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Sample records for group velocity tomography

  1. Rayleigh-Wave Group-Velocity Tomography of Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Tang, Zheng; Mai, P. Martin; Chang, Sung-Joon; Zahran, Hani

    2017-04-01

    We use surface-wave tomography to investigate the lithospheric structure of the Arabian plate, which is traditionally divided into the Arabian shield in the west and the Arabian platform in the east. The Arabian shield is a complicated mélange of crustal material, composed of several Proterozoic terrains separated by ophiolite-bearing suture zones and dotted by outcropping Cenozoic volcanic rocks. The Arabian platform is primarily covered by very thick Paleozoic, Mesozoic and Cenozoic sediments. We develop high-resolution tomographic images from fundamental-mode Rayleigh-wave group-velocities across Saudi Arabia, utilizing the teleseismic data recorded by the permanent Saudi National Seismic Network (SNSN). Our study extends previous efforts on surface wave work by increasing ray path density and improving spatial resolution. Good quality dispersion measurements for roughly 3000 Rayleigh-wave paths have been obtained and utilized for the group-velocity tomography. We have applied the Fast Marching Surface Tomography (FMST) scheme of Rawlinson (2005) to obtain Rayleigh-wave group-velocity images for periods from 8 s to 40 s on a 0.8° 0.8° grid and at resolutions approaching 2.5° based on the checkerboard tests. Our results indicate that short-period group-velocity maps (8-15 s) correlate well with surface geology, with slow velocities delineating the main sedimentary features including the Arabian platform, the Persian Gulf and Mesopotamia. For longer periods (20-40 s), the velocity contrast is due to the differences in crustal thickness and subduction/collision zones. The lower velocities are sensitive to the thicker continental crust beneath the eastern Arabia and the subduction/collision zones between the Arabian and Eurasian plate, while the higher velocities in the west infer mantle velocity.

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

    NASA Astrophysics Data System (ADS)

    Wu, Francis T.

    1993-07-01

    Group velocities of both Rayleigh and Love waves are used in a tomographic inversion to obtain group velocity maps of East Asia (60 deg E-140 deg E and 20 deg N-50 deg N). The period range studied is 30-70 seconds. For periods longer than 40 seconds, a high group velocity gradient clearly exists along longitude 105 deg E; the velocities are noticeably higher east of this longitude than west of this longitude. The Tibetan Plateau appears as a prominent low velocity (about 15%) structure in this area; central Tibet appears as the area with the lowest velocity. The North China Plain is an area of high velocities, probably as a result of thin crust. The variability of deep crustal and upper mantle structures underneath the different tectonic provinces in the study can clearly be seen. In a separate study, using the dataset above and that from the former Soviet Union, we have derived the Rayleigh tomographic images of a larger area (40 deg E-160 deg E and 20 deg N-70 deg N). While the Tibetan plateau still remains to be the most prominent low velocity features, two other features are also clear, a very high velocity Siberian platform and a high velocity ridge extending from Lake Baikal to Central Mongolia. These studies are useful in delineating tectonics.

  3. Accurate group velocity estimation for unmanned aerial vehicle-based acoustic atmospheric tomography.

    PubMed

    Rogers, Kevin J; Finn, Anthony

    2017-02-01

    Acoustic atmospheric tomography calculates temperature and wind velocity fields in a slice or volume of atmosphere based on travel time estimates between strategically located sources and receivers. The technique discussed in this paper uses the natural acoustic signature of an unmanned aerial vehicle as it overflies an array of microphones on the ground. The sound emitted by the aircraft is recorded on-board and by the ground microphones. The group velocities of the intersecting sound rays are then derived by comparing these measurements. Tomographic inversion is used to estimate the temperature and wind fields from the group velocity measurements. This paper describes a technique for deriving travel time (and hence group velocity) with an accuracy of 0.1% using these assets. This is shown to be sufficient to obtain highly plausible tomographic inversion results that correlate well with independent SODAR measurements.

  4. Improving mb:Ms discrimination using phase matched filters derived from regional group velocity tomography

    SciTech Connect

    Ford, S R; Hazler, S; Pasyanos, M E; Walter, W R

    1999-07-23

    This study reports on the ongoing investigation of surface wave group velocity dispersion across the Middle East and North Africa. Using broadband data gathered from various sources, we have measured group velocity using a multiple narrow-band filter method. To date, we have examined over 13,500 seismograms and made quality measurements for about 6500 Rayleigh and 3500 Love wave paths. A conjugate gradient method is used to perform the group velocity tomography at several periods. There is excellent agreement between short period structure and large known sedimentary features. Longer period structure is sensitive to crustal thickness, particularly the contrast between continental and oceanic regions and thicker crusts found beneath erogenic zones. We also find slow upper mantle velocities along rift systems. Correlation between the inversion results and known major tectonic features gives us confidence in our surface wave group velocities. Accurate group velocity maps can be used to construct phase matched filters. The filters can improve weak surface waves by compressing the dispersed signal. We are particularly interested in using the filters to calculate regionally determined M{sub s} measurements, which we hope can be used to extend the threshold of m{sub b}:M{sub s} discriminants to lower magnitude levels. A preliminary analysis of surface wave data processed using phase matched filters indicates a significant improvement in increasing the signal-to-noise ratio and improving magnitude estimates. Where signal-to-noise is very poor, phase matched filtering can still be useful in lowering the upper bound on M{sub s} measurements. We propose a series of tests in order to analyze the utility of phase matched filters. Goals of the study include determining at what distance and magnitude ranges we can expect to see improvement using the filters and the overall effect of the filters on discrimination capability. We also propose to look at seismic velocity models of

  5. Rayleigh wave group velocity tomography of Gujarat region, Western India and its implications to mantle dynamics

    NASA Astrophysics Data System (ADS)

    de Lorenzo, Salvatore; Michele, Maddalena; Emolo, Antonio; Tallarico, Andrea

    2017-02-01

    In the present study, fundamental Rayleigh waves with varying period from 10 to 80 s are used to obtain group velocity maps in the northwest Deccan Volcanic Province of India. About 350 paths are obtained using 53 earthquakes (4.8 ≤ M ≥ 7.9) recorded by the SeisNetG (Seismic Network of Gujarat). Individual dispersion curves of group velocity of Rayleigh wave for each source-station path are estimated using multiple filter technique. These curves are used to determine lateral distribution of Rayleigh wave group velocity by tomographic inversion method. Our estimated Rayleigh group velocity at varying depths showed conspicuous corroboration with three tectonic blocks [Kachchh Rift Basin (KRB), Saurashtra Horst (SH), and Mainland Gujarat (MG)] in the region. The seismically active KRB with a thicker crust is characterized as a low velocity zone at a period varying from 10 to 30 s as indicative of mantle downwarping or sagging of the mantle beneath the KRB, while the SH and MG are found to be associated with higher group velocities, indicating the existence of the reduced crustal thickness. The trend of higher group velocity was found prevailed adjacent to the Narmada and Cambay rift basins that also correspond to the reduced crust, suggesting the processes of mantle upwarping or uplifting due to mantle upwelling. The low velocities at periods longer than 40 s beneath the KRB indicate thicker lithosphere. The known Moho depth correlates well with the observed velocities at a period of about 30 s in the Gujarat region. Our estimates of relatively lower group velocities at periods varying from 70 to 80 s may correspond to the asthenospheric flow beneath the region. It is interesting to image higher group velocity for the thinner crust beneath the Arabian Sea adjacent to the west coast of Gujarat at the period of 40 s that may correspond to the upwarped or upwelled mantle beneath the Arabian Sea. Our results have better resolution estimated by a radius of equivalent

  6. Rayleigh wave group velocity tomography of Gujarat region, Western India and its implications to mantle dynamics

    NASA Astrophysics Data System (ADS)

    Dixit, Mayank; Singh, A. P.; Mishra, O. P.

    2017-07-01

    In the present study, fundamental Rayleigh waves with varying period from 10 to 80 s are used to obtain group velocity maps in the northwest Deccan Volcanic Province of India. About 350 paths are obtained using 53 earthquakes (4.8 ≤ M ≥ 7.9) recorded by the SeisNetG (Seismic Network of Gujarat). Individual dispersion curves of group velocity of Rayleigh wave for each source-station path are estimated using multiple filter technique. These curves are used to determine lateral distribution of Rayleigh wave group velocity by tomographic inversion method. Our estimated Rayleigh group velocity at varying depths showed conspicuous corroboration with three tectonic blocks [Kachchh Rift Basin (KRB), Saurashtra Horst (SH), and Mainland Gujarat (MG)] in the region. The seismically active KRB with a thicker crust is characterized as a low velocity zone at a period varying from 10 to 30 s as indicative of mantle downwarping or sagging of the mantle beneath the KRB, while the SH and MG are found to be associated with higher group velocities, indicating the existence of the reduced crustal thickness. The trend of higher group velocity was found prevailed adjacent to the Narmada and Cambay rift basins that also correspond to the reduced crust, suggesting the processes of mantle upwarping or uplifting due to mantle upwelling. The low velocities at periods longer than 40 s beneath the KRB indicate thicker lithosphere. The known Moho depth correlates well with the observed velocities at a period of about 30 s in the Gujarat region. Our estimates of relatively lower group velocities at periods varying from 70 to 80 s may correspond to the asthenospheric flow beneath the region. It is interesting to image higher group velocity for the thinner crust beneath the Arabian Sea adjacent to the west coast of Gujarat at the period of 40 s that may correspond to the upwarped or upwelled mantle beneath the Arabian Sea. Our results have better resolution estimated by a radius of equivalent

  7. Group velocity tomography of the upper crust in the eastern Tennessee seismic zone from ambient noise data

    NASA Astrophysics Data System (ADS)

    Brandmayr, Enrico; Kuponiyi, Ayodeji Paul; Arroucau, Pierre; Vlahovic, Gordana

    2016-10-01

    The eastern Tennessee seismic zone (ETSZ) is the second most seismically active area in the central and eastern United States after the New Madrid seismic zone, but the relatively weak seismicity and the absence of correlation between the seismicity distribution and the surface geology make its seismogenic potential controversial. In this work we investigate the structure of the upper crust in the ETSZ by means of group velocity tomography maps from seismic noise data. Results show that the seismic activity is associated with a relatively low velocity anomaly mainly located in one or more basement blocks. These blocks, bounded to the NW by the NY-AL lineament and to the SE by the Clingman lineaments, are buried beneath low velocity strata consistent with the presence of a relatively thick sedimentary cover. The imaged low velocity anomaly migrates towards the SE at increasing periods, suggesting a possible SE dipping weak structure where most of the seismic activity takes place. The correlation between the NY-AL magnetic signature and the position of the seismic velocity anomalies supports the interpretation of the low velocity zone as a major basement fault projected to the surface as the NY-AL magnetic lineaments. The fault juxtaposes Granite-Rhyolite basement to the NW with Grenville southern Appalachian basement to the SE.

  8. Group Velocity Tomography for Eastern Mexico and Crustal Structure for Tehuantepec Isthmus

    NASA Astrophysics Data System (ADS)

    Córdoba Montiel, F.; Iglesias, A.; Melgar, D.; Singh, S.; Perez-Campos, X.

    2013-05-01

    We use seismic noise records from the broadband network of the Mexican National Seismological Service (Servicio Sismológico Nacional) and from MASE and VEOX stations (two temporal seismic experiments) to compute the vertical-vertical component of noise cross correlations for station pairs. MASE (Mesoamerican Seismic Experiment) consisted of one hundred stations deployed along a profile perpendicular to the trench and starting in Acapulco,Gro. Mex. This experiment ran from December 2004 until May, 2007. Fifty of these stations were relocated in a N-S profile crossing the Tehuantepec Isthmus from the Gulf of Mexico to the Pacific coast. These stations were operated from July 2007 until February 2009 and this stage of the experiment was called VEOX (Veracruz-Oaxaca). From the cross correlation for each pair of stations, Rayleigh wave dispersion curves were computed which represents the average group velocity between stations pairs. Furthermore, regional earthquakes recorded by the stations, were used to compute Rayleigh wave dispersion curves, which represent the average group velocity between epicenter and station. This mixed set of group velocity measurements was inverted to obtain tomographic images in discrete periods (5-50 s). Resolution tests show that the better-covered regions are surrounding both temporal experiments. Good coverage is also achieved in the large area between both experiments. In order to find details of crustal structure in the Tehuantepec Isthmus we use a set of previously computed receiver functions (Melgar and Pérez-Campos, 2011), to perform a joint inversion together with local dispersion curves reconstructed from the tomographic images. Results show good agreement with previous results by Melgar and Pérez-Campos (2011).

  9. Interpretation of ambient noise cross-correlation traveltimes: Finite-frequency tomography of Love group velocities in the Czech Republic

    NASA Astrophysics Data System (ADS)

    Valentova, L.; Gallovic, F.; Ruzek, B.; de la Puente, J.

    2012-04-01

    In recent years, great emphasis has been laid on finite-frequency tomography. The inverted observables are considered to be dependent not only on model parameters along infinitely thin raypaths but to exhibit more complicated spatial dependency represented by so-called sensitivity kernels. Efficient tool for the calculation of the sensitivity kernels is adjoint method. It is based on two calculations: forward calculation of wavefield propagating from source to receivers in an initial model, and adjoint calculation where the residuals between observed data and synthetics backpropagate from the receivers to the source (so-called adjoint wavefield). The aim of the presented work is obtaining surface wave group velocity maps of the Czech Republic for specific periods in the range of 2 - 20 s. Data used in the inversion consist of crosscorrelation traveltimes of Love waves between stations located in the Czech Republic and adjacent areas acquired from ambient seismic noise band-pass filtered around the specific periods. The inverse problem for the L2 crosscorrelation traveltime misfit is solved by the conjugate gradient technique, with misfit gradients calculated using the adjoint method. Assuming that propagation of surface waves along Earth's surface can be approximated by membrane wave problem, the computations are reduced to only 2D domain. Therefore, the calculations could be performed using adjoint version of SeisSol, elastodynamic equation solver using Discontinuous Galerkin method with Arbitrary High Order time Derivatives (ADER-DG). More attention is paid to the inversion of data of the highest periods i.e. 16s and 20s. The main advantage are lower computational demands. Moreover, 16s and 20s Love waves have similar depth sensitivities, thus the travel times and the resulting models are expected to exhibit only very minor differences. However, in real application this may not be valid, as the data and their processing are subject to various kinds of errors

  10. Elliptical-anisotropic eikonal phase velocity tomography

    NASA Astrophysics Data System (ADS)

    de Ridder, S. A. L.; Biondi, B. L.; Nichols, D.

    2015-02-01

    We formulated an anisotropic eikonal tomography approach for phase velocities based on a two-dimensional elliptical-anisotropic wave equation. We can fit the parameters of the ellipse directly from measured first-order traveltime surface gradients and constrain these parameters to vary smoothly over space. The method is applied to Scholte waves in virtual seismic sources from stations in the Life of Field Seismic Ocean Bottom Cable array installed over the Ekofisk field. The fast directions of the azimuthally anisotropic Scholte wave velocities form a large circular pattern over the Ekofisk field. This pattern dominates the Scholte wave phase velocities at Ekofisk between 0.7 and 1.1 Hz. It results from the overburden stress state and from seafloor subsidence induced by decades of hydrocarbon extraction.

  11. Group velocity in lossy periodic structured media

    SciTech Connect

    Chen, P. Y.; McPhedran, R. C.; Sterke, C. M. de; Poulton, C. G.; Asatryan, A. A.; Botten, L. C.; Steel, M. J.

    2010-11-15

    In lossless periodic media, the concept of group velocity is fundamental to the study of propagation dynamics. When spatially averaged, the group velocity is numerically equivalent to energy velocity, defined as the ratio of energy flux to energy density of modal fields. However, in lossy media, energy velocity diverges from group velocity. Here, we define a modal field velocity which remains equal to the complex modal group velocity in homogeneous and periodic media. The definition extends to the more general situation of modal fields that exhibit spatial or temporal decay due to lossy elements or Bragg reflection effects. Our simple expression relies on a generalization of the concepts of energy flux and density. Numerical examples, such as a two-dimensional square array of silver rods in vacuum, are provided to confirm the result. Examples demonstrate how the dispersion relation of the periodic structure, the properties of its modes, and their group velocities change markedly in lossy media.

  12. Attenuation and Velocity tomography can we join them?

    NASA Astrophysics Data System (ADS)

    Debski, Wojciech

    2013-04-01

    Velocity tomography, is now routinely used to image velocity distributions which are subsequently interpreted in terms of the Earth or rock-sample structure. This technique has been successfully used in detailed mapping of the Earth in various scales ranging from the whole globe until very local rock-mass structure, e.g. in mines. It is also used in geo-technical (tunnels, mines, water dams, etc.) and laboratory measurements. The second tomography technique, namely attenuation tomography, is used to image another physical property of rocks: the acoustic attenuation structure usually describe by the parameter Q. This technique is, however, much more difficult than velocity tomography because the attenuation of seismic/acoustic waves is a much more subtle effect than a variation of delays of energy arrival times due to velocity heterogeneities. There exist a lot of factors that can easily disturb attenuation measurements so it is difficult to obtain a reliable image of the attenuation structure. For this reason, a very high quality of data used for attenuation tomography must be ensured. Nevertheless, the additional effort necessary to obtain an image of Q is worthwhile because Q is regarded to be more sensitive to the rock structure than seismic/acoustic wave velocity. Imaging the Q distribution can be achieved by inverting various characteristics of the measured signals: amplitudes, spectra decay, pulse broadening or central frequency shift. The advantages and limitations of each of these approaches are well known. In this presentation we discuss the approach developed for the acoustic ultrasonic tomography imaging and called Enhanced Velocity Tomography and possibility of its using in a ``global seismological'' framework. It consists in a combination of both velocity and attenuation tomography into one scheme to maximize the advantage of the robustness of velocity and the sensitivity to the micro-structure of attenuation.

  13. Decreased group velocity in compositionally graded films.

    PubMed

    Gao, Lei

    2006-03-01

    A theoretical formalism is presented that describes the group velocity of electromagnetic signals in compositionally graded films. The theory is first based on effective medium approximation or the Maxwell-Garnett approximation to obtain the equivalent dielectric function in a z slice. Then the effective dielectric tensor of the graded film is directly determined, and the group velocities for ordinary and extraordinary waves in the film are derived. It is found that the group velocity is sensitively dependent on the graded profile. For a power-law graded profile f(x)=ax(m), increasing m results in the decreased extraordinary group velocity. Such a decreased tendency becomes significant when the incident angle increases. Therefore the group velocity in compositionally graded films can be effectively decreased by our suitable adjustment of the total volume fraction, the graded profile, and the incident angle. As a result, the compositionally graded films may serve as candidate material for realizing small group velocity.

  14. High-Speed Vortex Wind Velocity Imaging by Acoustic Tomography

    NASA Astrophysics Data System (ADS)

    Li, H.; Ueki, T.; Hayashi, K.; Yamada, A.

    A technique for monitoring strong vortex wind fields is highly desired due to the rapid development of global warming. Vortex wind velocity imaging using an acoustic travel time tomography technique was developed to meet this need. The method can be implemented with a small number of parallel facing pairs of acoustic transmitters/receivers from just a single illumination view direction, so that high-speed data acquisition compatible with instantaneous wind-flow imaging was accomplished. A test using an indoor wind velocity tomography system demonstrated that vortex wind velocity profiles generated by an electric fan could be instantaneously reconstructed with satisfactory quantitative precision.

  15. Influence of flow velocity on flow field's optical tomography diagnosis

    NASA Astrophysics Data System (ADS)

    Chen, Yun-yun; Yu, Yang; Zhong, Xia; Zhang, Ying-ying

    2017-01-01

    The effect of flow velocity is usually neglected when optical computerized tomography (OCT) methods are chosen to measure the temperature distribution of the flow fields up to now. In this paper, two sets of experiment are supplied to verify the effect of flow velocity on flow field's moiré tomography. Specifically speaking, the temperature results with the assumption that it is an isobaric process (omit the effect of flow velocity) in the measured flame flow fields, manifest that the isobaric supposition is not suitable for all the flames. And then, a condition, which can be adopted to judge that when the effect of flow velocity on its temperature reconstruction can not be neglected any more, is proposed. This study would provide some reference to the temperature diagnosis by the optical methods which are based on the measurement of the refractive index.

  16. Reconstruction of velocity fields in electromagnetic flow tomography.

    PubMed

    Lehtikangas, Ossi; Karhunen, Kimmo; Vauhkonen, Marko

    2016-06-28

    Electromagnetic flow meters (EMFMs) are the gold standard in measuring flow velocity in process industry. The flow meters can measure the mean flow velocity of conductive liquids and slurries. A drawback of this approach is that the velocity field cannot be determined. Asymmetric axial flows, often encountered in multiphase flows, pipe elbows and T-junctions, are problematic and can lead to serious systematic errors. Recently, electromagnetic flow tomography (EMFT) has been proposed for measuring velocity fields using several coils and a set of electrodes attached to the surface of the pipe. In this work, a velocity field reconstruction method for EMFT is proposed. The method uses a previously developed finite-element-based computational forward model for computing boundary voltages and a Bayesian framework for inverse problems. In the approach, the vz-component of the velocity field along the longitudinal axis of the pipe is estimated on the pipe cross section. Different asymmetric velocity fields encountered near pipe elbows, solids-in-water flows in inclined pipes and in stratified or multiphase flows are tested. The results suggest that the proposed reconstruction method could be used to estimate velocity fields in complicated pipe flows in which the conventional EMFMs have limited accuracy. This article is part of the themed issue 'Supersensing through industrial process tomography'.

  17. Comparison of high group velocity accelerating structures

    SciTech Connect

    Farkas, Z.D.; Wilson, P.B.

    1987-02-01

    It is well known that waveguides with no perturbations have phase velocities greater than the velocity of light c. If the waveguide dimensions are chosen so that the phase velocity is only moderately greater than c, only small perturbations are required to reduce the phase velocity to be synchronous with a high energy particle bunch. Such a lightly loaded accelerator structure will have smaller longitudinal and transverse wake potentials and hence will lead to lower emittance growth in an accelerated beam. Since these structures are lightly loaded, their group velocities are only slightly less than c and not in the order of 0.01c, as is the case for the standard disk-loaded structures. To ascertain that the peak and average power requirements for these structures are not prohibitive, we examine the elastance and the Q for several traveling wave structures: phase slip structures, bellows-like structures, and lightly loaded disk-loaded structures.

  18. Reconstruction of velocity fields in electromagnetic flow tomography

    PubMed Central

    Lehtikangas, Ossi; Karhunen, Kimmo

    2016-01-01

    Electromagnetic flow meters (EMFMs) are the gold standard in measuring flow velocity in process industry. The flow meters can measure the mean flow velocity of conductive liquids and slurries. A drawback of this approach is that the velocity field cannot be determined. Asymmetric axial flows, often encountered in multiphase flows, pipe elbows and T-junctions, are problematic and can lead to serious systematic errors. Recently, electromagnetic flow tomography (EMFT) has been proposed for measuring velocity fields using several coils and a set of electrodes attached to the surface of the pipe. In this work, a velocity field reconstruction method for EMFT is proposed. The method uses a previously developed finite-element-based computational forward model for computing boundary voltages and a Bayesian framework for inverse problems. In the approach, the vz-component of the velocity field along the longitudinal axis of the pipe is estimated on the pipe cross section. Different asymmetric velocity fields encountered near pipe elbows, solids-in-water flows in inclined pipes and in stratified or multiphase flows are tested. The results suggest that the proposed reconstruction method could be used to estimate velocity fields in complicated pipe flows in which the conventional EMFMs have limited accuracy. This article is part of the themed issue ‘Supersensing through industrial process tomography’. PMID:27185961

  19. Chandra Observations of Low Velocity Dispersion Groups

    NASA Astrophysics Data System (ADS)

    Helsdon, Stephen F.; Ponman, Trevor J.; Mulchaey, J. S.

    2005-01-01

    Deviations of galaxy groups from cluster scaling relations can be understood in terms of an excess of entropy in groups. The main effect of this excess is to reduce the density and thus the luminosity of the intragroup gas. Given this, groups should also show a steep relationship between X-ray luminosity and velocity dispersion. However, previous work suggests that this is not the case, with many measuring slopes flatter than the cluster relation. Examining the group LX-σ relation shows that much of the flattening is caused by a small subset of groups that show very high X-ray luminosities for their velocity dispersions (or vice versa). Detailed Chandra study of two such groups shows that earlier ROSAT results were subject to significant (~30%-40%) point-source contamination but confirm that a significant hot intergalactic medium is present in these groups, although these are two of the coolest systems in which intergalactic X-ray emission has been detected. Their X-ray properties are shown to be broadly consistent with those of other galaxy groups, although the gas entropy in NGC 1587 is unusually low, and its X-ray luminosity is correspondingly high for its temperature when compared with most groups. This leads us to suggest that the velocity dispersion in these systems has been reduced in some way, and we consider how this might have come about.

  20. HALO VELOCITY GROUPS IN THE PISCES OVERDENSITY

    SciTech Connect

    Sesar, Branimir; Ivezic, Zeljko; Vivas, A. Katherina; Duffau, Sonia E-mail: zi@u.washington.ed E-mail: sonia.duffau@gmail.co

    2010-07-01

    We report spectroscopic observations of five faint (V {approx} 20) RR Lyrae stars associated with the Pisces overdensity conducted with the Gemini South Telescope. At a heliocentric and galactocentric distance of {approx}80 kpc, this is the most distant substructure in the Galactic halo known to date. We combined our observations with literature data and confirmed that the substructure is composed of two different kinematic groups. The main group contains eight stars and has (V{sub gsr}) = 50 km s{sup -1}, while the second group contains four stars at a velocity of (V{sub gsr}) = -52 km s{sup -1}, where V{sub gsr} is the radial velocity in the galactocentric standard of rest. The metallicity distribution of RR Lyrae stars in the Pisces overdensity is centered on [Fe/H] = -1.5 dex and has a width of 0.3 dex. The new data allowed us to establish that both groups are spatially extended making it very unlikely that they are bound systems, and are more likely to be debris of a tidally disrupted galaxy or galaxies. Due to small sky coverage, it is still unclear whether these groups have the same or different progenitors.

  1. The Circular Velocity Function of Group Galaxies

    NASA Astrophysics Data System (ADS)

    Abramson, Louis E.; Williams, Rik J.; Benson, Andrew J.; Kollmeier, Juna A.; Mulchaey, John S.

    2014-09-01

    A robust prediction of ΛCDM cosmology is the halo circular velocity function (CVF), a dynamical cousin of the halo mass function. The correspondence between theoretical and observed CVFs is uncertain, however: cluster galaxies are reported to exhibit a power-law CVF consistent with N-body simulations, but that of the field is distinctly Schechter-like, flattened compared to ΛCDM expectations at circular velocities v c <~ 200 km s-1. Groups offer a powerful probe of the role environment plays in this discrepancy as they bridge the field and clusters. Here, we construct the CVF for a large, mass- and multiplicity-complete sample of group galaxies from the Sloan Digital Sky Survey. Using independent photometric v c estimators, we find no transition from field to ΛCDM-shaped CVF above v c = 50 km s-1 as a function of group halo mass. All groups with 12.4 <~ log M halo/M ⊙ <~ 15.1 (Local Group analogs to rich clusters) display similar Schechter-like CVFs marginally suppressed at low v c compared to that of the field. Conversely, some agreement with N-body results emerges for samples saturated with late-type galaxies, with isolated late-types displaying a CVF similar in shape to ΛCDM predictions. We conclude that the flattening of the low-v c slope in groups is due to their depressed late-type fractions—environment affecting the CVF only to the extent that it correlates with this quantity—and that previous cluster analyses may suffer from interloper contamination. These results serve as useful benchmarks for cosmological simulations of galaxy formation.

  2. The circular velocity function of group galaxies

    SciTech Connect

    Abramson, Louis E.; Williams, Rik J.; Benson, Andrew J.; Kollmeier, Juna A.; Mulchaey, John S.

    2014-09-20

    A robust prediction of ΛCDM cosmology is the halo circular velocity function (CVF), a dynamical cousin of the halo mass function. The correspondence between theoretical and observed CVFs is uncertain, however: cluster galaxies are reported to exhibit a power-law CVF consistent with N-body simulations, but that of the field is distinctly Schechter-like, flattened compared to ΛCDM expectations at circular velocities v {sub c} ≲ 200 km s{sup –1}. Groups offer a powerful probe of the role environment plays in this discrepancy as they bridge the field and clusters. Here, we construct the CVF for a large, mass- and multiplicity-complete sample of group galaxies from the Sloan Digital Sky Survey. Using independent photometric v {sub c} estimators, we find no transition from field to ΛCDM-shaped CVF above v {sub c} = 50 km s{sup –1} as a function of group halo mass. All groups with 12.4 ≲ log M {sub halo}/M {sub ☉} ≲ 15.1 (Local Group analogs to rich clusters) display similar Schechter-like CVFs marginally suppressed at low v {sub c} compared to that of the field. Conversely, some agreement with N-body results emerges for samples saturated with late-type galaxies, with isolated late-types displaying a CVF similar in shape to ΛCDM predictions. We conclude that the flattening of the low-v {sub c} slope in groups is due to their depressed late-type fractions—environment affecting the CVF only to the extent that it correlates with this quantity—and that previous cluster analyses may suffer from interloper contamination. These results serve as useful benchmarks for cosmological simulations of galaxy formation.

  3. Explore Seismic Velocity Change Associated with the 2010 Kaohsiung Earthquake by Ambient Noise Tomography

    NASA Astrophysics Data System (ADS)

    Ku, Chin-Shang; Wu, Yih-Min; Huang, Bor-Shouh; Huang, Win-Gee; Liu, Chun-Chi

    2016-04-01

    A ML 6.4 earthquake occurred on 4 March 2010 in Kaohsiung, the southern part of Taiwan, this shallow earthquake is the largest one of that area in the past few years. Some damages occurred on buildings and bridges after the earthquake, obvious surface deformation up to few cm was observed and the transportation including road and train traffic was also affected near the source area. Some studies about monitoring the velocity change induced by the big earthquake were carried out recently, most of studies used cross-correlation of the ambient noise-based method and indicated velocity drop was observed immediately after the big earthquake. However, this method is not able to constrain the depth of velocity change, and need to assume a homogeneous seismic velocity change during the earthquake. In this study, we selected 25 broadband seismic stations in the southern Taiwan and time period is from 2009/03 to 2011/03. Then we explored the velocity change associated with the 2010 Kaohsiung earthquake by applying ambient noise tomography (ANT) method. ANT is a way of using interferometry to image subsurface seismic velocity variations by using surface wave dispersions extracted from the ambient noise cross-correlation of seismic station-pairs, then the 2-D group velocity map with different periods could be extracted. Compare to ambient noise-based cross-correlation analysis, we estimated sensitivity kernel of dispersion curves and converted 2-D group velocity map from "with the period" to "with the depth" to have more constraints on the depth of velocity change. By subtracting shear velocity between "before" and "after" the earthquake, we could explore velocity change associated with the earthquake. Our result shows velocity reduction about 5-10% around the focal depth after the 2010 Kaohsiung earthquake and the post-seismic velocity recovery was observed with time period increasing, which may suggest a healing process of damaged rocks.

  4. Measurement of the velocity of a quantum object: a role of group velocity

    NASA Astrophysics Data System (ADS)

    Rostovtsev, Yuri V.

    2013-03-01

    We consider a free motion of a quantum particle. Introducing an explicit measurement procedure for velocity, we demonstrate that the measured velocity is related to the group and phase velocities of the corresponding matter waves. We show that for long distances the measured velocity coincides with the matter wave group velocity.

  5. Rogue events in the group velocity horizon.

    PubMed

    Demircan, Ayhan; Amiranashvili, Shalva; Brée, Carsten; Mahnke, Christoph; Mitschke, Fedor; Steinmeyer, Günter

    2012-01-01

    The concept of rogue waves arises from a mysterious and potentially calamitous phenomenon of oceanic surfaces. There is mounting evidence that they are actually commonplace in a variety of different physical settings. A set of defining criteria has been advanced; this set is of great generality and therefore applicable to a wide class of systems. The question arises naturally whether there are generic mechanisms responsible for extreme events in different systems. Here we argue that under suitable circumstances nonlinear interaction between weak and strong waves results in intermittent giant waves with all the signatures of rogue waves. To obtain these circumstances only a few basic conditions must be met. Then reflection of waves at the so-called group-velocity horizon occurs. The connection between rogue waves and event horizons, seemingly unrelated physical phenomena, is identified as a feature common in many different physical systems.

  6. Rogue events in the group velocity horizon

    PubMed Central

    Demircan, Ayhan; Amiranashvili, Shalva; Brée, Carsten; Mahnke, Christoph; Mitschke, Fedor; Steinmeyer, Günter

    2012-01-01

    The concept of rogue waves arises from a mysterious and potentially calamitous phenomenon of oceanic surfaces. There is mounting evidence that they are actually commonplace in a variety of different physical settings. A set of defining criteria has been advanced; this set is of great generality and therefore applicable to a wide class of systems. The question arises naturally whether there are generic mechanisms responsible for extreme events in different systems. Here we argue that under suitable circumstances nonlinear interaction between weak and strong waves results in intermittent giant waves with all the signatures of rogue waves. To obtain these circumstances only a few basic conditions must be met. Then reflection of waves at the so-called group-velocity horizon occurs. The connection between rogue waves and event horizons, seemingly unrelated physical phenomena, is identified as a feature common in many different physical systems. PMID:23152941

  7. Wavelet-based group and phase velocity measurements: Method

    NASA Astrophysics Data System (ADS)

    Yang, H. Y.; Wang, W. W.; Hung, S. H.

    2016-12-01

    Measurements of group and phase velocities of surface waves are often carried out by applying a series of narrow bandpass or stationary Gaussian filters localized at specific frequencies to wave packets and estimating the corresponding arrival times at the peak envelopes and phases of the Fourier spectra. However, it's known that seismic waves are inherently nonstationary and not well represented by a sum of sinusoids. Alternatively, a continuous wavelet transform (CWT) which decomposes a time series into a family of wavelets, translated and scaled copies of a generally fast oscillating and decaying function known as the mother wavelet, is capable of retaining localization in both the time and frequency domain and well-suited for the time-frequency analysis of nonstationary signals. Here we develop a wavelet-based method to measure frequency-dependent group and phase velocities, an essential dataset used in crust and mantle tomography. For a given time series, we employ the complex morlet wavelet to obtain the scalogram of amplitude modulus |Wg| and phase φ on the time-frequency plane. The instantaneous frequency (IF) is then calculated by taking the derivative of phase with respect to time, i.e., (1/2π)dφ(f, t)/dt. Time windows comprising strong energy arrivals to be measured can be identified by those IFs close to the frequencies with the maximum modulus and varying smoothly and monotonically with time. The respective IFs in each selected time window are further interpolated to yield a smooth branch of ridge points or representative IFs at which the arrival time, tridge(f), and phase, φridge(f), after unwrapping and correcting cycle skipping based on a priori knowledge of the possible velocity range, are determined for group and phase velocity estimation. We will demonstrate our measurement method using both ambient noise cross correlation functions and multi-mode surface waves from earthquakes. The obtained dispersion curves will be compared with those by a

  8. Sleipner CCS site: velocity and attenuation model from seismic tomography

    NASA Astrophysics Data System (ADS)

    Rossi, G.; Chadwick, R. A.; Williams, G. A.

    2012-04-01

    The results of the travel-time and frequency shift tomographic inversion of the seismic data from one of the high-resolution lines acquired in 2006 on the Sleipner CO2 geological storage site are here presented. The work has been performed within the European project CO2ReMoVe, to produce an accurate model in-depth, of both seismic velocities and attenuation, to constrain better the quantification studies of the project's partners. Tomographic techniques have the advantage of not assuming horizontal layering or uniform lateral velocities, and of enabling an easy comparison of models, even if resulting from seismic data acquired with different geometries, unavoidable in a time-lapse data set. Through an iterative process, the differences in travel-times between observed direct, reflected or refracted arrivals and the same, calculated on a discrete model, with a ray-tracing based on the Fermat's principle, are minimized. Other minimization procedures provide the reflector/refractor geometries in -depth. Analogously, in attenuation tomography, the minimization process takes into account the observed and calculated spectral-centroid frequency-shift, due to the loss of the highest frequency of the seismic wave, while crossing an attenuating medium. The result is a seismic quality factor (Q) model in-depth, and hence of the attenuation that is known to be more sensitive to subtle changes in physical properties than seismic velocity. The model is across the center of the CO2 plume, on the in-line 1838, and is constituted by nine layers, four resulting by a preliminary analysis of the pre-injection 1994 data set, i.e. seabed, a strong reflection in the overburden and the top and bottom of the Utsira Sand, plus additional five horizons, four of which within Utsira Sands, and one just above the top of it. The layers within the reservoir are very close to each other and in some cases they merge together laterally. The accumulation of CO2 in the uppermost layer of the

  9. 3-D shear velocity model of the Eastern and Southern Alps from ambient noise tomography

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  11. Measurement of the velocity of a quantum object: A role of phase and group velocities

    NASA Astrophysics Data System (ADS)

    Lapinski, Mikaila; Rostovtsev, Yuri V.

    2017-08-01

    We consider the motion of a quantum particle in a free space. Introducing an explicit measurement procedure for velocity, we demonstrate that the measured velocity is related to the group and phase velocities of the corresponding matter waves. We show that for long distances the measured velocity coincides with the matter wave group velocity. We discuss the possibilities to demonstrate these effects for the optical pulses in coherently driven media or for radiation propagating in waveguides.

  12. Monitoring High Velocity Salt Tracer via 4D Electrical Resistivity Tomography - Possibility for Salt Tracer Tomography

    NASA Astrophysics Data System (ADS)

    Doro, K. O.; Cirpka, O. A.; Patzelt, A.; Leven, C.

    2014-12-01

    Hydrogeological testing in a tomographic sequence as shown by the use of hydraulic tomography, allows an improvement of the spatial resolution of subsurface parameters. In this regard, recent studies show increasing interest in tracer tomography which involves sequential and spatially separated tracer injections and the measurement of their corresponding tracer breakthrough at different locations and depths. Such concentration measurements however require large experimental efforts and can be simplified by geophysical tracer monitoring techniques such as electrical resistivity. In this study, we present the use of 4-D, cross-hole electrical resistivity tomography (ERT) for monitoring salt tracer experiments in high velocity flow fields. For our study, we utilized a set up that enables the conduction of salt tracer experiments with complete recovery within 84 hours over a transport distance of 16 m. This allows the repetition of the experiments with different injection depths for a tomographic salt tracer testing. For ERT monitoring, we designed modular borehole electrodes for repeated usage in a flexible manner. We also assess the use of a high speed resistivity data acquisition mode for field scale tracer monitoring ensuring high spatial and temporal resolution without sacrificing data accuracy. We applied our approach at the Lauswiesen test site, Tübingen, Germany. In our 10 m × 10 m tracer monitoring domain with 16 borehole electrodes, we acquired 4650 data points in less than 18 minutes for each monitoring cycle. Inversion results show that the tracer could be successfully imaged using this approach. The results show that repeated salt tracer tests can be efficiently monitored at a high resolution with ERT which gives the possibility for salt tracer tomography at field scale. Our results also provide a data base for extending current hydrogeophysical inversion approaches to field scale data.

  13. DIFFERENTIAL GROUP-VELOCITY DETECTION OF FLUID PATHS

    SciTech Connect

    Leland Timothy Long

    2005-12-20

    For nearly 50 years, surface waves that propagate through near-surface soils have been utilized in engineering for the determination of the small-strain dynamic properties of soils. These techniques, although useful, have not been sufficiently precise to use in detecting the subtle changes in soil properties that accompany short-term changes in fluid content. The differential techniques developed in this research now make it possible to monitor small changes (less than 3 cm) in the water level of shallow soil aquifers. Using inversion techniques and tomography, differential seismic techniques could track the water level distribution in aquifers with water being pumped in or out. Differential surface wave analysis could lead to new ways to monitor reservoir levels and verify hydrologic models. Field data obtained during this investigation have measured changes in surface-wave phase and group velocity before and after major rain events, and have detected subtle changes associated with pumping water into an aquifer and pumping water out of an aquifer. This research has established analysis techniques for observing these changes. These techniques combine time domain measurements to isolate surface wave arrivals with frequency domain techniques to determine the effects as a function of frequency. Understanding the differences in response as a function of wave frequency facilitates the inversion of this data for soil velocity structure. These techniques have also quantified many aspects of data acquisition and analysis that are important for significant results. These include tight control on the character of the source and proper placement of the geophones. One important application is the possibility that surface waves could be used to monitor and/or track fluid movement during clean-up operations, verifying that the fluid reached all affected areas. Extending this to a larger scale could facilitate monitoring of water resources in basins without having to drill many

  14. Crustal and uppermost mantle velocity structure beneath northwestern China from seismic ambient noise tomography

    NASA Astrophysics Data System (ADS)

    Li, Hongyi; Li, S.; Song, X. D.; Gong, M.; Li, X.; Jia, J.

    2012-01-01

    In this paper, we conduct ambient noise seismic tomography of northwestern China and adjacent regions. The data include 9 months (2009 January to 2009 September) three-component continuous data recorded at 146 seismic stations of newly upgraded China Provincial Digital Seismic Networks and regional Kyrgyzstan and Kazakhstan networks. Empirical Rayleigh and Love wave Green's functions are obtained from interstation cross-correlations. Group velocity dispersion curves for both Rayleigh and Love waves between 7 and 50 s periods were measured for each interstation path by applying the multiple-filter analysis method with phase-matched processing. The group velocity maps show clear lateral variations which correlate well with major geological structures and tectonic units in the study region. Shear wave velocity structures are inverted from Rayleigh wave and love wave dispersion maps. The results show that the Tibetan Plateau has a very thick crust with a low-velocity zone in its mid-lower crust. Along the northern margin of the plateau where a steep topographic gradient is present, the low-velocity zone does not extend to the Tarim basin which may indicate that crustal materials beneath the Tarim basin are colder and stronger than beneath the plateau, therefore inhibit the extension of mid-lower crustal flow and deformation of the Tibetan Plateau, resulting in very sharp topography contrasts. In the northeastern margin with a gentle topographic gradient toward the Ordos platform, the low-velocity zone diminishes around the eastern KunLun fault. Meanwhile, our results reveal obvious lateral velocity changes in the crust beneath the Tarim basin. In the upper crust, the Manjaer depression in the eastern Tarim basin is featured with very low velocities and the Bachu uplift in the western Tarim basin with high velocities; in the mid-lower crust, the northern Tarim basin in general displays lower velocities than the southern part along latitude ˜40° N with an east

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

  16. ML shear wave velocity tomography for the Iranian Plateau

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  17. Teleseismic P-wave Velocity Tomography Beneath The Arabian Peninsula

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

    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 short-period) spread throughout most of western Saudi Arabia. P wave travel time residuals were obtained for 131 earthquakes in the distance range from 30\\deg to 90\\deg, resulting in 1716 rays paths. We find a pronounced low velocity anomaly beneath the southeastern Arabian Shield and southern Red Sea that likely represents a northward continuation of the Afar hotspot. We also image smaller low velocity anomalies beneath the Dead Sea Transform, the Gulf of Aqaba, and the northeastern corner of the Arabian Shield. The origin of these low velocity anomalies is uncertain.

  18. Rayleigh Wave Phase Velocities in Alaska from Ambient Noise Tomography

    NASA Astrophysics Data System (ADS)

    Pepin, K. S.; Li, A.; Yao, Y.

    2016-12-01

    We have analyzed ambient noise data recorded at 136 broadband stations from the USArray Transportable Array and other permanent seismic networks in Alaska and westernmost Canada. Daily cross-correlations are obtained using vertical component seismograms and are stacked to form a single trace for each station pair. Rayleigh wave signals are extracted from the stacked traces and are used to calculate phase velocities in the Alaska region. Preliminary phase velocity maps show similar trends to those from previous studies, but also yield new anomalies given the wider geographical range provided by the Transportable Array. At short periods (6-12s), a high velocity anomaly is observed directly northeast of the Fairweather-Queen Charlotte fault, and a high velocity trend appears in the eastern Yukon terrane between the Denali and Tintina fault, probably reflecting mafic igneous crustal rocks. Significantly slow anomalies are present at the Prince William Sound, Cook Inlet, and the basins in southwestern and central Alaska, indicating sediment effects. The slow anomalies gradually shift to southeastern and south-central Alaska with increasing period (up to 40s), corresponding to the Wrangell volcano belt and the volcano arc near Cook Inlet. A broad high-velocity zone is also observed in central Alaska to the north of the Denali fault at long periods (30-40s). The Yakutat terrane is characterized as a high-velocity anomaly from period 14s to 25s but not imaged at longer periods due to poor resolution.

  19. Passive system with tunable group velocity for propagating electrical pulses from sub- to superluminal velocities.

    PubMed

    Haché, Alain; Essiambre, Sophie

    2004-05-01

    We report an observation of tunable group velocity from sub-luminal to superluminal in a completely passive system. Electric pulses are sent along a spatially periodic conducting medium containing a punctual nonlinearity, and the resulting amplitude-dependent phase shift allows us to control dispersion and the propagation velocity at the stop band frequency.

  20. Rayleigh-wave group velocity distribution in the Antarctic region

    NASA Astrophysics Data System (ADS)

    Kobayashi, Reiji; Zhao, Dapeng

    2004-03-01

    We determined 2D group velocity distribution of Rayleigh waves at periods of 20-150 s in the Antarctic region using a tomographic inversion technique. The data are recorded by both permanent networks and temporary arrays. In East Antarctica the velocities are high at periods of 90-150 s, suggesting that the root of East Antarctica is very deep. The velocities in West Antarctica are low at all periods, which may be related to the volcanic activity and the West Antarctic Rift System. Low velocity anomalies appear at periods of 40-140 s along the Southeastern Indian Ridge and the western part of the Pacific Antarctic Ridge. The velocities are only slightly low around the Atlantic Indian Ridge, Southwestern Indian Ridge, and the eastern part of the Pacific Antarctic Ridge, where the spreading rates are small. Around two hotspots, the Mount Erebus and Balleny Islands, the velocity is low at periods of 50-150 s.

  1. Negative group velocity of sound in a bubbly liquid

    NASA Astrophysics Data System (ADS)

    Leary, Del; de Bruyn, John R.; Page, John H.

    2001-03-01

    A wave pulse can propagate with a negative group velocity when it travels through a medium with anomalous dispersion, that is, when the derivative of the dispersion curve is negative. Recent reports of negative group velocities for light pulses have received considerable attention [1,2]. Here we report on the experimental observation of negative group velocities for pulses of ultrasound propagating ballistically through water containing gas bubbles. For frequencies near the resonant frequency of the bubbles, the absorption increases strongly and the group velocity becomes negative. Our experimental results are in good agreement with a theoretical model for sound propagation in bubbly liquids. 1. L. J. Wang, A. Kuzmich, and A. Dogariu, Nature (U.K.) 406, 277 (2000). 2. D. Mugnai, A. Ranfagni, and R. Ruggeri, Phys. Rev. Lett. 84, 4830 (2000).

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  3. Inverse characterization of plates using zero group velocity Lamb modes.

    PubMed

    Grünsteidl, Clemens; Murray, Todd W; Berer, Thomas; Veres, István A

    2016-02-01

    In the presented work, the characterization of plates using zero group velocity Lamb modes is discussed. First, analytical expressions are shown for the determination of the k-ω location of the zero group velocity Lamb modes as a function of the Poisson's ratio. The analytical expressions are solved numerically and an inverse problem is formulated to determine the unknown wave velocities in plates of known thickness. The analysis is applied to determine the elastic properties of tungsten and aluminum plates based on the experimentally measured frequency spectra. Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  6. 3D Shear Velocity Structure of Crust and Upper Mantle in China From Ambient Noise Tomography

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

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

  7. Group velocity and causality in standard relativistic resistive magnetohydrodynamics

    SciTech Connect

    Koide, Shinji; Morino, Ryogo

    2011-10-15

    Group velocity of electromagnetic waves in plasmas derived by standard relativistic resistive magnetohydrodynamics equations is superluminal. If we assume that the group velocity represents the propagation velocity of a signal, we have to worry about the causality problem. That is, some acausal phenomena may be induced, such as information transportation to the absolute past and a spontaneous decrease in the entropy. Here, we tried to find the acausal phenomena using standard relativistic resistive magnetohydrodynamics numerical simulations in the suggested situation of the acausal phenomena. The calculation results showed that even in such situations no acausal effect happens. The numerical result with respect to the velocity limit of the information transportation is consistent with a linear theory of wave train propagation. Our results assure that we can use these equations without the problems of acausal phenomena.

  8. Solving the Christoffel equation: Phase and group velocities

    NASA Astrophysics Data System (ADS)

    Jaeken, Jan W.; Cottenier, Stefaan

    2016-10-01

    We provide christoffel, a Python tool for calculating direction-dependent phase velocities, polarization vectors, group velocities, power flow angles and enhancement factors based on the stiffness tensor of a solid. It is built in a modular way to allow for efficient and flexible calculations, and the freedom to select and combine results as desired. All derivatives are calculated analytically, which circumvents possible numerical sampling problems. GNUPlot scripts are provided for convenient visualization.

  9. Imaging water velocity and volume fraction distributions in water continuous multiphase flows using inductive flow tomography and electrical resistance tomography

    NASA Astrophysics Data System (ADS)

    Meng, Yiqing; Lucas, Gary P.

    2017-05-01

    This paper presents the design and implementation of an inductive flow tomography (IFT) system, employing a multi-electrode electromagnetic flow meter (EMFM) and novel reconstruction techniques, for measuring the local water velocity distribution in water continuous single and multiphase flows. A series of experiments were carried out in vertical-upward and upward-inclined single phase water flows and ‘water continuous’ gas-water and oil-gas-water flows in which the velocity profiles ranged from axisymmetric (single phase and vertical-upward multiphase flows) to highly asymmetric (upward-inclined multiphase flows). Using potential difference measurements obtained from the electrode array of the EMFM, local axial velocity distributions of the continuous water phase were reconstructed using two different IFT reconstruction algorithms denoted RT#1, which assumes that the overall water velocity profile comprises the sum of a series of polynomial velocity components, and RT#2, which is similar to RT#1 but which assumes that the zero’th order velocity component may be replaced by an axisymmetric ‘power law’ velocity distribution. During each experiment, measurement of the local water volume fraction distribution was also made using the well-established technique of electrical resistance tomography (ERT). By integrating the product of the local axial water velocity and the local water volume fraction in the cross section an estimate of the water volumetric flow rate was made which was compared with a reference measurement of the water volumetric flow rate. In vertical upward flows RT#2 was found to give rise to water velocity profiles which are consistent with the previous literature although the profiles obtained in the multiphase flows had relatively higher central velocity peaks than was observed for the single phase profiles. This observation was almost certainly a result of the transfer of axial momentum from the less dense dispersed phases to the water

  10. Preliminary Seismic Velocity Structure Results from Ambient Noise and Teleseismic Tomography: Laguna del Maule Volcanic Field, Chile

    NASA Astrophysics Data System (ADS)

    Wespestad, C.; Thurber, C. H.; Zeng, X.; Bennington, N. L.; Cardona, C.; Singer, B. S.

    2016-12-01

    Laguna del Maule Volcanic Field is a large, restless, rhyolitic system in the Southern Andes that is being heavily studied through several methods, including seismology, by a collaborative team of research institutions. A temporary array of 52 seismometers from OVDAS (the Southern Andean Volcano Observatory), PASSCAL (Portable Array Seismic Studies of the Continental Lithosphere), and the University of Wisconsin-Madison was used to collect the 1.3 years worth of data for this preliminary study. Ambient noise tomography uses surface wave dispersion data obtained from noise correlation functions (NCFs) between pairs of seismic stations, with one of each pair acting as a virtual source, in order to image the velocity structure in 3-D. NCFs were computed for hour-long time windows, and the final NCFs were obtained with phase-weighted stacking. The Frequency-Time Analysis technique was then utilized to measure group velocity between station pairs. NCFs were also analyzed to detect temporal changes in seismic velocity related to magmatic activity at the volcano. With the surface wave data from ambient noise, our small array aperture limits our modeling to the upper crust, so we employed teleseismic tomography to study deeper structures. For picking teleseismic arrivals, we tested two different correlation and stacking programs, which utilize adaptive stacking and multi-channel cross-correlation, to get relative arrival time data for a set of high quality events. Selected earthquakes were larger than magnitude 5 and between 30 and 95 degrees away from the center of the array. Stations that consistently show late arrivals may have a low velocity body beneath them, more clearly visualized via a 3-D tomographic model. Initial results from the two tomography methods indicate the presence of low-velocity zones at several depths. Better resolved velocity models will be developed as more data are acquired.

  11. Velocity Fields in Stellar Atmospheres Probed by Tomography

    NASA Astrophysics Data System (ADS)

    Jorissen, Alain; Van Eck, Sophie; Kravchenko, Kateryna

    A tomographic method to probe velocity fields within stellar atmospheres is described. It relies on the design of spectral masks collecting lines forming at given, pre-specified ranges of optical depths. Different masks thus probe different line-formation depths in the stellar atmosphere. The masks are cross-correlated with the observed spectrum to yield cross-correlation functions (CCFs). The cross-correlation has two advantages: (i) to overcome line crowding, and (ii) to reveal minute line asymmetries by adding together many lines. In pulsating stars (long-period variables or Cepheids), the CCFs are double-peaked around maximum light, when the shock front associated with the stellar pulsation is located in the layer probed by the considered mask. Double-peaked CCFs originate in stellar layers where upward- and downward-moving matter co-exist, on each side of the shock front. The application of the tomographic method to long-period variables and supergiants is illustrated.

  12. Regionalized Rayleigh wave group velocities in southeastern Brazil

    NASA Astrophysics Data System (ADS)

    Souza, J. L.; Dos Santos, N. P.; Pacheco, R. P.

    2003-04-01

    Damped least-square inversion was used to regionalize a large quantity of source-station Rayleigh wave dispersion curves obtained from digital seismograms, which were recorded at twenty-three IRIS seismological stations located either in or around South America continent. The region including all source-station Rayleigh wave paths (defined by geographical coordinates : -125,45 and 25,-75) was divided into cells of 2 by 2 degrees, and a group velocity for each cell (visited by at least one Rayleigh wave path) of the grid was computed. The estimated group velocities were then related to the Preliminary Reference Earth Model (PREM) and their percentual deviation from PREM were used to construct velocity maps at different periods (from 10 to 102 sec). The group velocity anomalies maps show a strong correlation with the superficial limits of the main geologic provinces in the region. Both Tocantis and Sao Francisco cratonic nuclei were clearly identified and they have deep roots. Several group velocity anomalies in the maps also have a direct correlation with recent studies about geoid anomalies in the southeastern Brazil and adjacent regions. The high density of Rayleigh wave paths across southeastern Brazil has provided high resolutions throughout the region under investigation. In general, the spatial resolution in the grid is of two degrees or 200km.

  13. Photon number dependent group velocity in vacuum induced transparency

    NASA Astrophysics Data System (ADS)

    Lauk, Nikolai; Fleischhauer, Michael

    2015-05-01

    Vacuum induced transparency (VIT) is an effect which occurs in an ensemble of three level atoms in a Λ configuration that interact with two quantized fields. Coupling of one transition to a cavity mode induces transparency for the second field on the otherwise opaque transition similar to the well known EIT effect. In the strong coupling regime even an empty cavity leads to transparency, in contrast to EIT where the presence of a strong control field is required. This transparency is accompanied by a reduction of the group velocity for the propagating field. However, unlike in EIT the group velocity in VIT depends on the number of incoming photons, i.e. different photon number components propagate with different velocities. Here we investigate the possibility of using this effect to spatially separate different photon number components of an initially coherent pulse. We present the results of our calculations and discuss a possible experimental realization.

  14. SPIDER - IX. Classifying galaxy groups according to their velocity distribution

    NASA Astrophysics Data System (ADS)

    Ribeiro, A. L. B.; de Carvalho, R. R.; Trevisan, M.; Capelato, H. V.; La Barbera, F.; Lopes, P. A. A.; Schilling, A. C.

    2013-09-01

    We introduce a new method to study the velocity distribution of galaxy systems, the Hellinger Distance (HD), designed for detecting departures from a Gaussian velocity distribution. Testing different approaches to measure normality of a distribution, we conclude that HD is the least vulnerable method to type I and II statistical errors. We define a relaxed galactic system as the one with unimodal velocity distribution and a normality deviation below a critical value (HD < 0.05). In this work, we study the Gaussian nature of the velocity distribution of the Berlind group sample, and of the FoF groups from the Millennium simulation. For the Berlind group sample (z < 0.1), 67 per cent of the systems are classified as relaxed, while for the Millennium sample we find 63 per cent (z = 0). We verify that in multi-modal groups the average mass of modes in high-multiplicity (N ≥ 20) systems are significantly larger than in low-multiplicity ones (N < 20), suggesting that groups experience a mass growth at an increasing virialization rate towards z = 0, with larger systems accreting more massive subunits. We also investigate the connection between galaxy properties ([Fe/H], Age, eClass, g - r, Rpetro and <μpetro>) and the Gaussianity of the velocity distribution of the groups. Bright galaxies (Mr ≤ -20.7) residing in the inner and outer regions of groups do not show significant differences in the listed quantities regardless if the group has a Gaussian (G) or a Non-Gaussian (NG) velocity distribution. However, the situation is significantly different when we examine the faint galaxies (-20.7 < Mr ≤ -17.9). In G groups, there is a remarkable difference between the galaxy properties of the inner and outer galaxy populations, testifying how the environment is affecting the galaxies. Instead, in NG groups there is no segregation between the properties of galaxies in the inner and outer regions, showing that the properties of these galaxies still reflect the physical

  15. High-definition velocity-space tomography of fast-ion dynamics

    NASA Astrophysics Data System (ADS)

    Salewski, M.; Geiger, B.; Jacobsen, A. S.; Hansen, P. C.; Heidbrink, W. W.; Korsholm, S. B.; Leipold, F.; Madsen, J.; Moseev, D.; Nielsen, S. K.; Nocente, M.; Odstrčil, T.; Rasmussen, J.; Stagner, L.; Stejner, M.; Weiland, M.; the ASDEX Upgrade Team

    2016-10-01

    Velocity-space tomography of the fast-ion distribution function in a fusion plasma is usually a photon-starved tomography method due to limited optical access and signal-to-noise ratio of fast-ion D α (FIDA) spectroscopy as well as the strive for high-resolution images. In high-definition tomography, prior information makes up for this lack of data. We restrict the target velocity space through the measured absence of FIDA light, impose phase-space densities to be non-negative, and encode the known geometry of neutral beam injection (NBI) sources. We further use a numerical simulation as prior information to reconstruct where in velocity space the measurements and the simulation disagree. This alternative approach is demonstrated for four-view as well as for two-view FIDA measurements. The high-definition tomography tools allow us to study fast ions in sawtoothing plasmas and the formation of NBI peaks at full, half and one-third energy by time-resolved tomographic movies.

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

    NASA Astrophysics Data System (ADS)

    Fletcher, Jon B.; Erdem, Jemile

    2017-06-01

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

  17. Finite-frequency traveltime tomography of San Francisco Bay region crustal velocity structure

    USGS Publications Warehouse

    Pollitz, F.F.

    2007-01-01

    Seismic velocity structure of the San Francisco Bay region crust is derived using measurements of finite-frequency traveltimes. A total of 57 801 relative traveltimes are measured by cross-correlation over the frequency range 0.5-1.5 Hz. From these are derived 4862 'summary' traveltimes, which are used to derive 3-D P-wave velocity structure over a 341 ?? 140 km2 area from the surface to 25 km depth. The seismic tomography is based on sensitivity kernels calculated on a spherically symmetric reference model. Robust elements of the derived P-wave velocity structure are: a pronounced velocity contrast across the San Andreas fault in the south Bay region (west side faster); a moderate velocity contrast across the Hayward fault (west side faster); moderately low velocity crust around the Quien Sabe volcanic field and the Sacramento River delta; very low velocity crust around Lake Berryessa. These features are generally explicable with surface rock types being extrapolated to depth ???10 km in the upper crust. Generally high mid-lower crust velocity and high inferred Poisson's ratio suggest a mafic lower crust. ?? Journal compilation ?? 2007 RAS.

  18. High resolution P-wave velocity structure beneath Northeastern Tibet from multiscale seismic tomography

    NASA Astrophysics Data System (ADS)

    Guo, B.; Gao, X.; Chen, J.; Liu, Q.; Li, S.

    2016-12-01

    The continuing collision of the northward advancing Indian continent with the Eurasia results in the high elevations and thickened Tibetan Plateau. Numerous geologic and geophysical studies engaged in the mechanics of the Tibetan Plateau deformation and uplift. Many seismic experiments were deployed in south and central Tibet, such as INDEPTH and Hi-climb, but very few in northeastern Tibet. Between 2013 and 2015, The China Seismic Array-experiment operated 670 broadband seismic stations with an average station spacing of 35km. This seismic array located in northeastern Tibet and covered the Qilian Mountains, Qaidam Basin, and part of Songpan-Ganzi, Gobi-Alashan, Yangzi, and Ordos. A new multiscale seismic traveltime tomography technique with sparsity constrains were used to map the upper mantle P-wave velocity structure beneath northeastern Tibet. The seismic tomography algorithm employs sparsity constrains on the wavelet representation velocity model via the L1-norm regularization. This algorithm can efficiently deal with the uneven-sampled volume, and give multiscale images of the model. Our preliminary results can be summarized as follows: 1) in the upper mantle down to 200km, significate low-velocity anomalies exist beneath the northeastern Tibet, and slight high-velocity anomalies beneath the Qaidam basin; 2) under Gobi-Alashan, Yangzi, and Ordos, high-velocity anomalies appear to extend to a depth of 250km, this high-velocity may correspond to the lithosphere; 3) there exist relative high-velocity anomalies at depth of 250km-350km underneath north Tibet, which suggests lithospheric delamination; 4) the strong velocity contrast between north Tibet and Yangzi, Gabi-Alashan is visible down to 200km, which implies the north Tibet boundary.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  20. On electromagnetic waves with a negative group velocity

    SciTech Connect

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

    2010-12-15

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

  1. Net electron energy gain induced by superluminal phase velocity and subluminal group velocity of a laser in a plasma channel

    NASA Astrophysics Data System (ADS)

    Cheng, Li-Hong; Yao, Zheng-Wei; Zhang, Xiao-Bo; Xue, Ju-Kui

    2017-08-01

    We examine electron dynamics induced by laser-plasma interaction in a two-dimensional plasma channel, taking into action the laser phase velocity as well as the group velocity. The coupled effects of phase velocity, group velocity, and plasma channel on electron dynamics are discussed in detail. The superluminal phase velocity and the corresponding subluminal group velocity of the laser result in rich and complex electron dynamics, which are depicted in the plane of the phase velocity and plasma charge density. For weak superluminosity of the phase velocity, the effects of the phase velocity and the group velocity can be neglected. For moderate superluminosity of the phase velocity, a cross-over region can exist, where the highly energetic electron could be found and the net energy gain is several times greater than the energy gain in vacuum. For strong superluminosity of the phase velocity, the dephasing rate increases and thus limits the electron energy gain from the laser. However, the asymmetric laser pulse, attributed by the superluminal phase velocity and the subluminal group velocity, results in the electron getting adjustable net energy gain from the laser. The electron oscillations are no longer limited by the charge density threshold and the electron can always get net energy from the laser. These electron dynamics can also be modified by adjusting the polarization of the laser.

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

    NASA Astrophysics Data System (ADS)

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

    2005-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Jin, Ge; Gaherty, James B.

    2015-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  6. Using group velocities of seismic phases for regional event discrimination

    NASA Astrophysics Data System (ADS)

    Pinsky, Vladimir; Shapira, Avi; Gitterman, Yefim

    1999-06-01

    We examined over the Israel Seismic Network (ISN) the seismogram envelopes vs. group velocity V= R/ T, where R is the epicenter distance and T the travel time, and found out a persistent difference between quarry blasts and earthquakes. The data include 53 seismic events occurring in northern Israel with magnitudes of ML=1.0-2.6 and at distances of 15-310 km. Within the 1-4 km/s range we measured the velocity Vms at which the envelope reaches its maximum for each ISN station. A simple linear discrimination function c= b+0.33 a, based on an empirical relationship between the Vms and R: Vms= a+ b ln( R) provides effective separation between the regional earthquakes and explosions. These results are attributed to different excitation of regional surface waves from these two types of seismic events.

