measured compressional and shear wave velocities of Chauvigny limestone in triaxial compression tests and at hydrostatic pressures (30, 50, 70, 100 MPa). Chauvigny limestone is almost pure (~99 %) calcite with 17 % porosity. Tests were performed on dry specimens of 50 mm in diameter and 100 mm in length at room temperature and at a constant strain rate of 2.10-4s-1. Acoustic emission (AE) hypocenter locations were used to analyze the spatial damage distribution and we used first motion polarity, to define AE source types. Volumetric strains were recorded using strain gages. Our mechanical data during hydrostatic and triaxial compression experiments is similar to that of Tavel and Indiana limestone (Vajdova et al. 2004). For confining pressures ? 30 MPa, Chauvigny limestone samples show shear-enhanced compaction. For experiments performed at 30-50 MPa confining pressure, samples first compact and then show dilatancy with increasing axial strain. During the hydrostatic loading up to 140 MPa, P-wave velocities increase by only 2 % indicating that the samples are almost free of pre-existing cracks. During triaxial loading, a stress-induced anisotropy of P-wave velocities develops, with vertical velocity components being faster than horizontal velocities. Increasing confining pressure also significantly reduces P-wave anisotropy. These observations suggest the development of vertical cracks during the shear-enhanced compaction. P-wave velocity measured during depressurization remain lower than when measured during pressurization (decrease higher than 30 %), demonstrating the evolution of crack damage. Our microstructural observations indicate that samples deform by cataclastic flow.

Fortin, J.; Stanchits, S.; Dresen, G.; Gueguen, Y.

2006-12-01

309

Robust Computation of Global Surface Wave Phase Velocity Maps from Massive Dataset by the Clash  

NASA Astrophysics Data System (ADS)

The detection of seismic wave velocity heterogeneities enables to generate a present-day snapshot of the deep interior of the Earth. One modus operandi to compute a 3D body wave velocity model relies on the surface wave phase velocity measurements. Using a roller-coaster type algorithm, we determine the phase velocities of the fundamental and the first six overtone, integrated over the great circle epicenter-station paths. This new non-linear inverse approach tends to introduce the minimum number of a priori conditions. Every solution is tested and the model which achieves the best misfit function is retained. For each frequency of a given mode-branch, phase velocities are then expressed in terms of global heterogeneity maps. To this end, a new method, which includes azimuthal anisotropy in its comprehensive form, is developed and is reverently baptized the Computation of Large Anisotropic Seismic Heterogeneities (CLASH). The surface of the Earth is regularly discretized by means of a best fitting grid. Possible lacks of resolution due to an insufficient coverage are taken into account in the inverse resolution, which makes this method different from others. Several synthetic tests emphasize the robustness of this approach and the accuracy of the a posteriori uncertainties. Phase velocity maps of the Rayleigh fundamental and the first five higher modes are obtained from the processing a very large amount of seismograms recorded by global networks. The great similarity between the isotropic part of our models and previously published ones is encouraging in the project of using the CLASH to derive a new anisotropic shear wave velocity model of the Earth's mantle.

Beucler, E.; Guillot, L.; Stutzmann, E.; Montagner, J.; Roult, G.; Clevede, E.

2002-12-01

310

SAsia3D: A New Crustal and Upper Mantle P- and S- Velocity Model in Central and Southern Asia from Joint Body- and Surface-Wave Inversion  

NASA Astrophysics Data System (ADS)

Accurate travel-time and amplitude predictions for regional seismic phases are essential for locating and characterizing small seismic events with the accuracy needed for explosion monitoring decisions. Parameter estimates calculated through 3D Earth models have the best chance of achieving acceptable prediction errors, if the models are constrained by sufficient data. With this motivation, we have developed and applied a joint body- wave/surface-wave inversion method to produce a new 3D P and S velocity model (SAsia3D) for the crust and upper mantle to a depth of 400 km in the region of central and southern Asia between 10-50° N and 40- 110° E. The method uses Pn and Pg arrival times to determine the P velocity structure and Rayleigh-wave group velocities in the period range 10-150 s to constrain the S velocity structure and depth to Moho. The body- wave and surface-wave inverse problems are coupled through an assumed correlation coefficient between P and S velocity perturbations and the imposition of bounds on the velocities and Poisson's ratio as a function of depth. Both body-wave and surface-wave forward modeling are performed in 3D models with the aid of finite-difference numerical raytracing to calculate body-wave raypaths and 2D raytracing to calculate non-great circle surface-wave paths. Nonlinearity is addressed by iterating the inversion method with updated raypaths. The regional P-wave arrival-time observations used to obtain SAsia3D were collected from the Engdahl, van der Hilst and Buland (1998; EHB) bulletin, restricted to well-located earthquakes in the years 1988-2004. The group- velocity measurements were provided by groups at the University of Colorado and Lawrence Livermore National Laboratory. Our initial model for the inversion procedure was taken as a hybrid of the CRUST2.0 3D model (Bassin et al., 2000) and the upper mantle portion of the global 1D AK135 model (Kennett et al., 1995). SAsia3D was obtained with four iterations of our technique, achieving a fifty percent variance reduction for both the body- wave and surface-wave data. Relative velocity (in particular the P velocity) variations with respect to the AK135 mantle model are in good agreement with previous studies and reflect the major tectonic features across southern and central Asia. For example, at 250 km depth, P variations across new model range from -2.0 to +2.3%, while S variations vary from -2.1% to +1.5%. We have also noted intriguing differences between the P and S velocity models in regions of significant tectonic activity, such as the Tibetan Plateau and South Caspian Basin. Some of these variations may prove useful in explaining the tectonic evolution of the Indo-Asian collision zone. We have also completed a number of validation exercises to demonstrate the accuracy of SAsia3D in regional seismic event location. Most notably, SAsia3D performs well when both regional P and S phase arrivals are included in the location. The regional P/S location obtained with SAsia3D are frequently superior to the locations obtained with a large set of teleseismic and regional P arrivals and the AK135 reference model.

Reiter, D.; Rodi, W.

2007-12-01

311

Study of the dynamical mechanism of seasonal variation of Earth's rotational velocity  

Microsoft Academic Search

In this study, the seasonal variation of Earth's rotational velocity is studied from a dynamical point of view. Many studies have been conducted in recent years by methods of correlation analysis, dynamical calculation, and numerical simulation. In this paper, we use an analytical method that has not been attempted in this study area to establish a model in which the

Jinping Zhao; Weizheng Qu

1995-01-01

312

Measurement and analysis of angular velocity variations of twelve-cylinder diesel engine crankshaft  

Microsoft Academic Search

This paper presents the procedures for measuring and analyzing the angular velocity variation of twelve-cylinder diesel engine crankshaft on its free end and on the power-output end. In addition, the paper deals with important aspects of the measurement of crankshaft torsional oscillations. The method is based on digital encoders placed at two distances, and one of them is a sensor

Z. M. Bulatovic; M. S. Stavljanin; M. V. Tomic; D. M. Knezevic; S. Lj. Biocanin

2011-01-01

313

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

Microsoft Academic Search

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

Manuel Ignacio Monge García; Anselmo Gil Cano; Juan Carlos Díaz Monrové

2009-01-01

314

Intracyclic velocity variation and arm coordination assessment in swimmers with Down syndrome.  