  7. Zernike ultrasonic tomography for fluid velocity imaging based on pipeline intrusive time-of-flight measurements.

    PubMed

    Besic, Nikola; Vasile, Gabriel; Anghel, Andrei; Petrut, Teodor-Ion; Ioana, Cornel; Stankovic, Srdjan; Girard, Alexandre; d'Urso, Guy

    2014-11-01

    In this paper, we propose a novel ultrasonic tomography method for pipeline flow field imaging, based on the Zernike polynomial series. Having intrusive multipath time-offlight ultrasonic measurements (difference in flight time and speed of ultrasound) at the input, we provide at the output tomograms of the fluid velocity components (axial, radial, and orthoradial velocity). Principally, by representing these velocities as Zernike polynomial series, we reduce the tomography problem to an ill-posed problem of finding the coefficients of the series, relying on the acquired ultrasonic measurements. Thereupon, this problem is treated by applying and comparing Tikhonov regularization and quadratically constrained ℓ1 minimization. To enhance the comparative analysis, we additionally introduce sparsity, by employing SVD-based filtering in selecting Zernike polynomials which are to be included in the series. The first approach-Tikhonov regularization without filtering, is used because it is the most suitable method. The performances are quantitatively tested by considering a residual norm and by estimating the flow using the axial velocity tomogram. Finally, the obtained results show the relative residual norm and the error in flow estimation, respectively, ~0.3% and ~1.6% for the less turbulent flow and ~0.5% and ~1.8% for the turbulent flow. Additionally, a qualitative validation is performed by proximate matching of the derived tomograms with a flow physical model.

  8. Evidence of Velocity Variations During the Recent Mt. Etna Eruptive Activity Detected by Temporal Seismic Tomography

    NASA Astrophysics Data System (ADS)

    Barberi, G.; Zhang, H.; Cocina, O.; Patanè, D.; Thurber, C. H.

    2005-12-01

    After nearly 10 years without any major flank eruption, volcanic activity resumed at Mt. Etna on July 17, 2001, giving rise to the first of the two most striking flank eruptions on this volcano in recent times. Fifteen months after the end (August 09, 2001) of this eruptive episode, a new eruption started abruptly on October 26, 2002 with only a few hours of premonitory seismicity accompanying the opening of eruptive fissures along a bi-radial direction. Since the end of this last eruption (January 2003), a period of weak volcanic activity occurred. On September 7, 2004 a new eruption occurred along a WNW-ESE to NW-SE oriented fracture system at the base of the South East summit crater. Compared to the previous two flank eruptions, the 2004 eruption did not have any measurable short-period seismicity and deformation variations. Since 2001, Mt. Etna is well covered by the INGV-CT permanent network and some temporary networks. This provides a unique opportunity to investigate seismic velocity variations before, during and after the three most recent eruptions. Characterizing spatial and temporal variations in seismic velocity in detail will yield a better understanding of the complex plumbing system beneath Mt. Etna and the triggering mechanisms for each eruption. The conventional way to detect temporal velocity changes is to separately invert velocity models for each data set and then examine their differences. This may, however, cause some artifacts in the velocity changes due to different data quality and distribution. Here we present a true temporal seismic tomography algorithm by constraining velocity models for different periods through a temporal smoothing operator. This technique considers the fact that the main features of the velocity models for different periods are similar. The temporal seismic tomography algorithm is based on the double-difference tomography code tomoDD that uses both absolute and differential arrival times to simultaneously determine

  9. Optical coherence tomography in group 2A idiopathic juxtafoveolar telangiectasis.

    PubMed

    Gupta, Vishali; Gupta, Amod; Dogra, Mangat R; Agarwal, Anita

    2005-01-01

    To describe the optical coherence tomographic features in patients with group 2A idiopathic juxtafoveolar telangiectasis. Forty eyes of 20 consecutive patients with idiopathic juxtafoveolar telangiectasis seen between August 2002 and January 2004 were included in the study. All of the patients underwent color fundus photography, fluorescein angiography, and optical coherence tomography. The main outcome measure was optical coherence tomography findings. The most consistent finding between stages 2 through 5 of group 2A idiopathic juxtafoveolar telangiectasis seen in 35 (87.5%) eyes on optical coherence tomography was the presence of hyporeflective intraretinal spaces in the absence of retinal thickening. Other findings included the presence of hyperreflectivity in the middle or inner retinal layers, suggesting retinal pigment epithelium proliferation and migration corresponding to the stellate foci of pigmentation in stage 4 and features of choroidal or subretinal neovascular membrane in stage 5. The optical coherence tomography findings in group 2A idiopathic juxtafoveolar telangiectasis were characteristic and may be helpful in making the diagnosis and defining, as far as possible, the anatomical staging.

  10. 3D Velocity Structure in Southern Haiti from Local Earthquake Tomography

    NASA Astrophysics Data System (ADS)

    Douilly, R.; Ellsworth, W. L.; Kissling, E. H.; Freed, A. M.; Deschamps, A.; de Lepinay, B. M.

    2016-12-01

    We investigate 3D local earthquake tomography for high-quality travel time arrivals from aftershocks following the 2010 M7.0 Haiti earthquake on the Léogâne fault. The data were recorded by 35 stations, including 19 ocean bottom seismometers, from which we selected 595 events to simultaneously invert for hypocenter location and 3D Vp and Vs velocity structures in southern Haiti. We performed several resolution tests and concluded that clear features can be recovered to a depth of 15 km. At 5km depth we distinguish a broad low velocity zone in the Vp and Vs structure offshore near Gonave Island, which correlate with layers of marine sediments. Results show a pronounced low velocity zone in the upper 5 km across the city of Léogâne, which is consistent with the sedimentary basin location from geologic map. At 10 km depth, we detect a low velocity anomaly offshore near the Trois Baies fault and a NW-SE directed low velocity zone onshore across Petit-Goâve and Jacmel, which is consistent with a suspected fault from a previous study and that we refer to it in our study as the Petit-Goâve-Jacmel fault (PGJF). These observations suggest that low velocity structures delineate fault structures and the sedimentary basins across the southern peninsula, which is extremely useful for seismic hazard assessment in Haiti.

  11. Superfluid phase transition with activated velocity fluctuations: Renormalization group approach.

    PubMed

    Dančo, Michal; Hnatič, Michal; Komarova, Marina V; Lučivjanský, Tomáš; Nalimov, Mikhail Yu

    2016-01-01

    A quantum field model that incorporates Bose-condensed systems near their phase transition into a superfluid phase and velocity fluctuations is proposed. The stochastic Navier-Stokes equation is used for a generation of the velocity fluctuations. As such this model generalizes model F of critical dynamics. The field-theoretic action is derived using the Martin-Siggia-Rose formalism and path integral approach. The regime of equilibrium fluctuations is analyzed within the perturbative renormalization group method. The double (ε,δ)-expansion scheme is employed, where ε is a deviation from space dimension 4 and δ describes scaling of velocity fluctuations. The renormalization procedure is performed to the leading order. The main corollary gained from the analysis of the thermal equilibrium regime suggests that one-loop calculations of the presented models are not sufficient to make a definite conclusion about the stability of fixed points. We also show that critical exponents are drastically changed as a result of the turbulent background and critical fluctuations are in fact destroyed by the developed turbulence fluctuations. The scaling exponent of effective viscosity is calculated and agrees with expected value 4/3.

  12. Double-difference tomography velocity structure in Northern Oklahoma: Evidence for reduced basement velocity in the Nemaha Uplift

    NASA Astrophysics Data System (ADS)

    Stevens, N. T.; Keranen, K. M.; Lambert, C.

    2016-12-01

    Induced seismicity in northern Oklahoma presents risk for infrastructure, but also an opportunity to gain new insights to earthquake processes [Petersen et al., 2016]. Here we present a double-difference tomographic study using TomoDD [Zhang and Thurber, 2003] in northern Oklahoma utilizing records from a dense broadband network over a 1-year period, constituting a catalog of over 10,000 local seismic events. We image a shallow (depth < 4 km) high-velocity structure consistent with the Nemaha uplift [Gay, 2003a], bounded by shallow, lower-velocity regions on either side, likely sedimentary strata at this depth bounding uplifted basement. Velocities within the uplift are lower than expected in subjacent crystalline basement rock (depth > 4 km). We suggest that this low velocity anomaly stems from enhanced fracturing and/or weathering of the basement in the Nemaha uplift in northern Oklahoma. This velocity anomaly is not observed in basement off the shoulders of the structure, particularly to the southeast of the Nemaha bounding fault. Enhanced fracturing, and related increases to permeability, would ease pressure migration from injection wells linked to increased seismicity in the region, and may explain the relative absence of seismicity coincident with this structure compared to it periphery. References Gay, S. Parker, J. (2003), The Nemaha Trend-A System of Compressional Thrust-Fold, Strike-Slilp Structural Features in Kansas and Oklahoma, Part 1, Shale Shak., 9-49. Petersen, M. D., C. S. Mueller, M. P. Moschetti, S. M. Hoover, A. L. Llenos, W. L. Ellsworth, A. J. Michael, J. L. Rubinstein, A. F. McGarr, and K. S. Rukstales (2016), 2016 One-Year Seismic Hazard Forecast for the Central and Eastern United States from Induced and Natural Earthquakes, Open-File Rep., doi:10.3133/OFR20161035. Zhang, H., and C. H. Thurber (2003), Double-difference tomography: The method and its application to the Hayward Fault, California, Bull. Seismol. Soc. Am., 93(5), 1875-1889, doi

  13. Probing the Detailed Seismic Velocity Structure of Subduction Zones Using Advanced Seismic Tomography Methods

    NASA Astrophysics Data System (ADS)

    Zhang, H.; Thurber, C. H.

    2005-12-01

    Subduction zones are one of the most important components of the Earth's plate tectonic system. Knowing the detailed seismic velocity structure within and around subducting slabs is vital to understand the constitution of the slab, the cause of intermediate depth earthquakes inside the slab, the fluid distribution and recycling, and tremor occurrence [Hacker et al., 2001; Obara, 2002].Thanks to the ability of double-difference tomography [Zhang and Thurber, 2003] to resolve the fine-scale structure near the source region and the favorable seismicity distribution inside many subducting slabs, it is now possible to characterize the fine details of the velocity structure and earthquake locations inside the slab, as shown in the study of the Japan subduction zone [Zhang et al., 2004]. We further develop the double-difference tomography method in two aspects: the first improvement is to use an adaptive inversion mesh rather than a regular inversion grid and the second improvement is to determine a reliable Vp/Vs structure using various strategies rather than directly from Vp and Vs [see our abstract ``Strategies to solve for a better Vp/Vs model using P and S arrival time'' at Session T29]. The adaptive mesh seismic tomography method is based on tetrahedral diagrams and can automatically adjust the inversion mesh according to the ray distribution so that the inversion mesh nodes are denser where there are more rays and vice versa [Zhang and Thurber, 2005]. As a result, the number of inversion mesh nodes is greatly reduced compared to a regular inversion grid with comparable spatial resolution, and the tomographic system is more stable and better conditioned. This improvement is quite valuable for characterizing the fine structure of the subduction zone considering the highly uneven distribution of earthquakes within and around the subducting slab. The second improvement, to determine a reliable Vp/Vs model, lies in jointly inverting Vp, Vs, and Vp/Vs using P, S, and S

  14. Comparative velocity structure of active Hawaiian volcanoes from 3-D onshore-offshore seismic tomography

    USGS Publications Warehouse

    Park, J.; Morgan, J.K.; Zelt, C.A.; Okubo, P.G.; Peters, L.; Benesh, N.

    2007-01-01

    We present a 3-D P-wave velocity model of the combined subaerial and submarine portions of the southeastern part of the Island of Hawaii, based on first-arrival seismic tomography of marine airgun shots recorded by the onland seismic network. Our model shows that high-velocity materials (6.5-7.0??km/s) lie beneath Kilauea's summit, Koae fault zone, and the upper Southwest Rift Zone (SWRZ) and upper and middle East Rift Zone (ERZ), indicative of magma cumulates within the volcanic edifice. A separate high-velocity body of 6.5-6.9??km/s within Kilauea's lower ERZ and upper Puna Ridge suggests a distinct body of magma cumulates, possibly connected to the summit magma cumulates at depth. The two cumulate bodies within Kilauea's ERZ may have undergone separate ductile flow seaward, influencing the submarine morphology of Kilauea's south flank. Low velocities (5.0-6.3??km/s) seaward of Kilauea's Hilina fault zone, and along Mauna Loa's seaward facing Kao'iki fault zone, are attributed to thick piles of volcaniclastic sediments deposited on the submarine flanks. Loihi seamount shows high-velocity anomalies beneath the summit and along the rift zones, similar to the interpreted magma cumulates below Mauna Loa and Kilauea volcanoes, and a low-velocity anomaly beneath the oceanic crust, probably indicative of melt within the upper mantle. Around Kilauea's submarine flank, a high-velocity anomaly beneath the outer bench suggests the presence of an ancient seamount that may obstruct outward spreading of the flank. Mauna Loa's southeast flank is also marked by a large, anomalously high-velocity feature (7.0-7.4??km/s), interpreted to define an inactive, buried volcanic rift zone, which might provide a new explanation for the westward migration of Mauna Loa's current SWRZ and the growth of Kilauea's SWRZ. ?? 2007 Elsevier B.V. All rights reserved.

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

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

  16. Zero-group-velocity propagation of electromagnetic wave through nanomaterial

    NASA Astrophysics Data System (ADS)

    Fan, Taian

    This research will investigate the problem on the propagation of electromagnetic wave through a specific nanomaterial. The nanomaterial analyzed is a material consisting of a field of Pt nanorods. This field of Pt nanorods are deposited on a substrate which consists of a RuO2 nano structure. When the nanorod is exposed to an electron beam emitted by a TEM (Transmission electron microscopy). A wave disturbance has been observed. A video taken within the chamber shows a wave with a speed in the scale of um/s (10-6 m/s), which is 14 orders of magnitude lower than speed of light in free space (approximate 3x108 m/s ). A physical and mathematical model is developed to explain this phenomenon. Due to the process of fabrication, the geometry of the decorated Pt nanorod field is assumed to be approximately periodic. The nanomaterials possess properties similar to a photonic crystal. Pt, as a noble metal, shows dispersive behaviours that is different from those ones of a perfect or good conductors. A FDTD algorithm is implemented to calculate the band diagram of the nanomaterials. To explore the dispersive properties of the Pt nanorod field, the FDTD algorithm is corrected with a Drude Model. The analysis of the corrected band diagram illustrates that the group velocity of the wave packet propagating through the nanomaterial can be positive, negative or zero. The possible zero-group velocity is therefore used to explain the extremely low velocity of wave (wave envelope) detected in the TEM.

  17. Special Property of Group Velocity for Temporal Dark Soliton

    NASA Astrophysics Data System (ADS)

    Du, Ying-Jie; Yu, Jin-Ying; Bai, Jin-Tao

    2017-04-01

    We investigate the speed of temporal dark soliton based on an optical coherent medium. It is demonstrated that the temporal dark soliton is described by a nonlinear Schrodinger equation whose coefficients are decided by the coherent medium. It is found that the speed of temporal dark soliton not only relies on the linear responses including GV parameter, group velocity dispersion parameter as well as the amplitude of dark soliton, but also relies on the nonlinear response like self-phase modulation parameter. Additionally, the dark soliton in anomalous-dispersion regime propagates slower than bright soliton, while in normal-dispersion regime it inversely propagates faster than bright soliton. The complicated property of the speed for dark soliton is quite different from the bright soliton whose speed is commonly only related to the group velocity parameter. We attribute this feature to the modulation instability of the nonlinear system. Supported by the National Nature Science Foundation of China under Grant No. 11404260, the Education Department of Shaanxi Province (16JK1758) and the State Key Laboratory of Quantum Optics and Optical Device (KF201602)

  18. Huge group-velocity dispersion in a photonic crystal

    NASA Astrophysics Data System (ADS)

    Ouyang, Zhengbiao; Cai, Yanyan; Meng, Qingsheng; Lu, Yali; Sun, Yiling; Zhang, Dengguo; Ruan, Shuangchen; Li, Jingzhen

    2005-11-01

    We investigated the group-velocity dispersion of a one dimensional uniform photonic crystal by the optical transmission method. For application in optical communications, the wavelength should be near one of the two edges of a photonic bandgap. Four kinds of dispersion-compensation may be obtained with a photonic crystal. Huge negative and positive group-velocity-dispersion (GVD) about a zero-dispersion-point as large as 5.1 Tera- ps/nm/km by a photonic crystal of 100 periods can be realized. Such a value is about 50 Giga times the GVD of conventional dispersion-compensation fibers. The GVD reaches a maximum when the optical length ratio of the high refractive index material to the low refractive index material is 1.2 for given operating parameters. When we keep the optical length of each layer being constant, the GVD is found to increase rapidly with the refractive index ration of the high refractive index material to the low one and even more rapidly with the number of periods of a photonic crystal. Under quite common operating parameters, a thin piece of photonic crystal of 100 periods may play the role of an ordinary dispersion-compensation fiber with a length over 158 kilo-meters.

  19. Simultaneous Local and Teleseismic P-Wave Velocity Tomography in Western Mexico

    NASA Astrophysics Data System (ADS)

    Escudero, C. R.; Alarcon, E.; Ochoa, J.; Nuñez-Cornu, F. J.

    2015-12-01

    In western Mexico, the subduction of the Rivera and Cocos plates beneath the North America plate has deformed and fragmented the overriding plate, forming several structural rifts and crustal blocks. To improve the current tomographic images of the continental crust and uppermost mantle in this complex area, we used P-wave arrivals of local and teleseismic earthquakes along with the Fast Marching Method tomography technique. Our traveltime datasets include 2100 local earthquakes P-wave arrival times and 5,062 P-wave relative arrival time residuals of teleseismic earthquakes. The local earthquake phase picking was manually corrected and the relative arrival time residuals were estimated using the Multi-Channel Cross-Correlation method. All earthquakes occurred between 2006 and 2007 and were recorded by seismic stations deployed during the Mapping the Rivera Subduction Zone (MARS) experiment. The temporal seismic network consisted of 50 stations equipped with Streckeisen STS-2 and Quanterra Q330. We use an iterative nonlinear tomographic procedure and the fast marching method to map the residual patterns as P wave velocity anomalies. We followed an inversion scheme consisting of: (1) selection of a local and teleseismic earthquake, (2) estimation of improved 1-D reference velocity model, and (3) checkerboard testing to determine the optimum configuration of the velocity nodes, and inversion parameters, finally (4) perform final tomography and results analysis.

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  1. Using stochastic borehole seismic velocity tomography and Bayesian simulation to estimate Ni, Cu and Co grades.

    NASA Astrophysics Data System (ADS)

    Perozzi, Lorenzo; Gloaguen, Erwan; Rondenay, Stephane; Leite, André; McDowell, Glenn; Wheeler, Robert

    2010-05-01

    In the mining industry, classic methods to build a grade model for ore deposits are based on kriging or cokriging of grades for targeted minerals measured in drill core in fertile geological units. As the complexity of the geological geometry increases, so does the complexity of grade estimations. For example, in layered mafic or ultramafic intrusions, it is necessary to know the layering geometry in order to perform kriging of grades in the most fertile zones. Without additional information on geological framwork, the definition of fertile zones is a low-precision exercise that requires extensive experience and good ability from the geologist. Recently, thanks to computer and geophysical tool improvements, seismic tomography became very attractive for many application fields. Indeed, this non-intrusive technique allows inferring the mechanical properties of the ground using travel times and amplitude analysis of the transmitted wavelet between two boreholes, hence provide additional information on the nature of the deposit. Commonly used crosshole seismic velocity tomography algorithms estimate 2D slowness models (inverse of velocity) in the plane between the boreholes using the measured direct wave travel times from the transmitter (located in one of the hole) to the receivers (located in the other hole). Furthermore, geophysical borehole logging can be used to constrain seismic tomography between drill holes. Finally, this project aims to estimate grade of economically worth mineral by integrating seismic tomography data with respectively drill core measured grades acquired by Vale Inco for one of their mine sites in operation. In this study, a new type algorithm that combines geostatistical simulation and tomography in the same process (namely stochastic tomography) has been used. The principle of the stochastic tomography is based on the straight ray approximation and use the linear relationship between travel time and slowness to estimate the slowness

  2. Seismic Velocity Anomalies beneath Tatun Volcano Group, Northern Taiwan

    NASA Astrophysics Data System (ADS)

    Lin, Tzu-yu; Lin, Cheng-Horng; Yang, Tsanyao Frank; Chang, Li-Chin

    2015-04-01

    Volcanic eruption has been a natural disaster for human society. Taiwan is located in the Pacific Ring of Fire. Although there is no obvious phenomenon of volcanic activity in Taiwan, some volcanoes need to be monitored, especially the Tatun Volcano Group (TVG), which exhibits very active hydrothermal activity, is located on the tip of southwestern Ryukyu arc. TVG is about 15 km north to Taipei, capital of Taiwan, and is nearby two nuclear power plants along the northern coast of Taiwan. If TVG erupts, there must be a serious impact and damage to Taiwan. Since TVG is located within the Yangmingshan National Park, any artificial seismic source is not allowed to estimate possible eruption site and the degree of volcanic disaster. Instead, we use natural seismic waves generated by earthquakes to image the possible velocity anomaly of magma chamber and/or hydrothermal system beneath TVG. We systematically compare the differences of arrival times generated by some local earthquakes and recorded at 42 seismic stations in 2014 for finding any low-velocity zone within the crust. The results show that the arrival times always appeared significant delay at some particular seismic stations, such as Chi-Hsin-Shan (CHS), Siao-You-Keng (SYK) and some other stations at TVG, no matter where the earthquakes occurred. It implies that possible low-velocity zones, which could be the location of magma chamber and/or active hydrothermal system, exist beneath the CHS and SYK areas. This feature is generally consistent with the clustered micro-earthquakes in the shallow crust beneath the CHS area in the last decade.

  3. Phase-resolved optical coherence tomography and optical Doppler tomography for imaging blood flow in human skin with fast scanning speed and high velocity sensitivity

    SciTech Connect

    Zhao, Yonghua; Chen, Zhongping; Saxer, Christopher; Xiang, Shaohua; Boer, Johannes F. de; Nelson, J. Stuart

    2000-01-15

    We have developed a novel phase-resolved optical coherence tomography (OCT) and optical Doppler tomography (ODT) system that uses phase information derived from a Hilbert transformation to image blood flow in human skin with fast scanning speed and high velocity sensitivity. Using the phase change between sequential scans to construct flow-velocity imaging, this technique decouples spatial resolution and velocity sensitivity in flow images and increases imaging speed by more than 2 orders of magnitude without compromising spatial resolution or velocity sensitivity. The minimum flow velocity that can be detected with an axial-line scanning speed of 400 Hz and an average phase change over eight sequential scans is as low as 10 {mu}m/s , while a spatial resolution of 10 {mu}m is maintained. Using this technique, we present what are to our knowledge the first phase-resolved OCT/ODT images of blood flow in human skin. (c) 2000 Optical Society of America.

  4. Comparison of parallel group velocity of ECH waves with electron resonant velocity: Implication for electron diffusion by ECH waves

    NASA Astrophysics Data System (ADS)

    Tripathi, A. K.; Singhal, R. P.

    2009-10-01

    We have investigated the role of group velocity in the calculation of pitch-angle diffusion coefficients by electron cyclotron harmonic (ECH) waves in planetary magnetospheres. The assumption which is generally made that the parallel group velocity can be neglected in comparison with particle parallel velocity is examined in detail. It is found that for lowest harmonic band this assumption is quite good. It is found that in general it is not possible to ignore the parallel group velocity. However, for lowest harmonic band this assumption is quite good at low electron temperatures.

  5. Enhancement of the FIDA diagnostic at ASDEX Upgrade for velocity space tomography

    NASA Astrophysics Data System (ADS)

    Weiland, M.; Geiger, B.; Jacobsen, A. S.; Reich, M.; Salewski, M.; Odstrčil, T.; the ASDEX Upgrade Team

    2016-02-01

    Recent upgrades to the FIDA (fast-ion D-alpha) diagnostic at ASDEX Upgrade are discussed. The diagnostic has been extended from three to five line of sight arrays with different angles to the magnetic field, and a spectrometer redesign allows the simultaneous measurement of red- and blue-shifted parts of the Doppler spectrum. These improvements make it possible to reconstruct the 2D fast-ion velocity distribution f≤ft(E,{{v}\\parallel}/v\\right) from the FIDA measurements by tomographic inversion under a wide range of plasma parameters. Two applications of the tomography are presented: a comparison between the distributions resulting from 60 keV and 93 keV neutral beam injection and a velocity-space resolved study of fast-ion redistribution induced by a sawtooth crash inside and outside the sawtooth inversion radius.

  6. Velocity variations and uncertainty from transdimensional P-wave tomography of North America

    NASA Astrophysics Data System (ADS)

    Burdick, Scott; Lekić, Vedran

    2017-03-01

    High-resolution models of seismic velocity variations constructed using body-wave tomography inform the study of the origin, fate, and thermochemical state of mantle domains. In order to reliably relate these variations to material properties including temperature, composition, and volatile content, we must accurately retrieve both the patterns and amplitudes of variations and quantify the uncertainty associated with the estimates of each. For these reasons, we image the mantle beneath North America with P-wave traveltimes from USArray using a novel method for 3-D probabilistic body-wave tomography. The method uses a Transdimensional Hierarchical Bayesian (THB) framework with a reversible-jump Markov Chain Monte Carlo (rj-MCMC) algorithm in order to generate an ensemble of possible velocity models. We analyze this ensemble solution to obtain the posterior probability distribution of velocities, thereby yielding error bars and enabling rigorous hypothesis testing. Overall, we determine that the average uncertainty (1σ) of compressional wave velocity estimates beneath North America is ∼0.25% dVP/VP, increasing with proximity to complex structure and decreasing with depth. The addition of USArray data reduces the uncertainty beneath the Eastern US by over 50% in the upper mantle and 25-40% below the transition zone and ∼30% throughout the mantle beneath the Western US. In the absence of damping and smoothing, we recover amplitudes of variations 10-80% higher than a standard inversion approach. Accounting for differences in data coverage, we infer that the length-scale of heterogeneity is ∼50% longer at shallow depths beneath the continental platform than beneath tectonically active regions. We illustrate the model trade-off analysis for the Cascadia slab and the New Madrid Seismic Zone, where we find that smearing due to the limitations of the illumination is relatively minor.

  7. Velocity variations and uncertainty from transdimensional P-wave tomography of North America

    NASA Astrophysics Data System (ADS)

    Burdick, Scott; Lekić, Vedran

    2017-05-01

    High-resolution models of seismic velocity variations constructed using body-wave tomography inform the study of the origin, fate and thermochemical state of mantle domains. In order to reliably relate these variations to material properties including temperature, composition and volatile content, we must accurately retrieve both the patterns and amplitudes of variations and quantify the uncertainty associated with the estimates of each. For these reasons, we image the mantle beneath North America with P-wave traveltimes from USArray using a novel method for 3-D probabilistic body-wave tomography. The method uses a Transdimensional Hierarchical Bayesian framework with a reversible-jump Markov Chain Monte Carlo algorithm in order to generate an ensemble of possible velocity models. We analyse this ensemble solution to obtain the posterior probability distribution of velocities, thereby yielding error bars and enabling rigorous hypothesis testing. Overall, we determine that the average uncertainty (1σ) of compressional wave velocity estimates beneath North America is ˜0.25 per cent dVP/VP, increasing with proximity to complex structure and decreasing with depth. The addition of USArray data reduces the uncertainty beneath the Eastern US by over 50 per cent in the upper mantle and 25-40 per cent below the transition zone and ˜30 per cent throughout the mantle beneath the Western US. In the absence of damping and smoothing, we recover amplitudes of variations 10-80 per cent higher than a standard inversion approach. Accounting for differences in data coverage, we infer that the length scale of heterogeneity is ˜50 per cent longer at shallow depths beneath the continental platform than beneath tectonically active regions. We illustrate the model trade-off analysis for the Cascadia slab and the New Madrid Seismic Zone, where we find that smearing due to the limitations of the illumination is relatively minor.

  8. Group-velocity-locked vector soliton molecules in fiber lasers.

    PubMed

    Luo, Yiyang; Cheng, Jianwei; Liu, Bowen; Sun, Qizhen; Li, Lei; Fu, Songnian; Tang, Dingyuan; Zhao, Luming; Liu, Deming

    2017-05-24

    Physics phenomena of multi-soliton complexes have enriched the life of dissipative solitons in fiber lasers. By developing a birefringence-enhanced fiber laser, we report the first experimental observation of group-velocity-locked vector soliton (GVLVS) molecules. The birefringence-enhanced fiber laser facilitates the generation of GVLVSs, where the two orthogonally polarized components are coupled together to form a multi-soliton complex. Moreover, the interaction of repulsive and attractive forces between multiple pulses binds the particle-like GVLVSs together in time domain to further form compound multi-soliton complexes, namely GVLVS molecules. By adopting the polarization-resolved measurement, we show that the two orthogonally polarized components of the GVLVS molecules are both soliton molecules supported by the strongly modulated spectral fringes and the double-humped intensity profiles. Additionally, GVLVS molecules with various soliton separations are also observed by adjusting the pump power and the polarization controller.

  9. Spin-Orbit Twisted Spin Waves: Group Velocity Control

    NASA Astrophysics Data System (ADS)

    Perez, F.; Baboux, F.; Ullrich, C. A.; D'Amico, I.; Vignale, G.; Karczewski, G.; Wojtowicz, T.

    2016-09-01

    We present a theoretical and experimental study of the interplay between spin-orbit coupling (SOC), Coulomb interaction, and motion of conduction electrons in a magnetized two-dimensional electron gas. Via a transformation of the many-body Hamiltonian we introduce the concept of spin-orbit twisted spin waves, whose energy dispersions and damping rates are obtained by a simple wave-vector shift of the spin waves without SOC. These theoretical predictions are validated by Raman scattering measurements. With optical gating of the density, we vary the strength of the SOC to alter the group velocity of the spin wave. The findings presented here differ from that of spin systems subject to the Dzyaloshinskii-Moriya interaction. Our results pave the way for novel applications in spin-wave routing devices and for the realization of lenses for spin waves.

  10. An upper-mantle S-wave velocity model for East Asia from Rayleigh wave tomography

    NASA Astrophysics Data System (ADS)

    Li, Yonghua; Wu, Qingju; Pan, Jiatie; Zhang, Fengxue; Yu, Daxin

    2013-09-01

    We present a new shear velocity model of the upper mantle beneath the East Asia region derived by inverting Rayleigh wave group velocity measurements between 10 and 145 s combined with previously published Rayleigh wave phase velocity measurements between 150 and 250 s. Rayleigh wave group velocity dispersion curves along more than 9500 paths were measured and combined to produce 2D dispersion maps for 10-145 s periods. The group velocity maps benefit from the inclusion of new data recorded by the China National Seismic Network and surrounding global stations. The increase in available data has resulted in enhanced resolution compared with previously published group velocity maps; the horizontal resolution across the region is about 3° for the periods used in this study. The new shear-wave velocity models indicate varying velocity structure beneath eastern China, which yields estimates of a lithosphere-asthenosphere boundary depth from around 160 km beneath the Yangtze block to approximately 140 km beneath the western part of the North China Craton (NCC), up to depths of 70-100 km beneath the eastern NCC, Northeast China, and the Cathaysia block. The models reveal the subduction of two opposite-facing continental plates under the southern and northern margin of Tibet. An obvious low-velocity anomaly appears in the top 200 km of the upper mantle beneath northern Tibet, which is inconsistent with the presence of subducted Asian or Indian mantle lithosphere beneath northern Tibet. The Cenozoic volcanism fields in the Mongolian plateau are characterized by an obvious upper mantle negative anomaly, but no signature of deep-seated plume was observed.

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

    SciTech Connect

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

    2007-07-01

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

  12. Fully distributed absolute blood flow velocity measurement for middle cerebral arteries using Doppler optical coherence tomography

    PubMed Central

    Qi, Li; Zhu, Jiang; Hancock, Aneeka M.; Dai, Cuixia; Zhang, Xuping; Frostig, Ron D.; Chen, Zhongping

    2016-01-01

    Doppler optical coherence tomography (DOCT) is considered one of the most promising functional imaging modalities for neuro biology research and has demonstrated the ability to quantify cerebral blood flow velocity at a high accuracy. However, the measurement of total absolute blood flow velocity (BFV) of major cerebral arteries is still a difficult problem since it is related to vessel geometry. In this paper, we present a volumetric vessel reconstruction approach that is capable of measuring the absolute BFV distributed along the entire middle cerebral artery (MCA) within a large field-of-view. The Doppler angle at each point of the MCA, representing the vessel geometry, is derived analytically by localizing the artery from pure DOCT images through vessel segmentation and skeletonization. Our approach could achieve automatic quantification of the fully distributed absolute BFV across different vessel branches. Experiments on rodents using swept-source optical coherence tomography showed that our approach was able to reveal the consequences of permanent MCA occlusion with absolute BFV measurement. PMID:26977365

  13. Development of a State-Wide 3-D Seismic Tomography Velocity Model for California

    NASA Astrophysics Data System (ADS)

    Thurber, C. H.; Lin, G.; Zhang, H.; Hauksson, E.; Shearer, P.; Waldhauser, F.; Hardebeck, J.; Brocher, T.

    2007-12-01

    We report on progress towards the development of a state-wide tomographic model of the P-wave velocity for the crust and uppermost mantle of California. The dataset combines first arrival times from earthquakes and quarry blasts recorded on regional network stations and travel times of first arrivals from explosions and airguns recorded on profile receivers and network stations. The principal active-source datasets are Geysers-San Pablo Bay, Imperial Valley, Livermore, W. Mojave, Gilroy-Coyote Lake, Shasta region, Great Valley, Morro Bay, Mono Craters-Long Valley, PACE, S. Sierras, LARSE 1 and 2, Loma Prieta, BASIX, San Francisco Peninsula and Parkfield. Our beta-version model is coarse (uniform 30 km horizontal and variable vertical gridding) but is able to image the principal features in previous separate regional models for northern and southern California, such as the high-velocity subducting Gorda Plate, upper to middle crustal velocity highs beneath the Sierra Nevada and much of the Coast Ranges, the deep low-velocity basins of the Great Valley, Ventura, and Los Angeles, and a high- velocity body in the lower crust underlying the Great Valley. The new state-wide model has improved areal coverage compared to the previous models, and extends to greater depth due to the data at large epicentral distances. We plan a series of steps to improve the model. We are enlarging and calibrating the active-source dataset as we obtain additional picks from investigators and perform quality control analyses on the existing and new picks. We will also be adding data from more quarry blasts, mainly in northern California, following an identification and calibration procedure similar to Lin et al. (2006). Composite event construction (Lin et al., in press) will be carried out for northern California for use in conventional tomography. A major contribution of the state-wide model is the identification of earthquakes yielding arrival times at both the Northern California Seismic

  14. Tomographic Rayleigh wave group velocities in the Central Valley, California, centered on the Sacramento/San Joaquin Delta

    NASA Astrophysics Data System (ADS)

    Fletcher, Jon B.; Erdem, Jemile; Seats, Kevin; Lawrence, Jesse

    2016-04-01

    If shaking from a local or regional earthquake in the San Francisco Bay region were to rupture levees in the Sacramento/San Joaquin Delta, then brackish water from San Francisco Bay would contaminate the water in the Delta: the source of freshwater for about half of California. As a prelude to a full shear-wave velocity model that can be used in computer simulations and further seismic hazard analysis, we report on the use of ambient noise tomography to build a fundamental mode, Rayleigh wave group velocity model for the region around the Sacramento/San Joaquin Delta in the western Central Valley, California. Recordings from the vertical component of about 31 stations were processed to compute the spatial distribution of Rayleigh wave group velocities. Complex coherency between pairs of stations was stacked over 8 months to more than a year. Dispersion curves were determined from 4 to about 18 s. We calculated average group velocities for each period and inverted for deviations from the average for a matrix of cells that covered the study area. Smoothing using the first difference is applied. Cells of the model were about 5.6 km in either dimension. Checkerboard tests of resolution, which are dependent on station density, suggest that the resolving ability of the array is reasonably good within the middle of the array with resolution between 0.2 and 0.4°. Overall, low velocities in the middle of each image reflect the deeper sedimentary syncline in the Central Valley. In detail, the model shows several centers of low velocity that may be associated with gross geologic features such as faulting along the western margin of the Central Valley, oil and gas reservoirs, and large crosscutting features like the Stockton arch. At shorter periods around 5.5 s, the model's western boundary between low and high velocities closely follows regional fault geometry and the edge of a residual isostatic gravity low. In the eastern part of the valley, the boundaries of the low-velocity

  15. Tomographic Rayleigh-wave group velocities in the Central Valley, California centered on the Sacramento/San Joaquin Delta

    USGS Publications Warehouse

    Fletcher, Jon Peter B.; Erdem, Jemile; Seats, Kevin; Lawrence, Jesse

    2016-01-01

    If shaking from a local or regional earthquake in the San Francisco Bay region were to rupture levees in the Sacramento/San Joaquin Delta then brackish water from San Francisco Bay would contaminate the water in the Delta: the source of fresh water for about half of California. As a prelude to a full shear-wave velocity model that can be used in computer simulations and further seismic hazard analysis, we report on the use of ambient noise tomography to build a fundamental-mode, Rayleigh-wave group velocity model for the region around the Sacramento/San Joaquin Delta in the western Central Valley, California. Recordings from the vertical component of about 31 stations were processed to compute the spatial distribution of Rayleigh wave group velocities. Complex coherency between pairs of stations were stacked over 8 months to more than a year. Dispersion curves were determined from 4 to about 18 seconds. We calculated average group velocities for each period and inverted for deviations from the average for a matrix of cells that covered the study area. Smoothing using the first difference is applied. Cells of the model were about 5.6 km in either dimension. Checkerboard tests of resolution, which is dependent on station density, suggest that the resolving ability of the array is reasonably good within the middle of the array with resolution between 0.2 and 0.4 degrees. Overall, low velocities in the middle of each image reflect the deeper sedimentary syncline in the Central Valley. In detail, the model shows several centers of low velocity that may be associated with gross geologic features such as faulting along the western margin of the Central Valley, oil and gas reservoirs, and large cross cutting features like the Stockton arch. At shorter periods around 5.5s, the model’s western boundary between low and high velocities closely follows regional fault geometry and the edge of a residual isostatic gravity low. In the eastern part of the valley, the boundaries

  16. 3-D crustal velocity structure of western Turkey: Constraints from full-waveform tomography

    NASA Astrophysics Data System (ADS)

    Çubuk-Sabuncu, Yeşim; Taymaz, Tuncay; Fichtner, Andreas

    2017-09-01

    The Sea of Marmara and western Turkey are characterized by intense seismicity and crustal deformation due to transition tectonics between the North Anatolian Fault Zone (NAFZ) and the extensional Aegean. Seismic imaging of the crust and uppermost mantle in W-NW Turkey is crucial to obtain a better understanding of its seismotectonics and geodynamics. So far, the Sea of Marmara and surroundings were considered in various active and passive seismic experiments providing significant information on crustal properties. Here, we further investigate the 3-D seismic velocity structure in this rapidly deforming region using non-linear full-waveform tomography based on the adjoint method. Our model is constrained by complete waveforms of 62 regional earthquakes (epicentral distance < 10°) with magnitudes Mw ≥ 3.7, which occurred between 2007 and 2015. Validation tests show that our final 3-D Earth model is able to explain seismic waveforms from earthquakes not used in the inversion at periods from 8-100 s to within the data uncertainties. Furthermore, quantitative resolution analyses yield 15 to 35 km horizontal resolution lengths in the shallow and deep crust beneath well-covered areas of W-NW Turkey. Our full-waveform tomography results indicate the presence of strong lateral and vertical velocity variations (2.55 ≤ VS ≤ 4.0 km/s) down to depths of ∼35 km. The seismic velocity distribution is characteristic of highly deformed and distributed crustal features along major fault zones (e.g. NAFZ and its branches), historic and recent regional volcanism (e.g. Kula volcanic province), and metamorphic core complex developments (e.g. Menderes and Kazdağ massifs). Radial anisotropy is very strong (around 20%) throughout the crust, further attesting to strong deformation and heterogeneity. Generally, our 3-D model is overall consistent with the active tectonics of western Turkey.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  18. 3D Velocity Structure of Chukou Fault Area, Taiwan from Seismic Tomography

    NASA Astrophysics Data System (ADS)

    Chen, C.; Chang, W.; Jian, W.

    2009-12-01

    In this study, we used the seismic data that recorded by the broadband stations which deployed around the Chukou fault area, Taiwan. We have chosen 1661 earthquake events with high quality records in this research. The waveform cross correlation technique is applied to calculate the 143086 pairs of waveform data. By combining with data from the seismic catalog, there are 342202 absolute travel-time pairs through the double difference tomography method to relocate the seismicity and invert the 3D velocity structures beneath the Chukou fault area. Due to Taiwan Island is located in an active boundary zone between the Eurasia continental and Philippine Sea plates, the violent collision between the two plates which causes a series of imbricate fold-thrust belts to form between the western foothills and the coastal plain. The Chukou fault is just the boundary between the fold-thrust belts and the coastal plain in the Chia-Nan area, Taiwan. The seismotectonic structure beneath this area is more complex. From many studies, velocity structure can be used as an indicator of the geometry of fault and the general aspect of tectonics. Therefore, the first goal of this research is to analyze the degree of correlation between the velocity structure and the characteristics of seismicity and the tectonic implications of the area. The second intention is to study the distribution of seismic events and its association with fault activities. Our results indicate that the variation of velocity structure beneath fault area is caused by local geological structures, complex fault crossing. We also find that most earthquakes occur in the area that has Vp/Vs gradient varying rapidly. Finally, both using catalog and cross-correlation data in the inversion procedure are not only exhibit better resolution, but also can obtain the detail 3D velocity structure beneath the fault zone.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  1. Crustal and uppermost mantle velocity structure beneath northwestern China revealed by ambient noise tomography

    NASA Astrophysics Data System (ADS)

    Li, H.; Li, S.; Song, X.; Gong, M.; Li, X.; Jia, J.

    2010-12-01

    In this study three-component ambient noise data recorded at 148 seismic stations from newly upgraded provincial digital seismic network in northwestern China and adjacent region are used to obtain Rayleigh wave and Love wave group velocity maps. Cross-correlations are calculated in one-hour segments and stacked over 9 months from 2009 January to September to estimate empirical Rayleigh and Love wave Green's functions. Group velocity dispersion curves for both Rayleigh and Love waves between 7 s and 50 s periods were measured for each interstation path by applying the multiple filter analysis method with phase-matched processing. Our group velocity maps show clear lateral variations which are correlated well with major geological structures and tectonic units in the study region. Shear wave velocity structures are then inverted and show that the Tibetan Plateau has a very thick crust with a low-velocity zone in its mid-to-lower crust. Along the northern margin of the plateau with a steep topographic gradient, the low-velocity zone does not extend to the Tarim basin which may indicate that crustal materials beneath the Tarim basin are colder and stronger than beneath the plateau, therefore inhibit the extension of crustal flow and deformation of the Tibetan Plateau, resulting in very sharp topography contrasts. In the northeastern margin where the Tibetan Plateau, Alashan block and Ordos platform collided together, the low-velocity zone diminishes around the eastern end of the KunLun fault. Meanwhile, our results also reveal obvious lateral velocity changes in the crust beneath the Tarim basin. In the upper crust, the Manjaer depression is featured with very low velocities and the Bachu uplift with high velocities; in the mid-to-lower crust, the northern basin overall displays lower velocities than the southern part along the latitude 40°N with a west-east striking which is consistent with the high magnetic anomaly zone and may related to the central suture belt

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  3. S-wave velocity structure in southwest China from surface wave tomography and receiver functions

    NASA Astrophysics Data System (ADS)

    Wang, W.; Wu, J.; Fang, L.; Lai, G.; Yang, T.

    2013-12-01

    Using the surface wave records of 504 teleseismic events at 50 temporal and 92 permanent seismic stations in southwest China, we extracted the phase velocity dispersion curves with interstation correlation method, and obtained the phase velocity maps at 10, 15, 25, 40, 60 and 75 s with a grid space of 0.5×0.5 from surface wave tomography. Meanwhile, we obtained the S-wave velocity structures beneath three profiles from the joint inversion of receiver functions and surface waves. From the maps at short periods (10 and 15 s) and long periods (40, 60 and 75 s), different distribution features of high velocity zones (HVZs for short) and low velocity zones (LVZs for short) are shown in the study area: HVZs at short periods are shown in the Panzhihua - Emeishan region, Sichuan basin and Weixi-Lijiang region, surrounding the LVZs from Songpan-Ganzi block to the east of Lijiang where there are significant higher elevations; whereas HVZs at long periods are shown in the Weixi-Lijiang region, Panzhihua-Chuxiong basin and Kunming-Tonghai region and forming a line in the center part of the study area, and the fast polarization directions of the shear wave from SKS analysis on the two sides of the line change significantly. These phenomena indicate plateau material flow can be blocked in two different depth intervals and leads to different horizontal extensions. From the maps at long periods and the structures along the profiles, LVZs are shown in the upper mantle beneath rapid slip fault zones, such as Anninghe - Zemuhe - Xiaojiang fault zone, Red River fault zone and Xiaojinhe fault zone, implying these faults are deep penetrating faults. Figure (a-f) Rayleigh wave phase velocity maps at 10, 15, 25,40,60 and 75 s with a resolution of 100 km. The black lines represent faults. The red points represent M≥6 earthquakes. The colour scale changes in different panels. Figure (g) Distribution of the seismic stations and regional tectonic features in the study area. Figure (h

  4. Transdimensional Love-wave tomography of the British Isles and shear-velocity structure of the East Irish Sea Basin from ambient-noise interferometry

    NASA Astrophysics Data System (ADS)

    Galetti, Erica; Curtis, Andrew; Baptie, Brian; Jenkins, David; Nicolson, Heather

    2017-01-01

    We present the first Love-wave group-velocity and shear-velocity maps of the British Isles obtained from ambient noise interferometry and fully nonlinear inversion. We computed interferometric inter-station Green's functions by cross-correlating the transverse component of ambient noise records retrieved by 61 seismic stations across the UK and Ireland. Group-velocity measurements along each possible inter-station path were obtained using frequency-time analysis and converted into a series of inter-station traveltime data sets between 4 and 15 s period. Traveltime uncertainties estimated from the standard deviation of dispersion curves constructed by stacking randomly selected subsets of daily cross-correlations were observed to be too low to allow reasonable data fits to be obtained during tomography. Data uncertainties were therefore estimated again during the inversion as distance-dependent functionals. We produced Love-wave group-velocity maps within eight different period bands using a fully nonlinear tomography method which combines the transdimensional reversible-jump Markov chain Monte Carlo (rj-McMC) algorithm with an eikonal ray tracer. By modelling exact ray paths at each step of the Markov chain we ensured that the nonlinear character of the inverse problem was fully and correctly accounted for. Between 4 and 10 s period, the group-velocity maps show remarkable agreement with the known geology of the British Isles and correctly identify a number of low-velocity sedimentary basins and high-velocity features. Longer period maps, in which most sedimentary basins are not visible, are instead mainly representative of basement rocks. In a second stage of our study we used the results of tomography to produce a series of Love-wave group-velocity dispersion curves across a grid of geographical points focussed around the East Irish Sea sedimentary basin. We then independently inverted each curve using a similar rj-McMC algorithm to obtain a series of 1-D shear-velocity

  5. Transdimensional Love-wave tomography of the British Isles and shear-velocity structure of the East Irish Sea Basin from ambient-noise interferometry

    NASA Astrophysics Data System (ADS)

    Galetti, Erica; Curtis, Andrew; Baptie, Brian; Jenkins, David; Nicolson, Heather

    2016-08-01

    We present the first Love-wave group velocity and shear velocity maps of the British Isles obtained from ambient noise interferometry and fully non-linear inversion. We computed interferometric inter-station Green's functions by cross-correlating the transverse component of ambient noise records retrieved by 61 seismic stations across the UK and Ireland. Group velocity measurements along each possible inter-station path were obtained using frequency-time analysis and converted into a series of inter-station traveltime datasets between 4 and 15 seconds period. Traveltime uncertainties estimated from the standard deviation of dispersion curves constructed by stacking randomly-selected subsets of daily cross-correlations, were observed to be too low to allow reasonable data fits to be obtained during tomography. Data uncertainties were therefore estimated again during the inversion as distance-dependent functionals. We produced Love-wave group velocity maps within 8 different period bands using a fully non-linear tomography method which combines the transdimensional reversible-jump Markov chain Monte Carlo (rj-McMC) algorithm with an eikonal raytracer. By modelling exact raypaths at each step of the Markov chain we ensured that the non-linear character of the inverse problem was fully and correctly accounted for. Between 4 and 10 seconds period, the group velocity maps show remarkable agreement with the known geology of the British Isles and correctly identify a number of low-velocity sedimentary basins and high-velocity features. Longer period maps, in which most sedimentary basins are not visible, are instead mainly representative of basement rocks. In a second stage of our study we used the results of tomography to produce a series of Love-wave group velocity dispersion curves across a grid of geographical points focussed around the East Irish Sea sedimentary basin. We then independently inverted each curve using a similar rj-McMC algorithm to obtain a series of

  6. Local Earthquake Velocity and Attenuation Tomography of the Jalisco, Mexico Region

    NASA Astrophysics Data System (ADS)

    Watkins, W. D.; Thurber, C. H.; Abbott, E. R.; Brudzinski, M.; Grand, S. P.

    2015-12-01

    The states of Jalisco, Colima, and Michoacan in western Mexico overlie the boundary of the subducting Rivera and Cocos plates, presenting an appealing target for seismological inquiry to better understand the resulting mantle flow and regional volcanism. The different dips between the subducting plates is thought to provide a mantle conduit that has contributed to the Colima Volcanic Complex, but there is considerable debate on the shallowness of the Rivera plate and width of the resulting conduit. With data from the Mapping the Rivera Subduction Zone (MARS) and Colima Deep Seismic Experiment (CODEX) networks, two temporary broadband arrays deployed in the region between 2006-2008, we invert for three-dimensional P- and S- wave velocity and later attenuation structure of the upper ~80 km of the crust and mantle in the Jalisco region. We improve upon previous tomography work by utilizing double-difference tomography, which enables the use of higher-accuracy differential times to sharpen the earthquake locations, and the inclusion of S-wave data. Current models that utilize only analyst-picked phase arrivals from 590 earthquakes yield P-wave high velocity anomalies that suggest a slab under the coastal regions at 15-25 km depth, and low velocity anomalies that may be related to Colima Volcano or other geologic features. Most of the S-wave model is poorly resolved. We will use a newly developed auto-picker to attempt to substantially increase the size of the S-wave dataset and to a lesser extent the P wave dataset, in order to densify ray coverage and improve model resolution. Additionally, we plan to employ the waveforms from this expanded dataset to compute a path attenuation operator for each arrival, which will then be used to invert for 3D P and S-wave attenuation models. The attenuation models combined with the velocity models will provide multiple constraints on physical properties of the crust in this region as well as those of specific geologic features.

  7. Imaging of Time and Space Variation of Vortex Wind Velocity Fields Using Acoustic Tomography

    NASA Astrophysics Data System (ADS)

    Li, Haiyue; Ueki, Takaaki; Yamada, Akira

    2008-05-01

    A technique for monitoring the strong vortex wind field is much required with the rapid increase in global warming. For the realization of the technique, the acoustic tomography of two-dimensional vortex air flow profile was proposed, which can be reconstructed by arraying approximately 10 pairs of transmitters and receivers in parallel. To show the feasibility of the present method, experimental results of performance evaluation using an indoor simulation system are presented. In particular, the reproducibilities of time and space variations of the vortex wind fields passing through the monitoring region were examined. To achieve the real-time capability, a correction scheme for the error caused by the time lag in the sequential sampling was introduced. As a result, vortex wind velocity fields could be reconstructed with a high-speed frame rate while keeping a satisfactory tractability against time and space vortex wind field variations.

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

    PubMed

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

    2014-09-01

    Recent improvements in tomographic reconstruction techniques generated a renewed interest in short-range ultrasonic guided wave inspection for real-time monitoring of internal corrosion and erosion in pipes and other plate-like structures. Emerging evidence suggests that in most cases the fundamental asymmetric A0 mode holds a distinct advantage over the earlier market leader fundamental symmetric S0 mode. Most existing A0 mode inspections operate at relatively low inspection frequencies where the mode is highly dispersive therefore very sensitive to variations in wall thickness. This paper examines the potential advantages of increasing the inspection frequency to the so-called constant group velocity (CGV) point where the group velocity remains essentially constant over a wide range of wall thickness variation, but the phase velocity is still dispersive enough to allow accurate wall thickness assessment from phase angle measurements. This paper shows that in the CGV region the crucial issue of temperature correction becomes especially simple, which is particularly beneficial when higher-order helical modes are also exploited for tomography. One disadvantage of working at such relatively high inspection frequency is that, as the slower A0 mode becomes faster and less dispersive, the competing faster S0 mode becomes slower and more dispersive. At higher inspection frequencies these modes cannot be separated any longer based on their vibration polarization only, which is mostly tangential for the S0 mode while mostly normal for the A0 at low frequencies, as the two modes become more similar as the frequency increases. Therefore, we propose a novel method for suppressing the unwanted S0 mode based on the Poisson effect of the material by optimizing the angle of inclination of the equivalent transduction force of the Electromagnetic Acoustic Transducers (EMATs) used for generation and detection purposes. Copyright © 2014 Elsevier B.V. All rights reserved.

  9. Surface wave phase velocities from 2-D surface wave tomography studies in the Anatolian plate

    NASA Astrophysics Data System (ADS)

    Arif Kutlu, Yusuf; Erduran, Murat; Çakır, Özcan; Vinnik, Lev; Kosarev, Grigoriy; Oreshin, Sergey

    2014-05-01

    We study the Rayleigh and Love surface wave fundamental mode propagation beneath the Anatolian plate. To examine the inter-station phase velocities a two-station method is used along with the Multiple Filter Technique (MFT) in the Computer Programs in Seismology (Herrmann and Ammon, 2004). The near-station waveform is deconvolved from the far-station waveform removing the propagation effects between the source and the station. This method requires that the near and far stations are aligned with the epicentre on a great circle path. The azimuthal difference of the earthquake to the two-stations and the azimuthal difference between the earthquake and the station are restricted to be smaller than 5o. We selected 3378 teleseismic events (Mw >= 5.7) recorded by 394 broadband local stations with high signal-to-noise ratio within the years 1999-2013. Corrected for the instrument response suitable seismogram pairs are analyzed with the two-station method yielding a collection of phase velocity curves in various period ranges (mainly in the range 25-185 sec). Diffraction from lateral heterogeneities, multipathing, interference of Rayleigh and Love waves can alter the dispersion measurements. In order to obtain quality measurements, we select only smooth portions of the phase velocity curves, remove outliers and average over many measurements. We discard these average phase velocity curves suspected of suffering from phase wrapping errors by comparing them with a reference Earth model (IASP91 by Kennett and Engdahl, 1991). The outlined analysis procedure yields 3035 Rayleigh and 1637 Love individual phase velocity curves. To obtain Rayleigh and Love wave travel times for a given region we performed 2-D tomographic inversion for which the Fast Marching Surface Tomography (FMST) code developed by N. Rawlinson at the Australian National University was utilized. This software package is based on the multistage fast marching method by Rawlinson and Sambridge (2004a, 2004b). The

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

    SciTech Connect

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

    2012-01-10

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

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

  12. High resolution applications of seismic tomography: low velocity anomalies and static corrections using wave-equation datuming

    NASA Astrophysics Data System (ADS)

    Flecha, I.; Marti, D.; Escuder, J.; Perez-Estaun, A.; Carbonell, R.

    2003-04-01

    A detailed characterization of the internal structure and physical properties of shallow surface can be obtained using high-resolution seismic tomography. Two applications of high resolution seismic tomography are presented in this study. Several synthetics simulations have been carried out to asses the resolving power of this methodology in different cases. The first studied case is the detection of low velocity anomalies in the shallow subsoil. Underground cavities (mines), water flows (formation wich loose sand), etc., are geological features present in the shallow subsurface characterized by low seismic velocities, and are targets of considerable social interest. We have considered a 400m×50m two dimensional velocity model consisting of a background velocity gradient in depth from 3 to 4 Km/s which included a rectangular low velocity anomaly (300 m/s). This anomaly was placed between 10m and 30m in depth and between 180m and 220m in length. The inversions schemes provided estimates of the velocity, however the tomograms and the ray tracing diagrams indicated a low resolution for the anomaly. In the second case we have applied wave-equation datuming to pre-stack layer replacement. The standard seismic data processing applies a vertical time shift to the data traces. However, it is not a good option when we are dealing with rugged topography or bathymetry, and when the media presents a high heterogeneity. Wave-equation datuming extrapolates seismic time data to some level datum keeping consistency between raypaths and wavefield propagation. It improves considerably seismic reflectors imaging. In order to implement this technique a velocity model is required, and usually a constant velocity is used to propagate the wavefield; instead of it we have used seismic tomography to provide an accurate velocity model.

  13. Improved Near-surface Velocity Models from Waveform Tomography Applied to Vibroseis MCS Reflection Data

    NASA Astrophysics Data System (ADS)

    Smithyman, B.; Clowes, R. M.

    2009-12-01

    Multichannel vibroseis reflection surveys are prevalent in the land exploration seismic industry because of benefits in speed and cost, along with reduced environmental impact when compared to explosive sources. Since the downgoing energy must travel through the shallow subsurface, an improved model of near-surface velocity can in theory substantially improve the resolution of deeper reflections. We describe techniques aimed at allowing the use of vibroseis data for long-offset refraction processing of first-arrival traveltimes and waveforms. Refraction processing of surface vibroseis data is typically limited to near-offset refraction statics. Velocity models of the shallow subsurface can be built to facilitate CDP stacking and migration, but these models are typically coarse and of limited use for interpretation. Waveform tomography combines inversion of first-arrival traveltime data with full waveform inversion of densely-sampled refracted arrivals. Since inversion of the waveform amplitude and phase is not limited by the ray-theory approximation, identification of low-velocity zones and small scattering targets is possible. Incorporating a wide range of offsets is critical for a more complete characterization of the near-surface. Because of the use of a non-linear frequency-domain approach to the solution of this inverse problem, low data frequencies are important in comparison with conventional reflection processing. Through the use of waveform tomography, we plan to build useful, detailed near-surface velocity models for both the reflection work flow and direct interpretation. Several difficulties exist in first-arrival analysis and waveform inversion of vibroseis data. The mixed-phase vibroseis source signature exhibits variations in phase with offset that are difficult to quantify without detailed a priori knowledge of the near-surface. This causes difficulties with picking and initial model building, which is critical for non-linear waveform inversion. A

  14. Can we go From Tomographically Determined Seismic Velocities to Composition? Amplitude Resolution Issues in Local Earthquake Tomography

    NASA Astrophysics Data System (ADS)

    Wagner, L.

    2007-12-01

    There have been a number of recent papers (i.e. Lee (2003), James et al. (2004), Hacker and Abers (2004), Schutt and Lesher (2006)) which calculate predicted velocities for xenolith compositions at mantle pressures and temperatures. It is tempting, therefore, to attempt to go the other way ... to use tomographically determined absolute velocities to constrain mantle composition. However, in order to do this, it is vital that one is able to accurately constrain not only the polarity of the determined velocity deviations (i.e. fast vs slow) but also how much faster, how much slower relative to the starting model, if absolute velocities are to be so closely analyzed. While much attention has been given to issues concerning spatial resolution in seismic tomography (i.e. what areas are fast, what areas are slow), little attention has been directed at the issue of amplitude resolution (how fast, how slow). Velocity deviation amplitudes in seismic tomography are heavily influenced by the amount of regularization used and the number of iterations performed. Determining these two parameters is a difficult and little discussed problem. I explore the effect of these two parameters on the amplitudes obtained from the tomographic inversion of the Chile Argentina Geophysical Experiment (CHARGE) dataset, and attempt to determine a reasonable solution space for the low Vp, high Vs, low Vp/Vs anomaly found above the flat slab in central Chile. I then compare this solution space to the range in experimentally determined velocities for peridotite end-members to evaluate our ability to constrain composition using tomographically determined seismic velocities. I find that in general, it will be difficult to constrain the compositions of normal mantle peridotites using tomographically determined velocities, but that in the unusual case of the anomaly above the flat slab, the observed velocity structure still has an anomalously high S wave velocity and low Vp/Vs ratio that is most

  15. Dual-beam optical coherence tomography system for quantification of flow velocity in capillary phantoms

    NASA Astrophysics Data System (ADS)

    Daly, S. M.; Silien, C.; Leahy, M. J.

    2012-03-01

    The quantification of (blood) flow velocity within the vasculature has potent diagnostic and prognostic potential. Assessment of flow irregularities in the form of increased permeability (micro haemorrhaging), the presence of avascular areas, or conversely the presence of vessels with enlarged or increased tortuosity in the acral regions of the body may provide a means of non-invasive in vivo assessment. If assessment of dermal flow dynamics were performed in a routine manner, the existence and prevalence of ailments such as diabetes mellitus, psoriatic arthritis and Raynaud's condition may be confirmed prior to clinical suspicion. This may prove advantageous in cases wherein the efficacy of a prescribed treatment is dictated by a prompt diagnosis and to alleviate patient discomfort through early detection. Optical Coherence Tomography (OCT) is an imaging modality which utilises the principle of optical interferometry to distinguish between spatial changes in refractive index within the vasculature and thus formulate a multi-dimensional representation of the structure of the epi- and dermal skin layers. The use of the Doppler functionality has been the predominant force for the quantification of moving particles within media, elucidated via estimation of the phase shift in OCT A-scans. However, the theoretical formulation for the assessment of these phase shifts dictates that the angle between the incident light source and the vessel under question be known a priori; this may be achieved via excisional biopsy of the tissue segment in question, but is counter to the non-invasive premise of the OCT technique. To address the issue of angular dependence, an alternate means of estimating absolute flow velocity is presented. The design and development of a dual-beam (db) system incorporating an optical switch mechanism for signal discrimination of two spatially disparate points enabling quasi-simultaneous multiple specimen scanning is described. A crosscorrelation (c

  16. Three-dimensional S-wave velocity model of the Bohemian Massif from Bayesian ambient noise tomography

    NASA Astrophysics Data System (ADS)

    Valentová, Lubica; Gallovič, František; Maierová, Petra

    2017-10-01

    We perform two-step surface wave tomography of phase-velocity dispersion curves obtained by ambient noise cross-correlations in the Bohemian Massif. In the first step, the inter-station dispersion curves were inverted for each period (ranging between 4 and 20 s) separately into phase-velocity maps using 2D adjoint method. In the second step, we perform Bayesian inversion of the set of the phase-velocity maps into an S-wave velocity model. To sample the posterior probability density function, the parallel tempering algorithm is employed providing over 1 million models. From the model samples, not only mean model but also its uncertainty is determined to appraise the reliable features. The model is correlated with known main geologic structures of the Bohemian Massif. The uppermost low-velocity anomalies are in agreement with thick sedimentary basins. In deeper parts (4-20 km), the S-wave velocity anomalies correspond, in general, to main tectonic domains of the Bohemian Massif. The exception is a stable low-velocity body in the middle of the high-velocity Moldanubian domain and high-velocity body resembling a promontory of the Moldanubian into the Teplá-Barrandian domain. The most pronounced (high-velocity) anomaly is located beneath the Eger Rift that is a part of a Tertiary rift system across Europe.

  17. P-Wave Velocity Tomography from Local Earthquakes in Western Mexico

    NASA Astrophysics Data System (ADS)

    Ochoa-Chávez, Juan A.; Escudero, Christian R.; Núñez-Cornú, Francisco J.; Bandy, William L.

    2016-10-01

    In western Mexico, the subduction of the Rivera and Cocos plates beneath the North America plate has deformed and fragmented the overriding plate, forming several structural rifts and crustal blocks. To obtain a reliable subsurface image of the continental crust and uppermost mantle in this complex area, we used P-wave arrivals of local earthquakes along with the Fast Marching Method tomography technique. We followed an inversion scheme consisting of (1) the use of a high-quality earthquake catalog and corrected phase picks, (2) the selection of earthquakes using a maximum location error threshold, (3) the estimation of an improved 1-D reference velocity model, and (4) the use of checkerboard testing to determine the optimum configuration of the velocity nodes and inversion parameters. Surprisingly, the tomography results show a very simple δVp distribution that can be described as being controlled by geologic structures formed during two stages of the separation of the Rivera and Cocos plates. The earlier period represents the initial stages of the separation of the Rivera and Cocos plates beneath western Mexico; the later period represents the more advanced stage of rifting where the Rivera and Cocos plates had separated sufficiently to allow melt to accumulate below the Colima Volcanic complex. During the earlier period (14 or 10-1.6 Ma), NE-SW-oriented structures/lineaments (such as the Southern Colima Rift) were formed as the two plates separated. During the second period (1.6 Ma to the present), the deformation is attributed to magma, generated within and above the tear zone between the Rivera and Cocos plates, rising beneath the region of the Colima Volcanic Complex. The rising magma fractured the overlying crust, forming a classic triple-rift junction geometry. This triple-rift system is confined to the mid- to lower crust perhaps indicating that this rifting process is still in an early stage. This fracturing, along with fluid circulation and associated

  18. Surface wave group velocity in the Osaka sedimentary basin, Japan, estimated using ambient noise cross-correlation functions

    NASA Astrophysics Data System (ADS)

    Asano, Kimiyuki; Iwata, Tomotaka; Sekiguchi, Haruko; Somei, Kazuhiro; Miyakoshi, Ken; Aoi, Shin; Kunugi, Takashi

    2017-08-01

    Inter-station cross-correlation functions estimated using continuous ambient noise or microtremor records were used to extract the seismic wave propagation characteristics of the Osaka sedimentary basin, Japan. Temporary continuous observations were conducted at 15 sites in the Osaka basin between 2011 and 2013. The data were analyzed using seismic interferometry. The target period range was 2-8 s. Cross-correlations between all of the possible station pairs were calculated and stacked to produce a year-long data set, and Rayleigh wave signals in the vertical and radial components and Love wave signals in the transverse component were identified from the results. Simulation of inter-station Green's functions using the finite difference method was conducted to check the performance of the current three-dimensional velocity structure model. The measured time lag between the observed and theoretical Green's functions was less than 2 s for most station pairs, which is less than the wave period of interest in the target frequency range. Group velocity tomography was applied to group delay times estimated by means of multiple filter analysis. The estimated group velocities for longer periods of 5-8 s exhibited spatial variation within the basin, which is consistent with the bedrock depth distribution; however, the group velocities for shorter periods of 2-3 s were almost constant over the studied area. The waveform and group velocity information obtained by seismic interferometry analysis can be useful for future reconstruction of a three-dimensional velocity structure model in the Osaka basin.[Figure not available: see fulltext.