PubMed

This study examined the differences in intracycle velocity variation and arm coordination in front crawl in swimmers with Down syndrome in three breathing conditions. International swimmers with Down syndrome (N = 16) performed 3 × 20 m front crawl at 50 m race speed: without breathing, breathing to the preferred side, and breathing to the nonpreferred side. A two dimensional video movement analysis was performed using the APASystem. Breathing conditions were compared using Repeated Measures ANOVA. Swimming velocity was higher without breathing and intracyclic velocity variation was higher while breathing. Swimmers tended to a catch up arm coordination mode for both breathing conditions and a superposition mode when not breathing. These data reflect arm coordination compromising swimming performance, particularly when comparing with non disabled swimmers in literature. The physical and perhaps cognitive impairment associated with Down syndrome may result in a disadvantage in both propulsion and drag, more evident when breathing. PMID:23283027

Marques-Aleixo, Inês; Querido, Ana; Figueiredo, Pedro; Vilas-Boas, João Paulo; Corredeira, Rui; Daly, Daniel; Fernandes, Ricardo J

2013-01-01

315

A variational property of the velocity distribution in a system of material particles  

NASA Astrophysics Data System (ADS)

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 energy dissipation in the sticking collision of free rigid bodies. Special cases are also examined where not all the components of linear and angular momentum are conserved, corresponding to rigid bodies with a common fixed point or axis without friction. As a byproduct, a formal property of the tensor of inertia is derived, not commonly considered in mechanics textbooks. Along with the variational property of the velocity distribution, such a formal property of the tensor of inertia may be interesting for graduate and advanced undergraduate students.

Siboni, S.

2009-01-01

316

Length and activation dependent variations in muscle shear wave speed.  

PubMed

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 to 5.6 m s(-1) 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(-1) 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

Chernak, L A; DeWall, R J; Lee, K S; Thelen, D G

2013-05-29

317

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

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.

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

2009-07-06

318

Relations of cardiovascular risk factors to aortic pulse wave velocity in asymptomatic middle-aged women  

Microsoft Academic Search

Cross-sectional associations between aortic elasticity assessed by carotid to femoral pulse wave velocity (PWV) and cardiovascular risk factors were examined in 429 apparently healthy middle-aged women. PWV was strongly and positively related to blood pressure and hypertension. Weak but significant positive associations were also found between PWV and age, heart rate, some lipids and lipoproteins, blood glucose (either as a

A. Taquet; C. Bonithon-Kopp; A. Simon; J. Levenson; Y. Scarabin; A. Malmejac; P. Ducimetiere; L. Guize

1993-01-01

319

Modifications of point-to-point pulse wave velocity during cardiac cycle  

Microsoft Academic Search

Pulse wave velocity (PWV) is used as an index to evaluate arterial wall elasticity. It is usually calculated from the time shift between the appearance of a particular feature in two signals. Due to changes of internal arterial pressure during the cardiac cycle, the value of PWV is time-dependent. In this study, the data were recorded using multichannel impedance plethysmography.

F. Risacher; J. Jossinet; M. Schmitt

1995-01-01

320

Phase and Group Velocities of Rayleigh Waves in a Spherical, Gravitating Earth  

Microsoft Academic Search

Periods of spheroidal eigenvibrations, with order of spherical harmonic n >_ 20, have been computed for self-gravitating inhomogeneous spheres corresponding to a variety of earth models. The periods are used to deduce phase and group velocities for the fundamental and first higher modes of Rayleigh waves having periods less than 320 see. The mathematical methods, program checks and estimations of

Bruce A. Bolt; James Dorman

1961-01-01

321

Velocities of MagnetoElastic and Magneto-Electron Waves in Dark Molecular Clouds  

Microsoft Academic Search

We present analytic and numerical estimates for group velocity of wave motions in two models of cold interstellar medium presumably constituting the interior of cores of magnetically supported dark molecular clouds. Namely, in the model of gas-based ferrocolloidal soft matter and in the model of noncompensated electron magnetoplasma. The predictions of these models are given in juxtaposition with data on

S. Bastrukov; V. Papoyan; D. Podgainy; J. Yang

2002-01-01

322

Nonlinear effects in velocity space and drift wave transport in tokamaks.  

National Technical Information Service (NTIS)

It is pointed out that the use of kinetic models for drift wave transport in general makes it necessary to treat consistently the transport in both real space and velocity space. For a broad class of collisionless or marginally collisionless plasmas, nonl...

J. Weiland

1991-01-01

323

Azimuthal Anisotropy Signature in the Great Basin Lithosphere from Rayleigh Wave Phase Velocity Maps  

Microsoft Academic Search

We present new depth constraints on the origin of the azimuthal anisotropy observed in the Great Basin region by providing fundamental mode Rayleigh wave azimuthally anisotropic phase velocity maps at periods between 16 and 102s. The Great Basin, which lies in the northern Basin and Range Province of the western United States, has a complex deformation history and is currently

C. Beghein; J. A. Snoke; M. J. Fouch

2009-01-01

324

Association of pulse wave velocity with vascular and valvular calcification in hemodialysis patients  

Microsoft Academic Search

The recent Kidney Disease: Improving Quality Outcomes (KDIGO) recommendations called for an investigation of the relationship between various radiological methods to assess cardiovascular calcification and measures of arterial stiffness. Accordingly, in 131 adult maintenance hemodialysis patients, we investigated the association of aortic pulse wave velocity (PWV) with calcification of cardiac valves on echocardiography, coronary artery, and thoracic aorta calcium on

P Raggi; A Bellasi; E Ferramosca; T Islam; P Muntner; G A Block

2007-01-01

325

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

Microsoft Academic Search

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

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

2007-01-01

326

Effect of maturational status and training on upper limb pulse wave velocity  

Microsoft Academic Search

Cardiovascular adaptations to training may include changes in arterial distensibility, although studies involving sick and healthy individuals have yielded contradictory results. Moreover, despite the fact that endurance training frequently begins in childhood, its influence on arterial distensibility is less well characterised in children. This study was therefore to compare the upper limb pulse wave velocity (PWVUL) in highly trained prepubertal

Agnès Vinet; Stéphane Nottin; Lionel Beck; Antonia Pérez-Martin; Michel Dauzat; Philippe Obert

2005-01-01

327

Computation of the drift velocity of spiral waves using response functions  

NASA Astrophysics Data System (ADS)

Rotating spiral waves are a form of self-organization observed in spatially extended systems of physical, chemical, and biological nature. In the presence of a small perturbation, the spiral wave’s center of rotation and fiducial phase may change over time, i.e., the spiral wave drifts. In linear approximation, the velocity of the drift is proportional to the convolution of the perturbation with the spiral’s response functions, which are the eigenfunctions of the adjoint linearized operator corresponding to the critical eigenvalues ?=0,±i? . Here, we demonstrate that the response functions give quantitatively accurate prediction of the drift velocities due to a variety of perturbations: a time dependent, periodic perturbation (inducing resonant drift); a rotational symmetry-breaking perturbation (inducing electrophoretic drift); and a translational symmetry-breaking perturbation (inhomogeneity induced drift) including drift due to a gradient, stepwise, and localized inhomogeneity. We predict the drift velocities using the response functions in FitzHugh-Nagumo and Barkley models, and compare them with the velocities obtained in direct numerical simulations. In all cases good quantitative agreement is demonstrated.