  19. Application of acoustic tomography to reconstruct the horizontal flow velocity field in a shallow river

    NASA Astrophysics Data System (ADS)

    Razaz, Mahdi; Kawanisi, Kiyosi; Kaneko, Arata; Nistor, Ioan

    2015-12-01

    A novel acoustic tomographic measurement system capable of resolving sound travel time in extremely shallow rivers is introduced and the results of an extensive field measurements campaign are presented and further discussed. Acoustic pulses were transmitted over a wide frequency band of 20-35 kHz between eight transducers for about a week in a meandering reach of theBāsen River, Hiroshima, Japan. The purpose of the field experiment was validating the concept of acoustic tomography in rivers for visualizing current fields. The particular novelty of the experiment resides in its unusual tomographic features: subbasin scale (100 m × 270 m) and shallowness (0.5-3.0 m) of the physical domain, frequency of the transmitted acoustic signals (central frequency of 30 kHz), and the use of small sampling intervals (105 s). Inverse techniques with no a priori statistical information were used to estimate the depth-average current velocity components from differential travel times. Zeroth-order Tikhonov regularization, in conjunction with L-curve method deployed to stabilize the solution and to determine the weighting factor appearing in the inverse analysis. Concurrent direct environmental measurements were provided in the form of ADCP readings close to the right and left bank. Very good agreement found between along-channel velocities larger than 0.2 m/s obtained from the two techniques. Inverted quantities were, however, underestimated, perhaps due to vicinity of the ADCPs to the banks and strong effect of river geometry on the readings. In general, comparing the visualized currents with direct nodal measurements illustrate the plausibility of the tomographically reconstructed flow structures.

  20. Noninvasive microstructural and velocity imaging in humans by color Doppler optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Yazdanfar, Siavash

    The objective of this dissertation is to develop the optical instrumentation, electronics, and signal processing for high-resolution blood flow imaging using optical coherence tomography (OCT) in human subjects. In particular, in vivo OCT blood flow imaging, termed color Doppler OCT (CDOCT), is applied for the first time to measurements in human vasculature of the retina and skin. CDOCT is similar to color Doppler ultrasound, whereas depth-resolved flow information is extracted from reflectivity profiles obtained from phase-sensitive, low-coherence interferometry. Although CDOCT has been demonstrated in tissue-mimicking phantoms and in living animal models, the technique has not yet been extended to blood flow imaging in humans. In this project, CDOCT was integrated with a modified slit lamp biomicroscope for imaging of retinal blood flow, and additional technical requirements necessary for retinal flow imaging were met. This system was used to acquire the first high resolution, cross-sectional images of blood flow with OCT in humans. The image acquisition rate was increased to examine retinal hemodynamics in normal subjects. A method was introduced for improving the velocity resolution by approximately two orders of magnitude, down to ˜1 micrometer/sec, by calculating the change in the phase across sequential scans. This technique was used to achieve the highest velocity resolution to date in scattering media, and applied to imaging the human microvasculature down to the capillary level. Finally, a modification of CDOCT based on differential phase contrast was introduced for high resolution imaging in the presence of motion artifact. This technique measures the differential Doppler frequency between two beams of orthogonal polarization states that are laterally displaced on the sample. Using polarization diversity detection, the common-mode noise was removed, enabling the measurement of flow in scattering media down to the theoretical frequency resolution.

  1. High velocity anomaly beneath the Deccan volcanic province: Evidence from seismic tomography

    USGS Publications Warehouse

    Iyer, H.M.; Gaur, V.K.; Rai, S.S.; Ramesh, D.S.; Rao, C.V.R.; Srinagesh, D.; Suryaprakasam, K.

    1989-01-01

    Analysis of teleseismic P-wave residuals observed at 15 seismograph stations operated in the Deccan volcanic province (DVP) in west central India points to the existence of a large, deep anomalous region in the upper mantle where the velocity is a few per cent higher than in the surrounding region. The seismic stations were operated in three deployments together with a reference station on precambrian granite at Hyderabad and another common station at Poona. The first group of stations lay along a west-northwesterly profile from Hyderabad through Poona to Bhatsa. The second group roughly formed an L-shaped profile from Poona to Hyderabad through Dharwar and Hospet. The third group of stations lay along a northwesterly profile from Hyderabad to Dhule through Aurangabad and Latur. Relative residuals computed with respect to Hyderabad at all the stations showed two basic features: a large almost linear variation from approximately +1s for teleseisms from the north to-1s for those from the southeast at the western stations, and persistance of the pattern with diminishing magnitudes towards the east. Preliminary ray-plotting and three-dimensional inversion of the P-wave residual data delineate the presence of a 600 km long approximately N-S trending anomalous region of high velocity (1-4% contrast) from a depth of about 100 km in the upper mantle encompassing almost the whole width of the DVP. Inversion of P-wave relative residuals reveal the existence of two prominent features beneath the DVP. The first is a thick high velocity zone (1-4% faster) extending from a depth of about 100 km directly beneath most of the DVP. The second feature is a prominent low velocity region which coincides with the westernmost part of the DVP. A possible explanation for the observed coherent high velocity anomaly is that it forms the root of the lithosphere which coherently translates with the continents during plate motions, an architecture characteristic of precambrian shields. The low

  2. Cluster analysis applied to velocity, attenuation and gravity tomography: the case of Campanian district volcanoes (southern italy)

    NASA Astrophysics Data System (ADS)

    Troiano, A.; di Giuseppe, M.; Petrillo, Z.; de Siena, L.; Siniscalchi, A.; Berrino, G.

    2009-12-01

    The interpretation of the results of seismic velocity, attenuation and gravity inversion are usually based on the qualitative observation and comparison of the different tomographic images. A promising tool to jointly interpret tomographic models based on different parameters resides in the application of statistical classification methods, such as the k-means clustering method, which minimizes the logic distance among each group of observations having homogeneous physical properties and maximizes the same quantity between groups. The correlation between the models is subsequently examined and significant classes (volumes of high correlation) are identified. Such technique is able to spatially clusterize the zones having similar characteristics in a statistical sense. Each zone is finally identified by the barycenter (centroid) of the corresponding cluster. Although the Vp velocity, Qp and Qs attenuation structures and density anomalies of Mt.Vesuvius and Campi Flegrei area Italy, have been already interpreted, to obtain a quantitative interpretation gathered in a unified model consistent with the entire dataset, a cluster analysis was applied to these models. This analysis permitted to define a simplified model of the volcanic complexes in terms of the independent geophysical parameters, characterized by sharp and well defined boundaries . This post-interpretation technique on one hand is largely far from being quantitative in terms of rock lithology , but in the same time is fast, easy and useful to retrieve the main patterns of the investigated structures. In other words, k-means cluster analysis may act as a bridge between qualitative interpretation (based on the visual comparison of the different structures obtained with different tomography techniques) and more quantitative approaches (based on the joint inversion of multiple attributes).

  3. Extraction of the local phase velocity and the group velocity from surface noise source in microseismic monitoring.

    NASA Astrophysics Data System (ADS)

    Chmiel, Malgorzata; Roux, Philippe; Bardainne, Thomas

    2015-04-01

    The aim of this work is to demonstrate the extraction of the local phase velocity and the group velocity from surface noise source in microseismic monitoring. One of the biggest challenges in microseismic monitoring is surface seismic noise. Microseismic surface studies are often contaminated with instrumental and ambient seismic noise, originating from both natural (wind, rain) and anthropogenic sources (injection, pumps, infrastructure, traffic). The two primary ways to attenuate the undesired surface noise sources are via processing and acquisition strategies. At the acquisition stage, one solution is through the use of patch array. One patch is a group of 48 vertical sensors densely distributed on the area of~150m*150m, and one trace is the array of 12 vertical geophones. In the present work, 44 patches were sparsely distributed on a 41 square kilometer area. Benefitting from continuous recording, we used Matched Field Processing (MFP) methods to extract local phase and group velocities over the whole area. The aim of this technique is to detect and locate uncoherent noise sources while using array-processing methods. The method is based on the comparison between a recorded wave field per patch (the data vector) and a theoretical (or modeled) wave-field (the replica vector) in the frequency domain. The replica vector is a Green's function at a given frequency, which depends on the following parameters: position (x,y) in 2D-grid and a phase velocity. The noise source location is obtained by matching the data vector with the replica vector using a linear "low-resolution" algorithm or a nonlinear "high-resolution" adaptive processor. These algorithms are defined for each point in the 2D - grid and for each phase velocity. The phase velocity per patch is optimal if it maximizes the processor output. As a result, an ambiguity surface is produced which shows the probability of presence of primary noise sources per patch. The combination of all the maps per patch

  4. Microcavity confinement based on an anomalous zero group-velocity waveguide mode

    NASA Astrophysics Data System (ADS)

    Ibanescu, Mihai; Johnson, Steven G.; Roundy, David; Fink, Yoel; Joannopoulos, J. D.

    2005-03-01

    We propose and demonstrate a mechanism for small-modal-volume high-Q cavities based on an anomalous uniform waveguide mode that has zero group velocity at a nonzero wave vector. In a short piece of a uniform waveguide with a specially designed cross section, light is confined longitudinally by small group-velocity propagation and transversely by a reflective cladding. The quality factor Q is greatly enhanced by the small group velocity for a set of cavity lengths that are separated by approximately pi/k_0, where k_0 is the longitudinal wave vector for which the group velocity is zero.

  5. Anisotropic 3-D Crustal Velocity Structure of Idaho/ Oregon from a Joint Inversion of Group and Phase Velocities of Love and Rayleigh Waves from Ambient Seismic Noise: Results from the IDOR Project

    NASA Astrophysics Data System (ADS)

    Bremner, P. M.; Panning, M. P.; Russo, R.; Mocanu, V. I.; Stanciu, A. C.; Torpey, M. E.; Hongsresawat, S.; VanDecar, J. C.

    2015-12-01

    We present new 3-D radially anisotropic and isotropic crustal velocity models beneath central Idaho and eastern Oregon. We produced the velocity models from Love and horizontal component Rayleigh wave group and phase velocity measurements on the IDaho/ORegon (IDOR) Passive seismic network, 86 broadband seismic stations, dataset using ambient noise tomography and the methods of Gallego et. al (2010) and Lin et. al (2008). We calculated inter-station group/phase velocities in narrow frequency bands from travel-time measurements of the rotated stacked horizontal component cross-correlations (bandpass filtered between 2 and 30 seconds), which we used to invert for velocity structure beneath the network. We derived group and phase velocity maps for each frequency band using the damped least-squares inversion method of Tarantola (2005), and then jointly inverted for velocity with depth. Moho depths are prescribed in the joint inversions based on receiver functions, also from the IDOR seismic data, and provides a starting crustal velocity model. Goals of our work include refining models of crustal structure in the accreted Blue Mountain terranes in the western study area; determining the depth extent of the Salmon River Suture/West Idaho Shear Zone (WISZ), which crosses north-south through the middle of the network; determining the architecture of the Idaho batholith, an extensive largely crustal-derived pluton; and examining the nature of the autochthonous (?) North American crust and lithosphere beneath and east of the batholith.

  6. Anisotropic S-wave velocity structure from joint inversion of surface wave group velocity dispersion: A case study from India

    NASA Astrophysics Data System (ADS)

    Mitra, S.; Dey, S.; Siddartha, G.; Bhattacharya, S.

    2016-12-01

    We estimate 1-dimensional path average fundamental mode group velocity dispersion curves from regional Rayleigh and Love waves sampling the Indian subcontinent. The path average measurements are combined through a tomographic inversion to obtain 2-dimensional group velocity variation maps between periods of 10 and 80 s. The region of study is parametrised as triangular grids with 1° sides for the tomographic inversion. Rayleigh and Love wave dispersion curves from each node point is subsequently extracted and jointly inverted to obtain a radially anisotropic shear wave velocity model through global optimisation using Genetic Algorithm. The parametrization of the model space is done using three crustal layers and four mantle layers over a half-space with varying VpH , VsV and VsH. The anisotropic parameter (η) is calculated from empirical relations and the density of the layers are taken from PREM. Misfit for the model is calculated as a sum of error-weighted average dispersion curves. The 1-dimensional anisotropic shear wave velocity at each node point is combined using linear interpolation to obtain 3-dimensional structure beneath the region. Synthetic tests are performed to estimate the resolution of the tomographic maps which will be presented with our results. We envision to extend this to a larger dataset in near future to obtain high resolution anisotrpic shear wave velocity structure beneath India, Himalaya and Tibet.

  7. Imbalance of group velocities for amplitude and phase pulses propagating in a resonant atomic medium

    NASA Astrophysics Data System (ADS)

    Basalaev, M. Yu.; Taichenachev, A. V.; Yudin, V. I.

    2016-11-01

    The dynamics of light pulses with amplitude and phase modulations is investigated for a medium of resonant two-level atoms. It is shown that the pulse-like variations of the phase can be also described in terms of group velocity. It is found that in the nonlinear regime of atom-field interaction, the group velocities of amplitude and phase pulses can have a large imbalance. Namely, amplitude pulses travel at a velocity less than c , whereas the group velocity of phase pulses is greater than the velocity of light in free space or it is even negative. The predicted imbalance of the group velocities can be important in the case of chirped pulses propagating in a resonant medium.

  8. 3-D Crustal Velocity Structure of Central Idaho/ Eastern Oregon from Joint Inversion of Rayleigh Wave Group and Phase Velocities Derived from Ambient Seismic Noise: Newest Results from the IDOR Project

    NASA Astrophysics Data System (ADS)

    Bremner, P. M.; Panning, M. P.; Russo, R. M.; Mocanu, V. I.; Stanciu, A. C.; Torpey, M. E.; Hongsresawat, S.; VanDecar, J. C.

    2014-12-01

    We present the latest 3-D isotropic crustal velocity model beneath central Idaho and eastern Oregon. We produced the velocity model from vertical component Rayleigh wave group and phase velocity measurements on data from the IDaho/ORegon (IDOR) Passive seismic network, 86 broadband seismic stations, using ambient noise tomography and the methods of Gallego et. al (2010) and Lin et. al (2008). We calculated inter-station group/phase velocities in narrow frequency bands from travel-time measurements of the stacked cross-correlations (bandpass filtered between 2 and 30 seconds), which we used to invert for velocity structure beneath the network. Goals of our work include refining models of crustal structure in the accreted Blue Mountain terranes in the western study area; determining the depth extent of the Salmon River Suture/West Idaho Shear Zone (WISZ), which crosses north-south through the middle of the network; determining the architecture of the Idaho batholith, an extensive largely crustal-derived pluton; and examining the nature of the autochthonous (?) North American crust and lithosphere beneath and east of the batholith. We derived Rayleigh wave group and phase velocity maps for each frequency band using the damped least-squares inversion method of Tarantola (2005), and then jointly inverted for velocity with depth. Moho depths are prescribed in the joint inversions based on receiver functions, also from the IDOR seismic data, and provides a starting crustal velocity model. 3-D checkerboard resolution tests indicate lateral resolution of better than 40 km. Preliminary results show higher S wave velocities in the western study area, and lower velocities in the lower crust on the east side of the network, consistent with Basin-and-Range style extension there. A tabular velocity anomaly juxtaposing higher above lower seismic velocities dips shallow west in the midcrust on the west side of the network.

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

    PubMed

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

    1999-11-15

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

  10. Dynamical lag correlation exponent based method for gas-solid flow velocity measurement using twin-plane electrical capacitance tomography

    NASA Astrophysics Data System (ADS)

    Xue, Qian; Wang, Huaxiang; Yang, Chengyi; Cui, Ziqiang

    2012-08-01

    In a twin-plane electrical capacitance tomography (ECT) system, velocity measurement of two-phase flow is transformed into the time delay estimation problem, while the nongaussianity and nonstationarity of two-phase flow signals have put the validity of the conventional cross-correlation algorithm in jeopardy. To improve the robustness and reliability of flow velocity measurement, an alternative method is proposed based on the dynamical lag correlation exponent and applied to coal ash measurement in a pneumatic pipeline. Different from the cross-correlation method which picks the peak point of the cross-correlation function as the delayed frames between the upstream and downstream signals, the proposed method determines the delayed frames by finding the minimum point of the dynamical lag correlation exponent. The preliminary results of flow velocity measurement indicate that the proposed method is capable of detecting various velocities (8-25 m s-1), which is useful for monitoring and predicting flow instability.

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

    USGS Publications Warehouse

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

    2010-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

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

  13. Using electric fields for pulse compression and group-velocity control

    NASA Astrophysics Data System (ADS)

    Li, Qian; Kinos, Adam; Thuresson, Axel; Rippe, Lars; Kröll, Stefan

    2017-03-01

    In this article, we experimentally demonstrate a way of controlling the group velocity of an optical pulse by using a combination of spectral hole burning, the slow-light effect, and the linear Stark effect in a rare-earth-ion-doped crystal. The group velocity can be changed continuously by a factor of 20 without significant pulse distortion or absorption of the pulse energy. With a similar technique, an optical pulse can also be compressed in time. Theoretical simulations were developed to simulate the group-velocity control and the pulse compression processes. The group velocity as well as the pulse reshaping are solely controlled by external voltages which makes it promising in quantum information and quantum communication processes. It is also proposed that the group velocity can be changed even more in an Er-doped crystal while at the same time having a transmission band matching the telecommunication wavelength.

  14. Nonlinear inversion of borehole-radar tomography data to reconstruct velocity and attenuation distribution in earth materials

    USGS Publications Warehouse

    Zhou, C.; Liu, L.; Lane, J.W.

    2001-01-01

    A nonlinear tomographic inversion method that uses first-arrival travel-time and amplitude-spectra information from cross-hole radar measurements was developed to simultaneously reconstruct electromagnetic velocity and attenuation distribution in earth materials. Inversion methods were developed to analyze single cross-hole tomography surveys and differential tomography surveys. Assuming the earth behaves as a linear system, the inversion methods do not require estimation of source radiation pattern, receiver coupling, or geometrical spreading. The data analysis and tomographic inversion algorithm were applied to synthetic test data and to cross-hole radar field data provided by the US Geological Survey (USGS). The cross-hole radar field data were acquired at the USGS fractured-rock field research site at Mirror Lake near Thornton, New Hampshire, before and after injection of a saline tracer, to monitor the transport of electrically conductive fluids in the image plane. Results from the synthetic data test demonstrate the algorithm computational efficiency and indicate that the method robustly can reconstruct electromagnetic (EM) wave velocity and attenuation distribution in earth materials. The field test results outline zones of velocity and attenuation anomalies consistent with the finding of previous investigators; however, the tomograms appear to be quite smooth. Further work is needed to effectively find the optimal smoothness criterion in applying the Tikhonov regularization in the nonlinear inversion algorithms for cross-hole radar tomography. ?? 2001 Elsevier Science B.V. All rights reserved.

  15. Use of Seismic Reflection Data and Traveltime Tomography to Image the Near Surface Velocity Structure in the Mississippi Embayment

    NASA Astrophysics Data System (ADS)

    Ge, J.; Magnani, M.; Waldron, B.; Powell, C.

    2007-12-01

    The Memphis aquifer represents one of the highest quality reservoirs of drinking water in the nation and it is separated from the shallow unconfined aquifer by the Upper Claiborne clay. Recent studies show that the confining unit might be discontinuous over the greater Memphis area exposing the Memphis aquifer to potential contamination. We present the results of a seismic reflection profile collected near Memphis, TN with the goal of imaging the structures and potential breaches in the Upper Claiborne confining clay. The imaged area is characterized by a highly heterogeneous shallow velocity structure and low P wave velocities in the ultrashallow unconsolidated materials. The data were collected using a shotgun source and a 1 m source spacing, 0.25 m receiver spacing and a 168-geophone spread for a max offset of 42 m. Raw seismic data show several reflected arrivals in the first 200ms, widespread ground roll, and air wave energy as well as consistent refracted phases across the 1 km - long profile. In addition to the reflection profile we present the preliminary results of first arrival travel time tomography performed along the profile to constrain the velocity field in the shallow portion of the profile. The velocity was then used to remove the effect of the near surface velocity variations. The main data processing steps included elevation statics and frequency and FK filtering. First arrival travel time modeling started with an initial estimate of the 2-layer velocity model using the slope/intercept method. We then modeled first-arrival picks on 1095 shot gathers using the Geo TOMO+ package. The algorithm computes travel times by tracing turning rays and is also able to handle raypaths through low-velocity zones (blind zones). The final resolution is estimated through a ray-information density map, which shows the cumulative contribution of the ray segments traversing different areas of the model. Synthetic models were generated and tested for the tomography

  16. a Renormalization Group Calculation of the Velocity - and Density-Density Correlation Functions.

    NASA Astrophysics Data System (ADS)

    Cowan, Mark Timothy

    The velocity-velocity correlation function of a free field theory is obtained. The renormalization group, along with a 4-varepsilon expansion, is then used to find the leading order behavior of the velocity-velocity correlation function for an interacting field theory in the high temperature phase near the critical point. The details of the calculation of the density-density correlation function for Hedgehogs, in the context of a free field theory, is presented next. Finally the renormalization group, along with a 4-varepsilon expansion, is used to find the leading order behavior of the density-density correlation function for Hedgehogs in an interacting field theory near the critical point.

  17. Analyzing sound speed fluctuations in shallow water from group-velocity versus phase-velocity data representation.

    PubMed

    Roux, Philippe; Kuperman, W A; Cornuelle, Bruce D; Aulanier, Florian; Hodgkiss, W S; Song, Hee Chun

    2013-04-01

    Data collected over more than eight consecutive hours between two source-receiver arrays in a shallow water environment are analyzed through the physics of the waveguide invariant. In particular, the use of vertical arrays on both the source and receiver sides provides source and receiver angles in addition to travel-times associated with a set of eigenray paths in the waveguide. From the travel-times and the source-receiver angles, the eigenrays are projected into a group-velocity versus phase-velocity (Vg-Vp) plot for each acquisition. The time evolution of the Vg-Vp representation over the 8.5-h long experiment is discussed. Group speed fluctuations observed for a set of eigenrays with turning points at different depths in the water column are compared to the Brunt-Väisälä frequency.

  18. Detection of fault structure under a near-surface low velocity layer by seismic tomography: synthetics studies

    NASA Astrophysics Data System (ADS)

    Sanny, Teuku A.; Sassa, Koichi

    1996-09-01

    We have developed a new method to detect a fault structure under a near-surface low velocity layer (LVL) by seismic tomography. The field study showed that the tomography image reconstructed using borehole-surface configuration had a different result from that of using a crosshole configuration. The image reconstructed by using a borehole-surface configuration showed a decrease in seismic velocities along boreholes, and also the tomogram result using both configurations can not detect the subsurface fault structure. These phenomena are caused by the low velocity layer (LVL) at the top of investigation area. The basic idea hard is based on a downward continuation principle. By knowing the thickness of the LVL and the top of bedrock enables us to place 'virtual receiver' and/or 'virtual source' below the LVL. In this way, we can reconstruct the image by various tomographic methodologies. As an advantage, this method is easy to be use with the aid of ray tracing methodology. It can also reduce the effect of the near-surface LVL and can maximize the reconstructed image. The final result of our synthetic images by ILST, SIRT, and modified SIRT shows high accuracy and resolution for detection of fault structure under the low velocity layer.

  19. X-Ray Tomography to Measure Size of Fragments from Penetration of High-Velocity Tungsten Rods

    NASA Astrophysics Data System (ADS)

    Stone, Zach; Hanna, Romy; Bless, Stephan; Levinson, Scott; InstituteAdvanced Technology Collaboration; Department of Geological Sciences-UT Austin Collaboration

    2011-06-01

    Behind-armor debris that results from tungsten rods penetrating armor steel at 2 km/s was studied by analysis of recovered fragments. Fragment recovery was by means of particleboard. Individual fragments were analyzed by x-ray tomography, which provides information for fragment identification, mass, shape, and penetration down to masses of a few milligrams. The experiments were complemented by AUTODYN SPH calculations to provide the exit velocity and the strain rate at the time of particle formation. There were four types of fragments: steel or tungsten, and generated from the channel or from the breakout through the target rear surface. Channel fragment motions were well described by Tate theory. Breakout fragments had velocities from the projectile remnant to the channel velocity, apparently depending on where in the projectile a fragment originated. The fragment size distribution was extremely broad and did not correlate well with simple uniform-fragment-size models, e.g., Grady Kipp.

  20. Characteristics of group velocities of backward waves in a hollow cylinder.

    PubMed

    Cui, Hanyin; Lin, Weijun; Zhang, Hailan; Wang, Xiuming; Trevelyan, Jon

    2014-06-01

    It is known that modes in axially uniform waveguides exhibit backward-propagation characteristics for which group and phase velocities have opposite signs. For elastic plates, group velocities of backward Lamb waves depend only on Poisson's ratio. This paper explores ways to achieve a large group velocity of a backward mode in hollow cylinders by changing the outer to inner radius ratio, in order that such a mode with strong backward-propagation characteristics may be used in acoustic logging tools. Dispersion spectra of guided waves in hollow cylinders of varying radii are numerically simulated to explore the existence of backward modes and to choose the clearly visible backward modes with high group velocities. Analyses of group velocity characteristics show that only a small number of low order backward modes are suitable for practical use, and the radius ratio to reach the highest group velocity corresponds to the accidental degeneracy of neighboring pure transverse and compressional modes at the wavenumber k = 0. It is also shown that large group velocities of backward waves are achievable in hollow cylinders made of commonly encountered materials, which may bring cost benefits when using acoustic devices which take advantage of backward-propagation effects.

  1. Simultaneous realization of negative group velocity, fast and slow acoustic waves in a metamaterial

    NASA Astrophysics Data System (ADS)

    Li, Xiao-juan; Xue, Cheng; Fan, Li; Zhang, Shu-yi; Chen, Zhe; Ding, Jin; Zhang, Hui

    2016-06-01

    An acoustic metamaterial is designed based on a simple and compact structure of one string of side pipes arranged along a waveguide, in which diverse group velocities are achieved. Owing to Fabry-Perot resonance of the side pipes, a negative phase time is achieved, and thus, acoustic waves transmitting with negative group velocities are produced near the resonant frequency. In addition, both fast and slow acoustic waves are also observed in the vicinity of the resonance frequency. The extraordinary group velocities can be explained based on spectral rephasing induced by anomalous dispersion on the analogy of Lorentz dispersion in electromagnetic waves.

  2. Role of group and phase velocity in high-energy neutrino observatories

    NASA Astrophysics Data System (ADS)

    Price, P. B.; Woschnagg, K.

    2001-03-01

    Kuzmichev recently showed that use of phase velocity rather than group velocity for Cherenkov light signals and pulses from calibration lasers in high-energy neutrino telescopes leads to errors in track reconstruction and distance measurement. We amplify on his remarks and show that errors for four cases of interest to AMANDA, IceCube, and radio Cherenkov detector are negligibly small.

  3. A New Ionosphere Tomography Algorithm with Two-Grids Virtual Observations Constraints and 3D Velocity Profile

    NASA Astrophysics Data System (ADS)

    Kong, Jian; Yao, Yibin; Shum, Che-Kwan

    2014-05-01

    Due to the sparsity of world's GNSS stations and limitations of projection angles, GNSS-based ionosphere tomography is a typical ill-posed problem. There are two main ways to solve this problem. Firstly the joint inversion method combining multi-source data is one of the effective ways. Secondly using a priori or reference ionosphere models, e.g., IRI or GIM models, as the constraints to improve the state of normal equation is another effective approach. The traditional way for adding constraints with virtual observations can only solve the problem of sparse stations but the virtual observations still lack horizontal grid constraints therefore unable to fundamentally improve the near-singularity characteristic of the normal equation. In this paper, we impose a priori constraints by increasing the virtual observations in n-dimensional space, which can greatly reduce the condition number of the normal equation. Then after the inversion region is gridded, we can form a stable structure among the grids with loose constraints. We then further consider that the ionosphere indeed changes within certain temporal scale, e.g., two hours. In order to establish a more sophisticated and realistic ionosphere model and obtain the real time ionosphere electron density velocity (IEDV) information, we introduce the grid electron density velocity parameters, which can be estimated with electron density parameters simultaneously. The velocity parameters not only can enhance the temporal resolution of the ionosphere model thereby reflecting more elaborate structure (short-term disturbances) under ionosphere disturbances status, but also provide a new way for the real-time detection and prediction of ionosphere 3D changes. We applied the new algorithm to the GNSS data collected in Europe for tomography inversion for ionosphere electron density and velocity at 2-hour resolutions, which are consistent throughout the whole day variation. We then validate the resulting tomography model

  4. Velocity inversion in cross-hole seismic tomography bycounter-propagation neural network, genetic algorithmand evolutionary programming techniques

    NASA Astrophysics Data System (ADS)

    Nath, Sankar Kumar; Chakraborty, Subrata; Singh, Sanjiv Kumar; Ganguly, Nilanjan

    1999-07-01

    The disadvantages of conventional seismic tomographic ray tracing and inversion by calculus-based techniques include the assumption of a single ray path for each source-receiver pair, the non-inclusion of head waves, long computation times, and the difficulty in finding ray paths in a complicated velocity distribution. A ray-tracing algorithm is therefore developed using the reciprocity principle and dynamic programming approach. This robust forward calculation routine is subsequently used for the cross-hole seismic velocity inversion. Seismic transmission tomography can be considered to be a function approximation problem; that is, of mapping the traveltime vector to the velocity vector. This falls under the purview of pattern classification problems, so we propose a forward-only counter-propagation neural network (CPNN) technique for the tomographic imaging of the subsurface. The limitation of neural networks, however, lies in the requirement of exhaustive training for its use in routine interpretation. Since finding the optimal solution, sometimes from poor initial models, is the ultimate goal, global optimization and search techniques such as simulated evolution are also implemented in the cross-well traveltime tomography. Genetic algorithms (GA), evolution strategies and evolutionary programming (EP) are the main avenues of research in simulated evolution. Part of this investigation therefore deals with GA and EP schemes for tomographic applications. In the present work on simulated evolution, a new genetic operator called `region-growing mutation' is introduced to speed up the search process. The potential of the forward-only CPNN, GA and EP methods is demonstrated in three synthetic examples. Velocity tomograms of the first model present plausible images of a diagonally orientated velocity contrast bounding two constant-velocity areas by both the CPNN and GA schemes, but the EP scheme could not image the model completely. In the second case, while GA and EP

  5. 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)

    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

    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.

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

    SciTech Connect

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

    1998-10-01

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

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

    NASA Astrophysics Data System (ADS)

    Mandal, Prantik

    2017-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

    We present group velocity dispersion results from a study of regional fundamental mode Rayleigh and Love waves propagating across Iran and the surrounding region. Data for these measurements comes from field deployments within Iran by the University of Cambridge (GBR) and the Universite Joseph-Fourier (FRA) in conjunction with International Institute of Earthquake Engineering and Seismology (Iran), in addition to data from IRIS and Geofone. 1D path- averaged dispersion measurements have been made for ~5500 source-receiver paths using multiple filter analysis. We combine these observations in a tomographic inversion to produce group velocity images between 10 and 60 s period. Because of the dense path coverage, these images have substantially higher lateral resolution for this region than is currently available from global and regional group velocity studies. We observe variations in short-period wave group velocity which is consistent with the surface geology. Low group velocities (2.00-2.55 km/s) at short periods (10-20 s), for both Rayleigh and Love waves are observed beneath thick sedimentary deposits; The south Caspian Basin, Black Sea, the eastern Mediterranean, the Persian Gulf, the Makran, the southern Turan shield, and the Indus and Gangetic basins. Somewhat higher group velocity (2.80-3.15 km/s for Rayleigh, and 3.00-3.40 km/s for Love) at these periods occur in sediment poor regions, such as; the Turkish-Iranian plateau, the Arabian shield, and Kazakhstan. At intermediate periods (30-40 s) group velocities over most of the region are low (2.65-3.20 km/s for Rayleigh, and 2.80-3.45 km/s for love) compared to Arabia (3.40-3.70 km/s Rayleigh, 3.50-4.0 km/s Love). At longer periods (50-60 s) Love wave group velocities remain low (3.25-3.70 km/s) over most of Iran, but there are even lower velocities (2.80-3.00 km/s) still associated with the thick sediments of the south Caspian basin, the surrounding shield areas have much higher group velocities (3

  9. All-optical tunable group-velocity control of femtosecond pulse by quadratic nonlinear cascading interactions.

    PubMed

    Lu, Wenjie; Chen, Yuping; Miu, Lihong; Chen, Xianfeng; Xia, Yuxing; Zeng, Xianglong

    2008-01-07

    Based on cascading nonlinear interactions of second harmonic generation (SHG) and difference frequency generation (DFG), we present a novel scheme to control the group velocity of femtosecond pulse in MgO doped periodically poled lithium niobate crystal. Group velocity of tunable signal pulse can be controlled by another pump beam within a wide bandwidth of 180nm. Fractional advancement of 2.4 and fractional delay of 4 are obtained in our simulations.

  10. Ambient Noise Tomography of Southern California Images Dipping San Andreas-Parallel Structure and Low-Velocity Salton Trough Mantle

    NASA Astrophysics Data System (ADS)

    Barak, S.; Klemperer, S. L.; Lawrence, J. F.

    2014-12-01

    Ambient noise tomography (ANT) images the entire crust but does not depend on the spatial and temporal distribution of events. Our ANT high-resolution 3D velocity model of southern California uses 849 broadband stations, vastly more than previous studies, and four years of data, 1997-1998, 2007, and 2011, chosen to include our own broadband Salton Seismic Imaging Project, a 40-station transect across the Salton Trough, as well as other campaign stations in both Mexico and the U.S.A., and permanent stations. Our shear-wave model has 0.05° x 0.05° lateral and 1 km vertical blocks. We used the Harvard Community Velocity Model (CVM-H) as the initial model for the inversion. We show significant differences relative to the CVM-H model, especially in the lower crust and upper mantle. We observe prominent low-velocity anomalies in the upper mantle under the Salton Buttes and Cerro Prieto geothermal fields, indicating high-temperatures and possibly partial-melt. Similar low-velocity zones have been previously observed along the Gulf of California. We also observe vertical to gradually dipping lateral velocity contrasts in the lower crust under the southern part of the San Andreas Fault. The east to northeast dip may represent crustal fabric sheared by movement of the Pacific plate under the North American plate prior to the initiation of transform motion.

  11. Lithospheric structure beneath the extinct ridge of South China Sea: Constraints from Rayleigh wave phase velocity tomography using OBS data

    NASA Astrophysics Data System (ADS)

    Yang, T.; Le, B. M.; passive-Source Seismic Team, S.

    2016-12-01

    What would happen when a mid-ocean-ridge stops spreading? Global occurrences of such ridges appear to indicate that magmatic activities had continued for million years after ridges were abandoned and often formed seamount chains over ridges. The extinct ridge and the seamount chain at the South China Sea represent one classic example of such ridges. To understand this unique process and the lithospheric and deep mantle structure, we carry out a Rayleigh wave phase velocity tomography using data from a passive-source OBS array experiment in South China Sea from 2012 to 2013. We correct OBS clock errors by using Scholte waves retrieved through cross-correlating hydrophone records of each OBS pair. 60 regional and teleseismic events with high quality Rayleigh waves are selected and their dispersion curves at the OBS array are used to inverse the phase velocities of periods from 15 s to 100 s. The shear wave velocity model derived from phase velocities of all periods shows a strong low-velocity zone situated beneath the seamounts starting at about 30 km depth. The lithosphere thickness of the extinct ridge inferred from this model provide insights on the cooling process and magmatism at this unique oceanic setting. In addition, our model images the tear of the subducting South China Sea plate beneath the Manila trench and Luzon island, which is clearly generated by the subduction of the extinct ridge and overriding seamounts.

  12. Ultrahigh-velocity resolution imaging of the microcirculation in-vivo using color Doppler optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Yazdanfar, Siavash; Rollins, Andrew M.; Izatt, Joseph A.

    2001-05-01

    Color Doppler optical coherence tomography (CDOCT) is a method for noninvasive cross-sectional imaging of blood flow in vivo. In previous implementations, velocity estimates were obtained by measuring the frequency shift of discrete depth-resolved backscatter spectra, resulting in a velocity resolution on the order of 1 mm/s. We present a novel processing method that detects Doppler shifts calculated across sequential axial scans, enabling ultrahigh velocity resolution (~1 micron/s) flow measurement in scattering media. This method of sequential scan processing was calibrated with a moving mirror mounted on a precision motorized translator. Latex microspheres suspended in deuterium oxide were used as a highly scattering test phantom. Laminar flow profiles down to ~15 micron/s centerline velocity (0.02 cc/hr) were observed with a sensitivity of 1.2 micron/s. Finally, vessels on the order of 10 microns in diameter were imaged in living human skin, with a relative frequency sensitivity less than 4 x 10-5. To our knowledge, these results are the lowest velocities ever measured with CDOCT.

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

    SciTech Connect

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

    1997-07-15

    THis report presents preliminary results from a large scale study of surface wave group velocity dispersion throughout Northern Africa, the Mediterranean, Southern Europe and the Middle East. Our goal is to better define the 3D lithospheric shear-wave velocity structure within this region by improving the resolution of global surface wave tomographic studies. We hope to accomplish this goal by incorporating regional data at relatively short periods (less than 40 sec), into the regionalization of lateral velocity variation. Due to the sparse distributions of stations and earthquakes throughout the region (Figure 1) we have relied on data recorded at both teleseismic and regions; distances. Also, to date we have concentrated on Rayleigh wave group velocity measurements since valuable measurements can be made without knowledge of the source. In order to obtain Rayleigh wave group velocity throughout the region, vertical component teleseismic and regional seismograms were gathered from broadband, 3-component, digital MEDNET, GEOSCOPE and IRIS stations plus the portable PASSCAL deployment in Saudi Arabia. Figure 1 shows the distribution of earthquakes (black circles) and broadband digital seismic stations (white triangles) throughout southern Europe, the middle east and northern Africa used in this study. The most seismicly active regions of northern Africa are the Atlas mountains of Morocco and Algeria as well as the Red Sea region to the east. Significant seismicity also occurs in the Mediterranean, southern Europe and throughout the high mountains and plateaus of the middle-east. To date, over 1300 seismograms have been analyzed to determine the individual group velocities of 10-150 second Rayleigh waves. Travel times, for each period, are then inverted in a back projection tomographic method in order to determine the lateral group velocity variation throughout the region. These results are preliminary, however, Rayleigh wave group velocity maps for a range of

  14. [The assessment of flow velocity in carotid and intracranial arteries in three different age groups].

    PubMed

    Niebudek, S

    1998-01-01

    In this report we assess the systolic maximal flow velocity in carotid and intracranial arteries in 191 subjects with no history of cerebral vascular disease in 3 age groups: 20-40 years (1 group), 41-60 years (2 group), and above 60 years (3 group). The subjects were assessed using Sonomed Transcranial Doppler Spectrograph according to generally accepted principles. The purpose of the study was to establish the mean value of maximal flow velocity in each particular artery in three age groups, and to observe the changes in this parameter with age. The results were analyzed using statistical methods and a significant decrease in blood flow, Vmax, was found in all investigated arteries. A mean decrease of 8.02% in flow velocity Vmax was found, when comparing groups 2 and 1, and difference 15.99% comparing 3 and 1.

  15. Resolution of group velocity models obtained by adjoint inversion in the Czech Republic region

    NASA Astrophysics Data System (ADS)

    Valentova, Lubica; Gallovic, Frantisek; Ruzek, Bohuslav; de la Puente, Josep

    2013-04-01

    We performed tomographic inversion of crosscorrelation traveltimes of group waves in the Bohemian massif. The traveltimes used for inversion come from ambient seismic noise measurements between pairs of stations filtered for several period ranges between 2-20s. The inverse problem was solved by the conjugate gradients, which were calculated using efficient adjoint method. Assuming that the propagation of group waves can be approximated by membrane waves for each period separately, the computations are reduced to 2D domain. The numerical calculations were carried out using adjoint version of SeisSol, which solves elastodynamic system using Discontinuous Galerkin method with arbitrary high order time derivatives (ADER-DG). The adjoint inversion is based on computation of so called sensitivity kernels for each data, which are then combined into Fréchet kernel of misfit gradient. Therefore, if using only the longest wavelength data i.e. the traveltimes of 20s and 16s group waves, structures of even shorter wavelengths can be obtained by the inversion. However, these smaller-scale structures are possibly more affected by data noise and thus require careful treatment. Note that in the classical tomography based on ray method, such structures are subdued by regularization. This leads to question on the influence of data noise on the obtained models. Several synthetic tests were carried out to reveal the effect of data errors on the resulting model. Firstly, we tested the level of data noise required to obtain artificial small scale structures. As a target model we constructed simple heterogenous model consisting of one very long wavelength structure. The synthetic traveltime data were modified using random shifts for several distributions with different variances. The method appears to be extremely sensitive even for relatively small level of noise. The other set of tests concentrated on the main feature of models obtained from the real data. All models inverted using

  16. Propagation of smooth and discontinuous pulses through materials with very large or very small group velocities

    NASA Astrophysics Data System (ADS)

    Bigelow, Matthew S.; Lepeshkin, Nick N.; Shin, Heedeuk; Boyd, Robert W.

    2006-03-01

    We investigate the propagation of optical pulses through two different solid-state optical materials, ruby and alexandrite, for which the group velocity can be very small (v_{\\mathrm {g}} \\ll c ) or superluminal (v_{\\mathrm {g}} \\gg c or negative). We find that for smooth pulses the fractional delay or advancement is maximized through the use of pulses with durations comparable to the response time of the physical process—coherent population oscillations—that leads to these extreme group velocities. However, we find that the transmitted pulse shape becomes distorted unless the pulse is much longer or much shorter than this response time. We also investigate the transmission of pulses that possess an abrupt change in pulse amplitude. We find that, to within experimental accuracy, this nearly discontinuous jump propagates at the usual phase velocity of light c/n, even though the smoothly varying portions of the pulse propagate at the group velocity.

  17. MeV-range velocity-space tomography from gamma-ray and neutron emission spectrometry measurements at JET

    NASA Astrophysics Data System (ADS)

    Salewski, M.; Nocente, M.; Jacobsen, A. S.; Binda, F.; Cazzaniga, C.; Ericsson, G.; Eriksson, J.; Gorini, G.; Hellesen, C.; Hjalmarsson, A.; Kiptily, V. G.; Koskela, T.; Korsholm, S. B.; Kurki-Suonio, T.; Leipold, F.; Madsen, J.; Moseev, D.; Nielsen, S. K.; Rasmussen, J.; Schneider, M.; Sharapov, S. E.; Stejner, M.; Tardocchi, M.; Contributors, JET

    2017-05-01

    We demonstrate the measurement of a 2D MeV-range ion velocity distribution function by velocity-space tomography at JET. Deuterium ions were accelerated into the MeV-range by third harmonic ion cyclotron resonance heating. We made measurements with three neutron emission spectrometers and a high-resolution γ-ray spectrometer detecting the γ-rays released in two reactions. The tomographic inversion based on these five spectra is in excellent agreement with numerical simulations with the ASCOT-RFOF and the SPOT-RFOF codes. The length of the measured fast-ion tail corroborates the prediction that very few particles are accelerated above 2 MeV due to the weak wave-particle interaction at higher energies.

  18. X-ray tomography to measure size of fragments from penetration of high-velocity tungsten rods

    NASA Astrophysics Data System (ADS)

    Stone, Zach; Bless, Stephan; Tolman, John; McDonald, Jason; Levinson, Scott; Hanna, R.

    2012-03-01

    Behind-armor debris that results from tungsten rods penetrating armor steel at 2 km/s was studied by analysis of recovered fragments. Fragment recovery was by means of particle board. Individual fragments were analyzed by x-ray tomography, which provides information for fragment identification, mass, shape, and penetration down to masses of a few milligrams. The experiments were complemented by AUTODYN and EPIC calculations. Fragments were steel or tungsten generated from the channel or from the breakout through the target rear surface. Channel fragment motions were well described by Tate theory. Breakout fragments had velocities from the projectile remnant to the channel velocity, apparently depending on where in the projectile a fragment originated. The fragment size distribution was extremely broad and did not correlate well with simple uniform-fragment-size models.

  19. In vivo label-free measurement of lymph flow velocity and volumetric flow rates using Doppler optical coherence tomography

    PubMed Central

    Blatter, Cedric; Meijer, Eelco F. J.; Nam, Ahhyun S.; Jones, Dennis; Bouma, Brett E.; Padera, Timothy P.; Vakoc, Benjamin J.

    2016-01-01

    Direct in vivo imaging of lymph flow is key to understanding lymphatic system function in normal and disease states. Optical microscopy techniques provide the resolution required for these measurements, but existing optical techniques for measuring lymph flow require complex protocols and provide limited temporal resolution. Here, we describe a Doppler optical coherence tomography platform that allows direct, label-free quantification of lymph velocity and volumetric flow rates. We overcome the challenge of very low scattering by employing a Doppler algorithm that operates on low signal-to-noise measurements. We show that this technique can measure lymph velocity at sufficiently high temporal resolution to resolve the dynamic pulsatile flow in collecting lymphatic vessels. PMID:27377852

  20. In vivo label-free measurement of lymph flow velocity and volumetric flow rates using Doppler optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Blatter, Cedric; Meijer, Eelco F. J.; Nam, Ahhyun S.; Jones, Dennis; Bouma, Brett E.; Padera, Timothy P.; Vakoc, Benjamin J.

    2016-07-01

    Direct in vivo imaging of lymph flow is key to understanding lymphatic system function in normal and disease states. Optical microscopy techniques provide the resolution required for these measurements, but existing optical techniques for measuring lymph flow require complex protocols and provide limited temporal resolution. Here, we describe a Doppler optical coherence tomography platform that allows direct, label-free quantification of lymph velocity and volumetric flow rates. We overcome the challenge of very low scattering by employing a Doppler algorithm that operates on low signal-to-noise measurements. We show that this technique can measure lymph velocity at sufficiently high temporal resolution to resolve the dynamic pulsatile flow in collecting lymphatic vessels.

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  2. The deeper structure of the southern Dead Sea basin derived from neural network analysis of velocity and attenuation tomography

    NASA Astrophysics Data System (ADS)

    Braeuer, Benjamin; Haberland, Christian; Bauer, Klaus; Weber, Michael

    2014-05-01

    The Dead Sea basin is a pull-apart basin at the Dead Sea transform fault, the boundary between the African and the Arabian plates. Though the DSB has been studied for a long time, the available knowledge - based mainly on surface geology, drilling and seismic reflection surveys - gives only a partial picture of its shallow structure. Therefore, within the framework of the international DESIRE (DEad Sea Integrated REsearch) project, a dense temporary local seismological network was operated in the southern Dead Sea area. Within 18 month of recording 650 events were detected. In addition to an already published tomography study revealing the distribution of P velocities and the Vp/Vs ratios a 2D P-wave attenuation tomography (parameter Qp) was performed. The neural network technique of Self-organizing maps (SOM) is used for the joint interpretation of these three parameters (Vp, Vp/Vs, Qp). The resulting clusters in the petrophysical parameter space are assigned to the main lithological units below the southern part of the Dead Sea basin: (1) The basin sediments characterized by strong attenuation, high vp/vs ratios and low P velocities. (2) The pre-basin sediments characterized by medium to strong attenuation, low Vp/Vs ratios and medium P velocities. (3) The basement characterized by low to moderate attenuation, medium vp/vs ratios and high P velocities. Thus, the asymmetric southern Dead Sea basin is filled with basin sediments down to depth of 7 to 12 km. Below the basin sediments, the pre-basin sediments are extending to a depth between 13 and 18 km.

  3. Anisotropic velocity structure of the crust and upper mantle in the Taiwan region from local travel time tomography

    NASA Astrophysics Data System (ADS)

    Jakovlev, Andrey; Koulakov, Ivan; Wu, Yih-Min

    2014-05-01

    Taiwan Island located in a contact zone between the Eurasian and Philippine Sea plates, the tectonic processes in this area are mostly controlled by the relative kinematics of these two plates. In the east, the Philippine Sea plate subducts northward under the Eurasian plate along the Ryukyu trench. Off the southern tip of Taiwan, the South China Sea subplate, part of the Eurasian plate, subducts eastward under the Philippine Sea plate underneath the Luzon Island. The Taiwan Island is located at the junction between these two subduction zones. Here we present anisotropic velocity model of the crust and upper mantle in the Taiwan region derived from local travel time tomography. We use more than 300 000 P and more than 150 000 S rays coming from 12910 earthquakes occurred in the Taiwan region and registered by 816 stations of different local Taiwanese seismic networks. The ANITA algorithm, for iterative nonlinear inversion of local earthquake data in orthorhombic anisotropic media with one predefined vertical orientation, was used for the tomographic inversion. This algorithm presumes anisotropy for only P velocity described as horizontally oriented ellipsoid. For S velocity we presume an isotropic model. Results show a good agreement with tectonic structure of the region. Obtained isotropic P and S velocity models show fit to each other. The most prominent features of the models are Philippine Sea plate characterized by increased velocities and decreased velocities observed along the Luzon and Ryukyu arcs. We observe that orientation of the fast velocity axis within the Philippine Sea plate coincides with direction of its displacement. Along the Luzon and Ryukyu arcs orientation of the fast velocities axis coincide with the arcs extension. The results show that upper mantle beneath the eastern Taiwan characterized by decreased velocities and N-S orientation of the fast velocity axis. The western Taiwan characterized by alteration of the relatively small negative

  4. IAG Working Group on Regional Dense Velocity Fields: First Results and Steps Ahead

    NASA Astrophysics Data System (ADS)

    Bruyninx, Carine

    2010-05-01

    The IAG Working Group (WG) on "Regional Dense Velocity Fields" was created within IAG sub-commission 1.3 "Regional Reference Frames" at the IUGG General Assembly in Perugia in 2007. The goal of the Working Group is to densify the latest realization of the ITRS and provide regional dense velocity information in a common global reference frame. For that purpose, working group members join efforts with the regional sub-commissions (AFREF, NAREF, SIRGAS, EUREF, …) and analysis groups processing data from local/regional continuous and episodic GNSS stations. Up to now, dedicated region coordinators have gathered velocity solutions (in accordance with the WG requirements) for their region and combined these solutions with the sub-commission regional solutions to produce a regional cumulative combined solution. Two combination coordinators performed a first test combination of these regional solutions together with global solutions in order to identify the main problems when producing a dense velocity field based on multiple cumulative position and velocity solutions. First comparisons between different velocity solutions show an RMS agreement between 0.3 mm/yr and 0.5 mm/yr resp. for the horizontal and vertical velocities. In some cases, significant disagreements between the velocities of some of the networks are seen, but these are primarily caused by the inconsistent handling of discontinuity epochs and solution numbers. Consequently, this test identified the urgent need for a consensus on the attribution of discontinuity epochs for stations common to several solutions. Due to the use of different analysis strategies and software packages by the individual contributors, finding such a consensus is a challenge as most probably not the same discontinuities are seen by different people. A possible way to go ahead for the Working Group could be to combine solutions at the weekly level. This approach is one of the alternative procedures which are presently under

  5. Experimental investigation of computed tomography sound velocity reconstruction using incomplete data.

    PubMed

    Huang, Sheng-Wen; Li, Pai-Chi

    2004-09-01

    An approach for reconstructing the sound velocity distribution in the breast was previously proposed and verified by simulations, and the present study investigated the approach experimentally. The experimental setup comprised a 5-MHz, 128-channel linear array, a programmable digital array system, a phantom containing objects with differing physical properties, and a computer. The array system was used to collect channel data for simultaneous B-mode image formation and limited-angle tomographic sound velocity reconstruction. The phantom was constructed from materials mimicking the following tissues in the breast: glandular tissue, fat, cysts, high-attenuation tumors, and irregular tumors. The sound velocities in these materials matched those in the corresponding real tissues. The imaging setup is similar to that of x-ray mammography, in which a linear array is placed at the top of the breast and a metal plate is placed at the bottom for reflecting sound waves. Thus, both B-mode images and the sound velocity distribution can be acquired using the same setup. An algorithm based on a convex programming formulation was used to reconstruct the sound velocity images. By scanning the phantom at different positions, nine cases were evaluated. In each of the nine cases, the image object comprised a background (glandular tissue) and one or three regions of interest (fat, tumor, or cyst). The sound velocity was accurately estimated in the nine cases evaluated, with sound velocity errors being less than 5 m/s in 8 of 11 regions of interest. Thus, obtaining the sound velocity distribution is feasible with a B-mode imaging setup using linear arrays. Knowledge of the sound velocity distribution in the breast can be used to complement B-mode imaging and to enhance the detection of breast cancer.

  6. GNSS tomography, assembled multi model solution, initial results from first experiment of IAG GNSS tomography working group

    NASA Astrophysics Data System (ADS)

    Rohm, W.; Gaiger, A.; Brenot, H.; Bender, M.; Shangguan, M.; Bosy, J.

    2012-12-01

    The Global Navigation Satellite Systems (GNSS) troposphere delay, standard product of GNSS processing, among all other applications can be used as a data source for GNSS tomography. The path delays in the direction of satellites can be converted to a 3D distribution of atmospheric refractivity (total or wet), or water vapor density using Radon inverse transform. Although problem is linear the ill - conditionedess and ill-posedness of the equations, results in complexity of the problem. In the frame of IAG Sub-Commission SC 4.3 - "Remote sensing and modelling of the atmosphere", we proposed a Working Group "Inter-comparison and cross-validation of tomography models". The group aim is to tackle current challenges of GNSS tomography modeling like how to find best way to include space based GNSS observations, to deliver more reliable slant delay processing methods, to test robust algorithms to account for outliers in observations, to determine trustworthy precision and accuracy measures, to address problems linked with near real time processing, and how to provide effective cooperation channels with meteorological agencies. In this study the same GNSS data set has been processed for each tomographic model. To study the differences between obtained solutions, each solution step of GNSS tomography has been carefully analyzed. The methodical framework has been developed to allow comprehensive comparison and validation. In the GNSS tomography process flow several critical points have been selected, for each node a validation has been performed. This validation was based on meteorological observations carefully selected from in situ measurements, satellite measurements, and Numerical Weather Prediction models. Following nodes of GNSS tomography processing have been considered: GNSS raw data processing and preprocessing of path delays, voxel model outline and construction, observation selection, raytracing algorithms, a priori observations, observations noise, inversion

  7. High contrast air-coupled acoustic imaging with zero group velocity lamb modes.

    PubMed

    Holland, Stephen D; Chimenti, D E

    2004-04-01

    The well known zero in the group velocity of the first-order symmetric (S1) plate wave mode has been exploited in air-coupled ultrasonic imaging to obtain significantly higher sensitivity than can be achieved in conventional air-coupled scanning. At the zero group velocity point at the frequency minimum of the S1 mode, a broad range of wavenumbers couple into the first-order symmetric mode at nearly a constant frequency, greatly enhancing transmission at that frequency. Coupled energy remains localized near the coupling point because the group velocity is zero. We excite the mode with a broadband, focussing, air-coupled transducer at the frequency of the zero group velocity point in the S1 mode. By exploiting the efficient coupling at the zero group velocity frequency, we have easily imaged a single layer of Scotch tape attached to a 6.4-mm thick Plexiglas plate and 3.2-mm Teflon inserts in a composite laminate.

  8. Teleseismic tomography of the compressional wave velocity structure beneath the Long Valley region, California

    USGS Publications Warehouse

    Dawson, P.B.; Evans, J.R.; Iyer, H.M.

    1990-01-01

    In 1982 and 1984 the US 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 travel time residuals have been inverted to obtain a three-dimensional image of the velocity structure with resolution of 5-6 km to depths of 70 km beneath the array. Direct inversion of these data indicates that the 2- to 4-km-thick low-velocity caldera fill contaminates the signal from any midcrustal velocity anomalies beneath the caldera. Two methods were used to strip the effects of the upper crust from the travel time residuals and the resulting "stripped' models show two well-resolved midcrustal low-velocity bodies in the Long Valley region. The features are interpreted as silicic magma chambers and the presence of additional pockets of magma <5 km across in the upper crust is not ruled out. The high eruptive rate of the Mono Craters and upper mantle velocity anomalies suggest that the focus of volcanism is shifting north from Long Valley to the Mono Craters. -from Authors

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

    USGS Publications Warehouse

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

    2001-01-01

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

  10. Latitudinal velocity structures up to the solar poles estimated from interplanetary scintillation tomography analysis

    NASA Astrophysics Data System (ADS)

    Kojima, M.; Fujiki, K.; Ohmi, T.; Tokumaru, M.; Yokobe, A.; Hakamada, K.

    2001-08-01

    The Ulysses spacecraft observed high-speed wind at high latitudes up to 80° and found that the high-speed solar wind increased in velocity gradually with latitude and that the velocity had asymmetry between Northern and Southern Hemispheres. We have investigated the velocity increase up to the polar regions for the Carrington rotations of 1908-1915 in the year 1996. For this purpose we have made tomographic analyses of the latitudinal structure of the solar wind speed using interplanetary scintillation data obtained at heliocentric distances of 0.1-0.9 AU and latitudes up to 90°. The tomographic analysis method was modified from its previous version [Kojima et al., 1998] so that it could obtain more reliable solutions with better sensitivity in the polar region than the previous method. The results from the observations in 1996 showed that the velocity increased with latitude and had the N-S asymmetry as observed by Ulysses. These features persisted during the period analyzed. Since the asymmetry was found in rather short period observations of several Carrington rotations and at distances within 0.9 AU, it is caused neither by temporal evolution of the solar wind structures nor by interactions in the solar wind in interplanetary space. These global latitudinal velocity structures agree qualitatively with the magnetic flux expansion factor.

  11. Group velocity mismatch-absent nonlinear frequency conversions for mid-infrared femtosecond pulses generation

    PubMed Central

    Zhong, Haizhe; Zhang, Lifu; Li, Ying; Fan, Dianyuan

    2015-01-01

    A novel group velocity mismatch (GVM) absent scheme for nonlinear optical parametric procedure in mid-infrared was developed with type-I quasi phase matching by use of an off-digital nonlinear optical coefficient d31. This was achieved by matching of the group velocities of the pump and the signal waves, while the phase velocities were quasi phase matched. The system employs MgO-doped periodically poled LiNbO3 as the nonlinear medium. Desired group-velocity dispersion would be obtained via appropriately temperature regulation. To demonstrate its potential applications in ultrafast mid-infrared pulses generation, aiming at a typical mid-infrared wavelength of ~3.2 μm, design examples of two basic nonlinear frequency conversion procedures are studied for both the narrow-band seeding mid-IR optical parametric amplification (OPA) and the synchronously pumped femtosecond optical parametric oscillation (SPOPO). Compared with the conventional scheme of type-0 QPM, the quantum-efficiency can be more than doubled with nearly unlimited bandwidth. The proposed GVM- absent phase matching design may provide a promising route to efficient and broadband sub-100 fs mid-infrared ultrafast pulses generation without group-velocity walk-off. PMID:26099837

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

    PubMed Central

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

    2015-01-01

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

  13. Offshore Rayleigh group velocity observations of the South Island, New Zealand, from ambient noise data

    NASA Astrophysics Data System (ADS)

    Yeck, William L.; Sheehan, Anne F.; Stachnik, Joshua C.; Lin, Fan-Chi

    2017-05-01

    We present azimuthally anisotropic Rayleigh group velocity models from 8 to 35 s both offshore and onshore of the South Island of New Zealand. We use MOANA (Marine Observations of Anisotropy Near Aotearoa) broad-band ocean seismic data in combination with on land data from the New Zealand National Seismography Network to investigate the seismic structure of the flanks of the Australian-Pacific plate boundary. At 8 s, we observe low offshore group velocities best explained by the influence of the water layer and thick water-laden sediments. At long periods (20-30 s), group velocities are lower on the South Island relative to its offshore flanks, due to thickened crust beneath the island, with the lowest velocities primarily beneath the Southern Alps. Group velocity azimuthal anisotropy fast directions near the Alpine Fault align with the direction of relative plate motion between the Australian and Pacific plates. In the southern portion of the island, fast directions rotate anticlockwise, likely in response to a decrease in dextral shearing away from the plate boundary. Azimuthal anisotropy fast directions align with absolute plate motion offshore on the Pacific plate. Based on the depth sensitivity of our observations, we suggest diffuse deformation occurs throughout the crust. Our observations match trends in previous Pn anisotropy and SKS shear wave splitting observations, and therefore suggest a consistent pattern of distributed deformation throughout the lithosphere.

  14. Offshore Rayleigh Group Velocity Observations of the South Island, New Zealand, from Ambient Noise Data

    NASA Astrophysics Data System (ADS)

    Yeck, William L.; Sheehan, Anne F.; Stachnik, Joshua C.; Lin, Fan-Chi

    2017-02-01

    We present azimuthally anisotropic Rayleigh group velocity models from 8 - 35 s both offshore and onshore of the South Island of New Zealand. We use MOANA (Marine Observations of Anisotropy Near Aotearoa) broadband ocean seismic data in combination with on land data from the New Zealand National Seismography Network (NZNSN) to investigate the seismic structure of the flanks of the Australian-Pacific plate boundary. At 8 s, we observe low offshore group velocities best explained by the influence of the water layer and thick water-laden sediments. At long periods (20-30 s), group velocities are lower on the South Island relative to its offshore flanks, due to thickened crust beneath the island, with the lowest velocities primarily beneath the Southern Alps. Group velocity azimuthal anisotropy fast directions near the Alpine Fault align with the direction of relative plate motion between the Australian and Pacific plates. In the southern portion of the island, fast directions rotate anticlockwise, likely in response to a decrease in dextral shearing away from the plate boundary. Azimuthal anisotropy fast directions align with absolute plate motion offshore on the Pacific plate. Based on the depth sensitivity of our observations, we suggest diffuse deformation occurs throughout the crust. Our observations match trends in previous Pn anisotropy and SKS shear wave splitting observations, and therefore suggest a consistent pattern of distributed deformation throughout the lithosphere.

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

    USGS Publications Warehouse

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

    2011-01-01

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

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

    PubMed

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

    2017-04-01

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

  17. Dependence of extrinsic loss on group velocity in photonic crystal waveguides.

    PubMed

    O'Faolain, Liam; White, Thomas P; O'Brien, David; Yuan, Xiadong; Settle, Michael D; Krauss, Thomas F

    2007-10-01

    We examine the effects of disorder on propagation loss as a function of group velocity for W1 photonic crystal (PhC) waveguides. Disorder is deliberately and controllably introduced into the photonic crystal by pseudo-randomly displacing the holes of the photonic lattice. This allows us to clearly distinguish two types of loss. Away from the band-edge and for moderately slow light (group velocity c/20-c/30) loss scales sub-linearly with group velocity, whereas near the band-edge, reflection loss increases dramatically due to the random and local shift of the band-edge. The optical analysis also shows that the random fabrication errors of our structures, made on a standard e-beam lithography system, are below 1 nm root mean square.

  18. Low velocities in the oceanic upper mantle and their relation to plumes: insights from SEM-based waveform tomography

    NASA Astrophysics Data System (ADS)

    Lekic, V.; French, S. W.; Romanowicz, B. A.