Biktasheva, I. V.; Barkley, D.; Biktashev, V. N.; Foulkes, A. J.

2010-06-01

328

Acoustic-surface-wave velocity decrease produced by ion implantation in lithium niobate  

Microsoft Academic Search

Ion implantation was found to reduce the velocity of an acoustic surface wave propagating in lithium niobate. This frequency-dependent decrease may be mainly attributed to a reduction of the effective electromechanical coupling coefficient as reported in this letter. The impedance of 138-MHz interdigital transducers deposited on implanted niobate substrates has been determined versus ion dose.

P. Hartemann; J. K. Howard

1975-01-01

329

DETERMINATION OF 1-D SHEAR WAVE VELOCITIES USING THE REFRACTION MICROTREMOR METHOD  

Microsoft Academic Search

Current commonly used techniques of estimating shallow shear velocities for assessment of earthquake site response are too costly for use in most urban areas. They require large sources to be effective in noisy urban settings, or specialized independent recorders laid out in an extensive array. The refraction microtremor (ReMi) method (Louie, 2001) overcomes these problems by using standard P-wave recording

Satish Pullammanappallil; William Honjas; John N. Louie

2003-01-01

330

Development of a Non-intrusive System to Monitor Radial PulseWave Velocity  

Microsoft Academic Search

Understanding arterial distensibility has shown to be important in the pathogenesis of cardiovascular abnormalities like hypertension. It is also known that arterial pulse wave velocity (PWV) is a measure of the elasticity or stiffness of peripheral arterial blood vessels. However, it generally requires complex instrumentations to have an accurate measurement and not suited for continual monitoring. In this paper, it

J. Y. A. Foo; S. J. Wilson

2005-01-01

331

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

PubMed Central

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.

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

2012-01-01

332

Lateral Variations in Upper Mantle Shear Wave Attenuation  

NASA Astrophysics Data System (ADS)

%\\def\\tstar{t^*} %\\def\\tstarbar{\\overline{\\tstar}} %\\def\\deltstarbar{\\delta\\tstarbar} %\\def\\deg{{o\\ }} %\\def\\degn{{o}} We study the lateral variations in shear wave attenuation in the upper mantle by analyzing the spectra from S and SS arrivals from selected seismograms in the IRIS FARM database between 1988 and 1999. We use seismograms from shallow earthquakes (<=50~km depth) at epicentral distances of 40\\deg--80\\deg~ for S waves and 80\\deg--160\\deg~ for SS waves. Each spectrum is the product of source, receiver, and propagation response functions as well as local source- and receiver-side effects. We correct each spectrum for the known instrument response, a source model with an ? -2 falloff at high frequencies, and a one-dimensional Q? model. Since there are multiple receivers for each source and multiple sources for each receiver, we can approximate the source- and receiver-side terms by stacking the appropriate S log spectra. The resulting source-specific response functions include any remaining source spectrum and the effect of near-source attenuation in the upper mantle; the receiver stacks include the site response and near-receiver Q structure. We correct the SS log spectra for the appropriate source- and receiver-side stacks found from the S waves. Since attenuation in the lower mantle is small, the residual SS log spectrum approximates attenuation in the upper mantle near the SS bounce point, and can be used to estimate ? /line{t*} at frequencies between 0.01~and 0.1~Hz. The resulting bounce point ? /line{t*} measurements, which we smooth into caps of 5\\deg radius, show spatially coherent patterns of more and less attenuating regions. We will compare these patterns with our previous results using the same method for higher-frequency P wave attenuation and with other studies of lateral variations in shear wave attenuation.

Warren, L. M.; Shearer, P. M.

2001-12-01

333

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

USGS Publications Warehouse

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.

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

2001-01-01

334

Spatial variations in Acoustic velocity at Kuroshio region for the accurate ocean-bottom positioning  

NASA Astrophysics Data System (ADS)

We have developed a system for observing seafloor crustal deformation. This system combines GPS and acoustic techniques. One of the main errors in this system is heterogeneity of acoustic velocity in sea water. In this talk we discuss effects of lateral heterogeneity of the velocity in sea water on the location of a seafloor station. We evaluated lateral heterogeneity of the velocity in sea water for accurate determination of the ocean-bottom position. If we carry out CTD (Conductivity Temperature Depth profiler) measurements with a single ship, we cannot distinguish spatial and temporal variations from the measurement results. We therefore made simultaneous CTD measurements with two ships at the Kuroshio region (Kumano Basin). The distances between two ships are 2, 1, 0.6, 0.3, and 0.15 nautical miles (nm). The two ships were aligned parallel or orthogonal to the direction of ocean current. The CTD profilers used are SBE-19, SBE-25, and SBE-911plus of Sea-Bird Co., Ltd. The spatial variation is large at depths above 600 meters. It increases with the ship separation; and it is negligible at 0.15 nm separation. The spatial variation is up to 2.3 m/s when the two ships were aligned parallel to the direction of ocean current, and up to 6.6 m/s for the orthogonal direction at outside of Kuroshio region. At Kuroshio region, the variation is up to 2.8 m/s for parallel direction, and up to 7.0 m/s for the orthogonal direction. In addition, the spatial variation is long-period variation at Kuroshio region. We estimated the location error in ocean-bottom positioning caused by the spatial variation of the velocity structure using the CTD data. The data used in this calculation are five simultaneous CTD measurements inside of the Kuroshio region and eight measurements at outside of Kuroshio region. We modeled a 3-D velocity structure from the above dataset. Then we obtained the location of transmission from the travel time data. We searched the location of seafloor station which explains the travel time data assuming a homogeneous velocity structure. The difference is defined as lateral error between the true location and the estimated location. Results as follows: (1) Inside of the Kuroshio region The lateral error was negligible for parallel direction, and up to 50 cm for the orthogonal direction. (2) Outside of the Kuroshio region The lateral error was 20 cm for the parallel and orthogonal directions. On the basis of the results, we evaluate the effects of the spatial variations on the location error of a sea-floor position.

Yada, K.; Ikuta, R.; Ando, M.; Okuda, T.; Tadokoro, K.; Kuno, M.; Sugimoto, S.; Takatani, K.

2004-12-01

335

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

NASA Astrophysics Data System (ADS)

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.

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

2004-05-01

336

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

USGS Publications Warehouse

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

Borcherdt, Roger D.; Fumal, Thomas E.

2002-01-01

337

Investigation of the phase velocities of guided acoustic waves in soft porous layers.  