    2013-12-01

    The exchange of heat, mass and momentum between tectonic plates and mantle convection controls lithospheric evolution and hotspot volcanism, and must occur at a range of spatial scales. Yet, the detailed morphology of the associated convection patterns continues to elude geophysicists. Because seismic velocities are affected by temperature, seismic tomography can be used to map the patterns of flow in the Earth's mantle. Here, we present a global-scale long-period full-waveform seismic tomographic model SEMum2 constructed using the Spectral Element Method, which can very accurately model wave propagation through highly complex structures, and account for phenomena such as scattering, (de)focusing, and wavefront healing. Notably, SEMum2 achieves more realistic amplitudes of lateral heterogeneity - particularly low velocities in the upper 250km - than previous generations of global models, while still retrieving the long-wavelength structure present in earlier tomographic models. Cluster analysis of profiles of shear velocity in the SEMum2 oceanic upper mantle, confirms the presence of a well marked shear wave low velocity zone (LVZ) beneath the lithosphere, with a velocity minimum which deepens progressively as a function of age of the plate. The LVZ minimum in SEMum2 reaches values that are lower than in previous tomographic global models and in agreement with local estimates where available. Interestingly, reaching below this "classical" low velocity zone, the model reveals a pattern of alternating lower and higher velocities organized into elongated bands in the direction of absolute plate motion (APM), with a quasi-regular spacing of ~2000 km perpendicular to the APM. This fingerlike structure, most prominent around 200-250 km and extending down to 350-400 km, is most prominent beneath the Pacific plate, but also present under the eastern Antarctic plate, in the south Atlantic and in parts of the Indian Ocean Below this depth, the low velocities appear organized

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  1. Teleseismic tomography of the compressional wave velocity structure beneath the Long Valley region, California

    SciTech Connect

    Dawson, P.B.; Evans, J.R.; Iyer, H.M. )

    1990-07-10

    In 1982 and 1984 the U.S. Geological Survey used several seismic networks, totaling over 90 stations, to record teleseismic P waves and measure travel time residuals in an area centered on the Long Valley caldera. The authors inverted the travel time residuals to obtain a three-dimensional image of the velocity structure with resolution of 5-6 km to depths of 70 km beneath the array. Direct inversion of these data indicates that the 2- to 4-km-thick low-velocity caldera fill contaminates the signal from any midcrustal velocity anomalies beneath the caldera. Thus two methods were used to strip the effects of the upper crust from the travel time residuals: (1) ray tracing through upper crustal velocity models provided by seismic refraction experiments and gravity surveys, and (2) an iterative stripping scheme using the inversion itself. The methods produce essentially identical results and adequately remove the effects of the shallowest crustal structures, including the caldera fill and hydrothermal alteration effects. The resulting stripped models show two well-resolved midcrustal low-velocity bodies in the Long Valley region. The first body is centered between 7 and 20 km depth beneath the resurgent dome of the Long Valley caldera and has a volume of 150-600 km{sup 3}. The second, with a similar volume, is centered between 10 and 20 km depth beneath the Mono Craters, about 10 km north of Long Valley. Velocity contrasts in both of these bodies are about 6-10%, and the features are interpreted as silicic magma chambers. This experiment does not preclude the presence of additional pockets of magma smaller than 5 km across in the upper crust, particularly beneath the resurgent dome of the caldera (which would be removed with the stripping methods). The high eruptive rate of the Mono Craters and these upper mantle structures suggest that the focus of volcanism is shifting north from Long Valley to the Mono Craters

  2. Quantitative measurement of blood velocity in zebrafish with optical vector field tomography.

    PubMed

    Fieramonti, Luca; Foglia, Efrem A; Malavasi, Stefano; D'Andrea, Cosimo; Valentini, Gianluca; Cotelli, Franco; Bassi, Andrea

    2015-01-01

    Microscopy techniques can readily visualize the finest details of embryo vasculature, but still lack to provide a complete three-dimensional representation of blood flow parameters. We present an in-vivo 3D imaging technique, able to reconstruct the blood cell velocity vector over a large volume of zebrafish embryos. This low cost and relatively simple technique is exploited to quantitatively assess blood velocity in the zebrafish tail at different stages of development. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Uppermost mantle velocity from Pn tomography in the Gulf of Aden

    NASA Astrophysics Data System (ADS)

    Corbeau, Jordane; Rolandone, Frédérique; Leroy, Sylvie; Al-Lazki, Ali; Keir, Derek; Stuart, Graham; Stork, Anna

    2013-04-01

    We present an analysis of Pn traveltimes to determine lateral variations of velocity in the uppermost mantle and crustal thickness beneath the Gulf of Aden and its margins. No detailed tomographic image of the entire Gulf of Aden was available. Previous tomographic studies covered the eastern Gulf of Aden and were thus incomplete or at a large scale with a too low resolution to see the lithospheric structures. From 1990 to 2010, 49206 Pn arrivals were selected from the International Seismological Center catalogue. We also used temporary networks : YOCMAL (Young Conjugate Margins Laboratory) networks with broadband stations located in Oman, Yemen and Socotra from 2003 to 2011, and Djibouti network from 2009 to 2011. From these networks we picked Pn arrivals and selected 4110 rays. Using a least-squares tomographic code (Hearn, 1996), these data were analyzed to solve for velocity variations in the mantle lithosphere. We perform different inversions for shorter and longer ray path data sets in order to separate the shallow and deep structure within the mantle lid. In the upper lid, zones of low velocity (7.7 km/s) around Sanaa, Aden, Afar, and along the Gulf of Aden are related to active volcanism. Off-axis volcanism and a regional melting anomaly in the Gulf of Aden area may be connected to the Afar plume, and explained by the model of channeling material away from the Afar plume along ridge-axis. Our study validates the channeling model and shows that the influence of the Afar hotspot may extend much farther eastwards along the Aden and Sheba ridges into the Gulf of Aden than previously believed. Still in the upper lid, high Pn velocities (>8,2 km/s) are observed in Yemen and may be related to the presence of a magmatic underplating under the volcanic margin of Aden and under the Red Sea margins. In the lower lid, zones of low velocities are spatially located differently than in the upper lid. On the Oman margin, a low velocity zone (7.6 km/s) suggests deep partial

  4. Phase tunability of group velocity by modulated-pump-forced coherent population oscillations

    SciTech Connect

    Arrieta-Yanez, Francisco; Melle, Sonia; Calderon, Oscar G.; Anton, M. A.; Carreno, F.

    2009-07-15

    We propose a technique to obtain slow and fast light propagations based on coherent population oscillations forced by a modulated pump. This mechanism produces an enhancement of 1 order of magnitude of the delay or advancement of light signals. The relative phase between the pumps to the signal fields is used as a knob for changing light propagation from ultraslow group velocities to negative group velocities. The experimental realization of the phenomenon was carried out in an erbium-doped fiber amplifier at room temperature.

  5. Group velocity matching in high-order harmonic generation driven by mid-infrared lasers

    NASA Astrophysics Data System (ADS)

    Hernández-García, C.; Popmintchev, T.; Murnane, M. M.; Kapteyn, H. C.; Plaja, L.; Becker, A.; Jaron-Becker, A.

    2016-07-01

    We analyze the role of group-velocity matching (GVM) in the macroscopic build up of the high-harmonic signal generated in gas targets at high pressures. A definition of the walk-off length, associated with GVM, in the non-perturbative intensity regime of high-harmonic generation is given. Semiclassical predictions based on this definition are in excellent agreement with full quantum simulations. We demonstrate that group velocity matching is a relevant factor in high harmonic generation and the isolation of attosecond pulses driven by long wavelength lasers and preferentially selects contributions from the short quantum trajectories.

  6. Three-dimensional correction of conduction velocity in the embryonic heart using integrated optical mapping and optical coherence tomography

    PubMed Central

    Ma, Pei; Wang, Yves T.; Gu, Shi; Watanabe, Michiko; Jenkins, Michael W.; Rollins, Andrew M.

    2014-01-01

    Abstract. Optical mapping (OM) of cardiac electrical activity conventionally collects information from a three-dimensional (3-D) surface as a two-dimensional (2-D) projection map. When applied to measurements of the embryonic heart, this method ignores the substantial and complex curvature of the heart surface, resulting in significant errors when calculating conduction velocity, an important electrophysiological parameter. Optical coherence tomography (OCT) is capable of imaging the 3-D structure of the embryonic heart and accurately characterizing the surface topology. We demonstrate an integrated OCT/OM imaging system capable of simultaneous conduction mapping and 3-D structural imaging. From these multimodal data, we obtained 3-D activation maps and corrected conduction velocity maps of early embryonic quail hearts. 3-D correction eliminates underestimation bias in 2-D conduction velocity measurements, therefore enabling more accurate measurements with less experimental variability. The integrated system will also open the door to correlate the structure and electrophysiology, thereby improving our understanding of heart development. PMID:24996663

  7. Evaluation of the rockburst potential in longwall coal mining using passive seismic velocity tomography and image subtraction technique

    NASA Astrophysics Data System (ADS)

    Hosseini, Navid

    2017-09-01

    Rockburst is a typical dynamic disaster in underground coal mines which its occurrences relate to the mechanical quality of coal seam and surrounding rock mass and also the condition of stress distribution. The main aim of this paper is to study the potential of rockburst in a longwall coal mine by using of passive seismic velocity tomography and image subtraction technique. For this purpose, first by mounting an array of receivers on the surface above the active panel, the mining-induced seismic data as a passive source for several continuous days were recorded. Then, the three-dimensional tomograms using simultaneous iteration reconstruction technique (SIRT) for each day are created and by employing the velocity filtering, the overstressed zones are detected. In addition, the two-dimensional seismic velocity tomograms in coal seam level by slicing the three-dimensional tomograms are obtained. Then the state of stress changes in successive days by applying the image subtraction technique on these two-dimensional tomograms is considered. The results show that the compilation of filtered three-dimensional tomograms and subtracted images is an appropriate approach for detecting the overstressed zones around the panel and subsequent evaluation of rockburst potential. The research conclusion proves that the applied approach in this study in combination with field observations of rock mass status can effectively identify the rockburst-prone areas during the mining operation and help to improve the safety condition.

  8. Subduction zone in Java Island using primary wave tomography from Jacobian relocation method based on ak135 velocity model

    NASA Astrophysics Data System (ADS)

    Listyaningrum, Risca; Muhlis, Faid; Soesilo, Joko; Palupi, Indriati Retno

    2017-07-01

    The subduction zone occurs in Java Island analyzed based on data of tectonic earthquake. Earthquake data used is P wave velocity accessed from the ISC website from 1900-2013 years located along the Java Island. ISC is an organization that provides a variety of data tectonic earthquakes around the world, but the data used is the data before relocation. Relocation needs to reposition the hypocenter, so it can result a new position based on geological model. The relocation is using Jacobian's matrix and AK135 velocity model of P wave in each depth. The tomography process using FMTOMO software from result of new hypocenter represent the subsurface condition at a depth of 0-700 km. The result of hypocenter relocation is shifted horizontally to the southeast while vertically relatively shallow. The results obtained from the tomographic analysis of north-south section show the response of the velocity wave where high value shown in blue color as subduction zone and low value shown red color under volcanic as the partial melting. Tomographic 3D visualization displayed by Voxler software shows the different subduction in Java Island. Result of 3D analysis indicate that the subduction in West Java until Central Java relatively sloping than subduction in East Java.

  9. P wave crustal velocity structure in the greater Mount Rainier area from local earthquake tomography

    NASA Astrophysics Data System (ADS)

    Moran, Seth C.; Lees, Jonathan M.; Malone, Stephen D.

    1999-05-01

    We present results from a local earthquake tomographic imaging experiment in the greater Mount Rainier area. We inverted P wave arrival times from local earthquakes recorded at permanent and temporary Pacific Northwest Seismograph Network seismographs between 1980 and 1996. We used a method similar to that described by Lees and Crosson [1989], modified to incorporate the parameter separation method for decoupling the hypocenter and velocity problems. In the upper 7 km of the resulting model there is good correlation between velocity anomalies and surface geology. Many focal mechanisms within the St. Helens seismic zone have nodal planes parallel to the epicentral trend as well as to a north-south trending low-velocity trough, leading us to speculate that the trough represents a zone of structural weakness in which a moderate (M 6.5-7.0) earthquake could occur. In contrast, the western Rainier seismic zone does not correlate in any simple way with anomaly patterns or focal mechanism fault planes, leading us to infer that it is less likely to experience a moderate earthquake. A ˜10 km-wide low-velocity anomaly occurs 5 to 18 km beneath the summit of Mount Rainier, which we interpret to be a signal of a region composed of hot, fractured rock with possible small amounts of melt or fluid. No systematic velocity pattern is observed in association with the southern Washington Cascades conductor. A midcrustal anomaly parallels the Olympic-Wallowa lineament as well as several other geophysical trends, indicating that it may play an important role in regional tectonics.

  10. P wave crustal velocity structure in the greater Mount Rainier area from local earthquake tomography

    USGS Publications Warehouse

    Moran, S.C.; Lees, J.M.; Malone, S.D.

    1999-01-01

    We present results from a local earthquake tomographic imaging experiment in the greater Mount Rainier area. We inverted P wave arrival times from local earthquakes recorded at permanent and temporary Pacific Northwest Seismograph Network seismographs between 1980 and 1996. We used a method similar to that described by Lees and Crosson [1989], modified to incorporate the parameter separation method for decoupling the hypocenter and velocity problems. In the upper 7 km of the resulting model there is good correlation between velocity anomalies and surface geology. Many focal mechanisms within the St. Helens seismic zone have nodal planes parallel to the epicentral trend as well as to a north-south trending low-velocity trough, leading us to speculate that the trough represents a zone of structural weakness in which a moderate (M 6.5-7.0) earthquake could occur. In contrast, the western Rainier seismic zone does not correlate in any simple way with anomaly patterns or focal mechanism fault planes, leading us to infer that it is less likely to experience a moderate earthquake. A ???10 km-wide low-velocity anomaly occurs 5 to 18 km beneath the summit of Mount Rainier, which we interpret to be a signal of a region composed of hot, fractured rock with possible small amounts of melt or fluid. No systematic velocity pattern is observed in association with the southern Washington Cascades conductor. A midcrustal anomaly parallels the Olympic-Wallowa lineament as well as several other geophysical trends, indicating that it may play an important role in regional tectonics. Copyright 1999 by the American Geophysical Union.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  12. Three-dimensional velocity structure of the Galeras volcano (Colombia) from passive local earthquake tomography

    NASA Astrophysics Data System (ADS)

    Vargas, Carlos Alberto; Torres, Roberto

    2015-08-01

    A three-dimensional estimation of the Vp, Vs and Vp/Vs ratio structure at Galeras volcano was conducted by means of passive local earthquake tomography. 14,150 volcano-tectonic events recorded by 58 stations in the seismological network established for monitoring the volcanic activity by the Colombian Geological Survey - Pasto Volcano Observatory between the years 1989 and 2015, were inverted by using the LOTOS code. The seismic events are associated with shear-stress fractures in solid rock as a response to pressure induced by magma flow. Tomography resolution tests suggest a depth of imaging that yield 10 km from the summit of the main crater, illuminating a large portion of the volcanic structure and the interaction of tectonic features like the Buesaco and Silvia-Pijao faults. Full catalog tomographic inversion, that represents the stacked image of the volcanic structure or the most permanent features underneath the volcano, shows vertical structures aligned with seismicity beneath the main crater. We hypothesize that these structures correspond to a system of ducts or fractures through which magma and fluid phases flow up from deeper levels toward the top and related with the intersection of the surface traces of the Silvia-Pijao and Buesaco faults.

  13. Optical Tomography of a Sunspot. III. Velocity Stratification and the Evershed Effect

    NASA Astrophysics Data System (ADS)

    Westendorp Plaza, C.; del Toro Iniesta, J. C.; Ruiz Cobo, B.; Martínez Pillet, V.

    2001-02-01

    The stratification with optical depth of the line-of-sight (LOS) velocity of a simple, isolated, round sunspot observed with the Advanced Stokes Polarimeter (ASP; Elmore et al.) presented here completes this series of papers that investigates the stratification in optical depths of such a typical sunspot. These results have been obtained through the use of the SIR technique (Stokes Inversion based on Response functions of Ruiz Cobo & del Toro Iniesta). From these data we have confirmed that there are strong downflowing velocities at logτ5=0 that coincide spatially with the places where the magnetic field points downward (Westendorp Plaza et al.). Further confirmation is obtained by the application of the same method on a different sunspot, already analyzed with the Milne-Eddington inversion technique (Stanchfield, Thomas, & Lites). These downflows reconcile observations that have detected Evershed velocities outside sunspots together with suggestions of the possible return of the flow within the penumbra. The Evershed flow seems to be concentrated in elevated channels not thicker than 1 or 2 scale heights that are mostly located in the space between magnetic spines, i.e., in places where the magnetic field is more inclined, weaker in the inner-middle penumbra, and stronger in the outer penumbra and beyond the visible limits of the sunspot. This conclusion is based upon the tight correlation found between LOS velocities and the (reported in the second paper of this series) magnetic field strength and zenith angle. The upstreaming material is seen in the inner penumbra and the downstreaming in the outer penumbra. A strong increase with optical depth has been obtained for the LOS velocities that provides indications of the superposition of Evershed channels along the LOS. The differential opacity effect between the center-side and the limb-side penumbra, already reported in the second paper in this series, is also seen in the velocity maps and has suggested the

  14. Upper-mantle velocities below the Scandinavian Mountains from P- and S-wave traveltime tomography

    NASA Astrophysics Data System (ADS)

    Hejrani, Babak; Balling, Niels; Jacobsen, Bo Holm; England, Richard

    2017-01-01

    The relative traveltime residuals of more than 20 000 arrival times of teleseismic P and S waves measured over a period of more than 10 yr in five separate temporary and two permanent seismic networks covering the Scandinavian (Scandes) Mountains and adjacent areas of the Baltic Shield are inverted to 3-D tomograms of P and S velocities and the VP/VS ratio. Resolution analysis documents that good 3-D resolution is available under the dense network south of 64° latitude (Southern Scandes Mountains), and patchier, but highly useful resolution is available further north, where station coverage is more uneven. A pronounced upper-mantle velocity boundary (UMVB) that transects the study region is defined. It runs from SE Norway (east of the Oslo Graben) across the mountains to the Norwegian coast near Trondheim (around the Møre-Trøndelag Fault Complex), after which it follows closely along the coast further north. Seismic velocities in the depth interval 100-300 km change significantly across the UMVB from low relative VP and even lower relative VS on the western side, to high relative VP and even higher relative VS to the east. This main velocity boundary therefore also separates relatively high VP/VS ratio to the west and relatively low VP/VS to the east. Under the Southern Scandes Mountains (most of southern Norway), we find low relative VP, even lower relative VS and hence high VP/VS ratios. These velocities are indicative of thinner lithosphere, higher temperature and less depletion and/or fluid content in a relatively shallow asthenosphere. At first sight, this might support the idea of a mantle buoyancy source for the high topography. Under the Northern Scandes Mountains, we find the opposite situation: high relative VP, even higher relative VS and hence low VP/VS ratios, consistent with thick, dry, depleted lithosphere, similar to that in most of the Baltic Shield area. This demonstrates significant differences in upper-mantle conditions between the Southern

  15. Upper-mantle velocities below the Scandinavian Mountains from P- and S- wave traveltime tomography

    NASA Astrophysics Data System (ADS)

    Hejrani, Babak; Balling, Niels; Jacobsen, Bo Holm; England, Richard

    2016-09-01

    The relative traveltime residuals of more than 20,000 arrival-times of teleseismic P- and S-waves measured over a period of more than 10 years in five separate temporary and two permanent seismic networks covering the Scandinavian (Scandes) Mountains and adjacent areas of the Baltic Shield are inverted to 3D tomograms of P- and S- velocities and the VP/VS ratio. Resolution analysis documents that good 3D resolution is available under the dense network south of 64° latitude (Southern Scandes Mountains), and patchier, but highly useful resolution is available further north, where station coverage is more uneven. A pronounced upper-mantle velocity boundary (UMVB) that transects the study region is defined. It runs from SE Norway (east of the Oslo Graben) across the mountains to the Norwegian coast near Trondheim (around the Møre-Trøndelag Fault Complex), after which it follows closely along the coast further north. Seismic velocities in the depth interval 100-300 km change significantly across the UMVB from low relative VP and even lower relative VS on the western side, to high relative VP and even higher relative VS to the east. This main velocity boundary therefore also separates relatively high VP/VS ratio to the west and relatively low VP/VS to the east. Under the Southern Scandes Mountains (most of southern Norway) we find low relative VP, even lower relative VS and hence high VP/VS ratios. These velocities are indicative of thinner lithosphere, higher temperature and less depletion and/or fluid content in a relatively shallow asthenosphere. At first sight, this might support the idea of a mantle buoyancy source for the high topography. Under the Northern Scandes Mountains we find the opposite situation: high relative VP, even higher relative VS and hence low VP/VS ratios, consistent with thick, dry, depleted lithosphere, similar to that in most of the Baltic Shield area. This demonstrates significant differences in upper mantle conditions between the Southern

  16. Upper mantle velocity structure beneath the Arabian shield from Rayleigh surface wave tomography and its implications

    NASA Astrophysics Data System (ADS)

    Yao, Zhixiang; Mooney, Walter D.; Zahran, Hani M.; Youssef, Salah El-Hadidy

    2017-08-01

    We measured phase velocities at 13 periods from 20 s to 143 s using Rayleigh wave data recorded at recently installed, dense (135) broadband seismic stations in the Arabian shield and determined the shear-wave velocity structure. Our results clearly reveal a 300 km wide upper mantle seismic low-velocity zone (LVZ) beneath the western Arabian shield at a depth of 60 km and with a thickness of 130 km. The LVZ has a north-south trend and follows the late-Cenozoic volcanic areas. The lithosphere beneath the western Arabian shield is remarkably thin (60-90 km). The 130 km thick mantle LVZ does not appear beneath the western Red Sea and the spreading axis. Thus, the Red Sea at 20°-26°N is an asymmetric rift, with thin lithosphere located east of the Red Sea axis, as predicted by the low-angle detachment model for rift development. Passive rifting at the Red Sea and extensional stresses in the shield are probably driven by slab pull from the Zagros subduction zone. The low shear-wave velocity (4.0-4.2 km/s) and the geometry of LVZ beneath the western shield indicate northward flow of hot asthenosphere from the Afar hot spot. The upwelling of basaltic melt in fractures or zones of localized lithospheric thinning has produced extensive late Cenozoic volcanism on the western edge of the shield, and the buoyant LVZ has caused pronounced topography uplift there. Thus, the evolution of the Red Sea and the Arabian shield is driven by subduction of the Arabian plate along its northeastern boundary.

  17. Validated 3D Velocity Models in Asia from Joint Regional Body- and Surface-Wave Tomography

    DTIC Science & Technology

    2009-02-17

    90, 150 and 210 km. Some features of note in the new model include: • Crustal thickening beneath the major orogenic zones in the region...the low velocity area with respect to the background model beneath central Iran, which may have implications for the active subduction processes...occurring beneath the Eurasian continental collision zone . The slice on the right at 85°E cuts across the Himalayan Front, from northeastern India into

  18. Breed group effects for chute exit velocity as an indicator trait for temperament in weaner cattle

    USDA-ARS?s Scientific Manuscript database

    The objective of this study was to determine breed group differences in chute exit velocity (CEV) in weaner cattle (n=3176). Data were collected in 2004 through 2008 under procedures of objective 3, Southern Regional Research project S1013 with the following states contributing data: FL, LA, and MS...

  19. Relativistic effects of light in moving media with extremely low group velocity

    PubMed

    Leonhardt; Piwnicki

    2000-01-31

    A moving dielectric medium acts as an effective gravitational field on light. One can use media with extremely low group velocities [Lene Vestergaard Hau et al., Nature (London) 397, 594 (1999)] to create dielectric analogs of astronomical effects on Earth. In particular, a vortex flow imprints a long-ranging topological effect on incident light and can behave like an optical black hole.

  20. IGS Working Group "Regional Dense Velocity Fields": Objectives and Work Plan

    NASA Astrophysics Data System (ADS)

    Bruyninx, C.; Altamimi, Z.; Becker, M.; Craymer, M.; Combrinck, L.; Combrink, A.; Fernandes, R.; Govind, R.; Herring, T.; Kenyeres, A.; King, B.; Kreemer, C.; Lavallee, D.; Legrand, J.; Moore, M.; Sanchez, L.; Sella, G.; Woppelmann, G.

    2008-12-01

    The IAG Working Group (WG) on "Regional Dense Velocity Fields" was created within IAG sub-commission 1.3 "Regional Reference Frames" at the IUGG General Assembly in Perugia in 2007. The goal of the Working Group is to densify the latest realization of the ITRS and provide regional dense velocity information in a common global reference frame. For that purpose, working group members join efforts with the regional sub-commissions (AFREF, NAREF, SIRGAS, EUREF, ·s ) and analysis groups processing data from local/regional continuous and episodic GNSS stations. In a first step, dedicated region coordinators will gather as many as possible velocity solutions for their region (in accordance with the WG requirements) and combine these solutions with the sub-commission regional solutions to produce a regional cumulative combined solution in the SINEX format. In a second step, combination coordinators will perform combinations of the regional SINEX submissions and SINEX solutions from global GNSS networks like e.g. TIGA. The purpose of multiple combination coordinators is to evaluate both the results and different approaches. To assist in this task regional coordinators will solicit discontinuity tables in addition to the weekly SINEX solutions. At the same time, the WG will also study the strengths and shortcomings of local/regional and continuous/episodic GNSS solutions to determine site velocities, and define optimal strategies for the combination of regional and global SINEX solutions.

  1. Three-dimensional P-wave velocity structure in the greater Mount Rainier area from local earthquake tomography

    NASA Astrophysics Data System (ADS)

    Moran, Seth Charles

    1997-08-01

    One of the most striking features of seismicity in western Washington is the clustering of crustal earthquakes into one of several zones of concentrated seismicity. In this dissertation I explore the hypothesis that geologic structures, in conjunction with regional tectonic forces, are primarily responsible for controlling the location of seismicity in parts of western Washington. The primary tool for testing this hypothesis is a 3-dimensional image of the P-wave velocity structure of the greater Mount Rainier area that I derive using local earthquake tomography. I use P-wave arrival times from local earthquakes occurring between 1980 and 1996 recorded at short-period vertical component stations operated by the Pacific Northwest Seismograph Network (PNSN) and 18 temporary sites operated during a field experiment in 1995 and 1996. The tomographic methodology I use is similar to that described by Lees and Crosson (1989, 1990). In addition, I use the parameter separation method to decouple the hypocenter and velocity problems, don't use station corrections, and use ray-bending for 3-D raytracing, allowing for a full non-linear inversion. In the upper 4 km several low velocity features show good correlation with the Carbon River, Skate Creek, and Morton anticlines, as well as the Chehalis, Tacoma, and Seattle basins. There is also good correlation between high velocity features and surface exposures of several plutons. One seismic zone, the St. Helens Seismic Zone, correlates well with a planar low velocity feature. This correlation supports the idea that this seismic zone reflects a continuous structure roughly 50 km in length. A second zone, the Western Rainier Seismic Zone (WRSZ), does not correlate in any simple way with anomaly patterns, suggesting that the WRSZ does not represent a distinct fault. A 10 km-wide low velocity anomaly occurs 8 to 18 km beneath Mount Rainier, which I interpret to be due to a thermal aureole associated with the magmatic system beneath

  2. SDH detection of CFRP without pre-knowledge of anisotropic group velocity

    NASA Astrophysics Data System (ADS)

    Shao, Yongsheng; Lin, Jing; Zeng, Liang; Cao, Xuwei

    2017-04-01

    Ultrasonic phased array has been widely used for the nondestructive detection of carbon fiber-reinforced plastic (CFRP). The accurate anisotropic group velocity must be obtained beforehand for the detection imaging. It's a great challenge because of the anisotropy of CFRP. In this paper, a novel method is presented for the Side-Drilled Hole (SDH) detection in CFRP, in which the pre-knowledge of anisotropic group velocity is not needed. To begin with, the detection signal of CFRP with SDH was gained by the mode of FMC (full matrix capture). Then a limited angle range of the anisotropic group velocity is obtained by the back-wall reflection method (BRM). The angle range of velocity is extended by matching the delay time of back-wall and SDH reflection and analyzing the relation between the reflection of back-wall and SDH. Although the acquired angle range can't cover all the directions, it's still sufficient to image SDH. Finally, the total focusing method (TFM) is used to image CFRP. Furthermore, the weak defect located between SDH and back-wall may also be detected. An experiment was conducted on a sample of CFRP with SDH. The SDH can be seen clearly in the image.

  3. A detailed three-dimensional P-wave velocity structure in Italy from local earthquake tomography

    NASA Astrophysics Data System (ADS)

    di Stefano, Raffaele; Castello, Barbara; Chiarabba, Claudio; Grazia Ciaccio, Maria

    2010-05-01

    We here present an updated high resolution tomographic P-wave velocity model of the lithosphere in Italy, obtained by adding about 296,600 P-wave arrival observations from ~7.200 earthquakes, from the preliminary update of the CSI 2.0, recorded in the period 2003-2007, to the previously inverted dataset (165,000 P-wave arrivals).Additional events have been strictly selected for location quality (azimuthal gap < 135°; horizontal error <= 2km; vertical error <= 4km; rms < 1s) and a number of P-wave observations >= 8. Our results confirm the main structural features in the best resolved parts of the inverted volume and show a much better resolution in some of the previously less resolved areas, due to both the larger number of inverted phases and the more even distribution of seismic stations. Surface basins and relationships between the Adriatic, Tyrrhenian, and European plates are better imaged. The integrated analysis of 20 years of seismicity and the high resolution tomographic images obtained, allows us to add new constraints to the kynematics and the geodynamics of the lithosphere-asthenosphere system in this region. We also present preliminary results obtained by thickening the nodes spacing from 15km x15km to 10km x 10km and we finally compare the complex velocity structures imaged by the inversion of the two different grid spacing.

  4. Evaluation of flow velocities after carotid artery stenting through split spectrum Doppler optical coherence tomography and computational fluid dynamics modeling

    PubMed Central

    Vuong, Barry; Genis, Helen; Wong, Ronnie; Ramjist, Joel; Jivraj, Jamil; Farooq, Hamza; Sun, Cuiru; Yang, Victor X.D.

    2014-01-01

    Hemodynamics plays a critical role in the development of atherosclerosis, specifically in regions of curved vasculature such as bifurcations exhibiting irregular blood flow profiles. Carotid atherosclerotic disease can be intervened by stent implantation, but this may result in greater alterations to local blood flow and consequently further complications. This study demonstrates the use of a variant of Doppler optical coherence tomography (DOCT) known as split spectrum DOCT (ssDOCT) to evaluate hemodynamic patterns both before and after stent implantation in the bifurcation junction in the internal carotid artery (ICA). Computational fluid dynamics (CFD) models were constructed to simulate blood velocity profiles and compared to the findings achieved through ssDOCT images. Both methods demonstrated noticeable alterations in hemodynamic patterns following stent implantation, with features such as slow velocity regions at the neck of the bifurcation and recirculation zones at the stent struts. Strong correlation between CFD models and ssDOCT images demonstrate the potential of ssDOCT imaging in the optimization of stent implantation in the clinical setting. PMID:25574447

  5. Evaluation of flow velocities after carotid artery stenting through split spectrum Doppler optical coherence tomography and computational fluid dynamics modeling.

    PubMed

    Vuong, Barry; Genis, Helen; Wong, Ronnie; Ramjist, Joel; Jivraj, Jamil; Farooq, Hamza; Sun, Cuiru; Yang, Victor X D

    2014-12-01

    Hemodynamics plays a critical role in the development of atherosclerosis, specifically in regions of curved vasculature such as bifurcations exhibiting irregular blood flow profiles. Carotid atherosclerotic disease can be intervened by stent implantation, but this may result in greater alterations to local blood flow and consequently further complications. This study demonstrates the use of a variant of Doppler optical coherence tomography (DOCT) known as split spectrum DOCT (ssDOCT) to evaluate hemodynamic patterns both before and after stent implantation in the bifurcation junction in the internal carotid artery (ICA). Computational fluid dynamics (CFD) models were constructed to simulate blood velocity profiles and compared to the findings achieved through ssDOCT images. Both methods demonstrated noticeable alterations in hemodynamic patterns following stent implantation, with features such as slow velocity regions at the neck of the bifurcation and recirculation zones at the stent struts. Strong correlation between CFD models and ssDOCT images demonstrate the potential of ssDOCT imaging in the optimization of stent implantation in the clinical setting.

  6. Group velocity dispersion measurement method using sinusoidally phase-modulated continuous wave light based on cyclic nature of optical waveform change by group velocity dispersion.

    PubMed

    Yamamoto, Takashi; Mori, Takayoshi; Sakamoto, Taiji; Kurokawa, Kenji; Tomita, Shigeru; Tsubokawa, Makoto

    2010-09-20

    We show that any optical pulse train recovers its original waveform after passing through a group velocity dispersion (GVD) device when the total GVD value of the device is equal to an integral multiple of 1/(2πf(rep)(2)), where f(rep) is the repetition rate of the optical pulse train. In addition, we detail our proposed GVD measurement method, or optical phase-modulation (PM) method, which utilizes a sinusoidally PM continuous wave (CW) light as a probe light. The total GVD B(2) of a device under test (DUT) is derived by using a very simple equation, |B(2)|=1/(2πf(null)(2)), where f(null) is the smallest modulation frequency at which the sinusoidally PM light becomes CW light again after passing through the DUT.

  7. Micro X-ray Computed Tomography Imaging and Ultrasonic Velocity Measurements of Hydrate-Bearing Porous Media

    NASA Astrophysics Data System (ADS)

    Schindler, M.; Prasad, M.; Batzle, M. L.

    2015-12-01

    Naturally occurring gas hydrates contain significant amounts of natural gas which might be produced in the foreseeable future. Thus, it is necessary to understand the pore-space characteristics of hydrate reservoirs, especially the pore-scale distribution of hydrate and its interaction with the sediment. The goal of our research is to examine the distribution of hydrate in the pore space and the influence of hydrate pore-scale distribution on seismic velocities and sonic logs. We conducted laboratory measurements to obtain information about the distribution of hydrate in the pore space of synthetic porous media (glass beads). We used Tetrahydrofuran (THF) as a guest molecule since THF hydrate is a proxy for naturally occuring hydrate. We used micro X-ray computed tomography (MXCT) to image hydrate distribution in the pore space. In addition, we investigated the influence of hydrate saturation and distribution on ultrasonic velocities simultaneously with the MXCT imaging. We installed a torlon vessel and a cooling system in the MXCT scanner which allows us to form hydrate in the MXCT scanner at atmospheric pressure and a temperature of approximately 2°C. Both, MXCT images and ultrasonic velocity measurements, indicate that THF hydrate forms in the pore space while residual brine coats the grain surfaces and fills small pores. Our observations are in accordance with the pore-filling model of the effective medium theory of hydrate-bearing sediments. Based on this knowledge, it may be possible to calibrate seismic and well logging data to calculate the amount of natural gas stored in a hydrate reservoir. This information will help to make decisions regarding the producibility of methane hydrates and to develop safe production schemes.

  8. Analytical calculation of electron group velocity surfaces in uniform strained graphene

    NASA Astrophysics Data System (ADS)

    Gómez-Arias, Wilfrido A.; Naumis, Gerardo G.

    2016-12-01

    Electron group velocity for graphene under uniform strain is obtained analytically by using the tight-binding (TB) approximation. Such closed analytical expressions are useful in order to calculate the electronic, thermal and optical properties of strained graphene. These results allow to understand the behavior of electrons when graphene is subjected to strong strain and nonlinear corrections, for which the usual Dirac approach is no longer valid. Some particular cases of uniaxial and shear strain were analyzed. The evolution of the electron group velocity indicates a break-up of the trigonal warping symmetry, which is replaced by a warping consistent with the symmetry of the strained reciprocal lattice. To do this, analytical expressions for the shape of the first Brillouin zone (BZ) of the honeycomb strained reciprocal lattice are provided. Finally, the Fermi velocity becomes strongly anisotropic, i.e., for a strong pure shear strain (20% of the lattice parameter), the two inequivalent Dirac cones merge and the Fermi velocity is zero in one of the principal axis of deformation. We found that nonlinear terms are essential to describe the effects of deformation for electrons near or at the Fermi energy.

  9. Impact of Substrate and Bright Resonances on Group Velocity in Metamaterial without Dark Resonator.

    PubMed

    Hokmabadi, Mohammad Parvinnezhad; Kim, Ju-Hyung; Rivera, Elmer; Kung, Patrick; Kim, Seongsin M

    2015-09-23

    Manipulating the speed of light has never been more exciting since electromagnetic induced transparency and its classical analogs led to slow light. Here, we report the manipulation of light group velocity in a terahertz metamaterial without needing a dark resonator, but utilizing instead two concentric split-ring bright resonators (meta-atoms) exhibiting a bright Fano resonance in close vicinity of a bright Lorentzian resonance to create a narrowband transmittance. Unlike earlier reports, the bright Fano resonance does not stem from an asymmetry of meta-atoms or an interaction between them. Additionally, we develop a method to determine the metamaterial "effective thickness", which quantifies the influence of the substrate on the metamaterial response and has remained challenging to estimate so far. By doing so, very good agreement between simulated and measured group delays and velocities is accomplished. The proposed structure and method will be useful in designing optical buffers, delay lines, and ultra-sensitive sensors.

  10. Group velocity and pulse lengthening of mismatched laser pulses in plasma channels

    SciTech Connect

    Schroeder, Carl; Benedetti, Carlo; Esarey, Eric; van Tilborg, Jeroen; Leemans, Wim

    2011-07-07

    Analytic solutions are presented to the non-paraxial wave equation describing an ultra-short, low-power, laser pulse propagating in aplasma channel. Expressions for the laser pulse centroid motion and laser group velocity are derived, valid for matched and mismatchedpropagation in a parabolic plasma channel, as well as in vacuum, for an arbitrary Laguerre-Gaussian laser mode. The group velocity of amismatched laser pulse, for which the laser spot size is strongly oscillating, is found to be independent of propagation distance andsignificantly less than that of a matched pulse. Laser pulse lengthening of a mismatched pulse owing to laser mode slippage isexamined and found to dominate over that due to dispersive pulse spreading for sufficiently long pulses. Analytic results are shown tobe in excellent agreement with numerical solutions of the full Maxwell equations coupled to the plasma response. Implications for plasmachannel diagnostics are discussed.

  11. Estimation of modal group velocities with a single receiver for geoacoustic inversion in shallow water.

    PubMed

    Bonnel, Julien; Nicolas, Barbara; Mars, Jérome I; Walker, Shane C

    2010-08-01

    Due to the expense associated with at-sea sensor deployments, a challenge in underwater acoustics has been to develop methods requiring a minimal number of sensors. This paper introduces an adaptive time-frequency signal processing method designed for application to a single source-receiver sensor pair. The method involves the application of conjugate time-frequency warping transforms to improve the SNR and resolution of the time-frequency distribution (TFD) of the measured field. Such refined knowledge of the TFD facilitates efforts to extract tomographic information about the propagation medium. Here the method is applied to the case of modal propagation in a shallow ocean range independent environment to extract a refined TFD. Given knowledge of the source-receiver separation, the refined TFD is used to extract the frequency dependent group velocities of the individual modal components. The extracted group velocities are then incorporated into a computationally light tomographic inversion method. Simulated and experimental results are discussed.

  12. Vertical group and phase velocities of ionospheric waves derived from the MU radar

    NASA Astrophysics Data System (ADS)

    Liu, J. Y.; Hsiao, C. C.; Liu, C. H.; Yamamoto, M.; Fukao, S.; Lue, H. Y.; Kuo, F. S.

    2007-08-01

    The middle- and upper-atmosphere (MU) radar (34.85°N, 136.10°E) was operated in the incoherent scatter power-only mode to observe the ionosphere during 17 June 2001. Pronounced 200- to 300-min. waves in the echo power appeared in the F2 region during 0240-1250 local time on 17 June 2001. A procedure of Fourier analyses is conducted to derive power spectra, vertical phase, and group velocities of the pronounced waves. Results show that the center frequency of the waves is a function of the wave number. The opposite directions of the vertical phase and group velocities imply the presence of atmospheric gravity waves.

  13. Examination of group-velocity criterion for breakdown of vortex flow in a divergent duct

    NASA Technical Reports Server (NTRS)

    Tsai, C.-Y.; Widnall, S. E.

    1980-01-01

    A group-velocity criterion for vortex breakdown implied by wave trapping theory is applied to vortex flows in a slightly divergent duct that exhibits breakdown. The group velocities for both symmetric (n = 0) and nonsymmetric (n = plus or - 1) modes of wave propagation are calculated for the experimental data. It is found that the flow ahead of the breakdown region is always supercritical and stable to these modes of disturbances. However, the flow field behind the breakdown region may be either supercritical or subcritical to the modes n = 0 and n = 1, and always supercritical to mode n = -1. The flow field behind this breakdown region is unstable to the asymmetric mode disturbance (n = 1) for a finite range of wavenumbers. The calculated frequencies of the unstable disturbances are in good agreement with the frequencies obtained from the experimental measurements.

  14. Group velocity effect on resonant, long-range wake-fields in slow wave structures

    NASA Astrophysics Data System (ADS)

    Smirnov, A. V.

    2002-03-01

    Synchronous wake-fields in a dispersive waveguide are derived in a general explicit form on the basis of a rigorous electro-dynamical approach using Fourier transformations. The fundamental role of group velocity in wake-field propagation, calculation of attenuation, amplitudes, form-factors and loss-factors is analyzed for single bunch radiation. Adiabatic tapering of the waveguide and bunch density variation is taken into account analytically for the time-domain fields. Effects of field "compression/expansion" and group delays are demonstrated. The role of these effects is discussed for single bunch wake-fields, transient beam loading, BBU and HOMs. A novel waveguide structure with central rf coupling and both positive and negative velocities is proposed. It can be used effectively in both high-energy accelerators and single-section linacs.

  15. Pulse propagation near zero group-velocity dispersion in a femtosecond dye laser.

    PubMed

    Salin, F; Grangier, P; Georges, P; Brun, A

    1990-12-01

    The propagation of femtosecond pulses in a colliding-pulse mode-locked dye laser near zero group-velocity dispersion is studied. The pulse spectrum is shown to exhibit a double-peak structure. This structure and its dependence on the intracavity dispersion can be explained by nonlinear pulse propagation near zero dispersion. A value for the third-order dispersion of the laser cavity is deduced and is found to be predominant for pulses shorter than 50 fsec.

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

    NASA Technical Reports Server (NTRS)

    Li, Zhonghao; Zhou, Guosheng

    1996-01-01

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

  17. Ultrashort Laguerre-Gaussian pulses with angular and group velocity dispersion compensation.

    PubMed

    Zeylikovich, I; Sztul, H I; Kartazaev, V; Le, T; Alfano, R R

    2007-07-15

    Coherent optical vortices are generated from ultrashort 6.4 fs pulses. Our results demonstrate angular dispersion compensation of ultrashort 6.4 fs Laguerre-Gaussian (LG) pulses as well as what is believed to be the first direct autocorrelation measurement of 80 fs LG amplified pulses. A reflective-mirror-based 4f-compressor is proposed to compensate the angular and group velocity dispersion of the ultrashort LG pulses.

  18. Measurement of the group velocity of light in sea water at the ANTARES site

    NASA Astrophysics Data System (ADS)

    Adrián-Martínez, S.; Al Samarai, I.; Albert, A.; André, M.; Anghinolfi, M.; Anton, G.; Anvar, S.; Ardid, M.; Assis Jesus, A. C.; Astraatmadja, T.; Aubert, J.-J.; Baret, B.; Basa, S.; Bertin, V.; Biagi, S.; Bigi, A.; Bigongiari, C.; Bogazzi, C.; Bou-Cabo, M.; Bouhou, B.; Bouwhuis, M. C.; Brunner, J.; Busto, J.; Camarena, F.; Capone, A.; Cârloganu, C.; Carminati, G.; Carr, J.; Cecchini, S.; Charif, Z.; Charvis, Ph.; Chiarusi, T.; Circella, M.; Costantini, H.; Coyle, P.; Curtil, C.; De Bonis, G.; Decowski, M. P.; Dekeyser, I.; Deschamps, A.; Distefano, C.; Donzaud, C.; Dornic, D.; Dorosti, Q.; Drouhin, D.; Eberl, T.; Emanuele, U.; Enzenhöfer, A.; Ernenwein, J.-P.; Escoffier, S.; Fermani, P.; Ferri, M.; Flaminio, V.; Folger, F.; Fritsch, U.; Fuda, J.-L.; Galatà, S.; Gay, P.; Geyer, K.; Giacomelli, G.; Giordano, V.; Gómez-González, J. P.; Graf, K.; Guillard, G.; Halladjian, G.; Hallewell, G.; van Haren, H.; Hartman, J.; Heijboer, A. J.; Hello, Y.; Hernández-Rey, J. J.; Herold, B.; Hößl, J.; Hsu, C. C.; de Jong, M.; Kadler, M.; Kalekin, O.; Kappes, A.; Katz, U.; Kavatsyuk, O.; Kooijman, P.; Kopper, C.; Kouchner, A.; Kreykenbohm, I.; Kulikovskiy, V.; Lahmann, R.; Lamare, P.; Larosa, G.; Lattuada, D.; Lefèvre, D.; Lim, G.; Lo Presti, D.; Loehner, H.; Loucatos, S.; Mangano, S.; Marcelin, M.; Margiotta, A.; Martínez-Mora, J. A.; McMillan, J. E.; Meli, A.; Montaruli, T.; Moscoso, L.; Motz, H.; Neff, M.; Nezri, E.; Palioselitis, D.; Păvălaş, G. E.; Payet, K.; Payre, P.; Petrovic, J.; Piattelli, P.; Picot-Clemente, N.; Popa, V.; Pradier, T.; Presani, E.; Racca, C.; Reed, C.; Riccobene, G.; Richardt, C.; Richter, R.; Rivière, C.; Robert, A.; Roensch, K.; Rostovtsev, A.; Ruiz-Rivas, J.; Rujoiu, M.; Russo, G. V.; Salesa, F.; Samtleben, D. F. E.; Sapienza, P.; Schöck, F.; Schuller, J.-P.; Schüssler, F.; Seitz, T.; Shanidze, R.; Simeone, F.; Spies, A.; Spurio, M.; Steijger, J. J. M.; Stolarczyk, Th.; Sánchez-Losa, A.; Taiuti, M.; Tamburini, C.; Thompson, L. F.; Toscano, S.; Vallage, B.; Van Elewyck, V.; Vannoni, G.; Vecchi, M.; Vernin, P.; Wagner, S.; Wijnker, G.; Wilms, J.; de Wolf, E.; Yepes, H.; Zaborov, D.; Zornoza, J. D.; Zúñiga, J.

    2012-04-01

    The group velocity of light has been measured at eight different wavelengths between 385 nm and 532 nm in the Mediterranean Sea at a depth of about 2.2 km with the ANTARES optical beacon systems. A parametrisation of the dependence of the refractive index on wavelength based on the salinity, pressure and temperature of the sea water at the ANTARES site is in good agreement with these measurements.

  19. 3D ion velocity distribution function measurement in an electric thruster using laser induced fluorescence tomography.

    PubMed

    Elias, P Q; Jarrige, J; Cucchetti, E; Cannat, F; Packan, D

    2017-09-01

    Measuring the full ion velocity distribution function (IVDF) by non-intrusive techniques can improve our understanding of the ionization processes and beam dynamics at work in electric thrusters. In this paper, a Laser-Induced Fluorescence (LIF) tomographic reconstruction technique is applied to the measurement of the IVDF in the plume of a miniature Hall effect thruster. A setup is developed to move the laser axis along two rotation axes around the measurement volume. The fluorescence spectra taken from different viewing angles are combined using a tomographic reconstruction algorithm to build the complete 3D (in phase space) time-averaged distribution function. For the first time, this technique is used in the plume of a miniature Hall effect thruster to measure the full distribution function of the xenon ions. Two examples of reconstructions are provided, in front of the thruster nose-cone and in front of the anode channel. The reconstruction reveals the features of the ion beam, in particular on the thruster axis where a toroidal distribution function is observed. These findings are consistent with the thruster shape and operation. This technique, which can be used with other LIF schemes, could be helpful in revealing the details of the ion production regions and the beam dynamics. Using a more powerful laser source, the current implementation of the technique could be improved to reduce the measurement time and also to reconstruct the temporal evolution of the distribution function.

  20. Propagation lengths and group velocities of plasmons in chemically synthesized gold and silver nanowires.

    PubMed

    Wild, Barbara; Cao, Lina; Sun, Yugang; Khanal, Bishnu P; Zubarev, Eugene R; Gray, Stephen K; Scherer, Norbert F; Pelton, Matthew

    2012-01-24

    Recent advances in chemical synthesis have made it possible to produce gold and silver nanowires that are free of large-scale crystalline defects and surface roughness. Surface plasmons can propagate along the wires, allowing them to serve as optical waveguides with cross sections much smaller than the optical wavelength. Gold nanowires provide improved chemical stability as compared to silver nanowires, but at the cost of higher losses for the propagating plasmons. In order to characterize this trade-off, we measured the propagation length and group velocity of plasmons in both gold and silver nanowires. Propagation lengths are measured by fluorescence imaging of the plasmonic near fields. Group velocities are deduced from the spacing of fringes in the spectrum of coherent light transmitted by the wires. In contrast to previous work, we interpret these fringes as arising from a far-field interference effect. The measured propagation characteristics agree with numerical simulations, indicating that propagation in these wires is dominated by the material properties of the metals, with additional losses due to scattering from roughness or grain boundaries providing at most a minor contribution. The propagation lengths and group velocities can also be described by a simple analytical model that considers only the lowest-order waveguide mode in a solid metal cylinder, showing that this single mode dominates in real nanowires. Comparison between experiments and theory indicates that widely used tabulated values for dielectric functions provide a good description of plasmons in gold nanowires but significantly overestimate plasmon losses in silver nanowires.

  1. Maximum group velocity in a one-dimensional model with a sinusoidally varying staggered potential

    NASA Astrophysics Data System (ADS)

    Nag, Tanay; Sen, Diptiman; Dutta, Amit

    2015-06-01

    We use Floquet theory to study the maximum value of the stroboscopic group velocity in a one-dimensional tight-binding model subjected to an on-site staggered potential varying sinusoidally in time. The results obtained by numerically diagonalizing the Floquet operator are analyzed using a variety of analytical schemes. In the low-frequency limit we use adiabatic theory, while in the high-frequency limit the Magnus expansion of the Floquet Hamiltonian turns out to be appropriate. When the magnitude of the staggered potential is much greater or much less than the hopping, we use degenerate Floquet perturbation theory; we find that dynamical localization occurs in the former case when the maximum group velocity vanishes. Finally, starting from an "engineered" initial state where the particles (taken to be hard-core bosons) are localized in one part of the chain, we demonstrate that the existence of a maximum stroboscopic group velocity manifests in a light-cone-like spreading of the particles in real space.

  2. Velocity and Energy Distributions of Water Group Ion Around the Enceladus Plume

    NASA Astrophysics Data System (ADS)

    Sakai, S.; Cravens, T.; Pothapragada, S.; Kumar, A.

    2014-12-01

    Enceladus has a dynamic plume on its south pole which is emitting gas, including water vapor, and dust. The gas is ionized by solar EUV radiation and by electron impacts and extends throughout the inner magnetosphere of Saturn. The dust is negatively charged and forms the E ring. Hence, the inner magnetosphere within 10 RS contains a complex mixture of plasma, neutral gas and dust. Cassini observations show that the plasma velocities are less than the co-rotation velocity. The velocity and energy distributions of this need to be explained in order to understand the inner magnetospheric plasma physics. We have investigated the velocity and energy distributions of water group ions in the vicinity of Enceladus using test particle and Monte Carlo methods including collisional processes such as charge exchange and ion-neutral chemical reaction. The model results will be constrained by neutral and ion composition data from the Cassini Ion and Neutral Mass Spectrometer and ion energy spectra from the Plasma Spectrometer (CAPS). We will also discuss related plasma processed in the Enceladus torus.

  3. Simultaneous Negative Phase and Group Velocity of Light in a Metamaterial

    NASA Astrophysics Data System (ADS)

    Dolling, Gunnar; Enkrich, Christian; Wegener, Martin; Soukoulis, Costas M.; Linden, Stefan

    2006-05-01

    We investigated the propagation of femtosecond laser pulses through a metamaterial that has a negative index of refraction for wavelengths around 1.5 micrometers. From the interference fringes of a Michelson interferometer with and without the sample, we directly inferred the phase time delay. From the pulse-envelope shift, we determined the group time delay. In a spectral region, phase and group velocity are negative simultaneously. This means that both the carrier wave and the pulse envelope peak of the output pulse appear at the rear side of the sample before their input pulse counterparts have entered the front side of the sample.

  4. Monitoring of drug and stimulation induced cerebral blood flow velocity changes in rat sensory cortex using spectral domain Doppler optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Wang, Chuan; Yang, Yong; Ding, Zhihua; Meng, Jie; Wang, Kai; Yang, Wenwei; Xu, Ying

    2011-04-01

    Doppler optical coherence tomography (DOCT) provides a novel method to measure blood flow velocity in vessels with diameter at micrometer scale. In this study, a developed spectral domain DOCT system is applied to monitor cerebral blood flow velocity changes in a rat. An animal model with a cranial window is used, and by application of a drug, light, and electric stimulations, changes in blood flow velocity of the pial artery in sensory cortex are measured in real time. The results show significant differences in blood flow velocity before and after drug administration or light and electric stimulations, demonstrating the feasibility of DOCT in cerebral microcirculation study. Given its noninvasive nature, high spatial resolution, high velocity sensitivity, and high imaging speed, DOCT shows great promise in brain research by imaging blood flow changes at micrometer scale vessels, which helps to understand the pathogenesis of cerebral diseases and neurodegenerative diseases.

  5. Laser ultrasonic inspection of plates using zero-group velocity lamb modes.

    PubMed

    Clorennec, Dominique; Prada, Claire; Royer, Daniel

    2010-05-01

    A noncontact laser-based ultrasonic technique is proposed for detecting small plate thickness variations caused by corrosion and adhesive disbond between two plates. The method exploits the resonance at the minimum frequency of the S(1) Lamb mode dispersion curve. At this minimum frequency, the group velocity vanishes, whereas the phase velocity remains finite. The energy deposited by the laser pulse generates a local resonance of the plate. This vibration is detected at the same point by an optical interferometer. First experiments show the ability to image a 1.5-microm deep corroded area on the back side of a 0.5-mm-thick duralumin plate. Because of the finite wavelength of the S(1)- zero group velocity (ZGV) mode, the spatial resolution is limited to approximately twice the plate thickness. With the same technique we investigate the state of adhesive bonds between duralumin and glass plates. The S(1)-Lamb mode resonance is strongly attenuated when plates are rigidly bonded. In the case of thin adhesive layers, we observed other resonances, associated with ZGV modes of the multi-layer structure, whose frequencies and amplitudes vary with adhesive thickness. Experiments were carried out on real automotive adhesively bonded structures and the results were compared with images obtained by X-ray radiography.

  6. Velocity structures of Geothermal sites: A comparative study between different tomography techniques on the EGS-Soultz-sous-Forêts Site (France)

    NASA Astrophysics Data System (ADS)

    Calo', M. C.; Dorbath, C.

    2009-12-01

    One major goal of monitoring seismicity accompanying hydraulic fracturing of a reservoir is to recover the seismic velocity field in and around the geothermal site. In many cases the seismicity induced by the hydraulic stimulations allows us to roughly describe the velocity anomalies close to the hypocentral location, but only during the time period of the stimulation. Several studies have shown that the 4D (time dependent) seismic tomographies are very useful to illustrate and study the temporal variation of the seismic velocities conditioned by injected fluids. Nevertheless in geothermal fields local earthquake tomography (LET) is often inadequate to study the seismic velocities during the inter-injection periods, due to the lack of seismicity. In July 2000 an injection test that lasted 15 days performed at the Enhanced Geothermal System (EGS) site of Soultz-sous-Forêts (Alsace, France) produced about 7200 micro-earthquakes with Duration Magnitude ranging from -0.9 to 2.5. the earthquakes were located by down hole and surface seismic stations. We present here a comparison between three tomographic studies, 1) the “traditional” seismic tomography of Cuneot et al., 2008, 2) a Double Difference tomography using the TomoDD code of Zhang and Thurber (2003) and, 3) the models obtained by applying the Weighted Average Model method (WAM, Calo’ et al., 2009). the velocity models were obtained using the same dataset recorded during the stimulation. The WAM technique produces a more reliable reconstruction of the structures around and above the cluster of earthquakes, as demonstrated by the distribution of the velocity standard deviations. Although the velocity distributions obtained by the three tomographic approaches are qualitatively similar, the WAM results correlate better with independent data such the fracturing directions measured in the down-holes, the location of the clustered seimsicity) than those of the traditional and DD tomographies. To overcome the

  7. High resolution crustal and upper mantle velocity model of northern Ordos block from surface wave tomography: evidence for the on-going craton reactivation

    NASA Astrophysics Data System (ADS)

    Guo, Z.; LI, S.; Chen, Y. J.; Yang, Y.

    2016-12-01

    The Ordos block is the nuclei of the Archean craton of North China Craton (NCC), which had experienced significantly lithospheric reworking since the Mesozoic. A series of rifting zones developed surrounding the Ordos block during the Cenozoic. Here, we present a high-resolution crustal and upper mantle velocity model of the northern Ordos block from surface wave tomography. The seismic data are mainly from the recently deployed portable seismic array, the NODArray (North OrDos Array) with 102 stations, by Peking University. In addition, 221 permanent stations from CEA (China Earthquake Administration) and 106 portable stations from NCISP (North China Interior Structure Project) are also used in the tomography. Phase velocities at periods 6-40 s were obtained from ambient noise tomography and phase velocities between 25 and 143 s were measured from the two-plane-wave tomography with finite-frequency effects included. We then inverted for 3-D S-wave velocity model from the surface down to 250km depth beneath the Ordos block using a MCMC scheme (Markov Chain Monte Carlo). The resulting velocity model reveals significant lithospheric reactivation in the margins of the Ordos block. As expected, the prominent high velocity is shown beneath the interior of the Ordos block, suggesting the preservation of thick lithospheric root. However, beneath the Inner Mongolia Suture Zone (IMSZ), the Precambrian suture zone between the Ordos bock and Yinshan belt to the north of the Ordos block, we observed ultra-low velocity anomaly from the mid-to lower crust to upper mantle. The Yinshan belt and Trans-North China Orogen (TNCO) are also linked to low velocity anomalies in the upper mantle. The most significant feature of our model is the low velocity anomaly beneath the Datong volcano, which extends to at least 250-km depth. This continuous low velocity anomaly can be interpreted by a plume-like upwelling, which originates from the deep upper mantle and ascends into the lithosphere

  8. Quantitative imaging of cerebral blood flow velocity and intracellular motility using dynamic light scattering–optical coherence tomography

    PubMed Central

    Lee, Jonghwan; Radhakrishnan, Harsha; Wu, Weicheng; Daneshmand, Ali; Climov, Mihail; Ayata, Cenk; Boas, David A

    2013-01-01

    This paper describes a novel optical method for label-free quantitative imaging of cerebral blood flow (CBF) and intracellular motility (IM) in the rodent cerebral cortex. This method is based on a technique that integrates dynamic light scattering (DLS) and optical coherence tomography (OCT), named DLS–OCT. The technique measures both the axial and transverse velocities of CBF, whereas conventional Doppler OCT measures only the axial one. In addition, the technique produces a three-dimensional map of the diffusion coefficient quantifying nontranslational motions. In the DLS–OCT diffusion map, we observed high-diffusion spots, whose locations highly correspond to neuronal cell bodies and whose diffusion coefficient agreed with that of the motion of intracellular organelles reported in vitro in the literature. Therefore, the present method has enabled, for the first time to our knowledge, label-free imaging of the diffusion-like motion of intracellular organelles in vivo. As an example application, we used the method to monitor CBF and IM during a brief ischemic stroke, where we observed an induced persistent reduction in IM despite the recovery of CBF after stroke. This result supports that the IM measured in this study represent the cellular energy metabolism-related active motion of intracellular organelles rather than free diffusion of intracellular macromolecules. PMID:23403378

  9. TWO DISTANT HALO VELOCITY GROUPS DISCOVERED BY THE PALOMAR TRANSIENT FACTORY

    SciTech Connect

    Sesar, Branimir; Cohen, Judith G.; Levitan, David; Kirby, Evan N.; Kulkarni, Shrinivas R.; Prince, Thomas A.; Grillmair, Carl J.; Laher, Russ R.; Surace, Jason A.; Juric, Mario; Ofek, Eran O.

    2012-08-20

    We report the discovery of two new halo velocity groups (Cancer groups A and B) traced by eight distant RR Lyrae stars and observed by the Palomar Transient Factory survey at R.A. {approx} 129 Degree-Sign , decl. {approx} 20 Degree-Sign (l {approx} 205 Degree-Sign , b {approx} 32 Degree-Sign ). Located at 92 kpc from the Galactic center (86 kpc from the Sun), these are some of the most distant substructures in the Galactic halo known to date. Follow-up spectroscopic observations with the Palomar Observatory 5.1 m Hale telescope and W. M. Keck Observatory 10 m Keck I telescope indicate that the two groups are moving away from the Galaxy at v-bar{sub gsr}{sup A} = 78.0{+-}5.6 km s{sup -1} (Cancer group A) and v-bar{sub gsr}{sup B} = 16.3{+-}7.1 km s{sup -1} (Cancer group B). The groups have velocity dispersions of {sigma}{sub v{sub g{sub s{sub r}{sup A}}}} = 12.4{+-}5.0 km s{sup -1} and {sigma}B{sub v{sub g{sub s{sub r}{sup B}}}} =14.9{+-}6.2 km s{sup -1} and are spatially extended (about several kpc), making it very unlikely that they are bound systems, and more likely to be debris of tidally disrupted dwarf galaxies or globular clusters. Both groups are metal-poor (median metallicities of [Fe/H]{sup A} = -1.6 dex and [Fe/H]{sup B} = -2.1 dex) and have a somewhat uncertain (due to small sample size) metallicity dispersion of {approx}0.4 dex, suggesting dwarf galaxies as progenitors. Two additional RR Lyrae stars with velocities consistent with those of the Cancer groups have been observed {approx}25 Degree-Sign east, suggesting possible extension of the groups in that direction.

  10. Surface wave tomography of North America and the Caribbean using global and regional broad-band networks: Phase velocity maps and limitations of ray theory

    USGS Publications Warehouse

    Godey, S.; Snieder, R.; Villasenor, A.; Benz, H.M.

    2003-01-01

    We present phase velocity maps of fundamental mode Rayleigh waves across the North American and Caribbean plates. Our data set consists of 1846 waveforms from 172 events recorded at 91 broad-band stations operating in North America. We compute phase velocity maps in four narrow period bands between 50 and 150 s using a non-linear waveform inversion method that solves for phase velocity perturbations relative to a reference Earth model (PREM). Our results show a strong velocity contrast between high velocities beneath the stable North American craton, and lower velocities in the tectonically active western margin, in agreement with other regional and global surface wave tomography studies. We perform detailed comparisons with global model results, which display good agreement between phase velocity maps in the location and amplitude of the anomalies. However, forward modelling shows that regional maps are more accurate for predicting waveforms. In addition, at long periods, the amplitude of the velocity anomalies imaged in our regional phase velocity maps is three time larger than in global phase velocity models. This amplitude factor is necessary to explain the data accurately, showing that regional models provide a better image of velocity structures. Synthetic tests show that the raypath coverage used in this study enables one to resolve velocity features of the order of 800-1000 km. However, only larger length-scale features are observed in the phase velocity maps. The limitation in resolution of our maps can be attributed to the wave propagation theory used in the inversion. Ray theory does not account for off-great-circle ray propagation effects, such as ray bending or scattering. For wavelengths less than 1000 km, scattering effects are significant and may need to be considered.

  11. Spatial variation and azimuthal anisotropy of the Rayleigh phase velocity beneath Northeast China revealed by ambient noise eikonal tomography: results and implications

    NASA Astrophysics Data System (ADS)

    Han, J.; Ning, J.; Chen, Y. J.; Niu, F.; Grand, S.; Kawakatsu, H.; Tanaka, S.; Obayashi, M.; Ni, J. F.

    2012-12-01

    Northeast China consists of Songliao Basin in its center, the Great Xing'an Range to the west, the Changbaishan volcano to the east and the Archean Sino-Korean Craton to the south. Although it is generally believed that the evolution of the Songliao Basin and the Cenozoic volcanism in NE China are somehow related to the Pacific plate subduction beneath the area, there are no concrete geodynamical explanations of the genesis of the volcanism. Detailed seismic images are needed to understand the deep structures. We conducted a high-resolution Rayleigh wave tomography to study the crustal velocity and azimuthal anisotropy beneath NE China. We used continuous broadband records of the 120 NECESSArray stations and 266 CEA stations in NE China to construct Green's functions of ray paths between station pairs. We employed the Eikonal tomography method developed by Lin et al. (2009) to invert phase velocities in the area. At short periods, isotropic velocity is clearly correlated with the tectonic units. Songliao basin is characterized with very low velocity, while most mountain belts show relatively higher velocity except some sporadically distributed small low velocity zones to the east of the Dunhua-Mishan fault. As period increases, those sporadically distributed small low velocity zones gradually grow larger into several scattered low velocity fingers, northwestward. At period of 40 s, those scattered low velocity fingers expand into a singular wide low velocity anomaly and the image clearly shows the low velocity zone beneath the Songliao Basin. This large feature is located around Tanlu fault, Yilan-Yitong fault and Dunhua-Mishan fault and suggests that these faults penetrate through the lithosphere and possibly form the conduits for melting materials. To the west of the Great Xing'an Range, there is another large deep low velocity zone. Edge-driven small-scale convection process may be operating beneath the boundary between the hot and cold mantle and causing

  12. Dynamics of frequency-modulated soliton-like pulses in a longitudinally inhomogeneous, anomalous group velocity dispersion fibre amplifier

    SciTech Connect

    Zolotovskii, Igor' O; Korobko, D A; Okhotnikov, Oleg G; Sysolyatin, A A; Fotiadi, A A

    2012-09-30

    We examine conditions for the formation and amplification of frequency-modulated soliton-like pulses in longitudinally inhomogeneous, anomalous group velocity dispersion fibres. The group velocity dispersion profiles necessary for the existence and amplification of such pulses in active fibres are identified and the pulse duration and chirp are determined as functions of propagation distance. (optical fibres, lasers and amplifiers. properties and applications)

  13. Role of group velocity in tracking field energy in linear dielectrics

    NASA Astrophysics Data System (ADS)

    Ware, Michael J.; Glasgow, S. A.; Peatross, Justin B.

    2001-11-01

    A new context for the group delay function (valid for pulses of arbitrary bandwidth) is presented for electromagnetic pulses propagating in a uniform linear dielectric medium. The traditional formulation of group velocity is recovered by taking a narrowband limit of this generalized context. The arrival time of a light pulse at a point in space is defined using a time expectation integral over the Poynting vector. The delay between pulse arrival times at two distinct points consists of two parts: a spectral superposition of group delays and a delay due to spectral reshaping via absorption or amplification. The use of the new context is illustrated for pulses propagating both superluminally and subluminally. The inevitable transition to subluminal behavior for any initially superluminal pulse is also demonstrated.

  14. General analysis of group velocity effects in collinear optical parametric amplifiers and generators.

    PubMed

    Arisholm, Gunnar

    2007-05-14

    Group velocity mismatch (GVM) is a major concern in the design of optical parametric amplifiers (OPAs) and generators (OPGs) for pulses shorter than a few picoseconds. By simplifying the coupled propagation equations and exploiting their scaling properties, the number of free parameters for a collinear OPA is reduced to a level where the parameter space can be studied systematically by simulations. The resulting set of figures show the combinations of material parameters and pulse lengths for which high performance can be achieved, and they can serve as a basis for a design.

  15. Measurement of group velocity dispersion using white light interferometry: A teaching laboratory experiment

    NASA Astrophysics Data System (ADS)

    Cormack, I. G.; Baumann, F.; Reid, D. T.

    2000-12-01

    A teaching laboratory experiment is described which uses a basic Michelson interferometer arrangement to make fast and accurate measurements of the group velocity dispersion of an optical material using a method based on recording white-light fringes. We present a brief analysis of the theory behind the technique and describe two example measurements, one of the material dispersion of a KTP crystal and another of the reflectivity dispersion of a silver-coated mirror. Details are also given of our implementation of the data analysis using the MATLAB programming environment

  16. Measurement of ultrasonic phase and group velocities in human dental hard tissue

    PubMed Central

    2013-01-01

    Background The development of ultrasound for use in dental tissues is hampered by the complex, multilayered nature of the teeth. The purpose of this preliminary study was to obtain the phase and group velocities associated with several directions of ultrasonic wave propagation in relation to the tooth structure, which would then lead to the determination of the elastic constants in dental hard tissue. Knowledge of these elastic constants can be used to feed back into numerical models (such as finite element) in order to simulate/predict ultrasonic wave propagation and behavior in the teeth. This will help to optimize ultrasonic protocols as potential noninvasive therapeutic tools for novel dental regenerative therapies. Methods An extracted human second molar was used to determine time-of-flight information from A-scan signatures obtained at various angles of inclination and rotation using a scanning acoustic microscope at 10 MHz. Phase and group velocities and associated slowness curves were calculated in order to determine the independent elastic constants in the human teeth. Results Results show that as the tooth was inclined at three azimuthal angles (Θin = 0°, 15°, and 30°) and rotated from Φin = 0° to 360° in order to cover the whole perimeter of the tooth, slowness curves constructed from the computed phase and group velocities versus angle of rotation confirm the inhomogeneous and anisotropic nature of the tooth as indicated by the nonuniform appearance of uneven circular shape patterns of the measurements when compared to those produced in a control isotropic fused quartz sample. Conclusions This study demonstrates that phase and group velocities of ultrasound as determined by acoustic microscopy change and are dependent on the direction of the tooth structure. Thus, these results confirm that the tooth is indeed a multilayered anisotropic structure underscoring that there is no single elastic constant sufficient to represent the complex structure

  17. Measurement of the Group Velocity Dispersion of air using a femtosecond comb

    NASA Astrophysics Data System (ADS)

    Al salamah, Reem

    In this thesis, the Group Velocity Dispersion (GVD) of air has been measured by using a femtosecond frequency comb at 1.5 microm. By comparing the spectra from a balanced and unbalanced Mach - Zehnder interferometer, the need for vacuum tube is eliminated. The method employs the Fast Fourier Transform of both auto- and cross correlation to find the spectral and their differences. The GVD of air is then calculated from these spectral phase differences. With twenty-five independent measurements, the GVD of air was found to be 0.0120 fs2/mm, with a standard deviation of 0.0075 fs2/mm.

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

    PubMed

    Baggens, Oskar; Ryden, Nils

    2015-07-01

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

  19. Group-velocity-matched optical parametric oscillator in tilted quasi-phase-matched gratings.

    PubMed

    Zhang, Wei Quan

    2006-07-10

    An achromatic phase-matching scheme is reported for an optical parametric oscillator in tilted quasi-phase-matched gratings. The spectral angular dispersion is introduced in interaction waves such that each wave component satisfies the two-dimensional (noncollinear) quasi-phase matching. This is equivalent to simultaneous quasi-phase matching and group-velocity matching for ultrashort pulses. The phase-matching bandwidth for 10 mm periodically poled KTP increases by a factor of 12 at lambdas = 1.7 microm compared with one-dimensional quasi-phase matching. The effective interaction length will increase as a result of the matching.

  20. Measurement of group-velocity dispersion of Bloch modes in photonic-crystal-fiber rocking filters.

    PubMed

    Wong, G K L; Zang, L; Kang, M S; Russell, P St J

    2010-12-01

    We use low-coherence interferometry to measure the group-velocity dispersion (GVD) of the fast and slow Bloch modes of structural rocking filters, produced by twisting a highly birefringent photonic crystal fiber to and fro while scanning a focused CO(2) laser beam along it. The GVD curves in the vicinity of the resonant wavelength differ dramatically from those of the unperturbed fiber, suggesting that rocking filters could be used in the optimization of, e.g., four-wave mixing and supercontinuum generation. Excellent agreement is obtained between theory and experiment.

  1. Additional Value of Brachial-Ankle Pulse Wave Velocity to Single-Photon Emission Computed Tomography in the Diagnosis of Coronary Artery Disease.

    PubMed

    Jang, Kyeongmin; Kim, Hack-Lyoung; Park, Miri; Oh, Sohee; Oh, So Won; Lim, Woo-Hyun; Seo, Jae-Bin; Kim, Sang-Hyun; Zo, Joo-Hee; Kim, Myung-A

    2017-08-24

    The aim of this study was to investigate whether information on arterial stiffness can improve the value of single-photon emission computed tomography (SPECT) in the detection of obstructive coronary artery disease (CAD). A total of 233 patients (age: 62.2±10.8 years, 60.3% males) with detected ischemia on SPECT undergoing invasive coronary angiography (ICA) and brachial-ankle pulse wave velocity (baPWV) measurement within a month was retrospectively reviewed. Of the 233 patients, 190 (81.5%) had obstructive CAD (≥50% luminal stenosis). The difference in baPWV according to the presence of obstructive CAD was significant in patients in the mild ischemia group [summed stress score (SSS): 4-8] (1,770±364 cm versus 1,490±328 cm, p<0.001) but not in the moderate (SSS: 9-13) or severe (SSS: ≥14) ischemia groups (p>0.05 for each). Receiver operating characteristic curve analyses showed that the diagnostic value of baPWV for obstructive CAD was significant only in patients in the mild ischemia group (area under curve: 0.714; p=0.001) but not in the moderate or severe ischemia groups (p>0.05 for each). Adding information on baPWV to SPECT results and clinical parameters significantly increased diagnostic accuracy in the detection of obstructive CAD in patients with mild ischemia (integrated discrimination improvement p=0.006) but not in those with moderate or severe ischemia on SPECT (p>0.05 for each). The results of this study suggest that baPWV may have additional value to SPECT for the detection of obstructive CAD, especially in patients with mild ischemia on SPECT.

  2. 3D time-lapse seismic traveltime tomography for detecting near surface velocity variations: a case study from the Ketzin CO2 storage pilot site

    NASA Astrophysics Data System (ADS)

    Zhang, Fengjiao; Juhlin, Christopher; Huang, Fei; Lüth, Stefan

    2016-04-01

    Time-lapse seismic methods are an important tool for monitoring CO2 migration and storage in geological formations. Near surface variations are one of the major problems which may introduce time-lapse noise in the application of land based seismic monitoring. Conventional reflection seismic methods have difficulties in imaging near surface structures (10-30 m depth) due to the limitation of the methods themselves. Traveltime tomography is a commonly used method to reconstruct the subsurface velocity model. It can often provide extra information on near surface structures which is difficult to obtain by the conventional reflection seismic method. In this study, we apply traveltime tomography to 3D time-lapse seismic data sets acquired from at the Ketzin CO2 storage site. We also test different inversion strategies for traveltime tomography to investigate which one is more suitable for this case study. The results show good correlation with near surface variations obtained by other studies.

  3. Phase mapping of ultrashort pulses in bimodal photonic structures: A window on local group velocity dispersion

    NASA Astrophysics Data System (ADS)

    Gersen, H.; van Dijk, E. M. H. P.; Korterik, J. P.; van Hulst, N. F.; Kuipers, L.

    2004-12-01

    The amplitude and phase evolution of ultrashort pulses in a bimodal waveguide structure has been studied with a time-resolved photon scanning tunneling microscope (PSTM). When waveguide modes overlap in time intriguing phase patterns are observed. Phase singularities, arising from interference between different modes, are normally expected at equidistant intervals determined by the difference in effective index for the two modes. However, in the pulsed experiments the distance between individual singularities is found to change not only within one measurement frame, but even depends strongly on the reference time. To understand this observation it is necessary to take into account that the actual pulses generating the interference signal change shape upon propagation through a dispersive medium. This implies that the spatial distribution of phase singularities contains direct information on local dispersion characteristics. At the same time also the mode profiles, wave vectors, pulse lengths, and group velocities of all excited modes in the waveguide are directly measured. The combination of these parameters with an analytical model for the time-resolved PSTM measurements shows that the unique spatial phase information indeed gives a direct measure for the group velocity dispersion of individual modes. As a result interesting and useful effects, such as pulse compression, pulse spreading, and pulse reshaping become accessible in a local measurement.

  4. Phase mapping of ultrashort pulses in bimodal photonic structures: a window on local group velocity dispersion.

    PubMed

    Gersen, H; van Dijk, E M H P; Korterik, J P; van Hulst, N F; Kuipers, L

    2004-12-01

    The amplitude and phase evolution of ultrashort pulses in a bimodal waveguide structure has been studied with a time-resolved photon scanning tunneling microscope (PSTM). When waveguide modes overlap in time intriguing phase patterns are observed. Phase singularities, arising from interference between different modes, are normally expected at equidistant intervals determined by the difference in effective index for the two modes. However, in the pulsed experiments the distance between individual singularities is found to change not only within one measurement frame, but even depends strongly on the reference time. To understand this observation it is necessary to take into account that the actual pulses generating the interference signal change shape upon propagation through a dispersive medium. This implies that the spatial distribution of phase singularities contains direct information on local dispersion characteristics. At the same time also the mode profiles, wave vectors, pulse lengths, and group velocities of all excited modes in the waveguide are directly measured. The combination of these parameters with an analytical model for the time-resolved PSTM measurements shows that the unique spatial phase information indeed gives a direct measure for the group velocity dispersion of individual modes. As a result interesting and useful effects, such as pulse compression, pulse spreading, and pulse reshaping become accessible in a local measurement.

  5. Group velocity delay spectroscopy technique for industrial monitoring of electron beam induced vapors

    SciTech Connect

    Benterou, J J; Berzins, L V; Sharma, M N

    1998-09-24

    Spectroscopic techniques are ideal for characterization and process control of electron beam generated vapor plumes. Absorption based techniques work well for a wide variety of applications, but are difficult to apply to optically dense or opaque vapor plumes. We describe an approach for monitoring optically dense vapor plumes that is based on measuring the group velocity delay of a laser beam near an optical transition to determine the vapor density. This technique has a larger dynamic range than absorption spectroscopy. We describe our progress towards a robust system to monitor aluminum vaporization in an industrial environment. Aluminum was chosen because of its prevalence in high performance aircraft alloys. In these applications, composition control of the alloy constituents is critical to the deposition process. Data is presented demonstrating the superior dynamic range of the measurement. In addition, preliminary data demonstrating aluminum vapor rate control in an electron beam evaporator is presented. Alternative applications where this technique could be useful are discussed. Keywords: Group velocity delay spectroscopy, optical beat signal, optical heterodyne, index of refraction, laser absorption spectroscopy, external cavity diode laser (ECDL), electron beam vaporization, vapor density, vapor phase manufacturing, process control

  6. Label-free in-vivo measurement of lymph flow velocity using Doppler optical coherence tomography (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Blatter, Cedric; Meijer, Eelco F. J.; Nam, Ahhyun S.; Jones, Dennis; Padera, Timothy P.; Vakoc, Benjamin J.

    2016-03-01

    Alterations in lymphatic network function contribute to the lymphedema development, cancer progression and impairment in regional immune function. However, there are limited tools available to directly measure lymphatic vessel function and transport in vivo. Existing approaches such as fluorescence recovery after photo-bleaching (FRAP) require injection of exogenous labels which intrinsically alter the physiology of the local lymphatic network. A label-free approach to imaging lymph flow in vivo would provide direct and unaltered measurements of lymphatic vessel transport and could catalyze research in lymphatic biology. Here, we demonstrate and validate the use of Doppler optical coherence tomography (DOCT) to measure lymph flow in vivo at speeds as low as 50µm/s. Compared to blood, lymph is relatively acellular (under normal conditions), but contains similar soluble components to blood plasma. We demonstrate that the small but detectable scattering signal from lymph can be used to extract fluid velocity using a dedicated algorithm optimized for Doppler analysis in low signal-to-noise settings (0 to 6 dB typical). We demonstrate the accuracy of this technique by comparing DOCT to FRAP measurements, using an intralipid lymph proxy in microfluidic devices and in vivo in the mouse ear. Finally, we demonstrate the label free measurement of lymph speed in the hind-limb of mice with a temporal resolution of 0.25s that agree well with prior literature reports. We anticipate that DOCT can become a powerful new tool in preclinical lymphatic biology research—including the relationship between lymphatic function and metastasis formation—with the potential to later expand also to clinical settings.

  7. Optimizing 4D cone beam computed tomography acquisition by varying the gantry velocity and projection time interval

    NASA Astrophysics Data System (ADS)

    O'Brien, Ricky T.; Cooper, Benjamin J.; Keall, Paul J.

    2013-03-01

    Four dimensional cone beam computed tomography (4DCBCT) is an emerging clinical image guidance strategy for tumour sites affected by respiratory motion. In current generation 4DCBCT techniques, both the gantry rotation speed and imaging frequency are constant and independent of the patient’s breathing which can lead to projection clustering. We present a mixed integer quadratic programming (MIQP) model for respiratory motion guided-4DCBCT (RMG-4DCBCT) which regulates the gantry velocity and projection time interval, in response to the patient’s respiratory signal, so that a full set of evenly spaced projections can be taken in a number of phase, or displacement, bins during the respiratory cycle. In each respiratory bin, an image can be reconstructed from the projections to give a 4D view of the patient’s anatomy so that the motion of the lungs, and tumour, can be observed during the breathing cycle. A solution to the full MIQP model in a practical amount of time, 10 s, is not possible with the leading commercial MIQP solvers, so a heuristic method is presented. Using parameter settings typically used on current generation 4DCBCT systems (4 min image acquisition, 1200 projections, 10 respiratory bins) and a sinusoidal breathing trace with a 4 s period, we show that the root mean square (RMS) of the angular separation between projections with displacement binning is 2.7° using existing constant gantry speed systems and 0.6° using RMG-4DCBCT. For phase based binning the RMS is 2.7° using constant gantry speed systems and 2.5° using RMG-4DCBCT. The optimization algorithm presented is a critical step on the path to developing a system for RMG-4DCBCT.

  8. Characteristics of Shear Wave Velocity Structures Beneath the Gulf of St. Lawrence, Eastern Canada from Ambient Seismic Noise Tomography

    NASA Astrophysics Data System (ADS)

    Kuponiyi, A.; Kao, H.; Cassidy, J. F.; Dosso, S. E.; Spence, G.

    2016-12-01

    Continuous ambient seismic noise waveforms collected from 2005-2008 at 24 broadband stations located in and around the Gulf St. Lawrence (GSL) are processed to derive Rayleigh wave dispersion curves. We conduct both surface wave tomography inversion and trans-dimensional Bayesian inversion to characterize the 3-D shear wave velocity (Vs) structure beneath the GSL up to 20 km depth. Our results indicate that the entire GSL region can be divided into three broad sections. In the northern GSL, the Grenville Province (i.e., the Proterozoic edge) is dominated by high Vs. However, scattered low Vs structures can be found to correspond to well-known anorthorsite sites. In contrast, the central section corresponds to a weak belt with generally low Vs. The southernmost section of the GSL is characterized by high Vs structures belonging to the Meguma and Avalon terranes. The basement structure at the eastern segment of the Appalachian Structural Front is characterized by relatively low-Vs. Prominent low Vs are found to coincide with locations of most graben structures and sedimentary basins in the GSL. Both the depth of the sedimentary basement and the geometry of major sedimentary basins are well imaged with the thickest sedimentary layer (over 15 km) found near the western edge of the Magdalen basin. At both shallow and mid-crust depths, prominent high Vs are found near the boundaries of the Ordovician-Silurian Anticosti and the Carboniferous Magdalen Basins. The deepest prominent low Vs structures correspond to displaced/deformed Humber zone sediments buried deep beneath Dunnage zone of Newfoundland. High Vs structures with variable thicknesses are found to overlie parts of the Canadian Maritime Basins. These top high Vs structures are generally very thin (<3 km) and can be explained as the manifestation of top volcanic layers in the region.

  9. Optimizing 4D cone beam computed tomography acquisition by varying the gantry velocity and projection time interval.

    PubMed

    O'Brien, Ricky T; Cooper, Benjamin J; Keall, Paul J

    2013-03-21

    Four dimensional cone beam computed tomography (4DCBCT) is an emerging clinical image guidance strategy for tumour sites affected by respiratory motion. In current generation 4DCBCT techniques, both the gantry rotation speed and imaging frequency are constant and independent of the patient's breathing which can lead to projection clustering. We present a mixed integer quadratic programming (MIQP) model for respiratory motion guided-4DCBCT (RMG-4DCBCT) which regulates the gantry velocity and projection time interval, in response to the patient's respiratory signal, so that a full set of evenly spaced projections can be taken in a number of phase, or displacement, bins during the respiratory cycle. In each respiratory bin, an image can be reconstructed from the projections to give a 4D view of the patient's anatomy so that the motion of the lungs, and tumour, can be observed during the breathing cycle. A solution to the full MIQP model in a practical amount of time, 10 s, is not possible with the leading commercial MIQP solvers, so a heuristic method is presented. Using parameter settings typically used on current generation 4DCBCT systems (4 min image acquisition, 1200 projections, 10 respiratory bins) and a sinusoidal breathing trace with a 4 s period, we show that the root mean square (RMS) of the angular separation between projections with displacement binning is 2.7° using existing constant gantry speed systems and 0.6° using RMG-4DCBCT. For phase based binning the RMS is 2.7° using constant gantry speed systems and 2.5° using RMG-4DCBCT. The optimization algorithm presented is a critical step on the path to developing a system for RMG-4DCBCT.

  10. Group velocity dispersion of CdSSe/ZnS core-shell colloidal quantum dots measured with white light interferometry

    NASA Astrophysics Data System (ADS)

    VanEngen Spivey, Amelia G.

    2016-03-01

    We measure the group velocity dispersion coefficient of CdSSe/ZnS core-shell colloidal quantum dots in liquid suspension in the ∼700-900 nm wavelength range using a white-light Michelson interferometer. Two different sizes of dots are investigated. In both cases, the group velocity dispersion coefficient decreases with increasing wavelength above the absorption edge in the dots. For quantum dots in which the linear absorption spectrum shows clear peaks, the absorption characteristics of the dots can be used to accurately model the wavelength-dependence of the group velocity dispersion coefficient.

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

  12. Group and phase velocities from deterministic and ambient sources measured during the AlpArray-EASI experiment

    NASA Astrophysics Data System (ADS)

    Kolínský, Petr; Zigone, Dimitri; Fuchs, Florian; Bianchi, Irene; Qorbani, Ehsan; Apoloner, Maria-Theresia; Bokelmann, Götz; AlpArray-EASI Working Group

    2016-04-01

    The Eastern Alpine Seismic Investigation (EASI) was a complementary experiment to the AlpArray project. EASI was composed of 55 broadband seismic stations deployed in a winding swath of 540 km length along longitude 13.350 E from the Czech-German border to the Adriatic Sea. Average north-south inter-station distance was 10 km, the distance of each station to either side of the central line was 6 km. Such a dense linear network allows for surface wave dispersion measurements by both deterministic and ambient noise sources along the same paths. During the experiment (July 2014 - August 2015), three earthquakes ML = 2.6, 2.9 and 4.2 occurred in Austria and Northern Italy only several kilometers off the swath. We measure Rayleigh and Love wave group velocities between the source and a single station for the recorded earthquakes, as well as phase velocities between selected pairs of stations using the standard two-station method. We also calculate cross-correlations of ambient noise between selected pairs of stations and we determine the corresponding group velocity dispersion curves. We propose a comparison of phase velocities between two stations measured from earthquakes with group velocities obtained from cross-correlations for the same station pairs. We also compare group velocities measured at single station using earthquakes, which occurred along the swath, with group velocities measured from cross-correlations. That way we analyze velocities of both deterministic and ambient noise reconstructed surface waves propagating along the same path. We invert the resulting dispersion curves for 1D shear wave velocity profiles with depth and we compile a quasi-2D velocity model along the EASI swath.

  13. Propagation of a squeezed optical field in a medium with superluminal group velocity.

    PubMed

    Romanov, Gleb; Horrom, Travis; Novikova, Irina; Mikhailov, Eugeniy E

    2014-02-15

    We investigated the propagation of a squeezed optical field, generated via the polarization self-rotation effect, with a sinusoidally modulated degree of squeezing through an atomic medium with anomalous dispersion. We observed the advancement of the signal propagating through a resonant Rb vapor compared to the reference signal, propagating in air. The measured advancement time grew linearly with atomic density, reaching a maximum of 11±1  μs, which corresponded to a negative group velocity of v(g)≈-7,000  m/s. We also confirmed that the increasing advancement was accompanied by a reduction of output squeezing levels due to optical losses, in good agreement with theoretical predictions.

  14. Resonant gain suppression and superluminal group velocity in a multilevel system.

    PubMed

    Cui, Cui-Li; Fu, Chang-Bao; Yang, Hong; Bao, Qian-Qian; Xu, Huai-Liang; Wu, Jin-Hui

    2012-05-07

    We investigate the interaction of an open (N + 1)-level extended V-type atomic system (i.e. a closed (N + 2)-level atomic system) with N coherent laser fields and one incoherent pumping field through both analytical and numerical calculations. Our results show that the system can exhibit multiple resonant gain suppressions via perfect quantum destructive interference, which is usually believed to be absent in closed three-level V system and its extended versions involving more atomic levels, with at most N - 1 transparency windows associated with very steep anomalous dispersions occurring in the system. The superluminal group velocity of the probe-laser pulse with at most N - 1 negative values can also be generated and controlled with little gain or absorption.

  15. Velocity space diffusion and nongyrotropy of pickup water group ions at comet Grigg-Skjellerup

    NASA Technical Reports Server (NTRS)

    Coates, A. J.; Johnstone, A. D.; Wilken, B.; Neubauer, Fritz M.

    1993-01-01

    The diffusion of water group cometary ions in velocity space at comet Grigg-Skjellerup was measured during the Giotto spacecraft encounter. The evolution of the collapsed pitch angle and energy distributions during the inbound and outbound passes shows that the timescale for energy diffusion may be similar to that for pitch angle diffusion. Fully isotropic pitch angle distributions were never seen. Also the bulk parameters of the three-dimensional distributions are examined. Transformation of these parameters into a field-aligned solar wind frame allows us to test the gyrotropy of the distributions. These observations imply that there were deviations from gyrotropy throughout the encounter becoming most important near to closest approach.

  16. In situ fine tailoring of group velocity dispersion in optical microfibers via nanocoatings.

    PubMed

    Xu, Z Y; Li, Y H; Wang, L J

    2014-11-17

    We experimentally demonstrate a convenient technique for in situ fine group velocity dispersion (GVD) tailoring in optical microfibers via dielectric nanocoatings. This was elaborated by successively depositing poly-dimethylsiloxane (PDMS) nanocoatings around a 1.2 μm-diameter optical microfiber with a modified dip-coating method. In situ dispersion measurements showed that the GVD was tailored by 55 ps/nm•km at 1580 nm, and the zero-dispersion wavelength (ZDW) was red shifted by 30 nm. Numerical simulations showed that GVD tailoring in optical microfibers could bring signal (idler) tuning in spontaneous four-wave mixing (FWM) and spectral bandwidth expanding in supercontinuum (SC) generation, implying that this in situ fine GVD tailoring technique would offer optical microfibers with many new opportunities for applications in nonlinear optics.

  17. Group velocity delay spectroscopy technique for industrial monitoring of electron-beam-induced vapors

    NASA Astrophysics Data System (ADS)

    Benterou, Jerry J.; Berzins, Leon V.; Sharma, Manish N.

    1999-01-01

    Spectroscopic techniques are ideal for characterization and process control of electron beam generated beam generated vapor plumes. Absorption based techniques work well for a wide variety of applications, but are difficult to apply to optically dense or opaque vapor plumes. We describe an approach for monitoring optically dense vapor plumes that is based on measuring the group velocity delay of a laser beam near an optical transition to determine the vapor density. This technique has a larger dynamic range than absorption environment. Aluminum as chosen because of its prevalence in high performance aircraft alloys. In these applications, composition control of the alloy constituents is critical to the deposition process. Data is presented demonstrating the superior dynamic range of the measurement. In addition, preliminary data demonstrating aluminum vapor rate control in an electron beam evaporator is presented. Alternative applications where this technique could be useful are discussed.

  18. A group-velocity criterion for breakdown of vortex flow: An application to measured inlet profiles

    NASA Technical Reports Server (NTRS)

    Tsai, C. Y.; Widnall, S. E.

    1979-01-01

    Vortex flows exhibiting breakdown in a slightly divergent duct were measured. The slowly varying vortex flow field downstream of the entrance and upstream of the breakdown region is obtained numerically by using the inviscid quasi-cylindrical approximation. In these calculations, the Faler and Lebovich's experimental data were used as the starting conditions at the entrance of the duct. The group velocity of wave propagation for the axisymmetric mode (n = 0) and the asymmetric modes (n = + or - 1 and n = + or - 2) are calculated for the entrance conditions. For the theoretically predicted slowly varying flow field downstream of the entrance, the wave characteristics of the n = 0 and n = + or - 1 modes are presented. It was concluded that the flows which subsequently undergo vortex breakdown are all predicted to be supercritical and stable to infinitesimal inviscid disturbances, including the axially symmetric as well as the nonsymmetric perturbations.

  19. Effect of Group-Velocity Dispersion on Photon-Number Squeezing of Optical Pulses using Optical Fibers and Spectral Filter

    NASA Astrophysics Data System (ADS)

    Nishizawa, Norihiko; Horio, Takeo; Mori, Masakazu; Goto, Toshio; Yamane, Kazuo

    1999-04-01

    Photon-number squeezing of optical pulses using optical fibers and band-pass spectral filters is numerically analyzed. The evolution of the quantum noise in the optical pulse propagation is calculated in both the spectral and time domains. The mechanism of filtering squeezing and the role of the group-velocity dispersion are investigated.It is shown that the squeezing is realized owing to the interaction between the self-phase modulation and the group-velocity dispersion.

  20. Simultaneous measurement of the phase and group velocities of Lamb waves in a laser-generation based imaging method.

    PubMed

    Nishino, Hideo; Tanaka, Toshiro; Yoshida, Kenichi; Takatsubo, Junji

    2012-04-01

    This paper describes a novel approach to the simultaneous measurement of the phase and group velocities of Lamb waves based on images of their propagation. The laser-generation based imaging method was first introduced to obtain images of Lamb wave propagation. The time series of snapshot images is used to make a position-time diagram, and the velocities can be estimated based on the slopes of the position curves. Thus, the phase and group velocities can be obtained by measuring the phase advance and energy flow of the Lamb wave, respectively. Details of the principle of simultaneous measurement are presented herein. Experimental verification was also performed in the range of 0.2-3.0 MHz-mm using aluminum plates. The average errors between experiment and theory in the phase and group velocities were 3.31% and 5.68%, respectively.

  1. Phonon transport in silicon nanowires: The reduced group velocity and surface-roughness scattering

    NASA Astrophysics Data System (ADS)

    Zhu, Liyan; Li, Baowen; Li, Wu

    2016-09-01

    Using a linear-scaling Kubo simulation approach, we have quantitatively investigated the effects of confinement and surface roughness on phonon transport in silicon nanowires (SiNWs) as thick as 55 nm in diameter R . The confinement effect leads to significant reduction of phonon group velocity v in SiNWs compared to bulk silicon except at extremely low phonon frequencies f , which very likely persists in SiNWs several hundreds of nanometers thick, suggesting the inapplicability of bulk properties, including anharmonic phonon scattering, to SiNWs. For instance, the velocity can be reduced by more than 30% for phonons with f >4.5 THz in 55-nm-thick nanowires. In rough SiNWs Casimir's limit, which is valid in confined macroscopic systems, can underestimate the surface scattering by more than one order of magnitude. For a roughness profile with Lorentzian correlation characterized by root-mean-square roughness σ and correlation length Lr, the frequency-dependent phonon diffusivity D follows power-law dependences D ∝Rασ-βLrγ , where α ˜2 and β ˜1 . On average, γ increases from 0 to 0.5 as R /σ increases. The mean free path and the phonon lifetime essentially follow the same power-law dependences. These dependences are in striking contrast to Casimir's limit, i.e., D ˜v R /3 , and manifest the dominant role of the change in the number of atoms due to roughness. The thermal conductivity κ can vary by one order of magnitude with varying σ and Lr in SiNWs, and increasing σ and shortening Lr can efficiently lower κ below Casimir's limit by one order of magnitude. Our work provides different insights to understand the ultralow thermal conductivity of SiNWs reported experimentally and guidance to manipulate κ via surface roughness engineering.

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

    NASA Astrophysics Data System (ADS)

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

    2012-11-01

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

  3. The Formation of the Local Group and the High Velocity Clouds

    NASA Astrophysics Data System (ADS)

    Spergel, D. N.; Blitz, L.; Teuben, P. J.; Hartmann, D.; Burton, B.

    1996-12-01

    We simulate the formation and evolution of the Local Group. The dynamics of the Local Group is governed primarily by the its two largest members, Andromeda (M31) and the Galaxy (M0) and secondarily by the tidal effects of neighboring galaxies. In the simulation, a long filament forms which contains M31 and M0. While the gas near M31 and M0 is likely shock heated, we expect that much of the gas in the filament is cold. The kinematics of this gas in the simulation is remarkably similar to the kinematics of the High Velocity Clouds (HVCs). This similarity suggests reinterpreting the HVCs as primarily extragalactic. In this model, the HVCs are similar to the Lyman alpha clouds. Recent work (Hernquist et al. 996) suggests that the Lyman alpha clouds are primarily condensations in the filaments between galaxies. We suggest a similar picture for most of the HVCs: they are gravitationally confined, rather than pressure confined, clouds infalling into the Local Group and are likely associated with a substantial amount of dark matter. In this picture, the two phase structure seen in some of the HVCs (Wakker & Schwarz 1991) would be due to self shielding that arises in gas clouds ionized by external UV (Murakami & Ikeuchi 1990). This model suggests that there is a substantial amount of gas in the HVCs: ~ 1 x 10(10) M_sun. This gas is and was a reservoir of relatively unprocessed gas for both M31 and our Galaxy and likely plays an important role in the evolution of both galaxies. Hernquist, L, Katz, N., Weinberg, D. & Miralda-Escude, J. 1996, ApJ L 457, 51 Murakami, I. & Ikeuchi, S. 1990 PASJ, 41 , L11. Wakker, B.P. & Schwarz, U.J. 1991 A & A, 250, 48.

  4. Investigating the Relation between Galaxy Properties and the Gaussianity of the Velocity Distribution of Groups and Clusters

    NASA Astrophysics Data System (ADS)

    de Carvalho, R. R.; Ribeiro, A. L. B.; Stalder, D. H.; Rosa, R. R.; Costa, A. P.; Moura, T. C.

    2017-09-01

    We investigate the dependence of stellar population properties of galaxies on group dynamical stage for a subsample of the Yang catalog. We classify groups according to their galaxy velocity distribution into Gaussian (G) and Non-Gaussian (NG). Using two totally independent approaches, we have shown that our measurement of Gaussianity is robust and reliable. Our sample covers Yang’s groups in the redshift range 0.03 ≤slant z ≤slant 0.1, with mass ≥slant {10}14{M}⊙ . The new method, called Hellinger Distance, to determine whether a group has a velocity distribution Gaussian or NG is very effective in distinguishing between the two families. NG groups present halo masses higher than the G ones, confirming previous findings. Examining the skewness and kurtosis of the velocity distribution of G and NG groups, we find that faint galaxies in NG groups are mainly infalling, for the first time, into the groups. We show that considering only faint galaxies in the outskirts; those in NG groups are older and more metal-rich than those in G groups. Also, examining the Projected Phase Space of cluster galaxies, we see that bright and faint galactic systems in G groups are in dynamical equilibrium—which does not seem to be the case in NG groups. These findings suggest that NG systems have a higher infall rate, assembling more galaxies that have experienced preprocessing before entering the group.

  5. Thin layer thickness measurements by zero group velocity Lamb mode resonances.

    PubMed

    Cès, Maximin; Clorennec, Dominique; Royer, Daniel; Prada, Claire

    2011-11-01

    Local and non-contact measurements of the thickness of thin layers deposited on a thick plate have been performed by using zero group velocity (ZGV) Lamb modes. It was shown that the shift of the resonance frequency is proportional to the mass loading through a factor which depends on the mechanical properties of the layer and of the substrate. In the experiments, ZGV Lamb modes were generated by a Nd:YAG pulsed laser and the displacement normal to the plate surface was measured by an optical interferometer. Measurements performed at the same point that the generation on the non-coated face of the plate demonstrated that thin gold layers of a few hundred nanometers were detected through a 1.5-mm thick Duralumin plate. The shift of the resonance frequency (1.9 MHz) of the fundamental ZGV mode is proportional to the layer thickness: typically 10 kHz per μm. Taking into account the influence of the temperature, a 240-nm gold layer was measured with a ±4% uncertainty. This thickness has been verified on the coated face with an optical profiling system.

  6. Laser beam shaping for enhanced Zero-Group Velocity Lamb modes generation.

    PubMed

    Bruno, François; Laurent, Jérôme; Jehanno, Paul; Royer, Daniel; Prada, Claire

    2016-10-01

    Optimization of Lamb modes induced by laser can be achieved by adjusting the spatial source distribution to the mode wavelength (λ). The excitability of Zero-Group Velocity (ZGV) resonances in isotropic plates is investigated both theoretically and experimentally for axially symmetric sources. Optimal parameters and amplitude gains are derived analytically for spot and annular sources of either Gaussian or rectangular energy profiles. For a Gaussian spot source, the optimal radius is found to be λZGV/π. Annular sources increase the amplitude by at least a factor of 3 compared to the optimal Gaussian source. Rectangular energy profiles provide higher gain than Gaussian ones. These predictions are confirmed by semi-analytical simulation of the thermoelastic generation of Lamb waves, including the effect of material attenuation. Experimentally, Gaussian ring sources of controlled width and radius are produced with an axicon-lens system. Measured optimal geometric parameters obtained for Gaussian and annular beams are in good agreement with theoretical predictions. A ZGV resonance amplification factor of 2.1 is obtained with the Gaussian ring. Such source should facilitate the inspection of highly attenuating plates made of low ablation threshold materials like composites.

  7. Laser beam shaping for enhanced Zero-Group Velocity Lamb modes generation

    NASA Astrophysics Data System (ADS)

    Bruno, François; Laurent, Jérôme; Jehanno, Paul; Royer, Daniel; Prada, Claire

    2016-10-01

    Optimization of Lamb modes induced by laser can be achieved by adjusting the spatial source distribution to the mode wavelength ($\\lambda$). The excitability of Zero-Group Velocity (ZGV) resonances in isotropic plates is investigated both theoretically and experimentally for axially symmetric sources. Optimal parameters and amplitude gains are derived analytically for spot and annular sources of either Gaussian or rectangular energy profiles. For a Gaussian spot source, the optimal radius is found to be $\\lambda_{ZGV}/\\pi$. Annular sources increase the amplitude by at least a factor of 3 compared to the optimal Gaussian source. Rectangular energy profiles provide higher gain than Gaussian ones. These predictions are confirmed by semi-analytical simulation of the thermoelastic generation of Lamb waves, including the effect of material attenuation. Experimentally, Gaussian ring sources of controlled width and radius are produced with an axicon-lens system. Measured optimal geometric parameters obtained for Gaussian and annular beams are in good agreement with theoretical predictions. A ZGV resonance amplification factor of 2.1 is obtained with the Gaussian ring. Such source should facilitate the inspection of highly attenuating plates made of low ablation threshold materials like composites.

  8. Subluminal group velocity and dispersion of Laguerre Gauss beams in free space

    PubMed Central

    Bareza, Nestor D.; Hermosa, Nathaniel

    2016-01-01

    That the speed of light in free space c is constant has been a pillar of modern physics since the derivation of Maxwell and in Einstein’s postulate in special relativity. This has been a basic assumption in light’s various applications. However, a physical beam of light has a finite extent such that even in free space it is by nature dispersive. The field confinement changes its wavevector, hence, altering the light’s group velocity vg. Here, we report the subluminal vg and consequently the dispersion in free space of Laguerre-Gauss (LG) beam, a beam known to carry orbital angular momentum. The vg of LG beam, calculated in the paraxial regime, is observed to be inversely proportional to the beam’s divergence θ0, the orbital order ℓ and the radial order p. LG beams of higher orders travel relatively slower than that of lower orders. As a consequence, LG beams of different orders separate in the temporal domain along propagation. This is an added effect to the dispersion due to field confinement. Our results are useful for treating information embedded in LG beams from astronomical sources and/or data transmission in free space. PMID:27231195

  9. Subluminal group velocity and dispersion of Laguerre Gauss beams in free space

    NASA Astrophysics Data System (ADS)

    Bareza, Nestor D.; Hermosa, Nathaniel

    2016-05-01

    That the speed of light in free space c is constant has been a pillar of modern physics since the derivation of Maxwell and in Einstein’s postulate in special relativity. This has been a basic assumption in light’s various applications. However, a physical beam of light has a finite extent such that even in free space it is by nature dispersive. The field confinement changes its wavevector, hence, altering the light’s group velocity vg. Here, we report the subluminal vg and consequently the dispersion in free space of Laguerre-Gauss (LG) beam, a beam known to carry orbital angular momentum. The vg of LG beam, calculated in the paraxial regime, is observed to be inversely proportional to the beam’s divergence θ0, the orbital order ℓ and the radial order p. LG beams of higher orders travel relatively slower than that of lower orders. As a consequence, LG beams of different orders separate in the temporal domain along propagation. This is an added effect to the dispersion due to field confinement. Our results are useful for treating information embedded in LG beams from astronomical sources and/or data transmission in free space.

  10. Subluminal group velocity and dispersion of Laguerre Gauss beams in free space.

    PubMed

    Bareza, Nestor D; Hermosa, Nathaniel

    2016-05-27

    That the speed of light in free space c is constant has been a pillar of modern physics since the derivation of Maxwell and in Einstein's postulate in special relativity. This has been a basic assumption in light's various applications. However, a physical beam of light has a finite extent such that even in free space it is by nature dispersive. The field confinement changes its wavevector, hence, altering the light's group velocity vg. Here, we report the subluminal vg and consequently the dispersion in free space of Laguerre-Gauss (LG) beam, a beam known to carry orbital angular momentum. The vg of LG beam, calculated in the paraxial regime, is observed to be inversely proportional to the beam's divergence θ0, the orbital order ℓ and the radial order p. LG beams of higher orders travel relatively slower than that of lower orders. As a consequence, LG beams of different orders separate in the temporal domain along propagation. This is an added effect to the dispersion due to field confinement. Our results are useful for treating information embedded in LG beams from astronomical sources and/or data transmission in free space.

  11. Group velocity slowdown using phonon-induced transparencies in a quantum dot molecule

    NASA Astrophysics Data System (ADS)

    Jacobs, Andrew; Jennings, Cameron; Kerfoot, Mark; Scheibner, Michael

    2014-03-01

    In a recent study we have demonstrated coherent, non-dissipative behavior of phonons due to optical excitation, which is revealed via optical transparency. Using a single external driving field, the absorption of the molecule demonstrates a marked reduction as a Fano-type resonance of a spatially indirect exciton and direct polaron form a molecular polaron state. The phonon coherence contrasts the typical role of these particles as a channel for non-radiative state decay or pure state dephasing. The optical response of the system is indicative of a coherent phenomenon, similar to electromagnetically induced transparency. Here we investigate theoretically how this phonon coherence affects the optical response of a 3-level V-type system in a tunnel-coupled quantum dot molecule. From the properties of the molecular polaron, we are able to determine the slowdown factor of the driving field group velocity, as well as the dependence of the slowdown on system parameters such as polaron and exciton lifetimes, tunneling strength, and transition dipole moments. The presence of slow light suggests this system is suitable for use in quantum computational components such as optical storage or qubit logic gates.

  12. Crustal and upper mantle 3D shear wave velocity structure of the High Lava Plains, Oregon, determined from ambient noise tomography

    NASA Astrophysics Data System (ADS)

    Hanson-Hedgecock, S.; Wagner, L.; Fouch, M. J.; James, D. E.

    2011-12-01

    We present the results of inversions for 3D shear velocity structure of the crust and uppermost mantle beneath the High Lava Plains, Oregon using data from ~300 broadband stations of the High Lava Plains seismic experiment and the EarthScope/USArray Transportable Array (TA). The High Lava Plains (HLP) is a WNW progressive silicic volcanism, initiated ~14.5 Ma near the Owyhee Plateau and is currently active at the Newberry caldera. The Yellowstone Snake River Plain (YSRP) volcanic track is temporally contemporaneous with the HLP, but trends to the northeast, parallel to North American plate motion. The cause of volcanism along the HLP is debated and has been variously attributed to Basin and Range extension, back-arc extension, rollback of the subducting Juan de Fuca plate, and an intra-continental hotspot/plume source. Additionally the relationship between the HLP, YSRP, and Columbia River Basalts (CRB), the three major post-17Ma intracontinental volcanic provinces of the Pacific Northwest, is not well understood. The 3D shear velocity structure of the crust and uppermost mantle to ~65km depth is determined from fundamental mode Rayleigh wave ambient noise phase velocity maps at periods up to 40s. The use of ambient noise tomography with the dense station spacing of the combined High Lava Plains seismic experiment and the EarthScope/USArray Transportable Array (TA) datasets allows the shallow structure of the High Lava Plains to be imaged in finer detail than previous ANT studies that focused on the entire western United States. In the crust, low velocities in central Oregon are observed in association with the Brothers Fault Zone, Jordan and Diamond Craters and Steens Mountain regions in addition to the strong low velocity zone associated with the Cascades to the west. To the east of the HLP, low velocities are observed to about 10km depth in the western SRP. In the eastern SRP we observe a shallow veneer of low velocities underlain by a ~10km thick high velocity

  13. The High Velocity Galaxy Challenge to ΛCDM in the Local Group

    NASA Astrophysics Data System (ADS)

    Banik, Indranil

    2017-06-01

    In the Local Group (LG), Andromeda (M31) is approaching the Milky Way (MW) at ˜110 km/s despite the large scale cosmic expansion. To turn it around locally to this extent, their combined mass must lie in a narrow range of values. This constrains the gravitational field in the LG as there are no other objects of similar masses. We have conducted calculations solving test particle trajectories in this gravitational field using a 2D dynamical model including Cen A and the LMC (MNRAS, 459, 2237). Although few objects have radial velocities (RVs) much below the predictions of the best-fitting model, some have RVs much above them, sometimes by as much as 100 km/s. This situation persists even when we used a 3D model including perturbers and satellites (MNRAS, 467, 2180).The observations may be explained by a past close flyby of the MW and M31, which arises in Modified Newtonian Dynamics (MOND) but not ΛCDM. In this context, a simplified calculation suggests that the recently discovered plane of satellites around the MW and a similar plane around M31 could be explained by a past MW-M31 flyby, but only if they orbit within a particular plane. We used this information in a more detailed MOND simulation of the flyby and its effect on the rest of the LG, treating it as a cloud of ˜3×105 test particles. The high speeds of the MW and M31 at pericentre allow for efficient gravitational slingshots of these particles. Those flung out to the greatest distance tend to lie very close to the MW-M31 orbital plane, probably because the greatest impulses occur for objects flung out almost parallel to the motion of the perturber.I will describe this simulation and recent work (Arxiv: 1701.06559) showing that LG dwarfs with the most anomalously high RVs (relative to our 3D model) indeed lie close to a plane oriented similarly to our expected MW-M31 orbital plane based on considering their satellite systems. This plane of distant LG dwarfs passes within 140 kpc of the MW and M31 and

  14. A numerical study on finding an optimum model in velocity tomography by using the Extended Information Criterion

    NASA Astrophysics Data System (ADS)

    Nishizawa, O.; Lei, Xing-Lin

    1995-05-01

    We performed numerical experiments to show that Extended Information Criterion (EIC) can be utilized for determining an optimum model in velocity reconstruction problems, in which a wavefront tracing method was employed for finding the minimum travel time raypath. First, travel times were calculated from a specified velocity model, and simulated data were produced by adding random error to the travel times. Velocity models were then reconstructed from the simulated data by employing a Simultaneous Iterative Reconstruction Technique (SIRT) starting from different initial models. Finally, EIC values were calculated for each reconstructed velocity model at every iteration, and were used for selecting an optimum velocity model. Resutls indicated that EIC provides an objective method for selecting an optimum solution from a suite reconstructions obtained from different initial models.

  15. Phase-resolved functional optical coherence tomography: simultaneous imaging of in situ tissue structure, blood flow velocity, standard deviation, birefringence, and Stokes vectors in human skin

    NASA Astrophysics Data System (ADS)

    Ren, Hongwu; Ding, Zhihua; Zhao, Yonghua; Miao, Jianjun; Nelson, J. Stuart; Chen, Zhongping

    2002-10-01

    We describe a phase-resolved functional optical coherence tomography system that can simultaneously yield in situ images of tissue structure, blood flow velocity, standard deviation, birefringence, and the Stokes vectors in human skin. Multifunctional images were obtained by processing of analytical interference fringe signals derived from two perpendicular polarization-detection channels. The blood flow velocity and standard deviation images were obtained by comparison of the phases from pairs of analytical signals in neighboring A-lines in the same polarization state. The analytical signals from two polarization-diversity detection channels were used to determine the four Stokes vectors for four reference polarization states. From the four Stokes vectors, the birefringence image, which is not sensitive to the orientation of the optical axis in the sample, was obtained. Multifunctional in situ images of a port wine stain birthmark in human skin are presented.

  16. P- and S-velocity structure beneath the Three Gorges region (central China) from local earthquake tomography

    NASA Astrophysics Data System (ADS)

    Mei, B.; Xu, Y.; Zhang, Y.

    2013-05-01

    A seismic experiment provides new insights on the crustal structure of the head area of the Three Gorges Reservoir in central China. The region is characterized by a relatively high rate of reservoir-induced seismicity that is often triggered within those areas associated with the ascending water level. Our 3-D velocity model of the Three Gorges region shows that the Huangling anticline (HLA) is characterized by a high-velocity crust, and the Zigui Basin (ZGB) has lower crustal velocities. The 3-D tomographic inversions are conducted using 11 901 P-wave and 12 032 S-wave arrival times from 1342 events recorded by the local network of seismic stations from early 2001 to late 2006. Initial models with varying velocity gradients are extracted to constrain a data-driven optimum 1-D model for 3-D iterative inversion scheme. Checkerboard tests are applied to assess model reliability, indicating a reasonable level of lateral and vertical resolutions. The P- and S-tomographic models reveal a local high-velocity anomaly from 5 to 10 km beneath SW portion of the HLA and a strong, large low-velocity anomaly between about 5-10 km depths at the south margin of the ZGB. Moreover, the southwest border of HLA underthrust the ZGB with slightly bigger angle. Also, a prominent high-velocity anomaly is located below 5 km beneath Shazhenxi, and to the west, the velocity anomaly turns out to be negative. There is no record help explaining the dramatic feature since incorporating local tectonic and topography, it suggests sharp gap in velocity near surface is primarily due to several secondary fracture zones. The surface responses of velocity discontinuity are generally aligned parallel to the trending of fault. Relatively good agreement between regional features and the velocity perturbations promotes further interpretation. Earthquake swarm activities from source relocation occur on the outer portions of high-velocity anomaly with nearly perpendicular dip angle. Thus, the seismicity

  17. Relationships of the group velocity of the time-reversed Lamb wave with bone properties in cortical bone in vitro.

    PubMed

    Lee, Kang Il; Yoon, Suk Wang

    2017-04-11

    The present study aims to investigate the feasibility of using the time-reversed Lamb wave as a new method for noninvasive characterization of long cortical bones. The group velocity of the time-reversed Lamb wave launched by using the modified time reversal method was measured in 15 bovine tibiae, and their correlations with the bone properties of the tibia were examined. The group velocity of the time-reversed Lamb wave showed significant positive correlations with the bone properties (r=0.55-0.81). The best univariate predictor of the group velocity of the time-reversed Lamb wave was the cortical thickness, yielding an adjusted squared correlation coefficient (r(2)) of 0.64. These results imply that the group velocity of the time-reversed Lamb wave, in addition to the velocities of the first arriving signal and the slow guided wave, could potentially be used as a discriminator for osteoporosis. Copyright © 2017 Elsevier Ltd. All rights reserved.

  18. Swimming Training Assessment: The Critical Velocity and the 400-m Test for Age-Group Swimmers.

    PubMed

    Zacca, Rodrigo; Fernandes, Ricardo Jorge P; Pyne, David B; Castro, Flávio Antônio de S

    2016-05-01

    To verify the metabolic responses of oxygen consumption (V[Combining Dot Above]O2), heart rate (HR), blood lactate concentrations [La], and rate of perceived exertion (RPE) when swimming at an intensity corresponding to the critical velocity (CV) assessed by a 4-parameter model (CV4par), and to check the reliability when using only a single 400-m maximal front crawl bout (T400) for CV4par assessment in age-group swimmers. Ten age-group swimmers (14-16 years old) performed 50-, 100-, 200-, 400- (T400), 800-, and 1,500-m maximal front crawl bouts to calculate CV4par. V[Combining Dot Above]O2, HR, [La], and RPE were measured immediately after bouts. Swimmers then performed 3 × 10-minute front crawl (45 seconds rest) at CV4par. V[Combining Dot Above]O2, HR, [La], and RPE were measured after 10 minutes of rest (Rest), warm-up (Pre), each 10-minute repetition, and at the end of the test (Post). CV4par was 1.33 ± 0.08 m·s. V[Combining Dot Above]O2, HR, [La], and RPE were similar between first 10-minute and Post time points in the 3 × 10-minute protocol. CV4par was equivalent to 92 ± 2% of the mean swimming speed of T400 (v400) for these swimmers. CV4par calculated through a single T400 (92%v400) showed excellent agreement (r = 0.30; 95% CI: -0.04 to 0.05 m·s, p = 0.39), low coefficient of variation (2%), and root mean square error of 0.02 ± 0.01 m·s when plotted against CV4par assessed through a 4-parameter model. These results generated the equation CV4par = 0.92 × v400. A single T400 can be used reliably to estimate the CV4par typically derived with 6 efforts in age-group swimmers.

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

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

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

  20. Photonic bands and group-velocity dispersion in Si/SiO2 photonic crystals from white-light interferometry

    NASA Astrophysics Data System (ADS)

    Galli, M.; Bajoni, D.; Marabelli, F.; Andreani, L. C.; Pavesi, L.; Pucker, G.

    2004-03-01

    The phase delay of a light beam transmitted through (Si/SiO2)m multilayers with m=2,4,6,8 is measured by white-light interferometry based on a fixed Mach-Zehnder interferometer coupled to a scanning Michelson interferometer. Results for photonic band and group velocity dispersion are obtained in a wide frequency spectrum and compare successfully with the predictions of electromagnetic theory. In particular, a strong slowing down of the group velocity at the band edges and superluminal propagation within the gap are demonstrated.

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

    SciTech Connect

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

    2015-03-24

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

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

    DOE PAGES

    Adams, Aubreya N.; Wiens, Douglas A.; Nyblade, Andrew A.; ...

    2015-03-24

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

  3. P and S velocity tomography of the Mariana subduction system from a combined land-sea seismic deployment

    NASA Astrophysics Data System (ADS)

    Barklage, Mitchell; Wiens, Douglas A.; Conder, James A.; Pozgay, Sara; Shiobara, Hajime; Sugioka, Hiroko

    2015-03-01

    Seismic imaging provides an opportunity to constrain mantle wedge processes associated with subduction, volatile transport, arc volcanism, and back-arc spreading. We investigate the seismic velocity structure of the upper mantle across the Central Mariana subduction system using data from the 2003-2004 Mariana Subduction Factory Imaging Experiment, an 11 month deployment consisting of 20 broadband seismic stations installed on islands and 58 semibroadband ocean bottom seismographs. We determine the three-dimensional VP and VP/VS structure using over 25,000 local and over 2000 teleseismic arrival times. The mantle wedge is characterized by slow velocity and high VP/VS beneath the fore arc, an inclined zone of slow velocity underlying the volcanic front, and a strong region of slow velocity beneath the back-arc spreading center. The slow velocities are strongest at depths of 20-30 km in the fore arc, 60-70 km beneath the volcanic arc, and 20-30 km beneath the spreading center. The fore-arc slow velocity anomalies occur beneath Big Blue seamount and are interpreted as resulting from mantle serpentinization. The depths of the maximum velocity anomalies beneath the arc and back arc are nearly identical to previous estimates of the final equilibrium depths of mantle melts from thermobarometry, strongly indicating that the low-velocity zones delineate regions of melt production in the mantle. The arc and back-arc melt production regions are well separated at shallow depths, but may be connected at depths greater than 80 km.

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  6. Crustal high-velocity anomaly at the East European Craton margin in SE Poland (TESZ) modelled by 3-D seismic tomography of refracted and reflected arrivals

    NASA Astrophysics Data System (ADS)

    Środa, Piotr; Dec, Monika

    2016-04-01

    The area of Trans-European Suture Zone in SE Poland represents a contact of major tectonic units of different consolidation age - from the Precambrian East European Craton, through Palaeozoic West European Platform to Cenozoic Carpathian orogen. The region was built by several phases of crustal accretion, which resulted in a complex collage of tectonic blocks. In 2000, this region was studied by several seismic wide-angle profiles of CELEBRATION 2000 experiment, providing a dense coverage of seismic data in SE Poland and allowing for detailed investigations of the crustal structure and properties in this area. Beneath the marginal part of the EEC, the 2-D modelling of in-line data form several CELEBRATION profiles revealed a prominent high P-wave velocity anomaly in the upper crust, with Vp of 6.7-7.1 km/s, starting at 10-16 km depth (e.g., Środa et al., 2006). Anomalously high velocities are observed in the area located approximately beneath Lublin trough, to the NE of Teisseyre-Tornquist Zone. Based on 3-D tomography of first arrivals of in- and off-line CELEBRATION 2000 recordings (Malinowski et al., 2008), elevated velocities are also reported in the same area and seem to continue to the SW, off the craton margin. Gravimetric modelling also revealed anomalously high density in the same region at similar depths. High seismic velocities and densities are interpreted as indicative for a pronounced mafic intrusion, possibly related to extensional processes at the EEC margin. Previous 3-D models of the high-velocity intrusion were based on first arrivals (crustal refractions) only. In this study, also off-line reflections (not modelled up to now) are used, in order to enlarge the data set and to better constrain the geometry and properties of the velocity anomaly. A code for 3-D joint tomographic inversion of refracted and reflected arrivals, with model parametrization allowing for velocity discontinuities was used (Rawlinson, 2007). With this approach, besides the

  7. Generation of cumulative second-harmonic ultrasonic guided waves with group velocity mismatching: Numerical analysis and experimental validation

    NASA Astrophysics Data System (ADS)

    Xiang, Yanxun; Zhu, Wujun; Deng, Mingxi; Xuan, Fu-Zhen; Liu, Chang-Jun

    2016-11-01

    The generation of second-harmonic Lamb waves in a homogeneous, isotropic, stress-free elastic plate is analytically and experimentally investigated. The numerical analyses show that whether the matching condition of the group velocity is satisfied or not, the integrated amplitude of a second-harmonic Lamb wave accumulates with the propagation distance when both the finite duration of the primary Lamb wave tone burst and the phase velocity matching are given. The theoretical analyses are validated by experimental measurements of an aluminium plate. Our conclusions are different from those of the previous works that reported that the group velocity matching is required for the generation of the cumulative second-harmonic Lamb waves with the finite duration of tone bursts.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  9. Thin Lithosphere Beneath the Ethiopian Plateau Revealed by a Joint Inversion of Rayleigh Wave Group Velocities and Receiver Functions

    NASA Astrophysics Data System (ADS)

    Dugda, Mulugeta T.; Nyblade, Andrew A.; Julia, Jordi

    2007-08-01

    The seismic velocity structure of the crust and upper mantle beneath Ethiopia and Djibouti has been investigated by jointly inverting receiver functions and Rayleigh wave group velocities to obtain new constraints on the thermal structure of the lithosphere. Most of the data for this study come from the Ethiopia broadband seismic experiment, conducted between 2000 and 2002. Shear velocity models obtained from the joint inversion show crustal structure that is similar to previously published models, with crustal thicknesses of 35 to 44 km beneath the Ethiopian Plateau, and 25 to 35 km beneath the Main Ethiopian Rift (MER) and the Afar. The lithospheric mantle beneath the Ethiopian Plateau has a maximum shear wave velocity of about 4.3 km/s and extends to a depth of ˜70-80 km. Beneath the MER and Afar, the lithospheric mantle has a maximum shear wave velocity of 4.1-4.2 km/s and extends to a depth of at most 50 km. In comparison to the lithosphere away from the East African Rift System in Tanzania, where the lid extends to depths of ˜100-125 km and has a maximum shear velocity of 4.6 km/s, the mantle lithosphere under the Ethiopian Plateau appears to have been thinned by ˜30-50 km and the maximum shear wave velocity reduced by ˜0.3 km/s. Results from a 1D conductive thermal model suggest that the shear velocity structure of the Ethiopian Plateau lithosphere can be explained by a plume model, if a plume rapidly thinned the lithosphere by ˜30-50 km at the time of the flood basalt volcanism (c. 30 Ma), and if warm plume material has remained beneath the lithosphere since then. About 45-65% of the 1-1.5 km of plateau uplift in Ethiopia can be attributed to the thermally perturbed lithospheric structure.

  10. Understanding the relationship between image quality and motion velocity in gated computed tomography: preliminary work for 4-dimensional musculoskeletal imaging.

    PubMed

    Tay, Shian Chao; Primak, Andrew N; Fletcher, Joel G; Schmidt, Bernhard; An, Kai-Nan; McCollough, Cynthia H

    2008-01-01

    To study the effect of motion velocity on image quality to determine the requirements for 4-dimensional (4D; ie, 3D + time) musculoskeletal computed tomographic (CT) imaging. A phantom with resolution targets in both axial (x-y) and coronal (x-z) planes was attached to a motion device and scanned with 64-slice CT using a retrospectively gated CT protocol with pitch values of 0.1 and 0.2. Data were acquired with the phantom at rest and while moving periodically along the x axis at several velocities. Spatial resolution and motion artifacts were assessed both for the axial and coronal targets. A linear relationship was found between motion artifact severity and phantom velocity. Spatial resolution was better preserved in the coronal target. However, coronal images displayed banding artifacts, with band displacements being linearly related to motion velocity. The 4D CT imaging of periodically moving objects with velocities up to 20 mm/s is feasible using a pitch value of 0.1 and a motion frequency of 30 cycles per minute.

  11. Dielectric waveguide with transverse index variation that support a zero group velocity mode at a non-zero longitudinal wavevector

    DOEpatents

    Ibanescu, Mihai; Joannopoious, John D.; Fink, Yoel; Johnson, Steven G.; Fan, Shanhui

    2005-06-21

    Optical components including a laser based on a dielectric waveguide extending along a waveguide axis and having a refractive index cross-section perpendicular to the waveguide axis, the refractive index cross-section supporting an electromagnetic mode having a zero group velocity for a non-zero wavevector along the waveguide axis.

  12. The crustal structure of Uganda inferred from joint inversion of receiver functions and Rayleigh wave group velocities

    NASA Astrophysics Data System (ADS)

    Tugume, F. A.; Julia, J.; Nyblade, A.; Adams, A. N.

    2009-12-01

    The crustal structure of Uganda is imaged using joint inversion of teleseismic P wave receiver functions and fundamental-mode Rayleigh wave group velocities. The data used our study were recorded at 10 broadband seismic stations in Uganda. The data collection was done under the first phase of the AfricaArray East Africa seismic experiment, which took place from September 2007 through December 2008. Radial and transverse receiver functions are obtained for teleseimic events in the 300 to 900 epicentral distance range after by deconvolving the vertical component from the corresponding radial and transverse components using an iterative time-domain procedure. The Rayleigh wave group velocities were obtained from an independent tomographic study. Receiver functions are sensitive to shear-wave velocity contrasts and vertical travel times, and surface wave dispersion measurements are sensitive to vertical shear-wave velocity averages. Jointly inverting surface wave dispersion measurements and receiver functions provides integrated models of subsurface shear wave velocity structure that explain the observations better than models obtained from either data set separately. Preliminary results yield Moho depths of approximately 40-42 km for stations on the Archean Tanzania Craton, and 38-40 km for stations in the surrounding Proterozoic mobile belts. Estimates of the Moho depth beneath stations in the Western Branch of the East African rift system could not be reliably obtained because of reverberations in sedimentary layers

  13. Measurement of the blood flow rate and velocity in coronary artery stenosis using intracoronary frequency domain optical coherence tomography: Validation against fractional flow reserve.

    PubMed

    Zafar, Haroon; Sharif, Faisal; Leahy, Martin J

    2014-12-01

    The main objective of this study was to assess the blood flow rate and velocity in coronary artery stenosis using intracoronary frequency domain optical coherence tomography (FD-OCT). A correlation between fractional flow reserve (FFR) and FD-OCT derived blood flow velocity is also included in this study. A total of 20 coronary stenoses in 15 patients were assessed consecutively by quantitative coronary angiography (QCA), FFR and FD-OCT. A percutaneous coronary intervention (PCI) optimization system was used in this study which combines wireless FFR measurement and FD-OCT imaging in one platform. Stenoses were labelled severe if FFR ≤ 0.8. Blood flow rate and velocity in each stenosis segment were derived from the volumetric analysis of the FD-OCT pull back images. The FFR value was ≤ 0.80 in 5 stenoses (25%). The mean blood flow rate in severe coronary stenosis (n = 5) was 2.54 ± 0.55 ml/s as compared to 4.81 ± 1.95 ml/s in stenosis with FFR > 0.8 (n = 15). A good and significant correlation between FFR and FD-OCT blood flow velocity in coronary artery stenosis (r = 0.74, p < 0.001) was found. The assessment of stenosis severity using FD-OCT derived blood flow rate and velocity has the ability to overcome many limitations of QCA and intravascular ultrasound (IVUS).

  14. AWESoMe: A code for the calculation of phase and group velocities of acoustic waves in homogeneous solids

    NASA Astrophysics Data System (ADS)

    Muñoz-Santiburcio, Daniel; Hernández-Laguna, Alfonso; Soto, Juan I.

    2015-07-01

    We present AWESoMe, an implementation of a method for the evaluation of acoustic wave velocities in homogeneous solid media. The code computes the phase and group velocities for all the possible propagation directions, as well as some related parameters such as the polarization vectors, the power flow angle and the enhancement factor. The code is conveniently interfaced with GNUPLOT, thus offering immediate visualization of the results. AWESoMe is open-source software, available under the GNU General Public License v3.

  15. P-wave deep velocity structure of the Southern Tyrrhenian Subduction Zone from nonlinear teleseismic traveltime tomography

    NASA Astrophysics Data System (ADS)

    Cimini, Giovanni B.