PubMed

A new experimental method for measuring the phase velocities of guided acoustic waves in soft poroelastic or poroviscoelastic plates is proposed. The method is based on the generation of standing waves in the material and on the spatial Fourier transform of the displacement profile of the upper surface. The plate is glued on a rigid substrate so that it has a free upper surface and a nonmoving lower surface. The displacement is measured with a laser Doppler vibrometer along a line corresponding to the direction of propagation of plane surface waves. A continuous sine with varying frequencies was chosen as excitation signal to maximize the precision of the measurements. The spatial Fourier transform provides the wave numbers, and the phase velocities are obtained from the relationship between wave number and frequency. The phase velocities of several guided modes could be measured in a highly porous foam saturated by air. The modes were also studied theoretically and, from the theoretical results, the experimental results, and a fitting procedure, it was possible to determine the frequency behavior of the complex shear modulus and of the complex Poisson ratio from 200 Hz to 1.4 kHz, in a frequency range higher than the traditional methods. PMID:15759676

Boeckx, L; Leclaire, P; Khurana, P; Glorieux, C; Lauriks, W; Allard, J F

2005-02-01

338

Tomographic imaging of the P-wave velocity structure beneath the Kamchatka peninsula  

NASA Astrophysics Data System (ADS)

A total of 5270 shallow and intermediate-depth earthquakes recorded by the 32 stations of the regional seismic network of the Geophysical Service of Russia are used to assess the P-wave velocity structure beneath the Kamchatka peninsula in the Western Pacific. The tomographic inversion is carried out in three steps. First, a 1-D tomographic problem is solved in order to obtain an initial velocity model. Based on the 1-D velocity model, 3-D tomographic inversions with homogeneous and heterogeneous starting models are obtained. The Conrad (15 km depth) and Moho (35 km depth) discontinuities determined from the 1-D tomographic inversion, and the upper boundary of the subducting slab are taken into account in the heterogeneous starting model for the traveltimes and ray-path determinations. Both velocity structure and hypocentral locations are determined simultaneously in the inversion. The spacing of the grid nodes is a half-degree in the horizontal direction and 20-50 km in the vertical direction. A detailed P-wave tomographic image is determined down to a depth of 200 km. The resulting tomographic image has a prominent low-velocity anomaly that shows a maximum decrease in P-wave velocity of approximately 6 per cent at 30 km depth beneath a chain of active volcanoes. At depth, low-velocity anomalies are also observed in the mantle wedge extending down to a depth of approximately 150 km. These anomalies are apparently associated with the volcanic activity. The sedimentary basin of the Central Kamchatsky graben, to the west of the volcanic front, and the accretionary prism at the trench correlate with shallow low-velocity anomalies. High-velocity anomalies observed at a depth of 10 km may be associated with the location of metamorphic basements in the Ganalsky-Valaginskoe uplift and upper crust of Shipunsky cape. The results also suggest that the subducted Pacific plate has P-wave velocities approximately 2-7 per cent higher than those of the surrounding mantle and a thickness of approximately 70 km.

Gorbatov, A.; Domínguez, J.; Suárez, G.; Kostoglodov, V.; Zhao, D.; Gordeev, E.

1999-05-01

339

Simultaneous measurement of acoustic and streaming velocities in a standing wave using laser Doppler anemometry  

NASA Astrophysics Data System (ADS)

Laser Doppler anemometry (LDA) with burst spectrum analysis (BSA) is used to study the acoustic streaming generated in a cylindrical standing-wave resonator filled with air. The air column is driven sinusoidally at a frequency of approximately 310 Hz and the resultant acoustic-velocity amplitudes are less than 1.3 m/s at the velocity antinodes. The axial component of fluid velocity is measured along the resonator axis, across the diameter, and as a function of acoustic amplitude. The velocity signals are postprocessed using the Fourier averaging method [Sonnenberger et al., Exp. Fluids 28, 217-224 (2000)]. Equations are derived for determining the uncertainties in the resultant Fourier coefficients. The time-averaged velocity-signal components are seen to be contaminated by significant errors due to the LDA/BSA system. In order to avoid these errors, the Lagrangian streaming velocities are determined using the time-harmonic signal components and the arrival times of the velocity samples. The observed Lagrangian streaming velocities are consistent with Rott's theory [N. Rott, Z. Angew. Math. Phys. 25, 417-421 (1974)], indicating that the dependence of viscosity on temperature is important. The onset of streaming is observed to occur within approximately 5 s after switching on the acoustic field. .

Thompson, Michael W.; Atchley, Anthony A.

2005-04-01

340

Landstreamer Use for Near-Surface P- and S-Wave Velocities and Poisson's Ratio  

NASA Astrophysics Data System (ADS)

Seismic landstreamer use is becomingly increasingly important in shallow seismic investigations where cost or time efficiency is critical. Applications range from locating underground voids to investigating archaeological sites, and recently to determining engineering parameters such as Poisson's ratio and shear modulus. The advantage of a landstreamer is the capability to drag a geophone array from location to location rather than planting individual geophones by hand each time the array is moved. Comparison studies have shown that data quality from landstreamer geophones and conventionally planted spiked geophones is similar and often practically indistinguishable. The Geophysical Engineering Department at Montana Tech has been using seismic landstreamers to aid data collection for projects that use both diving wave tomographic inversion to produce P-wave velocity images and surface wave dispersion inversion to estimate S-wave velocity images. We then use the P-wave and S-wave velocity images to calculate a Poisson's ratio image. All of these are produced from the same set of recorded shot gathers using vertical component, gimbaled geophones in a landstreamer configuration. This combined use of landstreamers and single mode geophones proves to be an extremely efficient method for determining subsurface parameters of interest. We used this approach to image an open-top buried cement structure at a local geophysical test site. The two velocity images and Poisson's ratio image show good agreement with expected values and clearly show the location of the buried structure. We also used this approach to characterize a leaking earthen mine tailings dam. Results from this investigation highlight areas interpreted to be weak zones associated to known leakage locations.

Link, C. A.; Speece, M. A.

2006-12-01

341

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

NASA Astrophysics Data System (ADS)

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.

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

2007-08-01

342

Angular and Frequency-Dependent Wave Velocity and Attenuation in Fractured Porous Media  

NASA Astrophysics Data System (ADS)

Wave-induced fluid flow generates a dominant attenuation mechanism in porous media. It consists of energy loss due to P-wave conversion to Biot (diffusive) modes at mesoscopic-scale inhomogeneities. Fractured poroelastic media show significant attenuation and velocity dispersion due to this mechanism. The theory has first been developed for the symmetry axis of the equivalent transversely isotropic (TI) medium corresponding to a poroelastic medium containing planar fractures. In this work, we consider the theory for all propagation angles by obtaining the five complex and frequency-dependent stiffnesses of the equivalent TI medium as a function of frequency. We assume that the flow direction is perpendicular to the layering plane and is independent of the loading direction. As a consequence, the behaviour of the medium can be described by a single relaxation function. We first consider the limiting case of an open (highly permeable) fracture of negligible thickness. We then compute the associated wave velocities and quality factors as a function of the propagation direction (phase and ray angles) and frequency. The location of the relaxation peak depends on the distance between fractures (the mesoscopic distance), viscosity, permeability and fractures compliances. The flow induced by wave propagation affects the quasi-shear (qS) wave with levels of attenuation similar to those of the quasi-compressional (qP) wave. On the other hand, a general fracture can be modeled as a sequence of poroelastic layers, where one of the layers is very thin. Modeling fractures of different thickness filled with CO2 embedded in a background medium saturated with a stiffer fluid also shows considerable attenuation and velocity dispersion. If the fracture and background frames are the same, the equivalent medium is isotropic, but strong wave anisotropy occurs in the case of a frameless and highly permeable fracture material, for instance a suspension of solid particles in the fluid.