    A new 3-D model for the P-wave velocity structure of the Southern Tyrrhenian Subduction Zone (STSZ) is determined from nonlinear inversion of relative arrival times of teleseismic events. The data used in the imaging are the travel time residuals of both direct, P and PKPdf and secondary pP, sP, PcP, PKPbc phases, computed with respect to the global 1-D velocity model ak135. 2308 teleseismic waveforms were collected for this study from 109 events recorded by the Italian National Seismic Network (RSNC) during 1988-1998. The velocity perturbation field is reconstructed gradually by means an iterative sequence of linearized inversions, incorporating a 3-D minimum travel time ray tracing. The tomographic images reveal a broad high-velocity zone dominating the pattern of lateral variations beneath the Southern Tyrrhenian Sea and Calabria. This fast structure extends laterally for a maximum of ˜350 km, from northern Sicily to southern Campania, and vertically for at least 400 km, from the uppermost mantle down to 500 km depth. Below 350 km the geometry of the depicted slab is characterized by horizontal deflection of the subducting lithosphere towards the central Tyrrhenian basin.

  16. THE M31 VELOCITY VECTOR. II. RADIAL ORBIT TOWARD THE MILKY WAY AND IMPLIED LOCAL GROUP MASS

    SciTech Connect

    Van der Marel, Roeland P.; Sohn, Sangmo Tony; Anderson, Jay; Brown, Tom; Fardal, Mark; Besla, Gurtina; Beaton, Rachael L.; Guhathakurta, Puragra

    2012-07-01

    We determine the velocity vector of M31 with respect to the Milky Way and use this to constrain the mass of the Local Group, based on Hubble Space Telescope proper-motion measurements of three fields presented in Paper I. We construct N-body models for M31 to correct the measurements for the contributions from stellar motions internal to M31. This yields an unbiased estimate for the M31 center-of-mass motion. We also estimate the center-of-mass motion independently, using the kinematics of satellite galaxies of M31 and the Local Group, following previous work but with an expanded satellite sample. All estimates are mutually consistent, and imply a weighted average M31 heliocentric transverse velocity of (v{sub W} , v{sub N} ) = (- 125.2 {+-} 30.8, -73.8 {+-} 28.4) km s{sup -1}. We correct for the reflex motion of the Sun using the most recent insights into the solar motion within the Milky Way, which imply a larger azimuthal velocity than previously believed. This implies a radial velocity of M31 with respect to the Milky Way of V{sub rad,M31} = -109.3 {+-} 4.4 km s{sup -1}, and a tangential velocity of V{sub tan,M31} = 17.0 km s{sup -1}, with a 1{sigma} confidence region of V{sub tan,M31} {<=} 34.3 km s{sup -1}. Hence, the velocity vector of M31 is statistically consistent with a radial (head-on collision) orbit toward the Milky Way. We revise prior estimates for the Local Group timing mass, including corrections for cosmic bias and scatter, and obtain M{sub LG} {identical_to} M{sub MW,vir} + M{sub M31,vir} = (4.93 {+-} 1.63) Multiplication-Sign 10{sup 12} M{sub Sun }. Summing known estimates for the individual masses of M31 and the Milky Way obtained from other dynamical methods yields smaller uncertainties. Bayesian combination of the different estimates demonstrates that the timing argument has too much (cosmic) scatter to help much in reducing uncertainties on the Local Group mass, but its inclusion does tend to increase other estimates by {approx}10%. We

  17. Active high-resolution seismic tomography of compressional wave velocity and attenuation structure at Medicine Lake Volcano, Northern California Cascade Range

    NASA Astrophysics Data System (ADS)

    Evans, John R.; Zucca, John J.

    1988-12-01

    We determine compressional wave velocity and attenuation structures for the upper crust beneath Medicine Lake volcano in northeast California using a high-resolution active source seismic tomography method. Medicine Lake volcano is a basalt through rhyolite shield volcano of the Cascade Range, lying east of the range axis. The Pg wave from eight explosive sources which has traveled upward through the target volume to a dense array of 140 seismographs provides 1- to 2-km resolution in the upper 5 to 7 km of the crust beneath the volcano. The experiment tests the hypothesis that Cascade Range volcanoes of this type are underlain only by small silicic magma chambers. We image a low-velocity low-Q region not larger than a few tens of cubic kilometers in volume beneath the summit caldera, supporting the hypothesis. A shallower high-velocity high-density feature, previously known to be present, is imaged for the first time in full plan view; it is east-west elongate, paralleling a topographic lineament between Medicine Lake volcano and Mount Shasta. This lineament is interpreted to be the result of an old crustal weakness now affecting the emplacement of magma, both on direct ascent from the lower crust and mantle and in migration from the shallow silicic chamber to summit vents. Differences between this high-velocity feature and the equivalent feature at Newbeny volcano, a volcano in central Oregon resembling Medicine Lake volcano, may partly explain the scarcity of surface hydrothermal features at Medicine Lake volcano. A major low-velocity low-Q feature beneath the southeast flank of the volcano, in an area with no Holocene vents, is interpreted as tephra, flows, and sediments from the volcano deeply ponded on the downthrown side of the Gillem fault, a normal fault mapped at the surface north of the volcano. A high-Q normal-velocity feature beneath the north rim of the summit caldera may be a small, possibly hot, subsolidus intrusion. A high-velocity low-Q region

  18. Correction of phase velocity bias caused by strong directional noise sources in high-frequency ambient noise tomography: a case study in Karamay, China

    NASA Astrophysics Data System (ADS)

    Wang, K.; Luo, Y.; Yang, Y.

    2016-12-01

    We collect two months of ambient noise data recorded by 35 broadband seismic stations in a 9×11 km area near Karamay, China, and do cross-correlation of noise data between all station pairs. Array beamforming analysis of the ambient noise data shows that ambient noise sources are unevenly distributed and the most energetic ambient noise mainly comes from azimuths of 40o-70o. As a consequence of the strong directional noise sources, surface wave waveforms of the cross-correlations at 1-5 Hz show clearly azimuthal dependence, and direct dispersion measurements from cross-correlations are strongly biased by the dominant noise energy. This bias renders that the dispersion measurements from cross-correlations do not accurately reflect the interstation velocities of surface waves propagating directly from one station to the other, that is, the cross-correlation functions do not retrieve Empirical Green's Functions accurately. To correct the bias caused by unevenly distributed noise sources, we adopt an iterative inversion procedure. The iterative inversion procedure, based on plane-wave modeling, includes three steps: (1) surface wave tomography, (2) estimation of ambient noise energy and (3) phase velocities correction. First, we use synthesized data to test efficiency and stability of the iterative procedure for both homogeneous and heterogeneous media. The testing results show that: (1) the amplitudes of phase velocity bias caused by directional noise sources are significant, reaching 2% and 10% for homogeneous and heterogeneous media, respectively; (2) phase velocity bias can be corrected by the iterative inversion procedure and the convergences of inversion depend on the starting phase velocity map and the complexity of the media. By applying the iterative approach to the real data in Karamay, we further show that phase velocity maps converge after ten iterations and the phase velocity map based on corrected interstation dispersion measurements are more consistent

  19. Correction of phase velocity bias caused by strong directional noise sources in high-frequency ambient noise tomography: a case study in Karamay, China

    NASA Astrophysics Data System (ADS)

    Wang, Kai; Luo, Yinhe; Yang, Yingjie

    2016-05-01

    We collect two months of ambient noise data recorded by 35 broad-band seismic stations in a 9 × 11 km area (1-3 km station interval) near Karamay, China, and do cross-correlation of noise data between all station pairs. Array beamforming analysis of the ambient noise data shows that ambient noise sources are unevenly distributed and the most energetic ambient noise mainly comes from azimuths of 40°-70°. As a consequence of the strong directional noise sources, surface wave components of the cross-correlations at 1-5 Hz show clearly azimuthal dependence, and direct dispersion measurements from cross-correlations are strongly biased by the dominant noise energy. This bias renders that the dispersion measurements from cross-correlations do not accurately reflect the interstation velocities of surface waves propagating directly from one station to the other, that is, the cross-correlation functions do not retrieve empirical Green's functions accurately. To correct the bias caused by unevenly distributed noise sources, we adopt an iterative inversion procedure. The iterative inversion procedure, based on plane-wave modeling, includes three steps: (1) surface wave tomography, (2) estimation of ambient noise energy and biases and (3) phase velocities correction. First, we use synthesized data to test the efficiency and stability of the iterative procedure for both homogeneous and heterogeneous media. The testing results show that: (1) the amplitudes of phase velocity bias caused by directional noise sources are significant, reaching ˜2 and ˜10 per cent for homogeneous and heterogeneous media, respectively; (2) phase velocity bias can be corrected by the iterative inversion procedure and the convergence of inversion depends on the starting phase velocity map and the complexity of the media. By applying the iterative approach to the real data in Karamay, we further show that phase velocity maps converge after 10 iterations and the phase velocity maps obtained using

  20. Phase Control of Group Velocity in a Doppler-Broadened Λ-Type Three-Level System

    NASA Astrophysics Data System (ADS)

    Qiu, Tian-Hui; Xie, Min

    2016-06-01

    We theoretically investigate the phase control role on the group velocity of a weak probe field in a Doppler-broadened Λ-type three-level atomic system with the spontaneously generated coherence effect enhanced by an incoherence pump. We find that the absorption-dispersion of the probe field behaves phase and Doppler broadening-dependent phenomena, and testify that the quite large group index can be realized. The group velocity of the probe field can be switched from subluminal to superluminal or vice versa by modulating the relative phase of the two applied light fields. In contrast to the counterpropagating setting, the copropagating case is more suitable for the purpose considered in this paper due to the effectiveness of Doppler-free.

  1. Control over group velocity in a three-level closed Λ system via spontaneously generated coherence and dynamically induced coherence

    NASA Astrophysics Data System (ADS)

    Dutta, Sulagna; Dastidar, Krishna Rai

    2007-11-01

    The light propagation of a probe field in a three-level Λ system with incoherent pumping has been studied when both dynamically induced coherence (DIC) and spontaneously generated coherence (SGC) play a significant role. We have investigated the group velocity of probe field and hence the group index of a three-level Λ system with incoherent pumping when both DIC and SGC play a significant role. We have shown that by varying the probe field Rabi frequency one can control the interference between these two coherences which leads to different nonlinear response (amplification without inversion, electromagnetically induced transparency and electromagnetically induced absorption) leading to different (positive and negative) dispersion. Hence control over switching of group velocity from subluminal to superluminal and vice versa can be achieved. We have also shown that when the contributions from both the coherences are comparable, the dependence of group velocity of probe field in a three-level Λ system with incoherent pumping on phase difference between probe and coherent fields is different from that obtained under the weak probe field condition. Going beyond the weak probe field approximation we have derived analytical expressions for group velocity and hence the group index in the steady state limit (keeping all orders of system parameters) to generalize the analysis, and these expressions can be used for any set of system parameters without any restriction. The numerical values obtained by solving the density matrix equations agree well with these exact analytical values at a large time limit. We have proposed a scheme for experimental realization of EIT and hence subluminal light propagation in molecules by invoking spontaneously generated coherence.

  2. Lithospheric structure of the westernmost Mediterranean inferred from finite frequency Rayleigh wave tomography S-velocity model.

    NASA Astrophysics Data System (ADS)

    Palomeras, Imma; Villasenor, Antonio; Thurner, Sally; Levander, Alan; Gallart, Josep; Harnafi, Mimoun

    2016-04-01

    The Iberian Peninsula and Morocco, separated by the Alboran Sea and the Algerian Basin, constitute the westernmost Mediterranean. From north to south this region consists of the Pyrenees, the result of interaction between the Iberian and Eurasian plates; the Iberian Massif, a region that has been undeformed since the end of the Paleozoic; the Central System and Iberian Chain, regions with intracontinental Oligocene-Miocene deformation; the Gibraltar Arc (Betics, Rif and Alboran terranes) and the Atlas Mountains, resulting from post-Oligocene subduction roll-back and Eurasian-Nubian plate convergence. In this study we analyze data from recent broad-band array deployments and permanent stations on the Iberian Peninsula and in Morocco (Spanish IberArray and Siberia arrays, the US PICASSO array, the University of Munster array, and the Spanish, Portuguese, and Moroccan National Networks) to characterize its lithospheric structure. The combined array of 350 stations has an average interstation spacing of ~60 km, comparable to USArray. We have calculated the Rayleigh waves phase velocities from ambient noise for short periods (4 s to 40 s) and teleseismic events for longer periods (20 s to 167 s). We inverted the phase velocities to obtain a shear velocity model for the lithosphere to ~200 km depth. The model shows differences in the crust for the different areas, where the highest shear velocities are mapped in the Iberian Massif crust. The crustal thickness is highly variable ranging from ~25 km beneath the eastern Betics to ~55km beneath the Gibraltar Strait, Internal Betics and Internal Rif. Beneath this region a unique arc shaped anomaly with high upper mantle velocities (>4.6 km/s) at shallow depths (<65 km) is observed. We interpret this body as the subducting Alboran slab that is depressing the crust of the western Gibraltar arc to ~55 km depth. Low upper mantle velocities (<4.2 km/s) are observed beneath the Atlas, the northeastern end of the Betic Mountains and

  3. 3D Anisotropic Velocity Tomography of a Water Saturated Rock under True-Triaxial Stress in the Laboratory

    NASA Astrophysics Data System (ADS)

    Ghofrani Tabari, M.; Goodfellow, S. D.; Nasseri, M. B.; Young, R.

    2013-12-01

    A cubic specimen of water saturated Fontainebleau Sandstone is tested in the laboratory under true-triaxial loading where three different principal stresses are applied under drained conditions. Due to the loading arrangement, closure and opening of the pre-existing cracks in the rock, as well as creation and growth of the aligned cracks cause elliptical anisotropy and distributed heterogeneities. A Geophysical Imaging Cell equipped with an Acoustic Emission monitoring system is employed to image velocity structure of the sample during the experiment through repeated transducer to transducer non-destructive ultrasonic surveys. Apparent P-wave velocities along the rock body are calculated in different directions and shown in stereonet plots which demonstrate an overall anisotropy of the sample. The apparent velocities in the main three orthogonal cubic directions are used as raw data for building a mean spatial distribution model of anisotropy ratios. This approach is based on the concept of semi-principal axes in an elliptical anisotropic model and appointing two ratios between the three orthogonal velocities in each of the cubic grid cells. The spatial distribution model of anisotropy ratios are used to calculate the anisotropic ray-path segment matrix elements (Gij). These contain segment lengths of the ith ray in the jth cell in three dimensions where, length of each ray in each cell is computed for one principal direction based on the dip and strike of the ray and these lengths differ from the ones in an isotropic G Matrix. 3D strain of the squeezed rock and the consequent geometrical deformation is also included in the ray-path segment matrix. A Singular Value Decomposition (SVD) method is used for inversion from the data space of apparent velocities to the model space of P-wave propagation velocities in the three principal directions. Finally, spatial variation and temporal evolution of induced damages in the rock, representing uniformly distributed or

  4. Preliminary 3D seismic velocity model for the crustal structure of the southern part of the Korean Peninsula inferred from ambient noise tomography and waveform modeling

    NASA Astrophysics Data System (ADS)

    Rhie, J.; Kim, S.; Lee, S.

    2012-12-01

    We construct a preliminary 3D seismic velocity model for the crust beneath the southern part of the Korean Peninsula. Broadband waveforms obtained from seismic network in and around the study area are used. First, a quasi-3D S-wave model is estimated from Rayleigh wave tomography using ambient seismic noise. During the depth-inversion of dispersion curve for each inversion node, a Bayesian approach is used to introduce sharp boundaries and to provide a statistical assessment of inverted 1D Vsv models. Crustal thickness and average Vp/Vs ratio are constrained from the result of previous receiver function (RF) study. Then, Love wave dispersions are inverted for 1D Vsh models by allowing small velocity perturbations with respect to the previously defined 1D Vsv-wave models. Lastly, a series of forward 3D waveform modeling are performed based on the anisotropic S-wave model. The starting P-wave velocity model is determined by using Vp/Vs ratio from the RF study and an average model between Vsv and Vsh models. Values of Vp/Vs ratio, Vsv, Vsh, and crustal thickness are systematically varied during the forward modeling to fit observed three-component broadband (~0.05-0.3 Hz) waveforms. By doing this, we develop a preliminary 3D velocity model for the southern Korean Peninsula. Our model is a starting model of the realistic 3D model, which takes into account more data such as surface geological feature, high-frequency body wave travel times, and gravity. The final model will be used to predict strong g round motion of potential large scenario earthquakes after correcting site effects.

  5. Three-dimensional seismic velocity structure of Mauna Loa and Kilauea volcanoes in Hawaii from local seismic tomography

    USGS Publications Warehouse

    Lin, Guoqing; Shearer, Peter M.; Matoza, Robin S.; Okubo, Paul G.; Amelung, Falk

    2016-01-01

    We present a new three-dimensional seismic velocity model of the crustal and upper mantle structure for Mauna Loa and Kilauea volcanoes in Hawaii. Our model is derived from the first-arrival times of the compressional and shear waves from about 53,000 events on and near the Island of Hawaii between 1992 and 2009 recorded by the Hawaiian Volcano Observatory stations. The Vp model generally agrees with previous studies, showing high-velocity anomalies near the calderas and rift zones and low-velocity anomalies in the fault systems. The most significant difference from previous models is in Vp/Vs structure. The high-Vp and high-Vp/Vs anomalies below Mauna Loa caldera are interpreted as mafic magmatic cumulates. The observed low-Vp and high-Vp/Vs bodies in the Kaoiki seismic zone between 5 and 15 km depth are attributed to the underlying volcaniclastic sediments. The high-Vp and moderate- to low-Vp/Vs anomalies beneath Kilauea caldera can be explained by a combination of different mafic compositions, likely to be olivine-rich gabbro and dunite. The systematically low-Vp and low-Vp/Vs bodies in the southeast flank of Kilauea may be caused by the presence of volatiles. Another difference between this study and previous ones is the improved Vp model resolution in deeper layers, owing to the inclusion of events with large epicentral distances. The new velocity model is used to relocate the seismicity of Mauna Loa and Kilauea for improved absolute locations and ultimately to develop a high-precision earthquake catalog using waveform cross-correlation data.

  6. Lithospheric P- and S-wave velocity models of the Sicilian area using WAM tomography: procedure and assessments

    NASA Astrophysics Data System (ADS)

    Calò, Marco; Parisi, Laura; Luzio, Dario

    2013-10-01

    We present 3-D models of the P- and S-wave velocity distributions in the crust and uppermost mantle beneath Sicily, Calabria (Southern Italy), and surrounding submerged areas, obtained by tomographic inversion of traveltimes of regional body waves phases. Our method combines double-difference tomographic inversion with a post-processing procedure [Weighted Average Model method (WAM)]. This procedure was applied to a set of models consistent with the experimental data. We tested the ability of the WAM procedure to mitigate the uncertainty associated with the arbitrary nature of the many input parameters required for each inversion. The local reliability and resolution of the obtained models have been assessed through: synthetic tests, experimental tests carried out with independent data sets and unconventional tests based on the analysis of the internal consistency of the P- and S-velocity models. The tomographic images provide a detailed sketch of P- and S-wave velocity anomalies. These clearly show the shape of the Sicilian-Maghrebian belt beneath Sicily and Calabrian Arc at different depths. Low VP and Vs bodies are imaged beneath Stromboli and Marsili volcanoes in the southern Tyrrhenian, whereas high and low seismic velocities alternate beneath the Etna giving inferences on the possible depth of the mantle melting feeding the volcano. In the upper crust, the main sedimentary basins and tectonic features are also well imaged. Finally, tomographic cross sections show the trend of the Moho in the study area, where its depth ranges between 35 and 40 km beneath the Sicilian belt and between 15 and 22 km in the southern Tyrrhenian basin and Ionian Sea.

  7. Feasibility of capillary velocity assessment by statistical means using dual-beam spectral-domain Optical Coherence Tomography: a preliminary study.

    PubMed

    Daly, Susan M; Silien, Christophe; Leahy, Martin J

    2013-09-01

    The assessment of vascular dynamics has been shown to yield both qualitative and quantitative metrics and thus play a pivotal role in the diagnosis and prognosis of various diseases, which may manifest as microcirculatory irregularities. Optical Coherence Tomography (OCT) is an established imaging modality which utilises the principle of optical interferometry to distinguish between spatial changes in refractive index and thus formulate a multi-dimensional representation of a specimen in vivo. Nonetheless, difficulties remain in obtaining accurate data (morphological and/or transient) in an environment which is subject to such large biological variability. In an effort to address the issue of angular dependence as with Doppler based analysis, a dual-beam Spectral-domain OCT system for quasi-simultaneous specimen scanning is described. A statistical based method of phase correlation is outlined which is capable of quantifying velocity values in addition to the ability to discern bidirectionality, without the necessity of angular computation.

  8. Feeding volcanoes of the Kluchevskoy group from the results of local earthquake tomography

    NASA Astrophysics Data System (ADS)

    Koulakov, Ivan; Gordeev, Evgeniy I.; Dobretsov, Nikolay L.; Vernikovsky, Valery A.; Senyukov, Sergey; Jakovlev, Andrey

    2011-05-01

    We present a seismic model of the area beneath the Kluchevskoy volcano group (Kamchatka, Russia) based on the tomographic inversion of more than 66000 P and S arrival times from more than 5000 local earthquakes that occurred in 2004 and that were recorded by 17 permanent stations. Below a depth of 25 km beneath the Kluchevskoy volcano, we observed a very strong anomaly in the Vp/Vs ratio that reached as high as 2.2. This is a probable indicator of the presence of partially molten material with a composition corresponding to deeper mantle layers. The upper part of this anomaly at a depth of 25-30 km coincides with a cluster of strong seismicity that can be explained by strong mechanical stresses in the lowermost crust due to magma ascension, water release and/or phase transitions. In the crust, we observed regular seismicity clusters that link the mantle anomaly with the Kluchevskoy volcano and most likely indicate the paths of magma migration. Between depths of 8 and 13 km, we see several patterns of high Vp/Vs ratios, interpreted as intermediate-depth magma storages. Directly below the Kluchevskoy volcano, we observed a shallow body of high Vp/Vs, which probably represents the activated magma chamber just beneath the volcano cone, which erupted in the beginning of 2005. The existence of three levels of magma storage, based on results of local earthquake tomography, may explain the variety of the lava composition and eruption regimes in different volcanoes of the Kluchevskoy group.

  9. Rapid measurement of transversal flow velocity vector with high spatial resolution using speckle decorrelation optical coherence tomography.

    PubMed

    Fu, Lei; Su, Ya; Wang, Yimin; Chen, Lei; Li, Wenping; Wang, Hongjie; Li, Zhihong; Steve Yao, X

    2017-09-15

    We propose and demonstrate a novel method that uses only three sets of B-scans to accurately determine both the direction and the speed of a transversal flow using speckle decorrelation optical coherence tomography. Our tri-scan method has the advantages of high measurement speed, high spatial resolution, and insensitivity to the flow speed. By introducing error maps, we show that the flow angle inaccuracy can be minimized by choosing the measurement result with a lesser error between results obtained from the x- and y-scans. Finally, we demonstrate that the flow angle measurement accuracy can be further improved for the high-speed flows by increasing the speed of the x- and y-scans.

  10. High speed, wide velocity dynamic range Doppler optical coherence tomography (Part IV): split spectrum processing in rotary catheter probes.

    PubMed

    Vuong, Barry; Lee, Anthony M D; Luk, Timothy W H; Sun, Cuiru; Lam, Stephen; Lane, Pierre; Yang, Victor X D

    2014-04-07

    We report a technique for blood flow detection using split spectrum Doppler optical coherence tomography (ssDOCT) that shows improved sensitivity over existing Doppler OCT methods. In ssDOCT, the Doppler signal is averaged over multiple sub-bands of the interferogram, increasing the SNR of the Doppler signal. We explore the parameterization of this technique in terms of number of sub-band windows, width and overlap of the windows, and their effect on the Doppler signal to noise in a flow phantom. Compared to conventional DOCT, ssDOCT processing has increased flow sensitivity. We demonstrate the effectiveness of ssDOCT in-vivo for intravascular flow detection within a porcine carotid artery and for microvascular vessel detection in human pulmonary imaging, using rotary catheter probes. To our knowledge, this is the first report of visualizing in-vivo Doppler flow patterns adjacent to stent struts in the carotid artery.

  11. Reduction of heat capacity and phonon group velocity in silicon nanowires

    NASA Astrophysics Data System (ADS)

    Marchbanks, Christopher; Wu, Zhigang

    2015-02-01

    We report on ab initio linear-response calculations of lattice vibrations in narrow silicon nanowires on the order of 1 nm along the [001], [011], and [111] growth directions. The confinement and nanowire structure substantially alter phonon distributions, resulting in an 15% to 23% reduction in heat capacity and an averaged decrease of 31% in acoustic velocities compared with bulk silicon. Based on these, we estimate an improvement up to 4 fold on thermoelectric performance due solely to the modified lattice vibrations in narrow silicon nanowires over bulk silicon.

  12. Chirped distributed Bragg reflector for broad-band group velocity dispersion compensation in terahertz quantum cascade lasers

    NASA Astrophysics Data System (ADS)

    Xu, C.; Ban, D.

    2016-11-01

    Behaviors of chirped DBR for group velocity dispersion (GVD) compensation in THz QCLs with metal-metal waveguides have been investigated theoretically in both 1D and 3D models with COMSOL Multiphysics. The strategy of designing chirped DBR for GVD compensation in terahertz frequency range has been presented. In order to achieve broad-band GVD compensation with less distortion, a two-section chirped DBR structure is proposed.

  13. Phase control of group velocity of light in an InGaN/GaN quantum dot nanostructure

    SciTech Connect

    Jafarzadeh, H; Ahmadi Sangachin, E; Seyyed Hossein Asadpour

    2015-09-30

    By solving self-consistently Schrödinger–Poisson equations for a carrier in the conduction band of an InGaN/GaN quantum dot, a four-level quantum system is described. It is found that in the presence of terahertz signal radiation, the medium becomes phase dependent, which ensures the phase control of the group velocity of a weak probe pulse from slow to fast light. (nonlinear optical phenomena)

  14. Group-phase Velocity Difference and THz Oscillation of the Nonlinear Refractive Index in Air: Particle-like Solutions

    SciTech Connect

    Kovachev, L. M.

    2009-10-29

    We present an analytical approach to the theory of optical pulses with superbroad spectrum propagated in air. The corresponding modified amplitude envelope equation admits oscillated with terahertz frequency nonlinear term The fluctuation is due to the group and phase velocity difference. In the partial case of femtosecond pulses with power, little above the critical for self-focusing, exact (3+1)D particle-like solution is found.

  15. P, S velocity and VP/VS ratio beneath the Toba caldera complex (Northern Sumatra) from local earthquake tomography

    NASA Astrophysics Data System (ADS)

    Koulakov, Ivan; Yudistira, Tedi; Luehr, Birger-G.; Wandono

    2009-06-01

    In this paper, we investigate the crustal and uppermost mantle structure beneath Toba caldera, which is known as the location of one of the largest Cenozoic eruptions on Earth. The most recent event occurred 74000 yr BP, and had a significant global impact on climate and the biosphere. In this study, we revise data on local seismicity in the Toba area recorded by a temporary PASSCAL network in 1995. We applied the newest version of the LOTOS-07 algorithm, which includes absolute source location, optimization of the starting 1-D velocity model, and iterative tomographic inversion for 3-D seismic P, S (or the VP/VS ratio) and source parameters. Special attention is paid to verification of the obtained results. Beneath the Toba caldera and other volcanoes of the arc, we observe relatively moderate (for volcanic areas) negative P- and S-velocity anomalies that reach 18 per cent in the uppermost layer, 10-12 per cent in the lower crust and about 7 per cent in the uppermost mantle. Much stronger contrasts are observed for the VP/VS ratio that is a possible indicator of dominant effect of melting in origin of seismic anomalies. At a depth of 5 km beneath active volcanoes, we observe small patterns (7-15 km size) with a high VP/VS ratio that might be an image of actual magmatic chambers filled with partially molten material feeding the volcanoes. In the mantle wedge, we observe a vertical anomaly with low P and S velocities and a high VP/VS ratio that link the cluster of events at 120-140 km depth with Toba caldera. This may be an image of ascending fluids and melts released from the subducted slab due to phase transitions. However, taking into account poor vertical resolution, these results should be interpreted with prudence. Although the results show clear signatures that are quite typical for volcanic areas (low velocity and high VP/VS ratio beneath volcanoes), we do not observe any specific features in seismic structure that could characterize Toba as a super volcano.

  16. Self-induced transparency modelocking of quantum cascade lasers in the presence of saturable nonlinearity and group velocity dispersion.

    PubMed

    Talukder, Muhammad Anisuzzaman; Menyuk, Curtis R

    2010-03-15

    We consider the impact of saturable nonlinearity and group velocity dispersion on self-induced transparency (SIT) modelocking of quantum cascade lasers (QCLs). We find that self-induced transparency modelocking in QCLs can be obtained in the presence of saturable nonlinearity if the saturable loss or gain is below a critical limit. The limit for the saturable loss is significantly more stringent than the limit for the saturable gain. Stable modelocked pulses are also obtained in the presence of both normal and anomalous group velocity dispersion when its magnitude is below a critical value. The stability limit for the saturable loss becomes less stringent when group velocity dispersion is simultaneously present. However, the stability limit for the saturable gain is not significantly affected. All these limits depend on the ratio of the SIT-induced gain and absorpt n to the linear loss. Realistic values for both the saturable nonlinearity and chromatic dispersion are within the range in which SIT modelocking is predicted to be stable.

  17. Velocity space diffusion of pickup ions from the water group at Comet Halley

    NASA Technical Reports Server (NTRS)

    Coates, A. J.; Johnstone, A. D.; Wilken, B.; Jockers, K.; Glassmeier, K.-H.

    1989-01-01

    The diffusion in velocity space of cometary ions was studied using the distributions of ions measured by the implanted ion spectrometer in Giotto during the inbound pass. The measurements were transformed into a frame comoving with the solar wind and oriented with the magnetic field. The observations show the evolution of the pitch angle distribution in the solar wind turbulence to form a shell from the initial ring. Diffusion in energy takes place simultaneously but on a longer time scale. Comparison with theory is inhibited by the lack of a suitable spatial model, but the simple arguments that can be made indicate that pitch angle diffusion and the process of parallel pickup take place more slowly than theory suggests.

  18. Lateral seismic velocity heterogeneity along the fault system controlling the endpoints of earthquake rupture inferred from a 3D seismic tomography in the Ou Backbone Range, Northeast Japan

    NASA Astrophysics Data System (ADS)

    Aoyagi, Y.; Kimura, H.; Abe, S.

    2016-12-01

    The multideformed axial zone of the Ou backbone range provides a great opportunity to explore the influence of pre-existing cross-structures on the segmentation of active seismogenic reverse faults. Detailed 3D seismic velocity structure acquired by a tomography using a dense temporal network data clearly shows a strong lateral heterogeneity and its correlation to the hypocenter locations. Most ( 80%) of the hypocenters including aftershocks of the 2008 Iwate-Miyage Nairiku Earthquake (M7.2) are located in the bodies of high Vp ( 5.7-6.2 km/s) and low Vp/Vs ( 1.61-1.74). In contrast, few hypocenters are located in the other bodies of lower Vp and the higher Vp/Vs (>1.85). The estimated Poisson's ratios are 0.25 and 0.4, respectively in the seismogenic layer and in the aseismic layer. Such velocity contrasts in lateral are frequently recognized at the both sides of WNW-ESE boundaries across the N-S trending active fault system. Some of them are consistent with the known pre-existing cross-structures originally formed by the clockwise rotation of the NE Japan arc (Japan Sea opening) during the Miocene epoch. As the velocity boundaries continue also to the depth in the upper crust, the thicknesses of the seismogenic layer differ at the boundaries. Some of the rupture endpoints of the recent large earthquakes ( M7) are consistent with such boundaries decreasing seismogenic layer thickness from the source area to the adjacent area. It indicates that the lateral heterogeneity along the fault system is certainly an important factor in determining a segment boundary.

  19. Three-Dimensional P-wave Velocity Structure Beneath Long Valley Caldera, California, Using Local-Regional Double-Difference Tomography

    NASA Astrophysics Data System (ADS)

    Menendez, H. M.; Thurber, C. H.

    2011-12-01

    Eastern California's Long Valley Caldera (LVC) and the Mono-Inyo Crater volcanic systems have been active for the past ~3.6 million years. Long Valley is known to produce very large silicic eruptions, the last of which resulted in the formation of a 17 km by 32 km wide, east-west trending caldera. Relatively recent unrest began between 1978-1980 with five ML ≥ 5.7 non-double-couple (NDC) earthquakes and associated aftershock swarms. Similar shallow seismic swarms have continued south of the resurgent dome and beneath Mammoth Mountain, surrounding sites of increased CO2 gas emissions. Nearly two decades of increased volcanic activity led to the 1997 installation of a temporary three-component array of 69 seismometers. This network, deployed by the Durham University, the USGS, and Duke University, recorded over 4,000 high-frequency events from May to September. A local tomographic inversion of 283 events surrounding Mammoth Mountain yielded a velocity structure with low Vp and Vp/Vs anomalies at 2-3 km bsl beneath the resurgent dome and Casa Diablo hot springs. These anomalies were interpreted to be CO2 reservoirs (Foulger et al., 2003). Several teleseismic and regional tomography studies have also imaged low Vp anomalies beneath the caldera at ~5-15 km depth, interpreted to be the underlying magma reservoir (Dawson et al., 1990; Weiland et al., 1995; Thurber et al., 2009). This study aims to improve the resolution of the LVC regional velocity model by performing tomographic inversions using the local events from 1997 in conjunction with regional events recorded by the Northern California Seismic Network (NCSN) between 1980 and 2010 and available refraction data. Initial tomographic inversions reveal a low velocity zone at ~2 to 6 km depth beneath the caldera. This structure may simply represent the caldera fill. Further iterations and the incorporation of teleseismic data may better resolve the overall shape and size of the underlying magma reservoir.

  20. Three-dimensional P wave attenuation and velocity upper mantle tomography of the southern Apennines-Calabrian Arc subduction zone

    NASA Astrophysics Data System (ADS)

    Monna, Stephen; Dahm, Torsten

    2009-06-01

    We propose a 3-D crust-upper mantle seismic attenuation (QP) model of the southern Apennines-Calabrian Arc subduction zone together with a 3-D velocity (VP) model. The QP model is calculated from relative t* using the spectral ratio method and the VP from traveltime data. The final data set used for the inversion of the VP model consists of 2400 traveltime arrivals recorded by 34 short-period stations that are part of the Italian National Seismic Network, and for the QP model, 2178 Pn phases recorded by a subset of 32 stations. Traveltimes and waveforms come from 272 intermediate-depth Calabrian slab events. This 3-D model of attenuation, together with the 3-D velocity model, improves our knowledge of the slab/mantle wedge structure and can be a starting point in determining the physical state of the asthenosphere (i.e., its temperature, the presence of melt and/or fluids) and its relation to volcanism found in the study area. Main features of the QP and VP models show that the mantle wedge/slab, in particular, the area of highest attenuation, is located in a volume underlying the Marsili Basin. The existence and shape of this main low-QP (and low-VP) anomaly points to slab dehydration and fluid/material flow, a process that may explain the strong geochemical affinities between the subduction-related magmas from Stromboli and Vesuvius. Other interesting features in the models are strong lateral variations in QP and VP that are put in relation with known important tectonic structures and volcanic centers in the area.

  1. Non-perturbative renormalization group calculation of the quasi-particle velocity and the dielectric function of graphene

    NASA Astrophysics Data System (ADS)

    Sharma, Anand; Bauer, Carsten; Rueckriegel, Andreas; Kopietz, Peter

    We use a nonperturbative functional renormalization group approach to calculate the renormalized quasiparticle velocity v (k) and the static dielectric function ɛ (k) of suspended graphene as function of an external momentum k. We fit our numerical result for v (k) to v (k) /vF = A + Bln (Λ0 / k) , where vF is the bare Fermi velocity, Λ0 is an ultraviolet cutoff, and A = 1 . 37 , B = 0 . 51 for the physically relevant value (e2 /vF = 2 . 2) of the coupling constant. In stark contrast to calculations based on the static random-phase approximation, we find that ɛ (k) approaches unity for k --> 0 . Our result for v (k) agrees very well with a recent measurement by Elias etal. [Nat. Phys. 7, 701 (2011)]. With in the same approximation, we also explore an alternative scheme in order to understand the true nature of the low energy (momentum) behavior in graphene.

  2. Inclusion of In-Situ Velocity Measurements into the UCSD Time-Dependent Tomography to Constrain and Better-Forecast Remote-Sensing Observations

    NASA Astrophysics Data System (ADS)

    Jackson, B. V.; Hick, P. P.; Bisi, M. M.; Clover, J. M.; Buffington, A.

    2010-08-01

    The University of California, San Diego (UCSD) three-dimensional (3-D) time-dependent tomography program has been used successfully for a decade to reconstruct and forecast coronal mass ejections from interplanetary scintillation observations. More recently, we have extended this tomography technique to use remote-sensing data from the Solar Mass Ejection Imager (SMEI) on board the Coriolis spacecraft; from the Ootacamund (Ooty) radio telescope in India; and from the European Incoherent SCATter (EISCAT) radar telescopes in northern Scandinavia. Finally, we intend these analyses to be used with observations from the Murchison Widefield Array (MWA), or the LOw Frequency ARray (LOFAR) now being developed respectively in Australia and Europe. In this article we demonstrate how in-situ velocity measurements from the Advanced Composition Explorer (ACE) space-borne instrumentation can be used in addition to remote-sensing data to constrain the time-dependent tomographic solution. Supplementing the remote-sensing observations with in-situ measurements provides additional information to construct an iterated solar-wind parameter that is propagated outward from near the solar surface past the measurement location, and throughout the volume. While the largest changes within the volume are close to the radial directions that incorporate the in-situ measurements, their inclusion significantly reduces the uncertainty in extending these measurements to global 3-D reconstructions that are distant in time and space from the spacecraft. At Earth, this can provide a finely-tuned real-time measurement up to the latest time for which in-situ measurements are available, and enables more-accurate forecasting beyond this than remote-sensing observations alone allow.

  3. Geophysical Imaging of Asia and Siberia: Tomography for Seismic Velocity, Upper Mantle Gradient, Lg Attenuation, and Joint Inversion of Surface Wave Dispersion, Receiver Functions and Satellite Gravity Data

    DTIC Science & Technology

    2007-09-01

    Junggar Basin , N) Tibetan Plateau, O) Qaidam Basin , P) Panxi Rift, Q) Songpan-Ganzi, R) Sichuan Basin , S) Ordos Basin , T) Shanxi Graben, U) Baikal Rift...D) Tajik Basin , D) Hindu Kush, F) Tibetan Plateau, G) Sichuan Basin . By solving not only for two-dimensional Pn slowness, but also for 2-D upper...inversion method using gravity and surface-wave group velocity data, which has been applied to the Tarim and Junggar sedimentary basins in central Asia

  4. First Scientific Working Group Meeting of Airborne Doppler Lidar Wind Velocity Measurement Program

    NASA Technical Reports Server (NTRS)

    Kaufman, J. W. (Editor)

    1980-01-01

    The purpose of the first scientific working group meeting was fourfold: (1) to identify flight test options for engineering verification of the MSFC Doppler Lidar; (2) to identify flight test options for gathering data for scientific/technology applications; (3) to identify additional support equipment needed on the CV 990 aircraft for the flight tests; and (4) to identify postflight data processing and data sets requirements. The working group identified approximately ten flight options for gathering data on atmospheric dynamics processes, including turbulence, valley breezes, and thunderstorm cloud anvil and cold air outflow dynamics. These test options will be used as a basis for planning the fiscal year 1981 tests of the Doppler Lidar system.

  5. Three-dimensional P-wave velocity structure derived from local earthquakes at the Katmai group of volcanoes, Alaska

    USGS Publications Warehouse

    Jolly, A.D.; Moran, S.C.; McNutt, S.R.; Stone, D.B.

    2007-01-01

    The three-dimensional P-wave velocity structure beneath the Katmai group of volcanoes is determined by inversion of more than 10,000 rays from over 1000 earthquakes recorded on a local 18 station short-period network between September 1996 and May 2001. The inversion is well constrained from sea level to about 6??km below sea level and encompasses all of the Katmai volcanoes; Martin, Mageik, Trident, Griggs, Novarupta, Snowy, and Katmai caldera. The inversion reduced the average RMS travel-time error from 0.22??s for locations from the standard one-dimensional model to 0.13??s for the best three-dimensional model. The final model, from the 6th inversion step, reveals a prominent low velocity zone (3.6-5.0??km/s) centered at Katmai Pass and extending from Mageik to Trident volcanoes. The anomaly has values about 20-25% slower than velocities outboard of the region (5.0-6.5??km/s). Moderately low velocities (4.5-6.0??km/s) are observed along the volcanic axis between Martin and Katmai Caldera. Griggs volcano, located about 10??km behind (northwest of) the volcanic axis, has unremarkable velocities (5.0-5.7??km/s) compared to non-volcanic regions. The highest velocities are observed between Snowy and Griggs volcanoes (5.5-6.5??km/s). Relocated hypocenters for the best 3-D model are shifted significantly relative to the standard model with clusters of seismicity at Martin volcano shifting systematically deeper by about 1??km to depths of 0 to 4??km below sea level. Hypocenters for the Katmai Caldera are more tightly clustered, relocating beneath the 1912 scarp walls. The relocated hypocenters allow us to compare spatial frequency-size distributions (b-values) using one-dimensional and three-dimensional models. We find that the distribution of b is significantly changed for Martin volcano, which was characterized by variable values (0.8 < b < 2.0) with standard locations and more uniform values (0.8 < b < 1.2) after relocation. Other seismic clusters at Mageik (1.2 < b

  6. Temporal compression of cw diode-laser output into short pulses with cesium-vapor group-velocity dispersion.

    PubMed

    Choi, K; Menders, J; Ross, D; Korevaar, E

    1993-11-15

    Using a technique similar to chirped pulse compression, we have compressed the 50-mW cw output of a diode laser into pulses of greater than 500-mW peak power and less than 400-ps duration. By applying a small current modulation to the diode, we induced a small wavelength modulation in the vicinity of the 6s(1/2)-to-6p(3/2) cesium resonance transition at 852 nm. Group-velocity dispersion on propagation through a cesium vapor cell then led to pulse compression. We developed a simple model to make predictions of output pulse shapes by using different modulation waveforms.

  7. Off-axis Crustal Thickness and Lower Crustal Velocity Structure from Seismic Tomography on the Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Soule, D. C.; Wilcock, W. S.; Toomey, D. R.; Hooft, E. E.; Weekly, R. T.

    2013-12-01

    In August 2009, we conducted a seismic tomography experiment on the Endeavour segment of the Juan de Fuca Ridge to constrain the processes of crustal accretion. The experiment footprint extended 100 km along- and 60 km across-axis and covered the hydrothermally active central portion of the segment, two large overlapping spreading centers and the eastern end the Heck seamount chain. A total of 68 four-component ocean bottom seismometers were deployed at 64 sites and recorded 5567 shots of the 36-element, 6600 in.3 airgun array of the R/V Marcus G. Langseth. The data return rate was high, with good quality data recorded on either the vertical or hydrophone channel at all but two sites. In a prior study, 93,000 manually picked crustal refraction arrivals (Pg) were used to invert for three-dimensional upper crustal velocity. Here we add wide-angle PmP arrival times for non-ridge crossing paths in order to constrain the velocity of the lower crust and crustal thickness on both the Pacific and Juan de Fuca plates at crustal ages of 0.1-1.0 Ma. The starting model was obtained by extending the three-dimensional upper crustal model obtained from the Pg data downward, assuming no vertical velocity gradient in the lower crust and by adding a Moho at 6.3 km depth. Preliminary results using ~7000 PmP arrivals with reflection points at ages of 0.3-1.0 Ma show that crustal thicknesses varies from 6.1 to 7.6 km. The thickest crust is found beneath a 40-km-wide plateau located on the central portion of the Endeavour Segment. This region has been previously interpreted as a region of enhanced crustal production associated with the Heckle melt anomaly. Velocities at the base of the crust range from 6.9-7.2 km/s and tend to be slightly higher beneath the bathymetric plateau consistent with decreased levels of magmatic differentiation near the segment center. Thickened crust is also found on the Juan de Fuca plate beneath a failed propagator of the Cobb overlapping spreading center

  8. Slow group velocity propagation of sound via defect coupling in a one-dimensional acoustic band gap array

    NASA Astrophysics Data System (ADS)

    Robertson, W. M.; Baker, C.; Bennett, C. Brad

    2004-02-01

    A simple experimental system is presented in which the group velocity of acoustic wave packets traveling in an air-filled waveguide can be slowed to values much smaller than the speed of sound in air. The experiment is an acoustic analog of the much-studied optical phenomenon of slow light propagation. Slow (or even stopped) light propagation has been observed in atomic vapors in the vicinity of strong dispersion, typically associated with electromagnetically induced transparency. In the acoustic experiment described here, strong dispersion is produced by the introduction of a defect in an otherwise perfectly periodic one-dimensional acoustic band gap array. The defect produces a narrow transmission band within the forbidden acoustic band gap region resulting in strong dispersion. By tuning the carrier frequency of the acoustic wave packet to the peak transmission of the defect, the group velocity can be slowed to 0.24vs, where vs is the speed of sound in air. These results are shown to be consistent with theoretical calculations.

  9. Group velocity dispersion in fused-silica sample measured using white-light interferometry with the equalization wavelength determination

    NASA Astrophysics Data System (ADS)

    Hlubina, Petr

    Group velocity dispersion (GVD) in fused-silica sample of known thickness is measured in the spectral range from 490 to 870 nm using a new technique of white-light spectral interferometry. In the experimental set-up with the compensated Michelson interferometer and fused-silica sample inserted in it, the equalization wavelength as a function of the mirror displacement in the interferometer is measured by a low-resolution miniature fibre-optic spectrometer. From the measured values either the differential group refractive index of the sample as a function of the wavelength or the difference of the mirror displacements at two different wavelengths is obtained to determine the GVD in the sample. Moreover it is confirmed that the GVD in the fused-silica sample agrees well with that resulting from the Sellmeier dispersion equation.

  10. White-light interferometry with the equalization wavelength determination used to measure group velocity dispersion in optical samples

    NASA Astrophysics Data System (ADS)

    Hlubina, Petr

    2003-07-01

    A new white-light spectral-domain interferometric technique is used to measure the group velocity dispersion (GVD) in optical samples of known thicknesses. In the experimental setup comprising a halogen lamp, a Michelson interferometer with an optical sample, and a low-resolution spectrometer, the equalization wavelength as a function of the displacement of the interferometer mirror is measured by the spectrometer. From the measured equalization wavelengths either the differential group refractive index of the optical sample as a function of the equalization wavelength or the difference of the mirror displacements at two different equalization wavelengths is obtained to determine the GVD in the optical sample. The new white-light spectral-domain interferometric technique is applied to measure the GVD in two fused-silica optical samples of known thicknesses. In a broad spectral range it is confirmed that the GVD in both samples agrees well with the GVD resulting from the Sellmeier dispersion equation.

  11. Defining risk groups of patients with cancer of unknown primary site and cervical nodal metastases by F-18 fluorodeoxyglucose positron emission tomography and computed tomography imaging.

    PubMed

    Su, Yung-Yueh; Chen, Shih-Shin; Hsieh, Chia-Hsun; Liao, Chun-Ta; Lin, Chien-Yu; Kang, Chung-Jan; Yen, Tzu-Chen

    2016-08-01

    We sought to investigate the clinical utility of F-18 fluorodeoxyglucose (FDG) positron emission tomography and computed tomography (PET/CT) in Taiwanese patients with cancer of unknown primary site (CUP) and cervical nodal metastases. We also aimed to study the impact of F-18 FDG PET/CT on clinical treatment priority in this patient group. Between September 2006 and May 2014, patients with CUP and cervical nodal metastases who underwent F-18 FDG PET/CT imaging study were retrospectively identified. The clinicopathological risk factors and PET parameters were analyzed in relation to 2-year overall survival (OS) rates using univariate and multivariate analyses. Two-year OS curves were plotted with the Kaplan-Meier method. Of the eligible patients (n = 54), 12 (22.2%) had distant metastases (DM) at presentation. A total of 13 (24.1%) and 15 (27.8%) primary tumors were identified by FDG PET/CT imaging and an additional triple biopsy, respectively. The results of multivariate analysis identified smoking [p = 0.033, 95% confidence interval (CI) = 1.197-40.342], a maximum standardized uptake value (SUVmax) of cervical nodes ≥ 14.2 (p = 0.035, 95% CI = 1.134-28.029), and DM at presentation (p = 0.031, 95% CI = 1.257-114.854) as independent predictors of 2-year OS. Specifically, patients who carried ≥ 2 risk factors showed poorer outcomes (70.3% vs. 11.8%, p < 0.001). Fifteen study patients (27.8%) had their treatment modified by FDG PET/CT findings. We conclude that FDG PET/CT is clinically useful in CUP patients not only for tumor staging, but also for modifying treatment regimens.

  12. A Detailed 3D Seismic Velocity Structure of the Subducting Pacific Slab Beneath Hokkaido, Tohoku and Kanto, Japan, by Double-Difference Tomography

    NASA Astrophysics Data System (ADS)

    Tsuji, Y.; Nakajima, J.; Kita, S.; Okada, T.; Matsuzawa, T.; Hasegawa, A.

    2007-12-01

    Three-dimensional heterogeneous structure beneath northeastern (NE) Japan has been investigated by previous studies and an inclined seismic low-velocity zone is imaged in the mantle wedge sub-parallel to the down-dip direction of the subducting slab (Zhao et al., 1992, Nakajima et al., 2001). However, the heterogeneous structure within the slab has not been well studied even though it is very important to understand the whole process of water transportation from the slab to the surface. Here we show a detailed 3D seismic velocity structure within the subducted Pacific slab around Japan and propose a water-transportation path from the slab to the mantle wedge. In this study, we estimated 3D velocity structure within the Pacific slab by the double-difference tomography (Zhang and Thurber, 2003). We divided the study area, from Hokkaido to Kanto, into 6 areas due to the limitation of memory and computation time. In each area, arrival-time data of 7,500-17,000 events recorded at 70-170 stations were used in the analysis. The total number of absolute travel-time data was about 140,000-312,000 for P wave and 123,000-268,000 for S wave, and differential data were about 736,000-1,920,000 for P wave and 644,000-1,488,000 for S wave. Horizontal and vertical grid separations are 10-25 km and 6.5 km, respectively. RMS residuals of travel times for P wave decreased from 0.23s to 0.09s and for S wave from 0.35s to 0.13s. The obtained results are as follows: (1) a remarkable low-Vs zone exists in the uppermost part of the subducting slab, (2) it extends down to a depth of about 80 km, (3) the termination of this low-Vs zone almost corresponds to the "seismic belt" recently detected in the upper plane of the double seismic zone (Kita et al.,2006; Hasegawa et al., 2007), (4) at depths deeper than 80 km, a low-Vs and high-Vp/Vs zone is apparently distributed in the mantle wedge, immediately above the slab crust. We consider that these features reflect water-transportation processes

  13. Simultaneous measurement of group refractive index and thickness of optical samples using optical coherence tomography.

    PubMed

    Cheng, Hsu-Chih; Liu, Yi-Cheng

    2010-02-10

    Optical coherence tomography (OCT), based on a Michelson interferometer and utilizing low coherence light as the optical source, is a novel technique for the noninvasive imaging of optical scattering media. A simple OCT scheme based on a 3 x 3 fiber coupler is presented for the simultaneous measurement of the refractive index and thickness of optical samples. The proposed system enables the refractive index and thickness to be determined without any prior knowledge of the sample parameters and is characterized by a simple and compact configuration, a straightforward measurement procedure, and a low cost. The feasibility of the proposed approach is demonstrated experimentally using BK7 and B270 optical glass samples.

  14. Water velocity at water-air interface is not zero: Comment on "Three-dimensional quantification of soil hydraulic properties using X-ray computed tomography and image-based modeling" by Saoirse R. Tracy et al.

    NASA Astrophysics Data System (ADS)

    Zhang, X. X.; Fan, X. Y.; Li, Z. Y.

    2016-07-01

    Tracy et al. (2015, doi: 10.1002/2014WR016020) assumed in their recent paper that water velocity at the water-air interface is zero in their pore-scale simulations of water flow in 3-D soil images acquired using X-ray computed tomography. We comment that such a treatment is physically wrong, and explain that it is the water-velocity gradient in the direction normal to the water-air interface, rather than the water velocity, that should be assumed to be zero at the water-air interface if one needs to decouple the water flow and the air flow. We analyze the potential errors caused by incorrectly taking water velocity at the water-air interface zero based on two simple examples, and conclude that it is not physically sound to make such a presumption because its associated errors are unpredictable.

  15. Group velocity dispersion and relativistic effects on the wakefield induced by chirped laser pulse in parabolic plasma channel

    SciTech Connect

    Sohbatzadeh, F.; Akou, H.

    2013-04-15

    The excitation of wake field plasma waves by a short laser pulse propagating through a parabolic plasma channel is studied. The laser pulse is assumed to be initially chirped. In this regard, the effects of initial and induced chirp on the plasma wake field as well as the laser pulse parameters are investigated. The group velocity dispersion and nonlinear relativistic effects were taken into account to evaluate the excited wake field in two dimension using source dependent expansion method. Positive, negative, and un-chirped laser pulses were employed in numerical code to evaluate the effectiveness of the initial chirp on 2-D wake field excitation. Numerical results showed that for laser irradiances exceeding 10{sup 18}W/cm{sup 2}, an intense laser pulse with initial positive chirp generates larger wake field compared to negatively and un-chirped pulses.

  16. AWESOME 1.1: A code for the calculation of phase and group velocities of acoustic waves in homogeneous solids

    NASA Astrophysics Data System (ADS)

    Muñoz-Santiburcio, Daniel; Hernández-Laguna, Alfonso

    2017-08-01

    We present an improved version of the code AWESOME, capable of computing phase and group velocities, power flow angles and enhancement factors of acoustic waves in homogeneous solids. In this version, some algorithms are improved and the code provides a better estimation of the enhancement factor compared to the previous version. In addition, we include a quadruple-precision version of the code, which even though using the same numerical approach as the double-precision version, is able to calculate the exact values of the enhancement factor. The standard, double-precision version of the code has been interfaced and merged with the development version of CRYSTAL and will be available as part of its next stable release. Finally, we have improved the scripts for visualizing the results, which now are compatible with GNUPLOT 5.X.X, including new scripts for the visualization of the normal and ray surfaces.

  17. Supercontinuum spectrum upon filamentation of laser pulses under conditions of strong and weak anomalous group velocity dispersion in transparent dielectrics

    NASA Astrophysics Data System (ADS)

    Chekalin, S. V.; Kompanets, V. O.; Dormidonov, A. E.; Zaloznaya, E. D.; Kandidov, V. P.

    2017-04-01

    Using experiment and numerical simulation, we study the effect of anomalous group velocity dispersion (AGVD) on the formation of a visible supercontinuum band and light bullets arising in the course of filamentation of mid-IR femtosecond pulses in fused silica and fluorides. It is found that the anti-Stokes shift of the visible band increases with increasing energy of the pulse, the centre wavelength of which lies in the region of weak AGVD, and does not depend on this energy in the region of strong AGVD. A criterion is introduced for assessment of the AGVD ‘strength’, at which the stable visible supercontinuum band accompanies the formation of a robust light bullet in the mid-IR filament.

  18. Experimental and numerical study of the excitability of zero group velocity Lamb waves by laser-ultrasound.

    PubMed

    Grünsteidl, Clemens M; Veres, István A; Murray, Todd W

    2015-07-01

    The excitability of zero group velocity (ZGV) Lamb waves using a pulsed laser source is investigated experimentally and through numerical simulation. Experimentally, a laser based ultrasonic technique is used to find the optical spot size on the sample surface that allows an optimal coupling of the optical energy into the ZGV mode. Numerical simulations, using the time domain finite differences technique, are carried out to model the thermoelastic generation process by laser irradiation and the propagation of the generated acoustic waves. The experimental results are in good agreement with the numerical predictions. The experimentally and numerically obtained responses of the plate are investigated by a short-time Fourier transform. The responses show that the source diameter does not affect the fundamental behavior of the temporal decay of the ZGV mode.

  19. Filamentation of a phase-modulated pulse under conditions of normal, anomalous and zero group velocity dispersion

    SciTech Connect

    Chekalin, S V; Kompanets, V O; Smetanina, E O; Spirkov, A I; Kandidov, V P

    2014-06-30

    We have investigated experimentally and numerically the influence of the initial temporal phase modulation of a pulse on the spatiotemporal intensity distribution and the frequency-angular spectrum of femtosecond laser pulses with self-channelling in a condensed medium. We have detected a decrease in the intensity of divergent anti-Stokes frequency components during filamentation of radiation under conditions of normal group-velocity dispersion (GVD) and strong phase modulation. In the zero-GVD regime under conditions of the phase modulation of radiation, the spatiotemporal transformation of the pulse is similar to that in the normal-GVD regime, which leads to a qualitative change in the supercontinuum spectrum. In the anomalous-GVD regime, a sequence of 'light bullets' is formed in the filament for both a phase-modulated and a transform-limited pulse. (extreme light fields and their applications)

  20. Wavelet-based group and phase velocity measurements: application to ambient noise cross correlation observations from OBS survey offshore Taiwan

    NASA Astrophysics Data System (ADS)

    Wang, W. W.; Yang, H. Y.; Hung, S. H.; Kuo, B. Y.

    2016-12-01

    In recent years, empirical Green's functions (EGFs) reconstructed from ambient noise cross-correlation functions (NCFs) between paired stations provide the unprecedented interstation path coverage within highly instrumented regions for high-resolution tomographic imaging. Dispersion analysis of the retrieved signals including multimode surface waves and body waves often excited by highly nonstationary noise sources becomes a routine but essential task. Since 2008, a number of broadband OBS experiments from the Institute of Earth Sciences (IES), Academia Sinica of Taiwan and TAIGER, a US-Taiwan cooperative research project, have been conducted in deep sea east of Taiwan. In this study, we use continuous recordings of vertical displacements and differential pressure gauges in 36 broadband OBSs deployed offshore eastern Taiwan to investigate the subseafloor structures from extracted Rayleigh waves and the source origin contributing to the generation of very long-period infragravity waves. We apply a wavelet-based method to characterize the time-varying spectral properties and measure the frequency-dependent group and phase velocities of these waves. The results show fundamental mode Rayleigh waves in both the displacement and DPG derived NCFs with a dominant period of 3-5 s and relatively slow speed of 0.5-1.0 km/s, while the other group of earlier dispersive arrivals predominant at 1-3 s, likely associated with higher mode surface waves or body waves, only emerges in the DPG derived NCFs propagates at a much faster speed of 1.5-3 km/s. The infragravity waves at periods ranging from 50 to 160 s found in DPGs records show the speed of 0.05-0.1 km/s. With these robust dispersion measurements, we will conduct the Bayesian inversion to constrain the radial velocity structures beneath the seafloor.

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

    USGS Publications Warehouse

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

    2003-01-01

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

  2. New constraints on the 3D shear wave velocity structure of the upper mantle underneath Southern Scandinavia revealed from non-linear tomography

    NASA Astrophysics Data System (ADS)

    Wawerzinek, B.; Ritter, J. R. R.; Roy, C.

    2013-08-01

    We analyse travel times of shear waves, which were recorded at the MAGNUS network, to determine the 3D shear wave velocity (vS) structure underneath Southern Scandinavia. The travel time residuals are corrected for the known crustal structure of Southern Norway and weighted to account for data quality and pick uncertainties. The resulting residual pattern of subvertically incident waves is very uniform and simple. It shows delayed arrivals underneath Southern Norway compared to fast arrivals underneath the Oslo Graben and the Baltic Shield. The 3D upper mantle vS structure underneath the station network is determined by performing non-linear travel time tomography. As expected from the residual pattern the resulting tomographic model shows a simple and continuous vS perturbation pattern: a negative vS anomaly is visible underneath Southern Norway relative to the Baltic Shield in the east with a contrast of up to 4% vS and a sharp W-E dipping transition zone. Reconstruction tests reveal besides vertical smearing a good lateral reconstruction of the dipping vS transition zone and suggest that a deep-seated anomaly at 330-410 km depth is real and not an inversion artefact. The upper part of the reduced vS anomaly underneath Southern Norway (down to 250 km depth) might be due to an increase in lithospheric thickness from the Caledonian Southern Scandes in the west towards the Proterozoic Baltic Shield in Sweden in the east. The deeper-seated negative vS anomaly (330-410 km depth) could be caused by a temperature anomaly possibly combined with effects due to fluids or hydrous minerals. The determined simple 3D vS structure underneath Southern Scandinavia indicates that mantle processes might influence and contribute to a Neogene uplift of Southern Norway.

  3. Velocity structure of the crust and upper mantle at the northern group of Kamchatka volcanoes (Based on the travel time of P-waves from volcanic earthquakes)

    NASA Astrophysics Data System (ADS)

    Slavina, L. B.; Pivovarova, N. B.; Senyukov, S. L.

    2012-12-01

    The results of a calculation of the P-wave ( V P ) velocity fields are presented on the basis of the method of the reversible wave and the TAU parameter characterizing the V P / V S ratio of seismic waves from the local volcanic earthquakes that occurred at the northern group of Kamchatka volcanoes in 2005-2007. The 3D velocity cross sections were constructed along the SW-NE-trending volcanic group from the Ploskii Tolbachik volcano in the southwest up to the Shiveluch volcano in the northeast. The change of velocity field in time and depth is found. The problems of relating these changes to volcanic activity is reviewed.

  4. Rayleigh wave group tomography in southeast Australia and Tasmania from cross-correlation of the ambient noise wavefield recorded with WOMBAT, a rolling array experiment

    NASA Astrophysics Data System (ADS)

    Arroucau, P.; Rawlinson, N.; Sambridge, M.; Reading, A. M.

    2009-12-01

    Ambient noise cross-correlation is now a well established and powerful tool for studying the structure of the crust and upper mantle. In the past decade, it has given rise to a new class of seismic tomography which has been successfully applied at different scales and in various regions of the world. In this work, we exploit the ambient noise data from WOMBAT, an extensive program of temporary seismic array deployments in southeast Australia and Tasmania. With an interstation distance of a few tens of kilometers, and a cumulative total of approximately 500 sites occupied over the past decade, this dataset provides a unique opportunity to help address fundamental questions regarding the structure and tectonic evolution of the Lachlan and Delamarian orogens, which underpin the southern half of Palaeozoic eastern Australia. We computed the cross-correlation of the vertical component of the ambient noise for all simultaneously recording station pairs. Rayleigh wave group traveltimes were determined from the obtained cross-correlograms in a two-stage approach. In the first stage, preliminary dispersion curves for periods ranging from 1 to 20 s were constructed and averaged in order to build a phase-matched filter which was subsequently applied to the seismograms prior to a second round of traveltime picking. Theoretical studies have shown that the negative time derivative of the average noise correlation function provides an estimate of the Green's function of the intervening medium. Yet some studies have been successfully carried out using the correlation function without differentiation, assuming that results would not be significantly affected when dealing with group velocity only. In this work, traveltimes were picked on both and an average value was calculated for each period and station pair after some consistency check. Time picking uncertainties were assigned by determining the half-width of the time interval during which the amplitude of the envelope was 50% of

  5. Structure of the Crust beneath Cameroon, West Africa, from the Joint Inversion of Rayleigh Wave Group Velocities and Receiver Functions

    SciTech Connect

    Tokam, A K; Tabod, C T; Nyblade, A A; Julia, J; Wiens, D A; Pasyanos, M E

    2010-02-18

    Cameroon using 1-D shear wave velocity models obtained from the joint inversion of Rayleigh wave group velocities and P-receiver functions for 32 broadband seismic stations. From the 1-D shear wave velocity models, we obtain new insights into the composition and structure of the crust and upper mantle across Cameroon. After briefly reviewing the geological framework of Cameroon, we describe the data and the joint inversion method, and then interpret variations in crustal structure found beneath Cameroon in terms of the tectonic history of the region.

  6. Comparative investigation of methods to determine the group velocity dispersion of an endlessly single-mode photonic crystal fiber

    NASA Astrophysics Data System (ADS)

    Baselt, Tobias; Popp, Tobias; Nelsen, Bryan; Lasagni, Andrés. Fabián.; Hartmann, Peter

    2017-05-01

    Endlessly single-mode fibers, which enable single mode guidance over a wide spectral range, are indispensable in the field of fiber technology. A two-dimensional photonic crystal with a silica central core and a micrometer-spaced hexagonal array of air holes is an established method to achieve endless single-mode guidance. There are two possible ways to determine the dispersion: measurement and calculation. We calculate the group velocity dispersion GVD based on the measurement of the fiber structure parameters, the hole diameter and the pitch of a presumed homogeneous hexagonal array and compare the calculation with two methods to measure the wavelength-dependent time delay. We measure the time delay on a three hundred meter test fiber with a homemade supercontinuum light source, a set of bandpass filters and a fast detector and compare the results with a white light interferometric setup. To measure the dispersion of optical fibers with high accuracy, a time-frequency-domain setup based on a Mach-Zehnder interferometer is used. The experimental setup allows the determination of the wavelength dependent differential group delay of light travelling through a thirty centimeter piece of test fiber in the wavelength range from VIS to NIR. The determination of the GVD using different methods enables the evaluation of the individual methods for characterizing the endlessly single-mode fiber.

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

    SciTech Connect

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

    2009-07-06

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

  8. Speckle noise reduction for optical coherence tomography images via non-local weighted group low-rank representation

    NASA Astrophysics Data System (ADS)

    Tang, Chang; Cao, Lijuan; Chen, Jiajia; Zheng, Xiao

    2017-05-01

    In this work, a non-local weighted group low-rank representation (WGLRR) model is proposed for speckle noise reduction in optical coherence tomography (OCT) images. It is based on the observation that the similarity between patches within the noise-free OCT image leads to a high correlation between them, which means that the data matrix grouped by these similar patches is low-rank. Thus, the low-rank representation (LRR) is used to recover the noise-free group data matrix. In order to maintain the fidelity of the recovered image, the corrupted probability of each pixel is integrated into the LRR model as a weight to regularize the error term. Considering that each single patch might belong to several groups, and multiple estimates of this patch can be obtained, different estimates of each patch is aggregated to obtain its denoised result. The aggregating weights are exploited depending on the rank of each group data matrix, which can assign higher weights to those better estimates. Both qualitative and quantitative experimental results on real OCT images show the superior performance of the WGLRR model compared with other state-of-the-art speckle removal techniques.

  9. Tamm plasmon-polariton with negative group velocity induced by a negative index meta-material capping layer at metal-Bragg reflector interface.

    PubMed

    Liu, Cunding; Kong, Mingdong; Li, Bincheng

    2014-05-05

    Influence of a negative refractive index meta-material (NIM) capping layer on properties of Tamm plasmon-polariton at the interface of metal-Bragg reflector structure is investigated. Conditions for excitation of the plasmon-polariton is determined from reflectivity mapping calculation and analyzed with cavity mode theory. For specific thicknesses of capping layers, Tamm plasmon-polariton with negative group velocity is revealed in a wide region of frequency. Different from backward optical propagation induced by negative effective-group-refractive-index in dispersive media, negative group velocity of Tamm plasmon-polariton results from opposite signs of cross-section-integrated field energy and Poynting vector.

  10. Atmospheric coupling of Tsunami: observations from Tohoku and impact on tsunami physical properties and phase/group velocities

    NASA Astrophysics Data System (ADS)

    Lognonne, P. H.; Kherani, E. A.; Coisson, P.; Astafyeva, E.; Occhipinti, G.; Rolland, L. M.; Yahagi, T.; Khelfi, K.; Sladen, A.; Hebert, H.; Makela, J. J.

    2012-12-01

    Tsunamis, through a dynamic coupling between the ocean and atmosphere, are generating atmospheric waves, detected in the ionosphere for tsunamis with amplitudes as much as 1 cm in the open ocean. Signals associated to the Tohoku tsunami have therefore been observed with huge signal to noise ratio, not only over Japan, but all over the Pacific, up to Chili. These signals have been moreover modelled, not only for the Total Electronic Contents perturbation signals, but also of the airglow detected for the first time over Hawaii and for the magnetic perturbations detected in Japan. We present in this paper the two sides of this coupling. The first side resumes the different observations and modelling of the Tohoku ionospheric signals observed by GEONET, by the GSI magnetic network and by Airglow cameras in Hawaii and Chili. Comparison between data and modelling are shown. The second side present the effects of the atmospheric coupling on the tsunami properties, i.e. amplitudes, phase/group velocities and excitation coefficients. By taking into account the coupling of tsunami with both the solid Earth and atmosphere, we show that specific resonances between the ocean and the atmosphere exist, enabling to understand the large and peaked signal spectrum. Local Time and geographical variations of this coupling is studied, as well as its dependence with the ocean depth. The impacts of atmospheric coupling on the propagation travel time of tsunamis is finally presented and discussed.

  11. A novel method to estimate blood flow velocity in the left atrial appendage using enhanced computed tomography: role of Hounsfield unit density ratio at two distinct points within the left atrial appendage.

    PubMed

    Yasuoka, Ryobun; Kurita, Takashi; Kotake, Yasuhito; Akaiwa, Yuzuru; Hashiguchi, Naotaka; Motoki, Koichiro; Yamamoto, Hiromi; Kobuke, Kazuhiro; Iwanaga, Yoshitaka; Hirano, Yutaka; Miyazaki, Shunichi

    2017-07-01

    Low blood flow velocity in the left atrial appendage (LAA) indicates a high risk of thromboembolism. Although transesophageal echocardiography (TEE) has been the standard method with which to evaluate the LAA blood flow velocity, a clinically noninvasive method is desired. We hypothesized that the ratio of the Hounsfield unit (HU) density at two distinct points within the LAA represents the blood flow velocity in the LAA. We retrospectively investigated 60 consecutive patients with atrial fibrillation (paroxysmal type, n = 29) who underwent enhanced computed tomography (CT) and TEE. The peak emptying flow velocity in the LAA (LAAPV) was evaluated using TEE. HU density was measured at proximal and distal sites of the LAA (LAAp and LAAd) on CT images. The LAAd/LAAp ratio was correlated with the LAAPV (P < 0.01, r = 0.69). Among several indices, the HU ratio was the most significant parameter associated with the LAAPV (β = 0.469, CI 28.602-68.286, P < 0.001). Receiver-operating characteristic analysis (area under the curve, 0.91) demonstrated that an HU density ratio cutoff of 0.32 discriminated a low LAAPV (<25 cm/s) with sensitivity of 90% and specificity of 84%. Flow velocity of the LAA can be estimated by the HU density ratio at distal and proximal sites within the LAA. Our method might be a feasible substitution for TEE to discriminate patients with a reduced LAAPV.

  12. Current Global Absolute Plate Velocities Inferred from the Trends of Hotspot Tracks: Implications for Motion between Groups of Hotspots and Comparison and Combination with Absolute Velocities Inferred from the Orientation of Seismic Anisotropy

    NASA Astrophysics Data System (ADS)

    Wang, C.; Gordon, R. G.; Zheng, L.

    2016-12-01

    Hotspot tracks are widely used to estimate the absolute velocities of plates, i.e., relative to the lower mantle. Knowledge of current motion between hotspots is important for both plate kinematics and mantle dynamics and informs the discussion on the origin of the Hawaiian-Emperor Bend. Following Morgan & Morgan (2007), we focus only on the trends of young hotspot tracks and omit volcanic propagation rates. The dispersion of the trends can be partitioned into between-plate and within-plate dispersion. Applying the method of Gripp & Gordon (2002) to the hotspot trend data set of Morgan & Morgan (2007) constrained to the MORVEL relative plate angular velocities (DeMets et al., 2010) results in a standard deviation of the 56 hotspot trends of 22°. The largest angular misfits tend to occur on the slowest moving plates. Alternatively, estimation of best-fitting poles to hotspot tracks on the nine individual plates, results in a standard deviation of trends of only 13°, a statistically significant reduction from the introduction of 15 additional adjustable parameters. If all of the between-plate misfit is due to motion of groups of hotspots (beneath different plates), nominal velocities relative to the mean hotspot reference frame range from 1 to 4 mm/yr with the lower bounds ranging from 1 to 3 mm/yr and the greatest upper bound being 8 mm/yr. These are consistent with bounds on motion between Pacific and Indo-Atlantic hotspots over the past ≈50 Ma, which range from zero (lower bound) to 8 to 13 mm/yr (upper bounds) (Koivisto et al., 2014). We also determine HS4-MORVEL, a new global set of plate angular velocities relative to the hotspots constrained to consistency with the MORVEL relative plate angular velocities, using a two-tier analysis similar to that used by Zheng et al. (2014) to estimate the SKS-MORVEL global set of absolute plate velocities fit to the orientation of seismic anisotropy. We find that the 95% confidence limits of HS4-MORVEL and SKS

  13. Imaging Critical Zone Using High Frequency Rayleigh Wave Group Velocity Measurements Extracted from Ambient Seismic Fields Gathered With 2400 Seismic Nodes in Southeastern Wyoming.

    NASA Astrophysics Data System (ADS)

    Keifer, I. S.; Dueker, K. G.

    2016-12-01

    In an effort to characterize critical zone development in varying regions, seismologist conduct seismic surveys to assist in the realization of critical zone properties e.g. porosity and regolith thickness. A limitation of traditional critical zone seismology is that data is normally collected along lines, to generate two dimensional transects of the subsurface seismic velocity, even though the critical zone structure is 3D. Hence, we deployed six seismic 2D arrays in southeastern Wyoming to gather ambient seismic fields so that 3D shear velocity models could be produced. The arrays were made up of nominally 400 seismic stations arranged in a 200-meter square grid layout. Each array produced a half Terabyte data volume, so a premium was placed on computational efficiency throughout this study, to handle the roughly 65 billion samples recorded by each array. The ambient fields were cross-correlated on the Yellowstone Super-Computer using the pSIN code (Chen et al., 2016), which decreased correlation run times by a factor of 300 with respect to workstation computers. Group delay times extracted from cross-correlations using 8 Hz frequency bands from 10 Hz to 100 Hz show frequency dispersion at sites with shallow regolith underlain by granite bedrock. Dimensionally, the group velocity map inversion is overdetermined, even after extensive culling of spurious group delay times. Model Resolution matrices for our six arrays show values > 0.7 for most of the modal domain, approaching unity at the center of the model domain; we are then confident that we have an adequate number of rays covering our array space, and should experience minimal smearing of our resultant model due to application of inverse solution on the data. After inverting for the group velocity maps, a second inversion is performed of the group velocity maps for the 3D shear velocity model. This inversion is underdetermined and a second order Tikhonov regularization is used to obtain stable inverse images

  14. Constructing a starting 3D shear velocity model with sharp interfaces for SEM-based upper mantle tomography in North America

    NASA Astrophysics Data System (ADS)

    Calo, M.; Bodin, T.; Yuan, H.; Romanowicz, B. A.; Larmat, C. S.; Maceira, M.

    2013-12-01

    Seismic tomography is currently evolving towards 3D earth models that satisfy full seismic waveforms at increasingly high frequencies. This evolution is possible thanks to the advent of powerful numerical methods such as the Spectral Element Method (SEM) that allow accurate computation of the seismic wavefield in complex media, and the drastic increase of computational resources. However, the production of such models requires handling complex misfit functions with more than one local minimum. Standard linearized inversion methods (such as gradient methods) have two main drawbacks: 1) they produce solution models highly dependent on the starting model; 2) they do not provide a means of estimating true model uncertainties. However, these issues can be addressed with stochastic methods that can sample the space of possible solutions efficiently. Such methods are prohibitively challenging computationally in 3D, but increasingly accessible in 1D. In previous work (Yuan and Romanowicz, 2010; Yuan et al., 2011) we developed a continental scale anisotropic upper mantle model of north America based on a combination of long period seismic waveforms and SKS splitting measurements, showing the pervasive presence of layering of anisotropy in the cratonic lithosphere with significant variations in depth of the mid-lithospheric boundary. The radial anisotropy part of the model has been recently updated using the spectral element method for forward wavefield computations and waveform data from the latest deployments of USarray (Yuan and Romanowicz, 2013). However, the long period waveforms (periods > 40s) themselves only provide a relatively smooth view of the mantle if the starting model is smooth, and the mantle discontinuities necessary for geodynamical interpretation are not imaged. Increasing the frequency of the computations to constrain smaller scale features is possible, but challenging computationally, and at the risk of falling in local minima of the misfit function. In

  15. Time-lapse seismic noise correlation tomography at Valhall

    NASA Astrophysics Data System (ADS)

    de Ridder, S. A. L.; Biondi, B. L.; Clapp, R. G.

    2014-09-01

    We show that a reliable and statistically significant group velocity time-lapse difference between 2004 and 2010 can be retrieved from ambient seismic noise in an offshore hydrocarbon exploitation setting. We performed a direct comparison of Scholte wave group velocity images obtained using regularized tomography. We characterize the expected variation in group velocity images from the 2004 or 2010 recordings that result from fluctuations in the cross correlations by looking at cross correlations of portions of the recordings. We prove that the time-lapse difference is statistically significant. The time-lapse group velocity image from ambient noise data shows strong similarities with a time-lapse phase velocity map obtained from controlled source data. The most striking features are a northern and a southern group velocity increase due to compaction and subsidence as a result of reservoir production.

  16. Seismic velocity structure in the Hot Springs and Trifurcation areas of the San Jacinto fault zone, California, from double-difference tomography

    NASA Astrophysics Data System (ADS)

    Allam, A. A.; Ben-Zion, Y.; Kurzon, I.; Vernon, F.

    2014-08-01

    We present tomographic images of crustal velocity structures in the complex Hot Springs and Trifurcation areas of the San Jacinto Fault Zone (SJFZ) based on double-difference inversions of earthquake arrival times. We invert for VP, VS and hypocentre location within 50 × 50 × 20 km3 volumes, using 266 969 P and 148 249 S arrival times. We obtain high-fidelity images of seismic velocities with resolution on the order of a few kilometres from 2 to 12 km depth and validate the results using checkerboard tests. Due to the relatively large proportion of S-wave arrival times, we also obtain stable maps of VP/VS ratios in both regions. The velocity of the Trifurcation Area as a whole is lower than adjacent unfaulted material. We interpret a 4-km-wide low velocity zone with high VP/VS ratio in the trifurcation itself as related to fault zone damage. We also observe clear velocity contrasts across the Buck Ridge, Clark and Coyote Creek segments of the SJFZ. The Anza segment of the SJFZ, to the NW of the trifurcation area, displays a strong (up to 27 per cent) contrast of VS from 2 to 9 km depth. In the Hot Springs area, a low velocity zone between the Claremont and Casa Loma Strands narrows with depth, with clear velocity contrasts observed across both segments. A roughly 10-km-wide zone of low velocity and low VP/VS ratio at the NW tip of the Hot Springs fault is indicative of either unconsolidated sediments associated with the San Jacinto basin, or fluid-filled cracks within a broad deformation zone. High VP/VS ratios along the Anza segment could indicate a preferred nucleation location for future large earthquakes, while the across-fault velocity contrast suggests a preferred northwest rupture propagation direction for such events.

  17. Passive seismic velocity tomography and geostatistical simulation on longwall mining panel / Tomografia pasywna pola prędkości i symulacje geostatystyczne w obrębie pola ścianowego

    NASA Astrophysics Data System (ADS)

    Hosseini, Navid; Oraee, Kazem; Shahriar, Kourosh; Goshtasbi, Kamran

    2012-10-01

    Generally, the accurate determination of the stress in surrounding rock mass of underground mining area has an important role in stability and ground control. In this paper stress redistribution around the longwall face has been studied using passive seismic velocity tomography based on Simultaneous Iterative Reconstructive Technique (SIRT) and Sequential Gaussian Simulation (SGS). The mining-induced microseismic events are used as a passive source. Since such sources are used, the ray coverage is insufficient and in order to resolve this deficiency, the wave velocity is estimated in a denser network and by the SGS method. Consequently the three-dimensional images of wave velocity are created and sliced into the coal seam. To analyze the variations of stress around the panel during the study period, these images are interpreted. Results show that the state of stress redistribution around the longwall panel can be deduced from these velocity images. In addition, movements of the stressed zones, including front and side abutments and the goaf area, along the longwall face are evident. The applied approach illustrated in this paper can be used as a useful method to monitoring the stress changes around the longwall face continuously. This can have significant safety implications and contribute to improvements in operational productivity

  18. Empirical validation of statistical parametric mapping for group imaging of fast neural activity using electrical impedance tomography.

    PubMed

    Packham, B; Barnes, G; Dos Santos, G Sato; Aristovich, K; Gilad, O; Ghosh, A; Oh, T; Holder, D

    2016-06-01

    Electrical impedance tomography (EIT) allows for the reconstruction of internal conductivity from surface measurements. A change in conductivity occurs as ion channels open during neural activity, making EIT a potential tool for functional brain imaging. EIT images can have  >10 000 voxels, which means statistical analysis of such images presents a substantial multiple testing problem. One way to optimally correct for these issues and still maintain the flexibility of complicated experimental designs is to use random field theory. This parametric method estimates the distribution of peaks one would expect by chance in a smooth random field of a given size. Random field theory has been used in several other neuroimaging techniques but never validated for EIT images of fast neural activity, such validation can be achieved using non-parametric techniques. Both parametric and non-parametric techniques were used to analyze a set of 22 images collected from 8 rats. Significant group activations were detected using both techniques (corrected p  <  0.05). Both parametric and non-parametric analyses yielded similar results, although the latter was less conservative. These results demonstrate the first statistical analysis of such an image set and indicate that such an analysis is an approach for EIT images of neural activity.

  19. Application of repeated passive source travel time tomography to reveal weak velocity changes related to the 2011 Tohoku-Oki Mw 9.0 earthquake

    NASA Astrophysics Data System (ADS)

    Koulakov, Ivan; Gladkov, Valery; El Khrepy, Sami; Al-Arifi, Nassir; Fathi, Ismail Husain

    2016-06-01

    Temporal changes of seismic velocities may provide important information on the processes that occur inside the Earth. However, using body wave data with passive sources faces the problem of an uneven distribution of rays, which may cause artifacts with stronger amplitudes than the actual velocity changes in the Earth. We propose an algorithm for the selection of similar data sets in different time periods that minimize the artifacts related to variable data distributions. In this study, we used the data of the Japan Meteorological Agency for several years before and after the Mw 9.0 Tohoku-Oki event that occurred on 11 March 2011. We performed careful testing using different synthetic models, showing that the selected data subsets allow detecting weak velocity changes with amplitudes above 0.2%. The analysis of the experimental data revealed important features associated with the stress and deformation distributions after the megathrust event. In the upper crust, we found a large zone along the coast with significant P velocity increase likely caused by compression of crustal rocks. This zone was cut by several elongated anomalies with local velocity decrease coinciding with the limits of the maximum slip area. These anomalies possibly mark the areas of major ruptures and deformations after the Tohoku-Oki earthquake. In the coupling zone at a depth of 40 km, we observe a velocity decrease in the area of the Mw 7.7 aftershock representing strong fracturing in the focal zone. Beneath the volcanic arc, we observe significant (up to 0.5%) decrease of P velocity but less prominent S velocity changes.

  20. Shallow crustal velocities and volcanism suggested from ambient noise studies using a dense broadband seismic network in the Tatun Volcano Group of Taiwan

    NASA Astrophysics Data System (ADS)

    Huang, Yu-Chih; Lin, Cheng-Horng; Kagiyama, Tsuneomi

    2017-07-01

    The Tatun Volcano Group (TVG) is situated adjacent to the Taipei metropolis and was active predominantly around 0.8-0.2 Ma (Pleistocene). Various recent lines of evidence suggest that the TVG is a potentially active volcano and that future volcanic eruptions cannot be ruled out. Geothermal activities are largely constrained to faults, but the relationship between volcanism and detailed velocity structures is not well understood. We analyzed ambient seismic noise of daily vertical components from 2014 using a dense seismic network of 40 broadband stations. We selected a 0.02° grid spacing to construct 2D and 3D shallow crustal phase velocity maps in the 0.5-3 s period band. Two S-wave velocity profiles transect Chishingshan (Mt. CS) in the shallow 3 km crust are further derived. The footwall of the Shanchiao Fault is dominated by low velocity, which may relate to Tertiary bedrock buried under andesitic lava flows dozens to hundreds of meters thick. The hanging wall of the Shanchiao Fault is the location of recent major volcanic activities. Low velocity zones in the southeast of Dayoukeng (DYK) may be interpreted as hydrothermal reservoirs or water-saturated Tertiary bedrock related to Cenozoic structures in the shallow crust. High velocities conspicuously dominate the east of the TVG, where the earliest stages of volcanism in the TVG are located, but where surface hydro-geothermal activities were absent in recent times. Between the Shanchiao Fault and Kanchiao Fault high velocities were detected, which converge below Mt. CS and may be related to early stages of magma conduits that gradually consolidated. These two faults may play a significant role with the TVG. The submarine volcanism adjacent to the Keelung coastline also requires further attention.

  1. Application of the energy reassignment method to measure accurate Rayleigh and Love wave group velocities from ambient seismic noise cross-correlations

    NASA Astrophysics Data System (ADS)

    Witek, M.; Kang, T. S.; van der Lee, S.

    2015-12-01

    We have collected three-component data from 122 Korean accelerometer stations for the month of December in 2014. We apply similar techniques described by Zha et al. (2013) to retrieve accurate station orientation angles, in order to rotate the horizontal component data into the radial and transverse frame of reference, and for subsequent measurement of Love wave group velocity dispersion. We simultaneously normalize all three components of a daily noise record via the frequency-time normalization (FTN) method. Each component is divided by the average signal envelope in an effort to retain relative amplitude information between all three components. Station orientations are found by a grid search for the orientation azimuth which maximizes the coherency between the radial-vertical cross-correlation and the Hilbert transformed vertical-vertical cross-correlation. After measuring orientation angles, we cross-correlate and rotate the data. Typically, the group velocity dispersion curves are measured using the frequency time analysis technique (FTAN), effectively producing spectrograms with significant uncertainty in the time-frequency plane. The spectrogram approach retains only the amplitude information of the short-time Fourier transform (STFT). However, Kodera et al (1976) show that by taking into account the phase information, the concepts of instantaneous frequency and group-time delay can be used to compute the first moment of the signal power in the frequency and time domains. During energy reassignment, the signal power calculated using the STFT at a point (t0,f0t_0, f_0) is reassigned to the location of the first moment (t^g,f^ihat{t}_g,hat{f}_i), where t^ghat{t}_g is the group-time delay and f^ihat{f}_i is the instantaneous frequency. We apply the method of energy reassignment to produce precise Rayleigh and Love wave group velocity measurements in the frequency range 0.1 - 1.0 Hz. Tests on synthetic data show more accurate retrieval of group velocities at

  2. Volcano-tectonic implications of 3-D velocity structures derived from joint active and passive source tomography of the island of Hawaii

    USGS Publications Warehouse

    Park, J.; Morgan, J.K.; Zelt, C.A.; Okubo, P.G.

    2009-01-01

    We present a velocity model of the onshore and offshore regions around the southern part of the island of Hawaii, including southern Mauna Kea, southeastern Hualalai, and the active volcanoes of Mauna Loa, and Kilauea, and Loihi seamount. The velocity model was inverted from about 200,000 first-arrival traveltime picks of earthquakes and air gun shots recorded at the Hawaiian Volcano Observatory (HVO). Reconstructed volcanic structures of the island provide us with an improved understanding of the volcano-tectonic evolution of Hawaiian volcanoes and their interactions. The summits and upper rift zones of the active volcanoes are characterized by high-velocity materials, correlated with intrusive magma cumulates. These high-velocity materials often do not extend the full lengths of the rift zones, suggesting that rift zone intrusions may be spatially limited. Seismicity tends to be localized seaward of the most active intrusive bodies. Low-velocity materials beneath parts of the active rift zones of Kilauea and Mauna Loa suggest discontinuous rift zone intrusives, possibly due to the presence of a preexisting volcanic edifice, e.g., along Mauna Loa beneath Kilauea's southwest rift zone, or alternatively, removal of high-velocity materials by large-scale landsliding, e.g., along Mauna Loa's western flank. Both locations also show increased seismicity that may result from edifice interactions or reactivation of buried faults. New high-velocity regions are recognized and suggest the presence of buried, and in some cases, previously unknown rift zones, within the northwest flank of Mauna Loa, and the south flanks of Mauna Loa, Hualalai, and Mauna Kea. Copyright 2009 by the American Geophysical Union.

  3. Crustal and upper mantle shear velocities of Iberia, the Alboran Sea, and North Africa from ambient noise and ballistic finite-frequency Rayleigh wave tomography

    NASA Astrophysics Data System (ADS)

    Palomeras, I.; Villasenor, A.; Thurner, S.; Levander, A.; Gallart, J.; mimoun, H.

    2013-12-01

    The complex Mesozoic-Cenozoic Alpine deformation in the western Mediterranean extends from the Pyrenees in northern Spain to the Atlas Mountains in southern Morocco. The Iberian plate was accreted to the European plate in late Cretaceous, resulting in the formation of the Pyrenees. Cenozoic African-European convergence resulted in subduction of the Tethys oceanic plate beneath Europe. Rapid Oligocene slab rollback from eastern Iberia spread eastward and southward, with the trench breaking into three segments by the time it reached the African coast. One trench segment moved southwestward and westward creating the Alboran Sea, floored by highly extended continental crust, and building the encircling Betics Rif mountains comprising the Gibraltar arc, and the Atlas mountains, which formed as the inversion of a Jurassic rift. A number of recent experiments have instrumented this region with broad-band arrays (the US PICASSO array, Spanish IberArray and Siberia arrays, the University of Munster array), which, including the Spanish, Portuguese, and Moroccan permanent networks, provide a combined array of 350 stations having an average interstation spacing of ~60 km. Taking advantage of this dense deployment, we have calculated the Rayleigh waves phase velocities from ambient noise for short periods (4 s to 40 s) and teleseismic events for longer periods (20 s to 167 s). Approximately 50,000 stations pairs were used to measure the phase velocity from ambient noise and more than 160 teleseismic events to measure phase velocity for longer periods. The inversion of the phase velocity dispersion curves provides a 3D shear velocity for the crust and uppermost mantle. Our results show differences between the various tectonic regions that extend to upper mantle depths (~200 km). In Iberia we obtain, on average, higher upper mantle shear velocities in the western Variscan region than in the younger eastern part. We map high upper mantle velocities (>4.6 km/s) beneath the

  4. Seismic velocity structure in the Hemet Stepover and Trifurcation Areas of the San Jacinto Fault Zone from double-difference earthquake tomography

    NASA Astrophysics Data System (ADS)

    Allam, A. A.; Ben-Zion, Y.; Vernon, F.; Kurzon, I.

    2013-12-01

    We present tomographic images of crustal velocity structures in the Hemet Stepover and Trifurcation areas of the San Jacinto Fault Zone (SJFZ) based on double-difference inversions of earthquake arrival times. We discretize both regions with a horizontal 250m grid spacing and a vertical 500m spacing within 50km by 50km by 20km volumes. We invert for VP, VS, and hypocenter location using data from 16064 earthquakes recorded at 136 stations. In total, we use 266,969 P and 148,249 S arrivals to constrain the seismic velocity structures in the two regions. With large numbers of both arrivals, we are able to obtain images of VP and VS at similar resolutions, enabling us to make spatial maps of and interpret the VP/VS ratios. Though ray coverage is limited at shallow depths, we obtain high-fidelity images of seismic velocities from 2 to 12 km, and validate the results using checkerboard tests. The tomographic images indicate that the velocity of the trifurcation area as a whole is lower than adjacent unfaulted material. We interpret a 4km-wide low velocity zone in the trifurcation itself as fault zone damage related due to high VP/VS ratio. We also observe clear velocity contrasts across the Buck Ridge, Clark, and Coyote Creek segments of the SJFZ. The Anza segment of the SJFZ, to the NW of the trifurcation area, displays a strong (up to 27%) contrast of VS from 2km to 9km. In the Hemet Stepover, a low velocity zone between the Claremont and Casa Loma Strands narrows with depth, with clear velocity contrasts observed across both segments. A roughly 10km-wide zone of low velocity and low VP/VS ratio at the NW tip of the Hot Springs fault is indicative of either unconsolidated sediments associated with the San Jacinto basin, or fluid-filled cracks within a broad deformation zone. Relocated seismicity tends to align with the surface traces of the various fault strands, though it is offset to the northeast of the Casa Loma-Clark strand and to the southwest of the Hot Springs

  5. Cenozoic volcanism in the Bohemian Massif in the context of P- and S-velocity high-resolution teleseismic tomography of the upper mantle

    NASA Astrophysics Data System (ADS)

    Plomerová, Jaroslava; Munzarová, Helena; Vecsey, Luděk.; Kissling, Eduard; Achauer, Ulrich; Babuška, Vladislav

    2016-08-01

    New high-resolution tomographic models of P- and S-wave isotropic-velocity perturbations for the Bohemian upper mantle are estimated from carefully preprocessed travel-time residuals of teleseismic P, PKP and S waves recorded during the BOHEMA passive seismic experiment. The new data resolve anomalies with scale lengths 30-50 km. The models address whether a small mantle plume in the western Bohemian Massif is responsible for this geodynamically active region in central Europe, as expressed in recurrent earthquake swarms. Velocity-perturbations of the P- and S-wave models show similar features, though their resolutions are different. No model resolves a narrow subvertical low-velocity anomaly, which would validate the "baby-plume" concept. The new tomographic inferences complement previous studies of the upper mantle beneath the Bohemian Massif, in a broader context of the European Cenozoic Rift System (ECRIS) and of other Variscan Massifs in Europe. The low-velocity perturbations beneath the Eger Rift, observed in about 200km-broad zone, agree with shear-velocity models from full-waveform inversion, which also did not identify a mantle plume beneath the ECRIS. Boundaries between mantle domains of three tectonic units that comprise the region, determined from studies of seismic anisotropy, represent weak zones in the otherwise rigid continental mantle lithosphere. In the past, such zones could have channeled upwelling of hot mantle material, which on its way could have modified the mantle domain boundaries and locally thinned the lithosphere.

  6. Active high-resolution seismic tomography of compressional wave velocity and attenuation structure at Medicine Lake Volcano, northern California Cascade Range

    USGS Publications Warehouse

    Evans, J.R.; Zucca, J.J.

    1988-01-01

    Medicine Lake volcano is a basalt through rhyolite shield volcano of the Cascade Range, lying east of the range axis. The Pg wave from eight explosive sources which has traveled upward through the target volume to a dense array of 140 seismographs provides 1- to 2-km resolution in the upper 5 to 7 km of the crust beneath the volcano. The experiment tests the hypothesis that Cascade Range volcanoes of this type are underlain only by small silicic magma chambers. We image a low-velocity low-Q region not larger than a few tens of cubic kilometers in volume beneath the summit caldera, supporting the hypothesis. A shallower high-velocity high-density feature, previously known to be present, is imaged for the first time in full plan view; it is east-west elongate, paralleling a topographic lineament between Medicine Lake volcano and Mount Shasta. Differences between this high-velocity feature and the equivalent feature at Newberry volcano, a volcano in central regon resembling Medicine Lake volcano, may partly explain the scarcity of surface hydrothermal features at Medicine Lake volcano. A major low-velocity low-Q feature beneath the southeast flank of the volcano, in an area with no Holocene vents, is interpreted as tephra, flows, and sediments from the volcano deeply ponded on the downthrown side of the Gillem fault. A high-Q normal-velocity feature beneath the north rim of the summit caldera may be a small, possibly hot, subsolidus intrusion. A high-velocity low-Q region beneath the eastern caldera may be an area of boiling water between the magma chamber and the ponded east flank material. -from Authors

  7. Lithospheric structure across the central Tien Shan constrained by gravity anomalies and joint inversions of receiver function and Rayleigh group velocity data

    NASA Astrophysics Data System (ADS)

    Li, Yonghua; Shi, Lei; Gao, Jiayi

    2016-04-01

    Shear wave velocity structure across the central Tien Shan orogeny was generated by jointly inverting Rayleigh wave phase and group velocity with teleseismic P-wave receiver functions at 40 broad band seismic stations of the MANAS project. The inferred seismic structure was validated by forward modeling of the complete Bouguer anomaly data. The joint inversion result reveals larger crust thicknesses beneath the Kokshaal (~68-72 km) and Kyrgyz ranges (~62-64 km), while other units have crustal thicknesses between 48 and 58 km. A fast velocity layer (Vs = 3.6-3.9 km/s) in the upper crust is found in some seismic stations within the Kazakh Shield. Our models show the presence of high velocity and density layers in the lowermost crust throughout the region, consistent with the presence of mafic/ultramafic lithologies. The large crustal thickness is associated with a thickened mafic layer in the lower crust, indicating that the thickened crust may be partly caused by magmatic underplating. The low velocity and density anomaly in the middle crust, and low upper mantle velocity observed in our model beneath the middle Tien Shan reflects the presence of partial melt in the crust due to the intrusion of hot mantle material. The lack of correlation between Moho depth and topography, together with the gravity results, suggests that the topographic compensation in the central Tien Shan is not confined to the crust. This requires significant support from the mantle to account for the relative high elevation of the middle Tien Shan.

  8. THE M81 GROUP DWARF IRREGULAR GALAXY DDO 165. I. HIGH-VELOCITY NEUTRAL GAS IN A POST-STARBURST SYSTEM

    SciTech Connect

    Cannon, John M.; Most, Hans P.; Skillman, Evan D.; Weisz, Daniel R.; Warren, Steven R.; Cook, David; Dolphin, Andrew E.; Kennicutt, Robert C.; Lee, Janice; Seth, Anil; Walter, Fabian E-mail: skillman@astro.umn.edu E-mail: warren@astro.umn.edu E-mail: adolphin@raytheon.com E-mail: jlee@obs.carnegiescience.edu E-mail: walter@mpia.de

    2011-07-01

    We present new multi-configuration Very Large Array H I spectral line observations of the M81 group dwarf irregular post-starburst galaxy DDO 165. The H I morphology is complex, with multiple column density peaks surrounding a large region of very low H I surface density that is offset from the center of the stellar distribution. The bulk of the neutral gas is associated with the southern section of the galaxy; a secondary peak in the north contains {approx}15% of the total H I mass. These components appear to be kinematically distinct, suggesting that either tidal processes or large-scale blowout have recently shaped the interstellar medium (ISM) of DDO 165. Using spatially resolved position-velocity maps, we find multiple localized high-velocity gas features. Cross-correlating with radius-velocity analyses, we identify eight shell/hole structures in the ISM with a range of sizes ({approx}400-900 pc) and expansion velocities ({approx}7-11 km s{sup -1}). These structures are compared with narrow- and broadband imaging from the Kitt Peak National Observatory and the Hubble Space Telescope (HST). Using the latter data, recent works have shown that DDO 165's previous 'burst' phase was extended temporally ({approx}>1 Gyr). We thus interpret the high-velocity gas features, H I holes, and kinematically distinct components of the galaxy in the context of the immediate effects of 'feedback' from recent star formation (SF). In addition to creating H I holes and shells, extended SF events are capable of creating localized high-velocity motion of the surrounding interstellar material. A companion paper connects the energetics from the H I and HST data.

  9. Determination of a low risk group for having metastatic nodules not detected by computed tomography scan in lung metastases surgery.

    PubMed

    Zabaleta, Jon; Aguinagalde, Borja; Izquierdo, José Miguel; Mendoza, Mikel; Basterrechea, Francisco; Martin-Arruti, Maialen; Lobo, Carmen; Emparanza, José Ignacio

    2013-12-01

    In recent years, there has been debate regarding the diagnostic accuracy of computed tomography (CT) in the identification of lung metastases and the need for lung palpation to determine the number of metastatic nodules. The aim of this study was to determine in which patients the CT scan was more effective in detecting all metastases. We studied all patients who underwent curative thoracotomy for pulmonary metastasis between 1998 and 2012. All cases were reviewed by two expert pulmonary radiologists before surgery. Statistical analyses were performed using Systat version 13. The study included 183 patients (63.6% male) with a mean age of 61.7 years who underwent 217 interventions. The CT scan was correct in 185 cases (85.3%). Discrepancies observed: 26 patients (11.9%) with more metastases resected than observed and 6 cases (2.8%) with fewer metastases. In patients with one or two metastases of colorectal origin or a single metastasis of any other origin, the probability of finding extra nodules was 9.5%. In the remaining patients, the probability was 27.8%, with statistically significant differences (P=.001). The mean age of the patients in whom no unobserved nodules were detected was 62.9 years compared to 56.5 years on average in patients who were free from any metastases (P=.001). Patients older than 60 years, with one or two metastases of colorectal origin or a single metastasis from any other origin were considered to be the group with low probability of having more metastases resected than observed. Copyright © 2013 SEPAR. Published by Elsevier Espana. All rights reserved.

  10. Controlling of group velocity via terahertz signal radiation in a defect medium doped by four-level InGaN/GaN quantum dot nanostructure

    NASA Astrophysics Data System (ADS)

    Jafarzadeh, Hossein; Sangachin, Elnaz Ahmadi; Asadpour, Seyyed Hossein

    2015-07-01

    In this paper, we propose a novel scheme for controlling the group velocity of transmitted and reflected pulse from defect medium doped with four-level InGaN/GaN quantum dot nanostructure. Quantum dot nanostructure is designed numerically by Schrödinger and Poisson equations which solve self consistently. By size control of quantum dot and external voltage, one can design a four-level quantum dot with appropriate energy levels which can be suitable for controlling the group velocity of pulse transmission and reflection from defect slab with terahertz signal field. It is found that in the presence and absence of terahertz signal field the behaviors of transmission and reflection pulses are completely different. Moreover, it is shown that for strong terahertz signal field, by changing the thickness of the slab, simultaneous peak and dip for transmission and reflection pulse are obtained.

  11. Three dimensional images of geothermal systems: local earthquake P-wave velocity tomography at the Hengill and Krafla geothermal areas, Iceland, and The Geysers, California

    USGS Publications Warehouse

    Julian, B.R.; Prisk, A.; Foulger, G.R.; Evans, J.R.; ,

    1993-01-01

    Local earthquake tomography - the use of earthquake signals to form a 3-dimensional structural image - is now a mature geophysical analysis method, particularly suited to the study of geothermal reservoirs, which are often seismically active and severely laterally inhomogeneous. Studies have been conducted of the Hengill (Iceland), Krafla (Iceland) and The Geysers (California) geothermal areas. All three systems are exploited for electricity and/or heat production, and all are highly seismically active. Tomographic studies of volumes a few km in dimension were conducted for each area using the method of Thurber (1983).

  12. Seismic Velocity Structure Across the Quebrada and Gofar Oceanic Transform Faults from 2D Refraction Tomography - A Comparison of Faults with High and Low Seismic Slip Deficits

    NASA Astrophysics Data System (ADS)

    Roland, E. C.; McGuire, J. J.; Collins, J. A.; Lizarralde, D.

    2009-12-01

    We perform two 2-D tomographic inversions using data collected as a part of the Quebrada-Discovery-Gofar (QDG) Transform Fault Active/Passive Experiment. The QDG transform faults are located in the southern Pacific Ocean and offset the East Pacific Rise (EPR) at approximately 4° south. In the spring of 2008, two ~100 km refraction profiles were collected, each using 8 short period Ocean Bottom Seismometers (OBS) from OBSIP and over 900 shots from the RV Marcus Langseth, across the easternmost segments of the Quebrada and Gofar transform faults. The two refraction profiles are modeled using a 2-D tomographic code that allows joint inversion of the Pg, PmP, and Pn arrivals (Korenaga et al., 2000). Variations in crustal velocity and thickness, as well as the width and depth extent of a significant low velocity zone within and below the transform valley provide some insight into the material properties of each of the fault-zones. Reduced seismic velocities that are 0.5 to over 1.0 km/s slower than velocities associated with the oceanic crust outside the fault zone may indicate the highly fractured fault zone lithology. The low velocity zone associated with the Quebrada fault also extends to the south of the active fault zone, beneath a fossil fault trace. Because Gofar is offset by an intratransform spreading center, we are able to compare ‘normal’ oceanic crust produced at the EPR to the south of the fault with crust associated with the ~15 km intratransform spreading center to the north. These two high slip rate (14 cm/yr) faults look similar morphologically and demonstrate comparable microseismicity characteristics, however their abilities to generate large earthquakes differ significantly. Gofar generates large earthquakes (Mw ~6) regularly every few years, but in the past 24 years only one large (Mw 5.6) event has been reliably located on Quebrada. The contrasting seismic behavior of these faults represents the range of behavior observed in the global

  13. The American Association for Thoracic Surgery guidelines for lung cancer screening using low-dose computed tomography scans for lung cancer survivors and other high-risk groups.

    PubMed

    Jaklitsch, Michael T; Jacobson, Francine L; Austin, John H M; Field, John K; Jett, James R; Keshavjee, Shaf; MacMahon, Heber; Mulshine, James L; Munden, Reginald F; Salgia, Ravi; Strauss, Gary M; Swanson, Scott J; Travis, William D; Sugarbaker, David J

    2012-07-01

    Lung cancer is the leading cause of cancer death in North America. Low-dose computed tomography screening can reduce lung cancer-specific mortality by 20%. The American Association for Thoracic Surgery created a multispecialty task force to create screening guidelines for groups at high risk of developing lung cancer and survivors of previous lung cancer. The American Association for Thoracic Surgery guidelines call for annual lung cancer screening with low-dose computed tomography screening for North Americans from age 55 to 79 years with a 30 pack-year history of smoking. Long-term lung cancer survivors should have annual low-dose computed tomography to detect second primary lung cancer until the age of 79 years. Annual low-dose computed tomography lung cancer screening should be offered starting at age 50 years with a 20 pack-year history if there is an additional cumulative risk of developing lung cancer of 5% or greater over the following 5 years. Lung cancer screening requires participation by a subspecialty-qualified team. The American Association for Thoracic Surgery will continue engagement with other specialty societies to refine future screening guidelines. The American Association for Thoracic Surgery provides specific guidelines for lung cancer screening in North America. Copyright © 2012. Published by Mosby, Inc.

  14. MTCLAB: A MATLAB ®-based program for traveltime quality analysis and pre-inversion velocity tuning in 2D transmission tomography

    NASA Astrophysics Data System (ADS)

    Fernández-Martínez, J. L.; Fernández-Alvarez, J. P.; Pedruelo-González, L. M.

    2008-03-01

    A MATLAB ®-based computer code that analyses the traveltime distribution and performs quality analysis at the pre-inversion stage for 2D transmission experiments is presented. The core tools of this approach are the so-called mean traveltime curves. For any general recording geometry, the user may select any pair of subsets of contiguous sources and receivers. The portion of the domain swept by the implied rays defines a zone of analysis, and for each source (receiver) the outcoming (incoming) ray fan is named a source (receiver) gather. The empirical mean traveltime curves are constructed, for each zone, by assigning the average and the standard deviation of the traveltimes in the gathers to the positions of the sources (receivers). The theoretical expressions assume isotropic homogeneous velocity inside each zone. The empirical counterparts use the observed traveltimes and make no assumptions. Isotropic velocity in each zone is inferred by least-squares fitting of the empirical mean traveltime curves. The user may refine the analysis considering different zones (multi-zone analysis). Initially the whole domain is modelled as a single zone. The procedure compares empirical versus theoretical curves. In addition, residuals can be plotted using source-receiver positions as plane coordinates. The results are used to unravel the possible presence of anomalous gathers, heterogeneities, anisotropies, etc. Depending on the kind of anomalies, velocity estimation and mean time residuals are different in the source and receiver gather curves. This software helps to grasp a better understanding of the data variability before the inversion and provides to the geophysicist an approximate zonal isotropic model and a range of velocity variation that can be used in the inverse problem as a priori information (regularization term). Its use is described through tutorial examples. A guided user interface leads the user through the algorithm steps.

  15. Velocity contrast and 10km vertical Moho offset across the Denali fault from double-difference tomography and fault zone head wave analysis

    NASA Astrophysics Data System (ADS)

    Allam, A. A.; Ruppert, N. A.; Ross, Z.; Ben-Zion, Y.

    2015-12-01

    We present tomographic images of lithospheric structure along the Denali fault in central Alaska based on double-difference inversions of earthquake arrival times. We discretize the region with a uniform grid spacing of 3km within a 600km by 500km by 60km volume. We invert for VP, VS, and hypocenter location using data from 5634 earthquakes recorded at 326 stations, incorporating 715,000 P and 229,000 S wave phase arrivals. The use of this large dataset provides resolution throughout the crust and into the upper mantle, with diminishing resolution below 50km depth as determined with checkerboard tests and calculation of the inversion derivative weight sum. The tomographic results indicate that the Moho is offset by approximately 10km along the entire resolved length of the Denali fault, with the northern side having the shallower Moho depths around 30km. This indicates that the Denali fault is likely a deep lithospheric structure which penetrates into the upper mantle. The shallow crustal velocity structure of the Denali fault is more complicated with high-velocity plutonic bodies and low-velocity subsidiary fault zones, though the northern side of the fault generally has slightly lower velocities. In order to bolster the tomographic images we analyze more than 100 events recorded at 55 near-fault stations to find fault zone head waves, which offer a clear indication of a sharp across-fault velocity contrast. In addition to picking head waves manually using horizontal particle motion, we run an automated picker over the entire dataset using no assumptions about likely head wave distributions. Most of the head wave detections are located on the northern side of the fault fault near the town of Healy, though the source-receiver geometry may be suboptimal for detection in other portions of the fault zone. Taken together, the tomographic and head wave results have important implications for the shallow crust, deeper lithospheric structure, and tectonic history of the

  16. Measurement of near-surface seismic compressional wave velocities using refraction tomography at a proposed construction site on the Presidio of Monterey, California

    USGS Publications Warehouse

    Powers, Michael H.; Burton, Bethany L.

    2012-01-01

    The U.S. Army Corps of Engineers is determining the feasibility of constructing a new barracks building on the U.S. Army Presidio of Monterey in Monterey, California. Due to the presence of an endangered orchid in the proposed area, invasive techniques such as exploratory drill holes are prohibited. To aid in determining the feasibility, budget, and design of this building, a compressional-wave seismic refraction survey was proposed by the U.S. Geological Survey as an alternative means of investigating the depth to competent bedrock. Two sub-parallel profiles were acquired along an existing foot path and a fence line to minimize impacts on the endangered flora. The compressional-wave seismic refraction tomography data for both profiles indicate that no competent rock classified as non-rippable or marginally rippable exists within the top 30 feet beneath the ground surface.

  17. Electrical impedance tomography combined with FEM calculations for fast measurements of the concentration and velocity distributions in horizontal pipes for solid-liquid mixtures

    SciTech Connect

    Wiedenroth, W.

    1996-12-31

    The contribution will present the results of a number of tests the author ran during the last years with respect to the behavior of solid-liquid mixtures in test rigs. Two main subjects will be dealt with: the evaluation of the concentration distribution in a horizontal pipeline and the velocity of the solid matter transported. The objective is to overcome the great uncertainties recognized in commercial systems using inductive flowmeters and {gamma}-ray density meters. The results of th is theoretical and experimental work will be presented and discussed.

  18. Ambient noise surface wave tomography of the Iranian Plateau

    NASA Astrophysics Data System (ADS)

    Mottaghi, Ali Asghar; Rezapour, Mehdi; Korn, Michael

    2013-04-01

    Ambient noise tomography is used to retrieve Rayleigh wave group and phase velocity variations in the period range of 8-40 s based on the vertical component of cross-correlation functions from permanent broad-band and mid-band seismometers across the Iranian Plateau. The iterative, non-linear inversion method of fast marching surface tomography (FMST) is employed to produce 2-D group and phase velocity maps. Shear wave velocities are also estimated using a linear least-square method. Unlike most previous largescale tomographic results, our group, phase and shear wave velocity estimations, emphasize low velocity crustal structure (up to 50 km depth) beneath Zagros Fold and Thrust Belt (ZFTB) and Sanandaj-Sirjan metaphormic Zone (SSZ). The suture zone resulting from the subduction of the Arabian plate under the Central Iran is inferred along the boundary of SSZ and Urmieh-Dokhtar Magmatic Arc (UDMA). The velocity patterns show the main sedimentary basins, and reveal lateral velocity changes indicating the crustal thickening beneath ZFTB, SSZ and Lut Desert (LD), and the crustal thinning beneath Kavir Desert (KD) and UDMA are well inferred. A prominent low velocity is persistent in the whole crust beneath the central part of Alborz mountain range with high topography, and we suggest that it is likely due to elevated crustal temperatures within thin lithosphere.

  19. Crustal and uppermost mantle structure in the Middle East: assessing constraints provided by jointly modelling Ps and Sp receiver functions and Rayleigh wave group velocity dispersion curves

    NASA Astrophysics Data System (ADS)

    Agrawal, Mohit; Pulliam, Jay; Sen, Mrinal K.; Dutta, Utpal; Pasyanos, Michael E.; Mellors, Robert

    2015-05-01

    Seismic velocity models are found, along with uncertainty estimates, for 11 sites in the Middle East by jointly modelling Ps and Sp receiver functions and surface (Rayleigh) wave group velocity dispersion. The approach performs a search for models that satisfy goodness-of-fit criteria guided by a variant of simulated annealing and uses statistical tools to assess these products of searches. These tools, a parameter correlation matrix and marginal posterior probability density (PPD) function, allow us to evaluate quantitatively the constraints that each data type imposes on model parameters and to identify portions of each model that are well-constrained relative to other portions. This joint modelling technique, which we call `multi-objective optimization for seismology', does not require a good starting solution, although such a model can be incorporated easily, if available, and can reduce the computation time significantly. Applying the process described above to broadband seismic data reveals that crustal thickness varies from 15 km beneath Djibouti (station ATD) to 45 km beneath Saudi Arabia (station RAYN). A pronounced low velocity zone for both Vp and Vs is present at a depth of ˜12 km beneath station KIV located in northern part of greater Caucasus, which may be due to the presence of a relatively young volcano. Similarly, we also noticed a 6-km-thick low velocity zone for Vp beginning at 20 km depth beneath seismic station AGIN, on the Anatolian plateau, while positive velocity gradients prevail elsewhere in eastern Turkey. Beneath station CSS, located in Cyprus, an anomalously slow layer is found in the uppermost mantle, which may indicate the presence of altered lithospheric material. Crustal P- and S-wave velocities beneath station D2, located in the northeastern portion of central Zagros, range between 5.2-6.2 and 3.2-3.8 km s-1, respectively. In Oman, we find a Moho depth of 34.0 ± 1.0 km and 25.0 ± 1.0 to 30.0 ± 1.0 km beneath stations S02 and S

  20. Comparison of iron-bearing minerals in ordinary chondrites from H, L and LL groups using Mössbauer spectroscopy with a high velocity resolution.

    PubMed

    Maksimova, A A; Oshtrakh, M I; Petrova, E V; Grokhovsky, V I; Semionkin, V A

    2017-02-05

    Ordinary chondrites from H, L and LL groups were studied using Mössbauer spectroscopy with a high velocity resolution. Mössbauer parameters of spectral components were obtained using new fitting model excluding the effect of previous misfits of troilite component. Obtained parameters were related to corresponding iron-bearing minerals in ordinary chondrites. The differences of these minerals content as well as small differences in the hyperfine parameters of the same iron-bearing minerals were revealed for different meteorites. The temperatures of equilibrium cations distribution in silicates were estimated and suitable parameters for classification of H, L and LL chondrites were supposed using Mössbauer parameters.

  1. Comparison of iron-bearing minerals in ordinary chondrites from H, L and LL groups using Mössbauer spectroscopy with a high velocity resolution

    NASA Astrophysics Data System (ADS)

    Maksimova, A. A.; Oshtrakh, M. I.; Petrova, E. V.; Grokhovsky, V. I.; Semionkin, V. A.

    2017-02-01

    Ordinary chondrites from H, L and LL groups were studied using Mössbauer spectroscopy with a high velocity resolution. Mössbauer parameters of spectral components were obtained using new fitting model excluding the effect of previous misfits of troilite component. Obtained parameters were related to corresponding iron-bearing minerals in ordinary chondrites. The differences of these minerals content as well as small differences in the hyperfine parameters of the same iron-bearing minerals were revealed for different meteorites. The temperatures of equilibrium cations distribution in silicates were estimated and suitable parameters for classification of H, L and LL chondrites were supposed using Mössbauer parameters.

  2. Few-cycle laser-pulse collapse in Kerr media: The role of group-velocity dispersion and X -wave formation

    NASA Astrophysics Data System (ADS)

    Faccio, Daniele; Clerici, Matteo; Averchi, Alessandro; Lotti, Antonio; Jedrkiewicz, Ottavia; Dubietis, Audrius; Tamosauskas, Gintaras; Couairon, Arnaud; Bragheri, Francesca; Papazoglou, Dimitris; Tzortzakis, Stelios; di Trapani, Paolo

    2008-09-01

    We study ultrashort laser-pulse propagation and filamentation dynamics in dispersive Kerr media. We identify the regime for which the filamentation threshold (Pth) is considerably higher than the critical power (Pcr) for monochromatic beam collapse in pure Kerr media. In particular, we compare the threshold for the formation of filaments with that for the formation of X -waves. At powers Pcrgroup-velocity dispersion, and no filaments or X -waves are formed. At P⩾Pth , we observe X -wave formation and a weak filamentation regime. At P≫Pth , we observe both X -waves and fully formed filaments.

  3. Observations of asymmetric velocity fields and gas cooling in the NGC 4636 galaxy group X-ray halo

    NASA Astrophysics Data System (ADS)

    Ahoranta, Jussi; Finoguenov, Alexis; Pinto, Ciro; Sanders, Jeremy; Kaastra, Jelle; de Plaa, Jelle; Fabian, Andrew

    2016-08-01

    Aims: This study aims to probe the thermodynamic properties of the hot intragroup medium (IGM) plasma in the core regions of the NGC 4636 galaxy group by detailed measurements of several emission lines and their relative intensities. Methods: We analyzed deep XMM-Newton Reflection Grating Spectrometer (RGS) data in five adjacent spectral regions in the central parts of the NGC 4636 galaxy group. We examined the suppression of the Fe xvii resonance line (15.01 Å) as compared to the forbidden lines of the same ion (17.05 Å and 17.10 Å). The presence and radial dependence of the cooling flow was investigated through spectral modeling. Parallel analysis with deep Chandra Advances CCD Imaging Spectrometer (ACIS) data was conducted to gain additional information about the thermodynamical properties of the IGM. Results: The plasma at the group center to the north shows efficient Fe xvii ion resonant scattering, yielding (Iλ17.05 + Iλ17.10) /Iλ15.01 line ratios up to 2.9 ± 0.4, corresponding toabout twice the predicted line ratio. In contrast, no resonant scattering was detected at the south side. The regions featuring resonant scattering coincide with those embodying large amounts of cool (kT ≲ 0.4 keV) gas phases, and the spectral imprints of cooling gas with a total mass deposition rate of ~0.8 M⊙ yr-1 within the examined region of 2.4' × 5.0'. Conclusions: We interpret the results as possible evidence of asymmetric turbulence distribution in the NGC 4636 IGM: turbulence dominates the gas dynamics to the south, while collective gas motions characterize the dynamics to the north. X-ray images show imprints of energetic AGN at both sides, yet we find evidence of turbulence heating at the south and gas cooling at the north of the core. We infer that the observed asymmetry may be the result of the specific observation angle to the source, or arise from the turbulence driven by core sloshing at south side.

  4. Interaction of NGC 2276 with the NGC 2300 group - Fabry-Perot observations of the H-alpha velocity field

    NASA Technical Reports Server (NTRS)

    Gruendl, Robert A.; Vogel, Stuart N.; Davis, David S.; Mulchaey, John S.

    1993-01-01

    We report kinematic observations of H-alpha emission from the spiral galaxy NGC 2276 obtained with a Fabry-Perot Camera. The 'bow shock' appearance and enhanced star formation in NGC 2276 have been attributed by Mulchaey et al. (1993) to a ram-pressure interaction with the dense IGM detected in ROSAT observations of the NGC 2300 group of galaxies. Along the 'bow shock' limb of the galaxy, we observe strong H-alpha emission and significant kinematic perturbations located immediately interior to an abrupt decrease in the scale length of the optical disk. Although ram-pressure forces may be important in the evolution of the outer gaseous disk, the peculiar kinematics and the truncation in the stellar disk are difficult to explain in a ram-pressure model; a more likely cause is tidal interaction, probably with the elliptical galaxy NGC 2300.

  5. Controlling subluminal to superluminal behavior of group velocity in an f-deformed Bose-Einstein condensate beyond the rotating wave approximation

    NASA Astrophysics Data System (ADS)

    Haghshenasfard, Z.; Naderi, M. H.; Soltanolkotabi, M.

    2009-09-01

    In this paper, we investigate tunable control of the group velocity of a weak probe field propagating through an f-deformed Bose-Einstein condensate of Λ-type three-level atoms beyond the rotating wave approximation. For this purpose, we use an f-deformed generalization of an effective two-level quantum model of the three-level Λ-configuration without the rotating wave approximation in which the Gardiner's phonon operators for Bose-Einstein condensate are deformed by an operator-valued function, f(nˆ), of the particle-number operator nˆ. We consider the collisions between the atoms as a special kind of f-deformation where the collision rate κ is regarded as the deformation parameter. We demonstrate the enhanced effect of subluminal and superluminal propagation based on electromagnetically induced transparency and electromagnetically induced absorption, respectively. In particular, we find that (i) the absorptive and dispersive properties of the deformed condensate can be controlled effectively in the absence of the rotating wave approximation by changing the deformation parameter κ, the total number of atoms N^ and the counter-rotating terms parameter λ, (ii) by increasing the values of λ, κ and η = 1/ N, the group velocity of the probe pulse changes, from subluminal to superluminal and (iii) beyond the rotating wave approximation, the subluminal and superluminal behaviors of the probe field are enhanced.

  6. High speed, wide velocity dynamic range Doppler optical coherence tomography (Part V): Optimal utilization of multi-beam scanning for Doppler and speckle variance microvascular imaging.

    PubMed

    Chen, Chaoliang; Cheng, Kyle H Y; Jakubovic, Raphael; Jivraj, Jamil; Ramjist, Joel; Deorajh, Ryan; Gao, Wanrong; Barnes, Elizabeth; Chin, Lee; Yang, Victor X D

    2017-04-03

    In this paper, a multi-beam scanning technique is proposed to optimize the microvascular images of human skin obtained with Doppler effect based methods and speckle variance processing. Flow phantom experiments were performed to investigate the suitability for combining multi-beam data to achieve enhanced microvascular imaging. To our surprise, the highly variable spot sizes (ranging from 13 to 77 μm) encountered in high numerical aperture multi-beam OCT system imaging the same target provided reasonably uniform Doppler variance and speckle variance responses as functions of flow velocity, which formed the basis for combining them to obtain better microvascular imaging without scanning penalty. In vivo 2D and 3D imaging of human skin was then performed to further demonstrate the benefit of combining multi-beam scanning to obtain improved signal-to-noise ratio (SNR) in microvascular imaging. Such SNR improvement can be as high as 10 dB. To our knowledge, this is the first demonstration of combining different spot size, staggered multiple optical foci scanning, to achieve enhanced SNR for blood flow OCT imaging.

  7. 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

    DTIC Science & Technology

    2011-09-01

    DEVELOPING REGIONALIZED MODELS OF LITHOSPHERIC THICKNESS AND VELOCITY STRUCTURE ACROSS EURASIA AND THE MIDDLE EAST FROM JOINTLY INVERTING P-WAVE...09NA293221 and DE-AC52-07NA273442 Proposal No. BAA09-13 ABSTRACT The main goal of this project is to develop models of lithospheric velocity...of the lithosphere are key for accurately modeling not only travel times but also surface-wave dispersion velocities and full waveforms at regional

  8. Doppler Optical Coherence Tomography

    PubMed Central

    Leitgeb, Rainer A.; Werkmeister, René M.; Blatter, Cedric; Schmetterer, Leopold

    2014-01-01

    Optical Coherence Tomography (OCT) has revolutionized ophthalmology. Since its introduction in the early 1990s it has continuously improved in terms of speed, resolution and sensitivity. The technique has also seen a variety of extensions aiming to assess functional aspects of the tissue in addition to morphology. One of these approaches is Doppler OCT (DOCT), which aims to visualize and quantify blood flow. Such extensions were already implemented in time domain systems, but have gained importance with the introduction of Fourier domain OCT. Nowadays phase-sensitive detection techniques are most widely used to extract blood velocity and blood flow from tissues. A common problem with the technique is that the Doppler angle is not known and several approaches have been realized to obtain absolute velocity and flow data from the retina. Additional studies are required to elucidate which of these techniques is most promising. In the recent years, however, several groups have shown that data can be obtained with high validity and reproducibility. In addition, several groups have published values for total retinal blood flow. Another promising application relates to non-invasive angiography. As compared to standard techniques such as fluorescein and indocyanine-green angiography the technique offers two major advantages: no dye is required and depth resolution is required is provided. As such Doppler OCT has the potential to improve our abilities to diagnose and monitor ocular vascular diseases. PMID:24704352

  9. An evaluation of JPEG and JPEG 2000 irreversible compression algorithms applied to neurologic computed tomography and magnetic resonance images. Joint Photographic Experts Group.

    PubMed

    Savcenko, V; Erickson, B J; Persons, K R; Campeau, N G; Huston, J; Wood, C P; Schreiner, S A

    2000-05-01

    We performed visual comparison of 200 head magnetic resonance (MR) and 200 head computed tomography (CT) images compressed at two levels using standard Joint Photographic Experts Group (JPEG) irreversible compression and a preliminary version of the JPEG 2000 irreversible algorithm. Blinded evaluations by neuroradiologists compared original versus either JPEG or JPEG 2000. We found that this version of JPEG 2000 did not perform as well as the current JPEG for head CTs, but for MR images, JPEG 2000 performed as well or better. Around 7:1 compression ratio seemed to be a conservative point where there was no perceptible difference.

  10. ASCI 2010 appropriateness criteria for cardiac computed tomography: a report of the Asian Society of Cardiovascular Imaging Cardiac Computed Tomography and Cardiac Magnetic Resonance Imaging Guideline Working Group.

    PubMed

    Tsai, I-Chen; Choi, Byoung Wook; Chan, Carmen; Jinzaki, Masahiro; Kitagawa, Kakuya; Yong, Hwan Seok; Yu, Wei

    2010-02-01

    In Asia, the healthcare system, populations and patterns of disease differ from Western countries. The current reports on the criteria for cardiac CT scans, provided by Western professional societies, are not appropriate for Asian cultures. The Asian Society of Cardiovascular Imaging, the only society dedicated to cardiovascular imaging in Asia, formed a Working Group and invited 23 Technical Panel members representing a variety of Asian countries to rate the 51 indications for cardiac CT in clinical practice in Asia. The indications were rated as 'appropriate' (7-9), 'uncertain' (4-6), or 'inappropriate' (1-3) on a scale of 1-9. The median score was used for the final result if there was no disagreement. The final ratings for indications were 33 appropriate, 14 uncertain and 4 inappropriate. And 20 of them are highly agreed (19 appropriate and 1 inappropriate). Specifically, the Asian representatives considered cardiac CT as an appropriate modality for Kawasaki disease and congenital heart diseases in follow up and in symptomatic patients. In addition, except for some specified conditions, cardiac CT was considered to be an appropriate modality for one-stop shop ischemic heart disease evaluation due to its general appropriateness in coronary, structure and function evaluation. This report is expected to have a significant impact on the clinical practice, research and reimbursement policy in Asia.

  11. High-Frequency Seismic Waves generated by Building-Shaking Experiments and Surface Wave Group Velocity Estimates from the Cross-Correlation of Data

    NASA Astrophysics Data System (ADS)

    Tanimoto, T.; Okamoto, T.

    2013-12-01

    ) range between 1.637 and 1.638 Hz. We applied stacking procedure for overlapping 1-hour length time series and improved phase estimates within this frequency range. For about 30 stations, we can measure the gradient of phase with respect to frequency, from which we can make group velocity estimates. As expected from shallow confinement of energy, estimated velocities are mostly below 2 km/s and some stations were about 300 km in distance. Unfortunately, paths to most stations in the Los Angeles basin show large scatter and thus we cannot obtain group velocity estimates in the LA Basin, except for a few short-distance stations. The large scatters indicate that they contain information on statistical properties of velocity correlation for the shallow basin structure. But resolution of it will be our next analysis.

  12. BANYAN. III. Radial velocity, rotation, and X-ray emission of low-mass star candidates in nearby young kinematic groups

    SciTech Connect

    Malo, Lison; Artigau, Étienne; Doyon, René; Lafrenière, David; Albert, Loïc; Gagné, Jonathan E-mail: doyon@astro.umontreal.ca

    2014-06-10

    Based on high-resolution spectra obtained with PHOENIX at Gemini-South, CRIRES at VLT-UT1, and ESPaDOnS at the Canada-France-Hawaii Telescope, we present new measurements of the radial and projected rotational velocities of 219 low-mass stars. The target likely membership was initially established using the Bayesian analysis tool recently presented in Malo et al., taking into account only the position, proper motion, and photometry of the stars to assess their membership probability. In the present study, we include radial velocity as an additional input to our analysis, and in doing so we confirm the high membership probability for 130 candidates: 27 in β Pictoris, 22 in Tucana-Horologium, 25 in Columba, 7 in Carina, 18 in Argus and 18 in AB Doradus, and 13 with an ambiguous membership. Our analysis also confirms the membership of 57 stars proposed in the literature. A subsample of 16 candidates was observed at 3 or more epochs, allowing us to discover 6 new spectroscopic binaries. The fraction of binaries in our sample is 25%, consistent with values in the literature. Of the stars in our sample, 20% show projected rotational velocities (vsin i) higher than 30 km s{sup –1} and therefore are considered as fast rotators. A parallax and other youth indicators are still needed to fully confirm the 130 highly probable candidates identified here as new bona fide members. Finally, based on the X-ray emission of bona fide and highly probable group members, we show that for low-mass stars in the 12-120 Myr age range, the X-ray luminosity is an excellent indicator of youth and better than the more traditionally used R {sub X} parameter, the ratio of X-ray to bolometric luminosity.