Carcione, José M.; Gurevich, Boris; Santos, Juan E.; Picotti, Stefano

2013-02-01

343

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

PubMed Central

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

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

2011-01-01

344

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

PubMed

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

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

2011-12-01

345

Improved variational many-body wave function in light nuclei  

SciTech Connect

We propose and implement a simple method for improving the variational wave function of a many-body system. We have obtained a significant improvement in the binding energies, wave functions, and variance for the light nuclei {sup 3}H, {sup 4}He, and {sup 6}Li, using the fully realistic Argonne (AV{sub 18}) two-body and Urbana-IX (UIX) three-body interactions. The energy of {sup 4}He was improved by about 0.2 MeV and the {sup 6}Li binding energy was increased by {approx_equal}1.7 MeV compared to earlier variational Monte Carlo results. The latter result demonstrates the significant progress achieved by our method, and detailed analyses of the improved results are given. With central interactions the results are found to be in agreement with the 'exact' calculations. Our study shows that the relative error in the many-body wave functions, compared to two-body pair correlations, increases rapidly at least proportionally to the number of pairs in the system. However, this error does not increase indefinitely since the pair interactions saturate owing to convergence of cluster expansion.

Usmani, Q. N.; Anwar, K. [Institute of Engineering Mathematics, University Malaysia Perlis (Malaysia); Singh, A. [Department of Physics, School of Technology, Kalinga Institute of Industrial Technology, Bhubaneswar 751 024 (India); Rawitscher, G. [Department of Physics, University of Connecticut, Storrs, Connecticut 06269-3046 (United States)

2009-09-15

346

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

PubMed

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

Li, Li; Weidner, Donald J

2008-08-21

347

Redetermination of galactic spiral density wave parameters based on spectral analysis of masers radial velocities  

NASA Astrophysics Data System (ADS)

To redetermine the Galactic spiral density wave parameters, we have performed a spectral (Fourier) analysis of the radial velocities for 44 masers with known trigonometric parallaxes, proper motions, and line-of-sight velocities. The masers are distributed in awide range of Galactocentric distances (3.5 kpc < R < 13.2 kpc) and are characterized by a wide scatter of position angles ? in the Galactic XY plane. This has required an accurate allowance for the dependence of the perturbation phase both on the logarithm of the Galactocentric distances and on the position angles of the objects. To increase the significance of the extraction of periodicities from data series with large gaps, we have proposed and implemented a spectrum reconstruction method based on a generalized maximum entropy method. As a result, we have extracted a periodicity describing a spiral density wave with the following parameters from the maser radial velocities: the perturbation amplitude f R = 7.7{-1.5/+1.7} km s-1, the perturbation wavelength ? = 2.2{-0.1/+0.4} kpc, the pitch angle of the spiral density wave i = -5{-0.9°/+0.2°}, and the phase of the Sun in the spiral density wave ? ? = -147{-17°/+3°}.

Bajkova, A. T.; Bobylev, V. V.

2012-09-01

348

Phase and group velocities and Q of mantle Love and Rayleigh waves of the first two modes and their azimuthal dependences for the 1963 Kurile Islands earthquake  

NASA Astrophysics Data System (ADS)

Phase and group velocities and Q of mantle Love and Rayleigh waves from the 1963 Kurile Islands earthquake (Mw = 8.5) were determined over 37 great circle paths by a time variable filtering technique, in a period range 100-500 s for the fundamental modes and 100-275 s for the first higher modes. The preliminary reference Earth model (PREM) explains reasonably well the average dispersion results for the fundamental Love and Rayleigh waves. There exists a small, but significant inconsistency between the observation and the model for the first higher Love and Rayleigh waves. The Q structure of PREM is inconsistent with the observation for the fundamental Love waves, but explains other observations reasonably well. The dispersion of each mode shows a clear azimuthal dependence from which the four azimuthal windows were established. The phase and group velocity measurements for each window were, in general, shown to be mutually consistent. The azimuthal variations are largest for the first higher Rayleigh waves, indicating strong lateral heterogeneity in the structure of the low velocity zone. The first of the four windows is characterized by the largest fraction of Precambrian shields and the second window by the largest fraction of normal oceans. A comparison of these two windows may give some insight into deep lateral heterogeneity between continents and oceans. The observed phase and group velocities of the first window are systematically higher than those of the second window for the fundamental Love and Rayleigh waves at periods up to 400 s, and for the first higher Love and Rayleigh waves up to 175 s. Their differences are greatest for the first higher Rayleigh waves and least for the fundamental Rayleigh waves. Although the fundamental Rayleigh waves show the least velocity differences, their persistence up to a period of longer than 300 s is in striking contrast with some of the pure path phase velocities derived earlier for continents and oceans. A set of models for continents and oceans. PEM-C and PEM-O are not consistent with our observation. The third azimuthal window is characterized by trench-marginal seas and the fourth window by mountainous areas, typically the Asian high plateaus from northern China to the Middle East through Tibet. A comparison of these two windows gives some information about deep structural differences between subduction zones and continental collision zones, both belonging to plate convergence zones. For the fundamental and the first higher Love waves, the phase and group velocities for the third window are markedly low, whereas those for the fourth window are somewhat comparable to those for the second window. Slow Rayleigh waves are evident for two windows, with the fourth window apparently being the slowest for the fundamental Rayleigh above 200 s and for the first higher Rayleigh. For the fundamental Rayleigh waves, the third window is very slow below 200 s, but becomes progressively fast as the period increases and tends to be the fastest window around 400 s, suggesting a deep seated high velocity anomaly beneath trench-marginal seas. The dispersion characteristics of the fourth window indicate a thick high velocity lid with an extensive low velocity zone beneath it. The shield-like lithosphere, coupled with an extensive low velocity zone, may be a characteristic feature of continental collision zones. The particle motion of the fundamental Love waves was found not to be purely transverse to a great-circle connecting the epicenter to a station. The departure from the purely transverse motion is systematic among different periods, different G arrivals (G2, G3,...) and different stations, which may be interpreted as being due to lateral refraction.

Fukao, Yoshio; Kobayashi, Minoru

1983-04-01

349

Effect of high-low quartz transition on compressional and shear wave velocities in rocks under high pressure  

Microsoft Academic Search

The compressional and shear wave velocities in quarzite, granite, and granulite are determined at a fixed confining pressure\\u000a of 2 kb as a function of temperature up to 720 C. The high-low quartz transition of the constituent quartz minerals is associated\\u000a with a pronounced decrease in velocity of the compressional waves when approaching the transition and with a significant velocity

H. Kern

1979-01-01

350

Prediction of ultrasonic wave velocities in sintered materials based on the ultrasonic properties of green or partially sintered compacts  

Microsoft Academic Search

This paper reports a new method of estimating ultrasonic properties of sintered materials from the ultrasonic properties of\\u000a its powder compacts. The methodology is based on the observation that the ratio of ultrasonic shear wave velocity to longitudinal\\u000a wave velocity is a function of porosity only and varies linearly with longitudinal velocity. The efficacy of the proposed\\u000a method has been

K. K. Phani

2008-01-01

351

Third-Order Elastic Constants and the Velocity of Small Amplitude Elastic Waves in Homogeneously Stressed Media  

Microsoft Academic Search

Third-order elastic constants can be determined from the velocity of small amplitude sound waves in statically stressed media. For this purpose exact expressions are derived for the sound velocity and for a natural velocity and their stress derivatives, evaluated at zero stress, in terms of second- and third-order elastic constants. The formulas apply to arbitrary crystal symmetry and to arbitrary

R. N. Thurston; K. Brugger

1964-01-01

352

Rayleigh Wave Phase Velocity Structure of the Cameroon Volcanic Line Region  

NASA Astrophysics Data System (ADS)

The Cameroon Volcanic Line (CVL) is an 1800 km lineament of Cenozoic volcanism that extends from the Gulf of Guinea into Central Africa. With most of the line having experienced recent holocene volcanism, the CVL is one of the more prominent volcanic tracks exhibiting little to no discernible age progression. Previous interpretations of the CVL have been diverse and included volcanic activity associated with laterally transported material from a plume, multiple plumes, rift-flank processes, plate-driven Richter rolls, plume-fed small-scale convection cells, or propagating lithosphere cracks in order to reconcile the lack of age progression with the strong linearity and position of the CVL. Discriminating between these models can be significantly aided by the determination of the extent and depth of the source of the volcanism. In early 2005, a dense broadband seismometer array located over the continental section of the CVL was deployed to image the underlying mantle structure and resolve the source of the volcanism. This two-year PASSCAL deployment consisted of 8 trial stations for the first year and the following year was upgraded to 32 stations with a station spacing of 50 to 200 km. We present preliminary results of surface wave phase velocity maps from this new dataset that successfully image a low-velocity anomaly beneath the CVL as well as high velocities associated with the lithosphere of the Congo Craton. Phase velocity maps were determined by an inversion of teleseismic Rayleigh waves with Forsyth and Lee's two-plane wave method to reduce bias from multipathing. The low-velocity anomaly is observed over a period range of 20 to 140 s suggesting that the CVL anomaly extends across a substantial depth range of the lithosphere and asthenosphere. Furthermore, the lowest velocities of the anomaly are centered at the junction of the 'Y' in the volcanic track, 400 km northeast (inland) of the CVL's largest active volcano Mt. Cameroon.

Shore, P.; Euler, G. G.; Tibi, R.; Wiens, D. A.; Larson, A. M.; Nyblade, A.; Tokam, A. P.; Tabod, C.; Nnange, J. M.; Ateba, B.

2007-12-01

353

Seismic wave velocities in the sedimentary cover of Poland: Borehole data compilation  

NASA Astrophysics Data System (ADS)

A knowledge of seismic wave velocities in the sedimentary cover is of great importance for interpreting reflection and refraction seismic data, deep seismic soundings and regional and global seismic tomography. This is particularly true for regions characterized by significant thicknesses and a complex sedimentary cover structure. This paper presents the results of an analysis of seismic P-wave velocities in the sedimentary cover of Poland, a complex area of juxtaposition of major tectonic units: the Precambrian East European Craton, the Palaeozoic Platform of Central and Western Europe, and the Alpine orogen represented by the Carpathian Mountains. Based on vertical seismic profiling data from 1188 boreholes, the dependence of velocity versus depth was determined for regional geological units and for successions from the Tertiary and Quaternary to the Cambrian. The data have been approximated by polynomials, and velocity-depth formulas are given down to 6000 m depth. The velocities in the sedimentary cover have been compared with those from other areas in Europe.

Grad, Marek; Polkowski, Marcin

2012-08-01

354

Anisotropy of effective velocity for elastic wave propagation in two-dimensional phononic crystals at low frequencies  

Microsoft Academic Search

The propagation of elastic waves in two-dimensional phononic crystals is investigated theoretically in the long-wavelength limit. Exact analytical formulas for effective velocities of elastic waves are derived according to the method presented by Krokhin [Phys. Rev. Lett. 91, 264302 (2003)]. We find that the effective velocities for the propagating modes polarized in-plane (the SV and L waves) are distinct anisotropic,

Qing Ni; Jianchun Cheng

2005-01-01

355

Velocity and Timing of Multiple Spherically Converging Shock Waves in Liquid Deuterium  

SciTech Connect

The fuel entropy and required drive energy for an inertial confinement fusion implosion are set by a sequence of shocks that must be precisely timed to achieve ignition. This Letter reports measurements of multiple spherical shock waves in liquid deuterium that facilitate timing inertial confinement fusion shocks to the required precision. These experiments produced the highest shock velocity observed in liquid deuterium (U{sub s}=135 km/s at {approx}2500 GPa) and also the first observation of convergence effects on the shock velocity. Simulations model the shock-timing results well when a nonlocal transport model is used in the coronal plasma.

Boehly, T. R.; Goncharov, V. N.; Seka, W.; Hu, S. X.; Marozas, J. A. [Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623-1299 (United States); Barrios, M. A.; Celliers, P. M.; Hicks, D. G.; Collins, G. W. [Lawrence Livermore National Laboratory, Livermore, California 94551 (United States); Meyerhofer, D. D. [Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623-1299 (United States); Departments of Mechanical Engineering and Physics, University of Rochester, Rochester, New York 14623 (United States)

2011-05-13

356

Generation of dispersive acoustic waves by the phase velocity scanning of a laser beam  

NASA Astrophysics Data System (ADS)

The laser beam phase velocity scanning (PVS) method can selectively generate single-mode surface acoustic waves (SAWs) in multirole media for noncontacting NDT. The laser's rapid scanning causes a heat pulse, and the SAW generated by this pulse is coherently amplified when the dispersion is small. MHz-range SAWs are thus obtainable with greater-than-1 nm amplitude; the temperature increase of the tested object can be suppressed to less than 1 K. Dispersion curves are easily obtained by changing the scanning velocity.

Yamanaka, Kazushi; Nagata, Yoshihiko; Koda, Toshio

357

Characteristics of Light Reflected from a Dense Ionization Wave with a Tunable Velocity  

NASA Astrophysics Data System (ADS)

An optically dense ionization wave (IW) produced by two femtosecond (˜10/30fs) laser pulses focused cylindrically and crossing each other may become an efficient coherent x-ray converter in accordance with the Semenova-Lampe theory. The resulting velocity of a quasiplane IW in the vicinity of pulse intersection changes with the angle between the pulses from the group velocity of ionizing pulses to infinity allowing a tuning of the wavelength of x rays and their bunching. The x-ray spectra after scattering of a lower frequency and long coherent light pulse change from the monochromatic to high order harmoniclike with the duration of the ionizing pulses.

Zhidkov, A.; Esirkepov, T.; Fujii, T.; Nemoto, K.; Koga, J.; Bulanov, S. V.

2009-11-01

358

Characteristics of Light Reflected from a Dense Ionization Wave with a Tunable Velocity  

SciTech Connect

An optically dense ionization wave (IW) produced by two femtosecond (approx10/30 fs) laser pulses focused cylindrically and crossing each other may become an efficient coherent x-ray converter in accordance with the Semenova-Lampe theory. The resulting velocity of a quasiplane IW in the vicinity of pulse intersection changes with the angle between the pulses from the group velocity of ionizing pulses to infinity allowing a tuning of the wavelength of x rays and their bunching. The x-ray spectra after scattering of a lower frequency and long coherent light pulse change from the monochromatic to high order harmoniclike with the duration of the ionizing pulses.

Zhidkov, A.; Fujii, T.; Nemoto, K. [Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka, Kanagawa, 240-0196 Japan (Japan); Esirkepov, T.; Koga, J.; Bulanov, S. V. [Kansai Photon Science Institute, Japan Atomic Energy Agency, 8-1 Umemidai, Kizugawa, Kyoto, 619-0215 (Japan)

2009-11-20

359

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

SciTech Connect

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.

Bhatt, Neha S.; Zhang, Shiyong; Keast, S. S.; Neubert, M. E.; Rosenblatt, Charles

2001-06-01

360

S-wave velocity images of the Dead Sea Basin provided by ambient seismic noise  

NASA Astrophysics Data System (ADS)

Based on passive seismic interferometry applied to ambient seismic noise recordings between station pairs belonging to a small-scale array, we have obtained shear wave velocity images of the uppermost materials that make up the Dead Sea Basin. We extracted empirical Green's functions from cross-correlations of long-term recordings of continuous data, and measured inter-station Rayleigh wave group velocities from the daily correlation functions for positive and negative correlation time lags in the 0.1–0.5 Hz bandwidth. A tomographic inversion of the travel times estimated for each frequency is performed, allowing the laterally varying 3-D surface wave velocity structure below the array to be retrieved. Subsequently, the velocity-frequency curves are inverted to obtain S-wave velocity images of the study area as horizontal depth sections and longitude- and latitude-depth sections. The results, which are consistent with other previous ones, provide clear images of the local seismic velocity structure of the basin. Low shear velocities are dominant at shallow depths above 3.5 km, but even so a spit of land with a depth that does not exceed 4 km is identified as a salt diapir separating the low velocities associated with sedimentary infill on both sides of the Lisan Peninsula. The lack of low speeds at the sampling depth of 11.5 km implies that there are no sediments and therefore that the basement is near 10–11 km depth, but gradually decreasing from south to north. The results also highlight the bowl-shaped basin with poorly consolidated sedimentary materials accumulated in the central part of the basin. The structure of the western margin of the basin evidences a certain asymmetry both whether it is compared to the eastern margin and it is observed in north–south direction. Infill materials down to ˜8 km depth are observed in the hollow of the basin, unlike what happens in the north and south where they are spread beyond the western Dead Sea shore.

Badal, José; Chen, Yun; Chourak, Mimoun; Stankiewicz, Jacek

2013-10-01

361

Variational stereo imaging of oceanic waves with statistical constraints.  

PubMed

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

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

2013-06-26

362

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

SciTech Connect

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

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

2001-08-10

363

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

PubMed

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

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

2002-12-01

364

Coseismic velocity variations caused by static stress changes associated with the 2001 Mw = 4.3 Agios Ioanis earthquake in the Gulf of Corinth, Greece  

NASA Astrophysics Data System (ADS)

The analysis of temporal variations in the seismic velocity across faults can be used to estimate in situ stress changes. Seismic velocity of propagation depends on the fault stiffness, which is a function of stress. The coda wave interferometry technique is applied to seven families of repeating earthquakes (multiplets) recorded on the southern shore of the Gulf of Corinth, Greece, to estimate high precision velocity changes in the Earth's crust associated with the Mw = 4.3 Agios Ioanis earthquake. Results show that the Agios Ioanis event causes a perturbation in elastic properties at seismogenic depth, resulting in a reduction of 0.2% in the seismic velocity. The results are not consistent with either damage induced by dynamic stresses nor a fluid transient origin. In contrast, both the spatial distribution and magnitude of the velocity perturbation correlate well with modeled static stress variations. This suggests that the measured changes in the mechanical properties of the seismogenic crust can be attributed to a change in static stress field associated with the Mw = 4.3 Agios Ioanis earthquake. The velocity changes indicate an unclamping of the Pyrgaki fault at depth, which has local hazard implications.

Cociani, L.; Bean, C. J.; Lyon-Caen, H.; Pacchiani, F.; Deschamps, A.

2010-07-01

365

Energy cost and intracyclic variation of the velocity of the centre of mass in butterfly stroke  

Microsoft Academic Search

The purpose of this study was to examine the relationship between the intra-cycle variation of the horizontal velocity of displacement (dV) and the energy cost (EC) in butterfly stroke. Five Portuguese national level swimmers performed one maximal and two sub-maximal 200-m butterfly swims. The oxygen consumption was measured breath-by-breath by portable metabolic cart. A respiratory snorkel and valve system with

Tiago M. Barbosa; K. L. Keskinen; R. Fernandes; P. Colaço; A. B. Lima; J. P. Vilas-Boas

2005-01-01

366

Cyclic variation pattern of cerebral blood flow velocity and postconceptional age  

Microsoft Academic Search

In preterm neonates, the risk for intracerebral haemorrhage is linked to immaturity of cerebral autoregulation. The preterm's 2–5\\/min cyclic variation pattern of cerebral blood flow velocity is thought to reflect the degree of immaturity of autoregulation — a speculation to be tested. In a cross-sectional study 15 infants (gestational age 26–40 weeks, postconceptional age (PCA) 26–42 weeks, age 1–99 days

E. Michel; B. Zernikow; J. Steck; G. Kohlmann; K. von Siebenthal; S. Hirano; A. Fock; P. Casaer; G. Jorch

1994-01-01

367

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

USGS Publications Warehouse

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.

Shedlock, Kaye, M.; Roecker, Steven, W.

1985-01-01

368

Three Dimensional P and S Wave Velocity Structure and Vp\\/Vs Ratios for the Eastern Tennessee Seismic Zone  

Microsoft Academic Search

Three dimensional P and S wave velocity models have been constructed for the active eastern Tennessee seismic zone (ETSZ) using travel time tomography. The inversion utilized 5758 P wave and 4212 S wave arrival times, respectively, from 473 earthquakes recorded over the time period 1983 to 1994. Block size was 12 by 12 km horizontally by 4 km vertically. Model

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

2005-01-01

369

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

NASA Astrophysics Data System (ADS)

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.

Lindsay, P.

1996-12-01

370

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

NASA Astrophysics Data System (ADS)

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.

Farra, Véronique; Wittlinger, Gérard

2013-04-01

371

Interferometric determination of broadband ELF wave phase velocity within a region of transverse auroral ion acceleration  

NASA Astrophysics Data System (ADS)

Broadband electric field fluctuations with typical amplitudes of 10-20 mV/m peak-to-peak and frequencies from 0 Hz to 3 kHz (BB-ELF) were observed coincident with a region of ?200 eV transverse H+ acceleration (TAI) near the poleward edge of the pre-midnight aurora. The coherence and phase velocity of the electric fields were measured using a interferometric antenna array over the frequency range of ? 100 Hz to 3 kHz. These electric field fluctuations were found to have the following characteristics: 1) incoherence perpendicular to the geomagnetic field, 2) coherence parallel to the the geomagnetic field, 3) parallel phase velocity (?/k?) of 30-35 km/s upwards, 4) 0 < |k?/k?| < 0.22. We show that these properties are compatible with the emission being electrostatic H+ cyclotron (EHC) waves. We also discuss possible generation mechanisms for the waves, and their relationship to the TAI.

Bonnell, J.; Kintner, P.; Wahlund, J.-E.; Lynch, K.; Arnoldy, R.

372

Lithospheric Velocity Models of Eurasia and the Middle East From the Joint Inversion of P- and S-Wave Receiver Functions and Dispersion Velocicities  

NASA Astrophysics Data System (ADS)

The development of velocity models for the continental crust and lithosphere is critical in supporting ongoing efforts to monitor for clandestine nuclear explosions within the Comprehensive Nuclear-Test Ban Treaty (CTBT). Detailed velocity models are required to accurately predict travel-times for local and regional phases, such as Pg, Pn, Sn, and Lg, as well as body waves at upper-mantle triplication distances, and thus improve our ability to accurately locate small-yield events with sparse seismic networks. Taking advantage of the vast amounts of open data accumulated over the past decades at the Incorporated Research Institute for Seismology (IRIS), we are developing regionalized models of lithospheric velocity structure for a wide variety of tectonic regions throughout Eurasia and the Middle East. Velocity models have traditionally been obtained from separate analysis of different seismic observations, each having its own sensitivities, resolving power, and trade-offs. Our approach consists of combining complementary seismic observations through a joint inversion scheme to produce integrated velocity models that bridge resolution gaps and minimize trade-offs. Seismic observations in our study include P- and S-wave receiver functions for all the open broadband stations within the study area archived at the IRIS Data Management Center, and fundamental-mode, Rayleigh-wave group velocities from an independent, continental-scale surface-wave tomography study. We first obtain joint inversion models consisting of 1D velocity-depth profiles local to the recording stations, where crustal thickness is constrained by P-wave receiver functions, lithospheric thickness is constrained by S-wave receiver functions, and background S-velocity is constrained by surface-wave dispersion, and then combine the velocity-depth profiles within geologic/tectonic provinces to produce average velocity models for each region. Validation of the resulting velocity models through full waveform modeling of well-located local and regional events reveals that, in general, minor tuning of the regionalized models is required to satisfactorily explain the waveforms.

Julia, J.; Matzel, E.; Nyblade, A.; Rodgers, A. J.

2010-12-01

373

Anisotropic Changes in P-Wave Velocity and Attenuation during Deformation and Fluid Infiltration of Granite  

Microsoft Academic Search

4 Abstract. 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 V p\\/Vs ratio,

Sergei A. Stanchits; David A. Lockner; Alexander V. Ponomarev

2003-01-01

374

Impact of Metabolic Syndrome on Brachial-Ankle Pulse Wave Velocity in Japanese  

Microsoft Academic Search

The aim of this study was to determine the effect of metabolic syndrome on brachial-ankle pulse wave velocity (baPWV) by using the new guidelines for diagnosis of this syndrome in Japan. We examined 525 men and women without a history of cardiovascular disease or cancer, and an ankle-brachial index<0.9. The baPWV was measured using a device (Form PWV\\/ABI) that simultaneously

Akiko Tsubakimoto; Isao Saito; Toshifumi Mannami; Yoshihiko Naito; Shinobu Nakamura; Yoshiko Dohi; Kunio Yonemasu

2006-01-01

375

Permeability and P-wave velocity change in granitic rocks under freeze–thaw cycles  

Microsoft Academic Search

An extensive experimental investigation of microstructural changes in granites under freeze–thaw cycles using permeability and P-wave velocity measurements is described. Two types of natural granite rocks are considered and tested under dry and saturated conditions. The specimens were subjected to 200 heating–cooling cycles (??20°C\\/?+?20°C); each cycle had a duration of 24 h. The results indicate that the ageing process decreases the

M. Takarli; W. Prince

2007-01-01

376

Brachial–ankle pulse wave velocity: an index of central arterial stiffness?  

Microsoft Academic Search

Brachial–ankle pulse wave velocity (baPWV) is a promising technique to assess arterial stiffness conveniently. However, it is not known whether baPWV is associated with well-established indices of central arterial stiffness. We determined the relation of baPWV with aortic (carotid-femoral) PWV, leg (femoral-ankle) PWV, and carotid augmentation index (AI) by using both cross-sectional and interventional approaches. First, we studied 409 healthy

J Sugawara; K Hayashi; T Yokoi; M Y Cortez-Cooper; A E DeVan; M A Anton; H Tanaka

2005-01-01

377

Teleseismic tomography of the compressional wave velocity structure beneath the Long Valley region, California  

Microsoft Academic Search

In 1982 and 1984 the U.S. Geological Survey used several seismic networks, totaling over 90 stations, to record teleseismic P waves and measure travel time residuals in an area centered on the Long Valley caldera. The authors inverted the travel time residuals to obtain a three-dimensional image of the velocity structure with resolution of 5-6 km to depths of 70

P. B. Dawson; J. R. Evans; H. M. Iyer

1990-01-01

378

Carotid-femoral pulse-wave velocity in children and adolescents from 2–18 years  

Microsoft Academic Search

Carotid-femoral Pulse-Wave Velocity(PWV) is an indicator of arterial distensibility. Age-related atherosclerosis, increased by hypertension, results in an increased arterial stiffness and cardiovascular morbidity and mortality in adults. Little is known about arterial distensibility during the development and maturing stages of childhood and adolescence.AIM OF THE STUDY. To know the correlation of carotid-femoral PWV with parameters of somatic growing and pubertal

E. Ramos; J. A. Perez-Quintero; S. M. Encinas; J. Olivan; J. Gonzalez-Hachero; R. Perez-Cano

2000-01-01

379

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

Microsoft Academic Search

We have used both single-station and array methods to determine shallow shear velocity site profiles in the vicinity of the city of Cologne, Germany from ambient vibration records. Based on fk-analysis we assume that fundamental-mode Rayleigh waves dominate the analysed wavefield in the frequency range of 0.7-2.2 Hz. According to this view a close relation exists between H\\/V spectral ratios

Frank Scherbaum; Klaus-G. Hinzen; Matthias Ohrnberger

2003-01-01

380

Acoustic wave velocity and permeability evolution during pressure cycles on a thermally cracked granite  

Microsoft Academic Search

Compressional waves velocity VP and water permeability K were measured during long-term experiments in a high-pressure vessel (in the range 11–75MPa for confining pressures and 10–70MPa for pore pressures). Experiments were carried out on fractured granite specimens prepared by a controlled heating treatment at 510°C, which generated thermal cracks. A distinct effective pressure law was derived from the measurements within

M Darot; T Reuschlé

2000-01-01