  13. BANYAN. III. Radial Velocity, Rotation, and X-Ray Emission of Low-mass Star Candidates in Nearby Young Kinematic Groups

    NASA Astrophysics Data System (ADS)

    Malo, Lison; Artigau, Étienne; Doyon, René; Lafrenière, David; Albert, Loïc; Gagné, Jonathan

    2014-06-01

    Based on high-resolution spectra obtained with PHOENIX at Gemini-South, CRIRES at VLT-UT1, and ESPaDOnS at the Canada-France-Hawaii Telescope, we present new measurements of the radial and projected rotational velocities of 219 low-mass stars. The target likely membership was initially established using the Bayesian analysis tool recently presented in Malo et al., taking into account only the position, proper motion, and photometry of the stars to assess their membership probability. In the present study, we include radial velocity as an additional input to our analysis, and in doing so we confirm the high membership probability for 130 candidates: 27 in β Pictoris, 22 in Tucana-Horologium, 25 in Columba, 7 in Carina, 18 in Argus and 18 in AB Doradus, and 13 with an ambiguous membership. Our analysis also confirms the membership of 57 stars proposed in the literature. A subsample of 16 candidates was observed at 3 or more epochs, allowing us to discover 6 new spectroscopic binaries. The fraction of binaries in our sample is 25%, consistent with values in the literature. Of the stars in our sample, 20% show projected rotational velocities (vsin i) higher than 30 km s-1 and therefore are considered as fast rotators. A parallax and other youth indicators are still needed to fully confirm the 130 highly probable candidates identified here as new bona fide members. Finally, based on the X-ray emission of bona fide and highly probable group members, we show that for low-mass stars in the 12-120 Myr age range, the X-ray luminosity is an excellent indicator of youth and better than the more traditionally used R X parameter, the ratio of X-ray to bolometric luminosity.

  14. Fundamental steps of the group velocity for slow surface polaritons in the two-dimensional electron gas in a high magnetic field

    NASA Astrophysics Data System (ADS)

    Aronov, Igor E.; Beletskii, Nikolai N.

    1996-07-01

    A new type of collective electromagnetic excitation, namely surface polaritons (SP) - in a 2D electronic layer in a high magnetic field, is predicted. We have found the spectrum, damping, and polarization of the SP over a wide range of frequencies 0953-8984/8/27/005/img1 and wavevectors k. It is shown that near the cyclotron resonance (CR) 0953-8984/8/27/005/img2 the phase velocity of the SP is drastically slowed down and the group velocity undergoes fundamental steps defined by the fine-structure constant 0953-8984/8/27/005/img3. In the vicinity of a CR subharmonic 0953-8984/8/27/005/img4, negative (anomalous) dispersion of the SP occurs. The relaxation of electrons in the 2D layer gives rise to a new dissipative collective threshold-type mode of the SP. We suggest a method for calculating the kinetic coefficients for the 2D electronic layer in a high magnetic field, using the Wigner distribution function formalism, and determining their spatial and frequency dispersions. Using this method we have calculated the lineshapes of the CR, which are in good agreement with experimental data.

  15. Group velocity of neutrino waves

    NASA Astrophysics Data System (ADS)

    Indumathi, D.; Kaul, Romesh K.; Murthy, M. V. N.; Rajasekaran, G.

    2012-03-01

    We follow up on the analysis of Mecozzi and Bellini (arxiv:arXiv:1110.1253v1) where they showed, in principle, the possibility of superluminal propagation of neutrinos, as indicated by the recent OPERA result. We refine the analysis by introducing wave packets for the superposition of energy eigenstates and discuss the implications of their results with realistic values for the mixing and mass parameters in a full three neutrino mixing scenario. Our analysis shows the possibility of superluminal propagation of neutrino flavour in a very narrow range of neutrino parameter space. Simultaneously this reduces the number of observable events drastically. Therefore, the OPERA result cannot be explained in this frame-work.

  16. Butterfly-shaped and dromion-like optical waves in a tapered graded-index waveguide with variable group-velocity dispersion

    NASA Astrophysics Data System (ADS)

    Kaur, Harleen; Pal, Ritu; Raju, Thokala Soloman; Kumar, C. N.

    2016-11-01

    Butterfly-shaped and dromion-like optical waves in a tapered graded-index waveguide (GRIN) are reported for the first time. The generalized nonlinear Schrödinger equation, which describes wave propagation in GRIN with variable group-velocity dispersion (GVD), nonlinearity, PT symmetric optical potentials, is investigated and analytical solutions for this dynamical system are obtained. The physical effects affecting these waves are explicated in detail. The stability of dromion-like structures is analyzed when the GVD parameter is perturbed. We have observed oscillation structure exhibiting strong interference due to this applied perturbation. For a particular value of the modulation of the GVD parameter, the oscillation structure is transformed into two dromion-like structures. It indicates that the dromion-like structure is unstable, and the coherence intensity is affected by the modified perturbation parameter. We further demonstrate the phenomenon of unbreakable PT symmetry of these novel nonlinear waves for three explicit examples.

  17. Existence and switching behavior of bright and dark Kerr solitons in whispering-gallery mode resonators with zero group-velocity dispersion

    NASA Astrophysics Data System (ADS)

    Talla Mbé, Jimmi H.; Milián, Carles; Chembo, Yanne K.

    2017-07-01

    We use the generalized Lugiato-Lefever model to investigate the phenomenon of Kerr optical frequency comb generation when group-velocity dispersion is null. In that case, the first dispersion term that plays a leading role is third-order dispersion. We show that this term is sufficient to allow for the existence of both bright and dark solitons. We identify the areas in the parameter space where both kind of solitons can be excited inside the resonator. We also unveil a phenomenon of hysteretic switching between these two types of solitons when the power of the pump laser is cyclically varied. Contribution to the Topical Issue "Theory and Applications of the Lugiato-Lefever Equation", edited by Yanne K. Chembo, Damia Gomila, Mustapha Tlidi, Curtis R. Menyuk.

  18. Self-action of propagating and standing Lamb waves in the plates exhibiting hysteretic nonlinearity: Nonlinear zero-group velocity modes.

    PubMed

    Gusev, Vitalyi E; Lomonosov, Alexey M; Ni, Chenyin; Shen, Zhonghua

    2017-09-01

    An analytical theory accounting for the influence of hysteretic nonlinearity of micro-inhomogeneous plate material on the Lamb waves near the S1 zero group velocity point is developed. The theory predicts that the main effect of the hysteretic quadratic nonlinearity consists in the modification of the frequency and the induced absorption of the Lamb modes. The effects of the nonlinear self-action in the propagating and standing Lamb waves are expected to be, respectively, nearly twice and three times stronger than those in the plane propagating acoustic waves. The theory is restricted to the simplest hysteretic nonlinearity, which is influencing only one of the Lamé moduli of the materials. However, possible extensions of the theory to the cases of more general hysteretic nonlinearities are discussed as well as the perspectives of its experimental testing. Applications include nondestructive evaluation of micro-inhomogeneous and cracked plates. Copyright © 2017 Elsevier B.V. All rights reserved.

  19. Ambient Seismic Noise Tomography of a Loess High Bank at Dunaszekcső (Hungary)

    NASA Astrophysics Data System (ADS)

    Szanyi, Gyöngyvér; Gráczer, Zoltán; Győri, Erzsébet; Kaláb, Zdeněk; Lednická, Markéta

    2016-08-01

    Loess high banks along the right side of the Danube in Hungary are potential subjects of landslides. Small scale ambient seismic noise tomography was used at the Dunaszekcső high bank. The aim of the study was to map near surface velocity anomalies since we assume that the formation of tension cracks—which precede landslides—are represented by low velocities. Mapping Rayleigh wave group velocity distribution can help to image intact and creviced areas and identify the most vulnerable sections. The study area lies at the top of the Castle Hill of Dunaszekcső, which was named after Castellum Lugio, a fortress of Roman origin. The presently active head scarp was formed in April 2011, and our study area was chosen to be at its surroundings. Cross-correlation functions of ambient noise recordings were used to retrieve the dispersion curves, which served as the input of the group velocity tomography. Phase cross-correlation and time-frequency phase weighted stacking was applied to calculate the cross-correlation functions. The average Rayleigh wave group velocity at the loess high bank was found to be 171 ms^{-1}. The group velocity map at a 0.1 s period revealed a low-velocity region, whose location coincides with a highly creviced area, where slope failure takes place along a several meter wide territory. Another low velocity region was found, which might indicate a previously unknown loosened domain. The highest velocities were observed at the supposed remnants of Castellum Lugio.

  20. 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

    DTIC Science & Technology

    2010-09-01

    DEVELOPING REGIONALIZED MODELS OF LITHOSPHERIC THICKNESS AND VELOCITY STRUCTURE ACROSS EURASIA AND THE MIDDLE EAST FROM JOINTLY INVERTING P-WAVE... lithospheric velocity structure for a wide variety of tectonic regions throughout Eurasia and the Middle East. We expect the regionalized models will improve...important differences in lithospheric structure between the cratonic regions of Eastern Europe and the tectonic regions of Western Europe and the

  1. Refining Estimates of the Seismic Velocities of the Crust and Upper Mantle

    NASA Astrophysics Data System (ADS)

    BARMIN, M.; SHAPIRO, N. M.; Ritzwoller, M. H.; Levin, V.; Park, J.

    2001-12-01

    We discuss recent efforts to improve a global shear-velocity model of the crust and upper mantle by advancing surface wave methodology as well as by introducing new types of geophysical data in the inversion. The primary data-set used to construct the model consists of broad-band Rayleigh and Love wave group-velocity (CU-Boulder) and phase-velocity (Harvard, Utrecht) dispersion curves. The first step of the inversion is surface wave tomography in which group and phase velocity maps are constructed. We present a new method of surface wave tomography called "diffraction tomography" that is based on a physical model of the surface wave Fresnel zone rather than on ray-theory and ad hoc regularization. Diffraction tomography accounts for path-length dependent sensitivity, wave-form healing and associated diffraction effects, and provides a more accurate assessment of spatially variable resolution than traditional tomographic methods. The second step is Monte-Carlo inversion of the dispersion maps for an ensemble of acceptable shear velocity models of the crust and uppermost mantle. Because surface waves have limited vertical resolution, we apply constraints on the model derived from other types of geophysical observations. We consider two types of additional data: teleseismic receiver functions and heat flow measurements. Receivers functions are formed by P-S converted waves that arise from sharp boundaries close to the Earth's surface, and thus provide important constraints on the crustal structure. Their use in the inversion mitigates the tradeoff between the crust (where surface waves have poor sensitivity) and the deeper part of the model. Heat-flow data constrain mantle shear velocities through the conversion of heat-flow into temperature and subsequently into shear velocity at the top of the upper mantle. We present results from the joint inversion and discuss how the combination of different types of data reduces both uncertainties and systematic bias in the

  2. Joint Inversion of Receiver Functions and Surface Wave Group Velocities from the MANAS data set to Determine Custal Thickness Variations in theTien Shan

    NASA Astrophysics Data System (ADS)

    Gilligan, A.; Priestley, K. F.; Roecker, S. W.

    2012-12-01

    The Tien Shan is the largest active intracontinental orgogenic belt on the Earth. To better understand the processes causing mountains to form in this location distant from a plate boundary, we analyze passive source seismic data collected on 40 broad band stations of the MANAS project (2005-2007) to determine variations in crustal thickness and wavespeed across the range. The linear MANAS array transects the Tien Shan just to the east of the Talas Fergana fault and extends from the Tarim Basin north over the Kokshal Range and across the Naryn Valley to the Kyrgyz Range and the Kazakh Shield. This data set has a denser station spacing (~10 km) than that available in previous studies. We combine P- and S-wave receiver functions with surface wave observations from both earthquakes and ambient noise analysis to reduce the ambiguity inherent in the images obtained from the techniques applied individually. In particular, fundamental-mode surface-wave dispersion observations are sensitive to absolute wavespeed averages rather than contrasts, while receiver functions are primarily sensitive to wavespeed contrasts and vertically integrated travel times rather than absolute wavespeeds. Moreover, analysis of the ambient noise allows dispersion measurements at shorter periods which improves constraints for the upper crust. We jointly invert P- and S-wave receiver functions, fundamental mode Rayleigh wave group velocity determined from 1.75 years of continuous seismic ambient noise for periods 4-28s, and group velocity data for periods 10-70s from the surface wave study of Acton et al. (2010). The resulting crustal model show a strong variation in the Moho depth across the range. We find the thickest crust (~60 km) beneath the Kokshal range, while that beneath the Naryn Valley, in the middle of the Tien Shan is thin (~45 km) and is of similar thickness to that beneath the Tarim Basin and Kazakh shield. This suggests a lack of crustal shortening, or shortening of a previously

  3. Direct Simulations of Coupled Transport and Reaction on Nano-Scale X-Ray Computed Tomography Images of Platinum Group Metal-Free Catalyst Cathodes

    SciTech Connect

    Ogawa, S.; Komini Babu, S.; Chung, H. T.; Zelenay, P.; Litster, S.

    2016-08-22

    The nano/micro-scale geometry of polymer electrolyte fuel cell (PEFC) catalyst layers critically affects cell performance. The small length scales and complex structure of these composite layers make it challenging to analyze cell performance and physics at the particle scale by experiment. We present a computational method to simulate transport and chemical reaction phenomena at the pore/particle-scale and apply it to a PEFC cathode with platinum group metal free (PGM-free) catalyst. Here, we numerically solve the governing equations for the physics with heterogeneous oxygen diffusion coefficient and proton conductivity evaluated using the actual electrode structure and ionomer distribution obtained using nano-scale resolution X-ray computed tomography (nano-CT). Using this approach, the oxygen concentration and electrolyte potential distributions imposed by the oxygen reduction reaction are solved and the impact of the catalyst layer structure on performance is evaluated.

  4. Direct Simulations of Coupled Transport and Reaction on Nano-Scale X-Ray Computed Tomography Images of Platinum Group Metal-Free Catalyst Cathodes

    DOE PAGES

    Ogawa, S.; Komini Babu, S.; Chung, H. T.; ...

    2016-08-22

    The nano/micro-scale geometry of polymer electrolyte fuel cell (PEFC) catalyst layers critically affects cell performance. The small length scales and complex structure of these composite layers make it challenging to analyze cell performance and physics at the particle scale by experiment. We present a computational method to simulate transport and chemical reaction phenomena at the pore/particle-scale and apply it to a PEFC cathode with platinum group metal free (PGM-free) catalyst. Here, we numerically solve the governing equations for the physics with heterogeneous oxygen diffusion coefficient and proton conductivity evaluated using the actual electrode structure and ionomer distribution obtained using nano-scalemore » resolution X-ray computed tomography (nano-CT). Using this approach, the oxygen concentration and electrolyte potential distributions imposed by the oxygen reduction reaction are solved and the impact of the catalyst layer structure on performance is evaluated.« less

  5. Early morphological changes and functional abnormalities in group 2A idiopathic juxtafoveolar retinal telangiectasis using spectral domain optical coherence tomography and microperimetry.

    PubMed

    Maruko, I; Iida, T; Sekiryu, T; Fujiwara, T

    2008-11-01

    To report early morphological changes and functional abnormalities in group 2A idiopathic juxtafoveolar retinal telangiectasis (IJRT) using spectral domain optical coherence tomography (SD-OCT) and microperimetry. Six eyes (three patients; average age, 64 years) with group 2A IJRT were examined using SD-OCT and microperimetry. On SD-OCT, breaks in the highly reflective line, considered the boundary between the photoreceptor inner and outer segments, at the temporal to the fovea and corresponding to the telangiectasis lesions were observed in all eyes. Highly reflective tissue was observed in the outer retinal layer in five eyes. In three eyes with a right-angle venule, the outer retinal layer was replaced by the highly reflective tissue and was contiguous to the inner retinal layer. Microperimetry showed the reduction in the retinal sensitivity thresholds at the temporal to the fovea in five eyes. Early morphological alterations in group 2A IJRT in SD-OCT were observed. These finding might be visualisation of Müller cell abnormality on SD-OCT. At the same time, the disorder of photoreceptors occurs at the telangiectasis lesions from MP-1. Detailed observation of these abnormalities provides an understanding of the morphological and functional features of group 2A IJRT.

  6. Nasal endoscopy and paranasal sinus computerised tomography (CT) findings in an Irish cystic fibrosis adult patient group.

    PubMed

    Casserly, P; Harrison, M; O'Connell, O; O'Donovan, N; Plant, B J; O'Sullivan, P

    2015-11-01

    Cystic fibrosis (CF) is a common inherited disorder in Caucasians in Ireland having the highest reported incidence. CF has well-recognised clinical sequelae in several physiological systems. Its' impact on the sinonasal system is less well established. We evaluated symptoms, endoscopic and computerised tomographic (CT) findings in an Irish adult CF group with the aim of characterising the relationship between these clinical features in an Irish CF group. Adult CF patients attending a specialist clinic underwent prospective evaluation of sinonasal symptoms using a specifically designed questionnaire. They subsequently underwent nasoendoscopy and CT scanning of their paranasal sinuses. Abnormalities identified were quantified using established radiological (Lund-Mackay) and endoscopic (Lund-Kennedy) scoring systems. The relationship between symptoms of chronic rhinosinusitis (CRS), endoscopic findings and CT abnormalities were then compared. Sixty-three CF patients (n = 63) were studied. 29 patients had a CT scan. Thirty-three CF patients (52%) had no symptoms of CRS. Fifty CF patients (80% of CF group) had evidence of CRS on nasoendoscopy including thirteen patients (20%) with nasal polyposis. 98% of patients scanned have positive findings on CT scan. There was no significant difference between symptomatic and asymptomatic CF groups with respect to their Lund-Kennedy endoscopic score or their Lund-Mackay CT score. 86% demonstrated one or more hypoplastic sinus. There was no increased incidence of hypoplastic sinuses amongst Δf508 homozygotes than other mutation groups.

  7. Seismic Surface-Wave Tomography of Waste Sites - Final Report

    SciTech Connect

    Long, Timothy L.

    2000-09-14

    The objective of this study was to develop analysis programs for surface-wave group-velocity tomography, and apply these to three test areas. We succeeded by obtaining data covering two square areas that were 30 meters on a side, and a third area that was 16 meters on a side, in addition to a collaborative effort wherein we processed data from the Oak Ridge National Laboratory site. At all sites, usable group velocities were obtained for frequencies from 16 to 50 Hz using a sledgehammer source. The resulting tomographic images and velocity anomalies were sufficient to delineate suspected burial trenches (one 4-meters deep) and anomalous velocity structure related to rocks and disturbed soil. The success was not uniform because in portions of one area the inversion for shear-wave structure became unstable. More research is needed to establish a more robust inversion technique.

  8. Sellmeier equations, group velocity dispersion, and thermo-optic dispersion formulas for CaLnAlO4 (Ln = Y, Gd) laser host crystals.

    PubMed

    Loiko, Pavel; Becker, Petra; Bohatý, Ladislav; Liebald, Christoph; Peltz, Mark; Vernay, Sophie; Rytz, Daniel; Serres, Josep Maria; Mateos, Xavier; Wang, Yicheng; Xu, Xiaodong; Xu, Jun; Major, Arkady; Baranov, Alexander; Griebner, Uwe; Petrov, Valentin

    2017-06-15

    We studied the refractive index and dispersive properties of the tetragonal rare-earth calcium aluminates, CaLnAlO4 (Ln=Gd or Y). Sellmeier equations were derived for the spectral range of 0.35-2.1 μm. The group velocity dispersion (GVD) in CaGdAlO4 is positive at ∼1  μm, 95  fs2/mm and negative at ∼2  μm, -40  fs2/mm. The GVD values for CaYAlO4 are similar. In addition, thermo-optic coefficients, dn/dT, and thermal coefficients of the optical path were determined for CaYAlO4. dn/dT is negative at ∼1  μm, dno/dT=-7.8, and dne/dT=-8.7×10-6  K-1. Thermo-optic dispersion formulas were constructed. The obtained data are of key importance to the design of high-power mode-locked oscillators at ∼1 and ∼2  μm based on such laser hosts.

  9. Modification of the Zero Group Velocity (impact Echo) Resonance Frequency in the Presence of Voids for the Inspection of Tendon Ducts

    NASA Astrophysics Data System (ADS)

    Abraham, O.; Popovics, J. S.; Cottineau, L.-M.

    2011-06-01

    Non-destructive testing of the civil engineering infrastructure for diagnosis, residual service life estimation and/or structural health monitoring, is increasing in importance and need. For example, post-tensioned concrete bridges may be subject to sudden collapse due to tendon breakage. In France, tendon ducts are currently investigated with gamma ray radiometry, but alternative non ionizing techniques are currently sought. Since the mid-nineties, the impact echo method has been proposed to detect voids in tendon ducts, where a void indicates a possible location for tendon corrosion and rupture. The impact echo method is currently used in civil engineering to determine thicknesses or depths by measuring the resonance frequency of the S1 Lamb mode associated to its zero group velocity (ZGV) frequency. A downward shift of the ZGV frequency is commonly associated with the presence of an internal void, but evidence of such phenomena in case of fully filled ducts calls for deeper physical insight. In this paper we show impact-echo results obtained with a laser interferometer on a 0.25 m thick concrete test wall containing filled and partially or fully empty ducts, with both thin and thick duct walls. The data corroborate ZGV frequency shift to the modification of the local stiffness of the wall.

  10. Uncertainty analysis in seismic tomography

    NASA Astrophysics Data System (ADS)

    Owoc, Bartosz; Majdański, Mariusz

    2017-04-01

    Velocity field from seismic travel time tomography depends on several factors like regularization, inversion path, model parameterization etc. The result also strongly depends on an initial velocity model and precision of travel times picking. In this research we test dependence on starting model in layered tomography and compare it with effect of picking precision. Moreover, in our analysis for manual travel times picking the uncertainty distribution is asymmetric. This effect is shifting the results toward faster velocities. For calculation we are using JIVE3D travel time tomographic code. We used data from geo-engineering and industrial scale investigations, which were collected by our team from IG PAS.

  11. Experimental measurement and numerical analysis of group velocity dispersion in cladding modes of an endlessly single-mode photonic crystal fiber

    NASA Astrophysics Data System (ADS)

    Baselt, Tobias; Taudt, Christopher; Nelsen, Bryan; Lasagni, Andrés. Fabián.; Hartmann, Peter

    2017-06-01

    The optical properties of the guided modes in the core of photonic crystal fibers (PCFs) can be easily manipulated by changing the air-hole structure in the cladding. Special properties can be achieved in this case such as endless singlemode operation. Endlessly single-mode fibers, which enable single-mode guidance over a wide spectral range, are indispensable in the field of fiber technology. A two-dimensional photonic crystal with a silica central core and a micrometer-spaced hexagonal array of air holes is an established method to achieve endless single-mode properties. In addition to the guidance of light in the core, different cladding modes occur. The coupling between the core and the cladding modes can affect the endlessly single-mode guides. There are two possible ways to determine the dispersion: measurement and calculation. We calculate the group velocity dispersion (GVD) of different cladding modes based on the measurement of the fiber structure parameters, the hole diameter and the pitch of a presumed homogeneous hexagonal array. Based on the scanning electron image, a calculation was made of the optical guiding properties of the microstructured cladding. We compare the calculation with a method to measure the wavelength-dependent time delay. We measure the time delay of defined cladding modes with a homemade supercontinuum light source in a white light interferometric setup. To measure the dispersion of cladding modes of optical fibers with high accuracy, a time-domain white-light interferometer based on a Mach-Zehnder interferometer is used. The experimental setup allows the determination of the wavelengthdependent differential group delay of light travelling through a thirty centimeter piece of test fiber in the wavelength range from VIS to NIR. The determination of the GVD using different methods enables the evaluation of the individual methods for characterizing the cladding modes of an endlessly single-mode fiber.

  12. Energy Velocity Defined by Brillouin

    NASA Astrophysics Data System (ADS)

    Hosono, Hiroyuki; Hosono, Toshio

    The physical meaning of the energy velocity in lossy Lorentz media is clarified. First, two expressions for the energy velocity, one by Brillouin and another by Diener, are examined. We show that, while Diener's is disqualified, Brillouin's is acceptable as energy velocity. Secondly, we show that the signal velocity defined by Brillouin and Baerwald is exactly identical with the Brillouin's energy velocity. Thirdly, by using triangle-modulated harmonic wave, we show that the superluminal group velocity plays its role as a revelator only after the arrival of the signal traveling at the subluminal energy velocity. In short, nothing moves at the group velocity, and every frequency component of a signal propagates at its own energy velocity.

  13. Dynamic analysis for mental sweating of a group of eccrin sweat glands on a human fingertip by optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Ohmi, Masato; Tanigawa, Motomu; Wada, Yuki; Haruna, Masamitsu

    2011-05-01

    OCT is highly potential for in vivo observation of human sweating dynamics which affects activity of the sympathetic nerve. In this paper, we demonstrate dynamic OCT analysis of mental sweating of a group of eccrin sweat glands. The sweating dynamics is tracked simultaneously for nineteen sweat glands by time-sequential piled-up en-face OCT images with the frame spacing of 3.3 sec. Strong non-uniformity is observed in mental sweating where the amount of excess sweat is different for each sweat gland although the sweat glands are adjacent to each other. The non-uniformity should be necessary to adjust as precisely the total amount of excess sweat as possible through the sympathetic nerve in response to strength of the stress.

  14. Accurate Group Delay Measurement for Radial Velocity Instruments Using the Dispersed Fixed Delay Interferometer Method. II. Application of Heterodyne Combs Using an External Interferometer Filter

    NASA Astrophysics Data System (ADS)

    Wang, Ji; Ge, Jian; Wan, Xiaoke; De Lee, Nathan; Lee, Brian

    2012-11-01

    A fixed delay interferometer is the key component in a DFDI (dispersed fixed delay interferometer) instrument for an exoplanet search using the radial velocity (RV) technique. Although the group delay (GD) of the interferometer can be measured with white light combs (WLCs), the measurement precision is limited by the comb visibility, and the wavelength coverage is constrained by the comb sampling. For instance, this method can calibrate only half of the SDSS-III MARVELS spectra and reach a precision of 2.2 m s-1. This article introduces an innovative method using a sine source for precision delay calibration over very broad wavelengths. The sine source is made of a monolithic Michelson interferometer fed with white light. The interferometer modulated white light (in a sinusoidal form) is fed into a DFDI instrument for calibration. Due to an optimal GD of the sine source, Fourier components from the DFDI interferometer, the sine source, and their frequency beating can be clearly separated and effectively extracted with a chirped Fourier transform to allow precision measurements of the interferometer GD over the entire range of operation wavelengths. The measurements of the MARVELS interferometer with a sine source show that this new calibration method has improved the wavelength coverage by a factor of 2 and the precision by a factor of 3. The RV measurement error induced by GD measurement uncertainties is controlled to be less than 1 m s-1, which has met the requirements for MARVELS moderate-to-high Doppler precision (∼5–30 m s-1) for exoplanet search around V ∼ 8–12 solar-type stars. Heterodyne combs using an external interferometer source can be applied in other areas of optics measurement and calibration.

  15. A proposed protocol for acceptance and constancy control of computed tomography systems: a Nordic Association for Clinical Physics (NACP) work group report.

    PubMed

    Kuttner, Samuel; Bujila, Robert; Kortesniemi, Mika; Andersson, Henrik; Kull, Love; Østerås, Bjørn Helge; Thygesen, Jesper; Tarp, Ivanka Sojat

    2013-03-01

    Quality assurance (QA) of computed tomography (CT) systems is one of the routine tasks for medical physicists in the Nordic countries. However, standardized QA protocols do not yet exist and the QA methods, as well as the applied tolerance levels, vary in scope and extent at different hospitals. To propose a standardized protocol for acceptance and constancy testing of CT scanners in the Nordic Region. Following a Nordic Association for Clinical Physics (NACP) initiative, a group of medical physicists, with representatives from four Nordic countries, was formed. Based on international literature and practical experience within the group, a comprehensive standardized test protocol was developed. The proposed protocol includes tests related to the mechanical functionality, X-ray tube, detector, and image quality for CT scanners. For each test, recommendations regarding the purpose, equipment needed, an outline of the test method, the measured parameter, tolerance levels, and the testing frequency are stated. In addition, a number of optional tests are briefly discussed that may provide further information about the CT system. Based on international references and medical physicists' practical experiences, a comprehensive QA protocol for CT systems is proposed, including both acceptance and constancy tests. The protocol may serve as a reference for medical physicists in the Nordic countries.

  16. Seismic Surface-Wave Tomography of Waste Sites

    SciTech Connect

    Leland Timothy Long

    2002-12-17

    Surface-wave group-velocity tomography is an efficient way to obtain images of the group velocity over a test area. Because Rayleigh-wave group velocity depends on frequency, there are separate images for each frequency. Thus, at each point in these images the group velocities define a dispersion curve, a curve that relates group velocity to frequency. The objective of this study has been to find an accurate and efficient way to find the shear-wave structure from these dispersion curves. The conventional inversion techniques match theoretical and observed dispersion curves to determine the structure. These conventional methods do not always succeed in correctly differentiating the fundamental and higher modes, and for some velocity structures can become unstable. In this research a perturbation technique was developed. The perturbation method allows the pre-computation of a global inversion matrix which improves efficiency in obtaining solutions for the structure. Perturbation methods are stable and mimic the averaging process in wave propagation; hence. leading to more accurate solutions. Finite difference techniques and synthetic trace generation techniques were developed to define the perturbations. A new differential trace technique was developed for slight variations in dispersion. The improvements in analysis speed and the accuracy of the solution could lead to real-time field analysis systems, making it possible to obtain immediate results or to monitor temporal change in structure, such as might develop in using fluids for soil remediation.

  17. Chest electrical impedance tomography examination, data analysis, terminology, clinical use and recommendations: consensus statement of the TRanslational EIT developmeNt stuDy group

    PubMed Central

    Frerichs, Inéz; Amato, Marcelo B P; van Kaam, Anton H; Tingay, David G; Zhao, Zhanqi; Grychtol, Bartłomiej; Bodenstein, Marc; Gagnon, Hervé; Böhm, Stephan H; Teschner, Eckhard; Stenqvist, Ola; Mauri, Tommaso; Torsani, Vinicius; Camporota, Luigi; Schibler, Andreas; Wolf, Gerhard K; Gommers, Diederik; Leonhardt, Steffen; Adler, Andy

    2017-01-01

    Electrical impedance tomography (EIT) has undergone 30 years of development. Functional chest examinations with this technology are considered clinically relevant, especially for monitoring regional lung ventilation in mechanically ventilated patients and for regional pulmonary function testing in patients with chronic lung diseases. As EIT becomes an established medical technology, it requires consensus examination, nomenclature, data analysis and interpretation schemes. Such consensus is needed to compare, understand and reproduce study findings from and among different research groups, to enable large clinical trials and, ultimately, routine clinical use. Recommendations of how EIT findings can be applied to generate diagnoses and impact clinical decision-making and therapy planning are required. This consensus paper was prepared by an international working group, collaborating on the clinical promotion of EIT called TRanslational EIT developmeNt stuDy group. It addresses the stated needs by providing (1) a new classification of core processes involved in chest EIT examinations and data analysis, (2) focus on clinical applications with structured reviews and outlooks (separately for adult and neonatal/paediatric patients), (3) a structured framework to categorise and understand the relationships among analysis approaches and their clinical roles, (4) consensus, unified terminology with clinical user-friendly definitions and explanations, (5) a review of all major work in thoracic EIT and (6) recommendations for future development (193 pages of online supplements systematically linked with the chief sections of the main document). We expect this information to be useful for clinicians and researchers working with EIT, as well as for industry producers of this technology. PMID:27596161

  18. Chest electrical impedance tomography examination, data analysis, terminology, clinical use and recommendations: consensus statement of the TRanslational EIT developmeNt stuDy group.

    PubMed

    Frerichs, Inéz; Amato, Marcelo B P; van Kaam, Anton H; Tingay, David G; Zhao, Zhanqi; Grychtol, Bartłomiej; Bodenstein, Marc; Gagnon, Hervé; Böhm, Stephan H; Teschner, Eckhard; Stenqvist, Ola; Mauri, Tommaso; Torsani, Vinicius; Camporota, Luigi; Schibler, Andreas; Wolf, Gerhard K; Gommers, Diederik; Leonhardt, Steffen; Adler, Andy

    2017-01-01

    Electrical impedance tomography (EIT) has undergone 30 years of development. Functional chest examinations with this technology are considered clinically relevant, especially for monitoring regional lung ventilation in mechanically ventilated patients and for regional pulmonary function testing in patients with chronic lung diseases. As EIT becomes an established medical technology, it requires consensus examination, nomenclature, data analysis and interpretation schemes. Such consensus is needed to compare, understand and reproduce study findings from and among different research groups, to enable large clinical trials and, ultimately, routine clinical use. Recommendations of how EIT findings can be applied to generate diagnoses and impact clinical decision-making and therapy planning are required. This consensus paper was prepared by an international working group, collaborating on the clinical promotion of EIT called TRanslational EIT developmeNt stuDy group. It addresses the stated needs by providing (1) a new classification of core processes involved in chest EIT examinations and data analysis, (2) focus on clinical applications with structured reviews and outlooks (separately for adult and neonatal/paediatric patients), (3) a structured framework to categorise and understand the relationships among analysis approaches and their clinical roles, (4) consensus, unified terminology with clinical user-friendly definitions and explanations, (5) a review of all major work in thoracic EIT and (6) recommendations for future development (193 pages of online supplements systematically linked with the chief sections of the main document). We expect this information to be useful for clinicians and researchers working with EIT, as well as for industry producers of this technology.

  19. Radiolabeling of Poly(lactic-co-glycolic acid) (PLGA) Nanoparticles with Biotinylated F-18 Prosthetic Groups and Imaging of Their Delivery to the Brain with Positron Emission Tomography

    PubMed Central

    2015-01-01

    The avidin–biotin interaction permits rapid and nearly irreversible noncovalent linkage between biotinylated molecules and avidin-modified substrates. We designed a biotinylated radioligand intended for use in the detection of avidin-modified polymer nanoparticles in tissue with positron emission tomography (PET). Using an F-18 labeled prosthetic group, [18F]4-fluorobenzylamine, and a commercially available biotin derivate, NHS-PEG4-biotin, [18F]-fluorobenzylamide-poly(ethylene glycol)4-biotin ([18F]NPB4) was prepared with high purity and specific activity. The attachment of the [18F]NPB4 radioligand to avidin-modified poly(lactic-co-glycolic acid) (PLGA) nanoparticles was tested by using PET imaging to measure the kinetics of convection-enhanced delivery (CED) of nanoparticles of varying size to the rat brain. PET imaging enabled the direct observation of nanoparticle delivery by measurement of the spatial volume of distribution of radiolabeled nanoparticles as a function of time, both during and after the infusion. This work thus validates new methods for radiolabeling PEG-biotin derivatives and also provides insight into the fate of nanoparticles that have been infused directly into the brain. PMID:25322194

  20. Impact of urinary stone volume on computed tomography stone attenuations measured in Hounsfield units in a large group of Austrian patients with urolithiasis.

    PubMed

    Al-Ali, Badereddin Mohamad; Patzak, Johanna; Lutfi, Andre; Pummer, Karl; Augustin, Herbert

    2014-01-01

    To investigate retrospectively the impact of urinary stone volume on computed tomography stone attenuations measured in Hounsfield units in 253 patients with urolithiasis. CT scans were performed in 253 patients with suspected urinary stone disease from 2008 to 2010 using CT-Scanner Siemens, SOMATOM, Sensation 64. One experienced radiologist (A.L) who was blinded to the chemical composition of the stones retrospectively reviewed images and analyzed data to determine the composition of the stones. The results were compared with the biochemical analysis results obtained by infrared spectroscopy (100 FTIR, PerkinElmer). 253 consecutive patients from 2008 to 2010 were included into analysis: 189 males, and 64 females. Mean age was 51.2. According to stone volume, stones were divided into 2 groups: 126 stones with volume of 4.3 mm or more, 127 stones with volume less than 4.3 mm. There was a significant relationship between stone volume and its CT attenuation only in stones with a volume 4.3 mm or more (p <0.05). We failed to show a significant relationship between stone volume and its attenuations in Hounsfield units. We could not distinguish uric acid stones from non uric acid stones.

  1. Impact of urinary stone volume on computed tomography stone attenuations measured in Hounsfield units in a large group of Austrian patients with urolithiasis

    PubMed Central

    Patzak, Johanna; Lutfi, Andre; Pummer, Karl; Augustin, Herbert

    2014-01-01

    Introduction To investigate retrospectively the impact of urinary stone volume on computed tomography stone attenuations measured in Hounsfield units in 253 patients with urolithiasis. Material and methods CT scans were performed in 253 patients with suspected urinary stone disease from 2008 to 2010 using CT–Scanner Siemens, SOMATOM, Sensation 64. One experienced radiologist (A.L) who was blinded to the chemical composition of the stones retrospectively reviewed images and analyzed data to determine the composition of the stones. The results were compared with the biochemical analysis results obtained by infrared spectroscopy (100 FTIR, PerkinElmer). Results 253 consecutive patients from 2008 to 2010 were included into analysis: 189 males, and 64 females. Mean age was 51.2. According to stone volume, stones were divided into 2 groups: 126 stones with volume of 4.3 mm or more, 127 stones with volume less than 4.3 mm. There was a significant relationship between stone volume and its CT attenuation only in stones with a volume 4.3 mm or more (p <0.05). Conclusions We failed to show a significant relationship between stone volume and its attenuations in Hounsfield units. We could not distinguish uric acid stones from non uric acid stones. PMID:25247090

  2. Enhanced monitoring of hazardous waste site remediation: Electrical conductivity tomography and citizen monitoring of remediation through the EPA's community advisory group program

    NASA Astrophysics Data System (ADS)

    Hort, Ryan D.

    In situ chemical oxidation using permanganate has become a common method for degrading trichloroethene (TCE) in contaminated aquifers. Its effectiveness, however, is dependent upon contact between the oxidant and contaminant. Monitoring permanganate movement after injection is often hampered by aquifer heterogeneity and insufficient well coverage. Time lapse electrical conductivity tomography increases the spatial extent of monitoring beyond well locations. This technique can create two- or three-dimensional images of the electrical conductivity within the aquifer to monitor aquifer chemistry changes caused by permanganate injection and oxidation reactions. In-phase and quadrature electrical conductivity were measured in homogeneous aqueous and porous media samples to determine the effects of TCE and humate oxidation by permanganate on both measures of conductivity. Further effects of clean sand, 10% kaolinite (v/v), and 10% smectite (v/v) on both types of conductivity were studied as well. Finally, in-phase electrical conductivity was measured over time after injecting permanganate solution into two-dimensional tanks containing artificial groundwater with and without TCE to observe the movement of the permanganate plume and its interaction with TCE and to examine the effectiveness of time-lapse conductivity tomography for monitoring the plume's movement. In-phase electrical conductivity after oxidation reactions involving permanganate, TCE, and humate could be accurately modeled in homogeneous batch samples. Use of forward modeling of in-phase conductivity from permanganate concentrations may be useful for improving recovery of conductivity values during survey inversion, but further work is needed combining the chemistry modeling with solute transport models. Small pH-related quadrature conductivity decreases were observed after TCE oxidation, and large quadrature conductivity increases were observed as a result of sodium ion addition; however, quadrature

  3. Static corrections in mountainous areas using Fresnel-wavepath tomography

    NASA Astrophysics Data System (ADS)

    Zhang, Jianzhong; Shi, Tai-kun; Zhao, Yasheng; Zhou, Hua-wei

    2014-12-01

    We propose a 3-D Fresnel-wavepath tomography based on simultaneous iterative reconstruction technique (SIRT) with adaptive relaxation factors, in order to obtain effective near-surface velocity models for static corrections. We derived a formula to calculate the optimal relaxation factor for tomographic inversion to increase the convergence rate and thus the efficiency of the Fresnel-wavepath tomography. A forward method based on bilinear traveltime interpolation and the wavefront group marching is applied to achieve fast and accurate computation of the wavefront traveltimes in 3-D heterogeneous models. The new method is able to achieve near-surface velocity models effective in estimating long-period static corrections, and the remaining traveltime residuals after the tomographic inversion are used to estimate the short-period static corrections via a surface-consistent decomposition. The new method is tested using 3-D synthetic data and 3-D field dataset acquired in a complex mountainous area in southwestern China.

  4. Striatal Dopamine Transporter Modulation After Rotigotine: Results From a Pilot Single-Photon Emission Computed Tomography Study in a Group of Early Stage Parkinson Disease Patients.

    PubMed

    Rossi, Carlo; Genovesi, Dario; Marzullo, Paolo; Giorgetti, Assuero; Filidei, Elena; Corsini, Giovanni Umberto; Bonuccelli, Ubaldo; Ceravolo, Roberto

    Several in vitro data have reported negative interference by dopamine-agonists on the expression of dopamine transporter (DAT), whereas the majority of imaging studies have shown that neither L-dopa nor dopamine-agonists interfere with DAT availability. As yet, there are no in vivo studies on DAT expression after treatment with rotigotine. We evaluated presynaptic nigrostriatal function in 8 patients with de novo Parkinson disease (age, 59 ± 6.2 years; male/female sex, 5/3) using 123-I- N-ω-fluoropropyl-2-β-carbomethoxy-3-β-(4-iodophenyl)nortropane (FP-CIT) single-photon emission computed tomography before and after 3 months of treatment with rotigotine (mean dose, 7.75 ± 1.98 mg). For data analysis, specific (left and right caudate, left and right putamen) to nonspecific (occipital cortex) binding ratios, putamen-to-caudate ratios, and asymmetry indices were calculated. After rotigotine, motor symptoms improved in all patients (Unified Parkinson Disease Rating Scale III mean score, 11.88 ± 2.59 vs 7.63 ± 1.92 on therapy; P = 0.0022). Striatal FP-CIT levels showed a significant improvement in every patient at the follow-up scan. Comparisons between before and after treatment in the whole group revealed a significant improvement in FP-CIT uptake in both caudate and putamen (P < 0.001 in each nucleus). Putamen-to-caudate ratio and asymmetry indices did not show any significant difference before and after treatment. Although the study population was small, we found DAT overexpression after chronic treatment with rotigotine, presumably related to its pharmacological profile. The DAT upregulation by rotigotine in an opposite direction with respect to early Parkinson disease compensatory mechanisms might reduce the risk of dyskinesia, but it could imply less motor benefit because of less stimulation by the dopamine itself on dopaminergic receptors.

  5. Near-surface study at the Valhall oil field from ambient noise surface wave tomography

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

    We used 6 hr of continuous seismic noise records from 2320 four-component sensors of the Valhall `Life of Field Seismic' network to compute cross-correlations (CCs) of ambient seismic noise. A beamforming analysis showed that at low frequencies (below 2 Hz) the seismic noise sources were spatially homogeneously distributed, whereas at higher frequencies (2-30 Hz), the dominant noise source was the oil platform at the centre of the network. Here, we performed an ambient noise surface wave tomography at frequencies below 2 Hz. We used vertical-component geophones CCs to extract and measure the Scholte waves group velocities dispersion curves that were then processed with a set of quality criteria and inverted to build group velocity maps of the Valhall area. Although Scholte wave group velocity depends on S wave, our group velocity maps show features similar to that was previously obtained from P-wave velocity full-waveform inversion of an active seismic data set. Since the dominant noise source at high frequency (above 3 Hz) was the oil platform, we determined a 2-D S-wave velocity model along a profile aligned with the platform by inverting group velocity dispersion curves of Love waves from transverse-component geophones CCs. We found that S-wave velocity down to 20 m was low and varied along the profile, and could be used to estimate S-wave static.

  6. Minimum 1D P- and S- Velocity Models for Montenegro and Vicinity

    NASA Astrophysics Data System (ADS)

    Vucic, Ljiljana; Kissling, Edi; Spakman, Wim; Glavatovic, Branislav

    2015-04-01

    The territory of Montenegro and its vicinity are characterized by high-seismicity rate and very complex tectonics. Namely, southern Adria microplate subducts beneath Eurasia, forming the Dinarides fold-and-thrust belt which spreads through whole Montenegro and the western Balkans. Present-day lithosphere structure of the Adria-Dinarides collision zone in general is not constrained very well and, consequently, there is a lack of three-dimensional (3D) velocity models in this region. For these reasons, high resolution 3D tomography modeling of this area is considered to be of great importance. As part of preparatory phase for conducting a 3D local earthquake tomography study, a substantial amount of waveform data was collected, from all surroundings national seismic networks including 130 seismic stations from 11 countries. The data set comprises waveforms from 1452 earthquakes in the region recorded during time period 1990 - 2014. The collected data were obtained in different formats and the data base was harmonized by converting and integrating all data to miniseed format. The potential resolution of collected data for seismic tomography purpose was analyzed by ray density testing, using specially developed software for this specific purpose. The result is expressed as the number of rays between selected group of earthquake hypocenters and seismic stations, penetrating through the 3D model of the Earth crust and it documents the great potential of the data set for 3D seismic tomography. As a prerequisite to 3D tomography and for consistent high-precision earthquake locations, a minimum 1D velocity model has been calculated. The data set of around 400 earthquakes was selected from the main database and consistent wave onsets picking was performed, including seismic phase interpretation and its quality assessment. This highly consistent travel time data set is used for calculation of 1D velocity models for the region under study. The minimum 1D models were derived

  7. Early [¹⁸F]fluorodeoxyglucose positron emission tomography-based response evaluation after treatment with gemcitabine and vinorelbine for refractory Hodgkin disease: a children's oncology group report.

    PubMed

    Cole, Peter D; McCarten, Kathleen M; Drachtman, Richard A; Alarcon, Pedro de; Chen, Lu; Trippett, Tanya M; Schwartz, Cindy L

    2010-11-01

    The International Harmonization Project defined complete response (CR) after treatment for Hodgkin disease (HD) by absence of fluorodeoxyglucose avidity, regardless of the size of residual masses. Residual avidity after initial treatment is known to predict inferior survival. In the setting of retrieval therapy, early positron emission tomography (PET) scans may improve assessment of treatment efficacy. Retrospective analysis after 2 cycles of gemcitabine and vinorelbine for refractory HD revealed 6 CR among 13 patients by PET and 1 CR in 13 by computed tomography (CT). No relationship between PET response and event-free or overall survival could be discerned, presumably because of the heterogeneity of subsequent therapies.

  8. Adaptive ambient noise tomography and its application to the Garlock Fault, southern California

    NASA Astrophysics Data System (ADS)

    Li, Peng; Lin, Guoqing

    2014-05-01

    Traditional ambient noise tomography methods using regular grid nodes are often ill posed because the inversion grids do not always represent the distribution of ray paths. Large grid spacing is usually used to reduce the number of inversion parameters, which may not be able to solve for small-scale velocity structure. We present a new adaptive tomography method with irregular grids that provides a few advantages over the traditional methods. First, irregular grids with different sizes and shapes can fit the ray distribution better and the traditionally ill-posed problem can become more stable owing to the different parametrizations. Secondly, the data in the area with dense ray sampling will be sufficiently utilized so that the model resolution can be greatly improved. Both synthetic and real data are used to test the newly developed tomography algorithm. In synthetic data tests, we compare the resolution and stability of the traditional and adaptive methods. The results show that adaptive tomography is more stable and performs better in improving the resolution in the area with dense ray sampling. For real data, we extract the ambient noise signals of the seismic data near the Garlock Fault region, obtained from the Southern California Earthquake Data Center. The resulting group velocity of Rayleigh wave is well correlated with the geological structures. High-velocity anomalies are shown in the cold southern Sierra Nevada, the Tehachapi Mountains and the Western San Gabriel Mountains. In contrast, low velocity values are prominent in the southern San Joaquin Valley and western Mojave.

  9. Generation of 3.6  μm radiation and telecom-band amplification by four-wave mixing in a silicon waveguide with normal group velocity dispersion.

    PubMed

    Kuyken, B; Verheyen, P; Tannouri, P; Liu, X; Van Campenhout, J; Baets, R; Green, W M J; Roelkens, G

    2014-03-15

    Mid-infrared light generation through four-wave mixing-based frequency down-conversion in a normal group velocity dispersion silicon waveguide is demonstrated. A telecom-wavelength signal is down-converted across more than 1.2 octaves using a pump at 2190 nm in a 1 cm-long waveguide. At the same time, a 13 dB on-chip parametric gain of the telecom signal is obtained.

  10. Seismic crosshole curved ray reflection plus transmission tomography

    SciTech Connect

    Wu, L.; Song, W.; Zhang, M.

    1994-12-31

    This paper provides a new seismic crosshole tomography method, Curved Ray Reflection + Transmission Tomography (CCRTT). The method could enhance the resolution of oil and gas reservoir beds tomography image, and it is suitable for the area with thin reservoir beds and high velocity contrast between the adjacent beds.

  11. High S/N Echelle spectroscopy in young stellar groups. II. Rotational velocities of early-type stars in SCO OB2.

    NASA Astrophysics Data System (ADS)

    Brown, A. G. A.; Verschueren, W.

    1997-03-01

    We investigate the rotational velocities of early-type stars in the Sco OB2 association. We measure v.sin(i) for 156 established and probable members of the association. The measurements are performed with three different techniques, which are in increasing order of expected v.sin(i): 1) converting the widths of spectral lines directly to v.sin(i), 2) comparing artificially broadened spectra of low v.sin(i) stars to the target spectrum, 3) comparing the HeI λ4026 line profile to theoretical models. The sample is extended with literature data for 47 established members of Sco OB2. Analysis of the v.sin(i) distributions shows that there are no significant differences between the subgroups of Sco OB2. We find that members of the binary population of Sco OB2 on the whole rotate more slowly than the single stars. In addition, we find that the B7-B9 single star members rotate significantly faster than their B0-B6 counterparts. We test various hypotheses for the distribution of v.sin(i) in the association. The results show that we cannot clearly exclude any form of random distribution of the direction and/or magnitude of the intrinsic rotational velocity vector. We also investigate the effects of rotation on colours in the Walraven photometric system. We show that positions of B7-B9 single dwarfs above the main sequence are a consequence of rotation. This establishes the influence of rotation on the Walraven colours, due primarily to surface gravity effects.

  12. ADCIGs extraction and reflection tomography modeling for elastic wave

    NASA Astrophysics Data System (ADS)

    Liu, Ruihe; Qin, Ning; Yin, Xingyao

    2017-08-01

    Based on the theory of elastic wave, we derive the migration angle formula of P- and S-wave in the Gaussian beam migration and implement the ADCIGs (angle domain common imaging gathers) extraction for Gaussian beam of PP- and PS-wave firstly. Then, we derive the reflection tomography equations for elastic wave velocity analysis. They are used for the tomography velocity modeling base on the Gaussian beam ADCIGs. Making reflection tomography and depth migration into the same velocity modeling process, this method can not only use ADCIGs of elastic wave to update the velocities, but also can apply the migration results of tomography in each iteration as quality control, until the end of whole process in velocity modeling and finally we can get the prestack depth migration results after tomography. Synthetic and field examples validate the correctness and practicability of this method.

  13. Ambient noise tomography of the western Corinth Rift, Greece

    NASA Astrophysics Data System (ADS)

    Giannopoulos, Dimitrios; Rivet, Diane; Sokos, Efthimios; Deschamps, Anne; Mordret, Aurelien; Lyon-Caen, Hélène; Bernard, Pascal; Paraskevopoulos, Paraskevas; Tselentis, G.-Akis

    2017-10-01

    Three years of continuous waveform data recorded at 22 stations from the Corinth Rift Laboratory and the Hellenic Unified Seismological Network are used to perform an ambient noise surface wave tomography of the western Corinth Rift. All available vertical component time-series were cross-correlated to extract empirical Rayleigh-wave Green's functions. Group velocity dispersion curves were measured for each station-pair by applying frequency-time analysis and then inverted to build 2-D group velocity maps between 1 and 6 s period. Finally, we locally inverted these velocity maps using a neighbourhood algorithm to assess the 3-D shear-velocity model of the shallow crustal structure of the western Corinth Rift. Across all studied periods the southern coast of the Corinth Gulf is generally imaged as a region of lower velocities compared to the northern coast. At periods up to 3 s, the spatial variation of the group velocities is correlated with the surface geology of the area. Lower velocities are observed in areas where mostly Plio-Quaternary syn-rift sediments are present, such as offshore regions of the rift, the Mornos delta and the largest part of the southern coast. Higher velocities are observed in pre-rift basement structures which are dominated mostly by carbonates. At periods above 3 s, where Rayleigh-waves begin to sense deeper structures below the sediments within the underlying basement, our study highlights the presence of a distinct zone of lower velocities across the southern part of the rift with an elongation in the WNW-ESE direction. The interpretation of this low velocity includes two arguments, the present-day active tectonic regime and the possible involvement of fluids circulation processes at depth within a highly fractured upper crust in the vicinity of the major faults zones. In general, the results demonstrate good agreement with the major geological and tectonic features of the area, as well as with previous local earthquake tomography

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  15. Weak middle-to-lower crust in the southeastern margin of the Tibetan Plateau revealed by ambient noise tomography

    NASA Astrophysics Data System (ADS)

    Fang, L.; Wu, J.; Wang, W.; Wang, C.

    2012-12-01

    As the conjunction between the Tibetan Plateau and the Yangtze Indo-China blocks and the southern end of the trans-China seismicity belt, the southeastern margin of the Tibetan Plateau is particularly important for understanding the collision process between Indian and Eurasian plates and studying the mechanisms for the buildup and eastward expansion of the Tibetan Plateau. We perform Rayleigh wave tomography in SE Tibetan Plateau by applying the ambient noise method to broadband data recorded at 134 permanent stations and 50 temporal stations. Cross-correlations of vertical-component ambient noise data are computed and stacked from January to December 2010. Then Rayleigh wave group dispersion curves from 4 to 40 s were measured using the multiple-filter analysis method. Group velocity maps at periods from 4 to 40 s were inverted. We present the group velocity maps with highest resolution in southeastern Tibetan Plateau so far. The lateral resolution is estimated to be 40-60 km in the central part. The tomography maps reveal some unprecedented details. (1) In the period range between 4 and 20 s, low group velocities are clearly observed in Sichuan Basin, reflecting thick sedimentary deposits. The velocity contrasts across Longmenshan fault, Xianshuihe fault and Xiaojiang fault is very strong, suggesting these faults are major tectonic boundaries. (2) In the period range between 20 and 30 s, a wide, continuous low velocity zone is observed between Lancangjiang fault and Xianshuihe-Xiaojiang fault. Combined with other geophysical observables (e.g., heat flow, resistivity, Poisson's ratio) the low velocity zone indicates low (mechanical) rigidity and may represent loci of ductile deformation in the middle-to-lower crust. The new tomography results support deformation models involving intra-crustal flow. Since the low velocity zones are interconnected, this may indicate the existence of a regional scale channel flow. (3) In the period range between 30 and 40 s the

  16. Acoustic tomography. Laboratory technique Implementation.

    NASA Astrophysics Data System (ADS)

    Galvis, Jorge; Carvajal, Jenny

    2010-05-01

    From geomechanical tests carried out on rocks it is possible to determine its physico-mechanical properties, which relate the strain and applied stress; even so, conventional tests do not allow to identify how stress is distributed and how it has affected porous media. Today, techniques like acoustic tomography widely used in medicine, geophysics and others sciences, generates images by sections of the interior of a body. Acoustic tomography allows inferring the stress state within porous media; since wave velocities are closely related to media density, if a stress is applied to a rock, it will generate grains compaction and this will be showed by an increase of wave velocity. Implementation was conducted on rock plugs under diverse stress fields, simultaneously recording P-wave velocities (Compressional) on perpendicular planes to sample vertical axis. Transmission and reception of acoustic waves through porous media were done by piezoelectric crystals (PZT) used as sensors. A transmitting crystal excited by a voltage pulse causes a mechanical vibration, which travels across media; this is known as inverse piezoelectric effect. This vibration is recorded by a receiving crystal in which the direct piezoelectric effect appears; which dictates that if a piezoelectric is disturbed mechanically, an electrical signal between its terminals will appear. This electrical signal is used to obtain the wave velocity. Nevertheless, acoustic tomography corresponds to one of those called inverse Problems that arise when from observed data the model parameters must be obtained; in this way, tomography involves iterative reconstruction techniques (ART or SIRT) which are projections of observed data and its later inversion. Obtained results are cross-sectional images of velocity within the rock. In these images it is possible to identify where stress has a greater concentration observing the color map generated; thus, a greater velocity density area corresponding to a greater

  17. Upper crustal structure of Madeira Island revealed from ambient noise tomography

    NASA Astrophysics Data System (ADS)

    Matos, Catarina; Silveira, Graça; Matias, Luís; Caldeira, Rita; Ribeiro, M. Luísa; Dias, Nuno A.; Krüger, Frank; Bento dos Santos, Telmo

    2015-06-01

    We present the first image of the Madeira upper crustal structure, using ambient seismic noise tomography. 16 months of ambient noise, recorded in a dense network of 26 seismometers deployed across Madeira, allowed reconstructing Rayleigh wave Green's functions between receivers. Dispersion analysis was performed in the short period band from 1.0 to 4.0 s. Group velocity measurements were regionalized to obtain 2D tomographic images, with a lateral resolution of 2.0 km in central Madeira. Afterwards, the dispersion curves, extracted from each cell of the 2D group velocity maps, were inverted as a function of depth to obtain a 3D shear wave velocity model of the upper crust, from the surface to a depth of 2.0 km. The obtained 3D velocity model reveals features throughout the island that correlates well with surface geology and island evolution.

  18. Eikonal Tomography of the Southern California Plate Boundary Region

    NASA Astrophysics Data System (ADS)

    Qiu, H.; Ben-Zion, Y.; Zigone, D.; Lin, F. C.

    2016-12-01

    We use eikonal tomography to derive directionally-dependent phase velocities of surface waves for the plate boundary region in southern CA sensitive to the approximate depth range 1-20 km. Seismic noise data recorded by 346 stations in the area provide a spatial coverage with 5-25 km typical station spacing and period range of 1-20 s. Noise cross-correlations are calculated for vertical component data recorded in year 2014. Rayleigh wave group and phase travel times between 2 and 13 sec period are derived for each station pair using frequency-time analysis. For each common station, all available phase travel time measurements with sufficient signal to noise ratio and envelope peak amplitude are used to construct a travel time map for a virtual source at the common station location. By solving the eikonal equation, both phase velocity and propagation direction are evaluated at each location for each virtual source. Isotropic phase velocities and 2-psi azimuthal anisotropy and their uncertainties are determined statistically using measurements from different virtual sources. Following the method of Barmin et al. (2001), group velocities are also inverted using all the group travel times that pass quality criteria. The obtained group and phase dispersions of Rayleigh waves are then inverted on a 6 x 6 km2 grid for local 1D piecewise shear wave velocity structures using the procedure of Herrmann (2013). The results agree well with previous observations of Zigone et al. (2015) in the overlapping area. Clear velocity contrasts and low velocity zones are seen for the San Andreas, San Jacinto, Elsinore and Garlock faults. We also find 2-psi azimuthal anisotropy with fast directions parallel to geometrically-simple fault sections. Details and updated results will be presented in the meeting.

  19. Seismicity and Improved Velocity Structure in Kuwait

    NASA Astrophysics Data System (ADS)

    Gok, R.; Rodgers, A.; Al-Enezi, A.

    2005-12-01

    The Kuwait National Seismic Network (KNSN) began operation in 1997 and consists of nine three-component stations (eight short-period and one broadband). Although the region is largely believed to be aseismic, considerable local seismicity is recorded by KNSN. Seismic events in Kuwait are clustered in two main groups, one in the south and another in the north. The KNSN station distribution is able to capture the southern cluster within the footprint of the network but the northern cluster is poorly covered. We have analyzed KNSN recordings of nearly 200 local events to improve understanding of seismic events and crustal structure in Kuwait, performing several analyses with increasing complexity. First, we obtained an optimized one-dimensional (1D) velocity model for the entire region using the KNSN bulletin locations. We observe a consistency of this model with the model obtained from the joint inversion of receiver function and surface wave group velocities. Crustal structure is capped by the thick (~ 7 km) sedimentary rocks of the Arabian Platform and normal velocities for stable continental crust. We then used a double-difference tomography technique (tomoDD) and the optimized 1D model to jointly locate the events and estimate three-dimensional (3D) structure by tomographic inversion. TomoDD is based on hypoDD relocation algorithm and it makes use of both absolute and relative arrival times. We obtained ~1500 absolute P and S arrival times and ~3200 P and S wave arrival time differences. Finally, we calculated Mw's of nearly 100 events using the coda magnitude technique of Mayeda et al., (2003). Although the current studies will not be able to reveal the source of current seismicity in Kuwait, we obtain a considerable amount of improvement in the velocity model and the reduced scatter of travel time residuals relative to the routine KNSN bulletin. The new velocity model and moment magnitudes will be utilized in ground motion prediction and hazard estimate studies

  20. Does the presence of glenoid bone loss influence coracoid bone graft osteolysis after the Latarjet procedure? A computed tomography scan study in 2 groups of patients with and without glenoid bone loss.

    PubMed

    Di Giacomo, Giovanni; de Gasperis, Nicola; Costantini, Alberto; De Vita, Andrea; Beccaglia, Mario A Rojas; Pouliart, Nicole

    2014-04-01

    Coracoid bone graft osteolysis and fibrous union are the principal causes of failure in patients treated with the Latarjet procedure. This study aims to investigate the hypothesis that coracoid bone graft osteolysis is more pronounced in cases without glenoid bone loss, which may be due to a diminished mechanotransduction effect at the bone healing site. We prospectively followed up 34 patients, treated with a mini-plate Latarjet procedure, divided into 2 groups (group A patients had glenoid bone loss >15% and group B patients had no glenoid bone loss). A computed tomography scan evaluation with 3-dimensional reconstruction was then performed on all patients to evaluate coracoid bone graft osteolysis according to our coracoid bone graft osteolysis classification. The computed tomography scan analysis showed a different distribution of osteolysis between group A and group B. The statistical analysis showed a significant difference (P < .01, Bonferroni test) between groups A and B for the following sections: proximal/lateral/superficial, proximal/medial/deep, distal/lateral/superficial, and distal/lateral/deep. On average, the coracoid grafts in group A patients showed less osteolysis than the coracoid grafts in group B patients (39.6% vs 65.1%). The coracoid bone graft underwent much less osteolysis in patients with significant glenoid bone loss (>15%) than in those without it. Because factors of blood supply, compression, and surgical technique were the same for both groups, we believe that the mechanotransduction effect from the humeral head on the graft influences its remodeling. The results of this study suggest that the bone graft part of the Latarjet procedure plays a role in patients with significant coracoid bone loss but much less so when there is no bone loss. Copyright © 2014 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Mosby, Inc. All rights reserved.

  1. Microseismic Velocity Imaging of the Fracturing Zone

    NASA Astrophysics Data System (ADS)

    Zhang, H.; Chen, Y.

    2015-12-01

    Hydraulic fracturing of low permeability reservoirs can induce microseismic events during fracture development. For this reason, microseismic monitoring using sensors on surface or in borehole have been widely used to delineate fracture spatial distribution and to understand fracturing mechanisms. It is often the case that the stimulated reservoir volume (SRV) is determined solely based on microseismic locations. However, it is known that for some fracture development stage, long period long duration events, instead of microseismic events may be associated. In addition, because microseismic events are essentially weak and there exist different sources of noise during monitoring, some microseismic events could not be detected and thus located. Therefore the estimation of the SRV is biased if it is solely determined by microseismic locations. With the existence of fluids and fractures, the seismic velocity of reservoir layers will be decreased. Based on this fact, we have developed a near real time seismic velocity tomography method to characterize velocity changes associated with fracturing process. The method is based on double-difference seismic tomography algorithm to image the fracturing zone where microseismic events occur by using differential arrival times from microseismic event pairs. To take into account varying data distribution for different fracking stages, the method solves the velocity model in the wavelet domain so that different scales of model features can be obtained according to different data distribution. We have applied this real time tomography method to both acoustic emission data from lab experiment and microseismic data from a downhole microseismic monitoring project for shale gas hydraulic fracturing treatment. The tomography results from lab data clearly show the velocity changes associated with different rock fracturing stages. For the field data application, it shows that microseismic events are located in low velocity anomalies. By

  2. The preliminary results: Seismic ambient noise Rayleigh wave tomography around Merapi volcano, central Java, Indonesia

    SciTech Connect

    Trichandi, Rahmantara; Yudistira, Tedi; Nugraha, Andri Dian; Zulhan, Zulfakriza; Saygin, Erdinc

    2015-04-24

    Ambient noise tomography is relatively a new method for imaging the shallow structure of the Earth subsurface. We presents the application of this method to produce a Rayleigh wave group velocity maps around the Merapi Volcano, Central Java. Rayleigh waves group velocity maps were reconstructed from the cross-correlation of ambient noise recorded by the DOMERAPI array which consists 43 broadband seismometers. In the processing stage, we first filtered the observation data to separatethe noise from the signal that dominated by the strong volcanic activities. Next, we cross-correlate the filtered data and stack to obtain the Green’s function for all possible station pairs. Then we carefully picked the peak of each Green’s function to estimate the dispersion trend and appliedMultiple Filter Technique to obtain the dispersion curve. Inter-station group velocity curvesare inverted to produceRayleigh wave group velocity maps for periods 1 to 10 s. The resulted Rayleigh group velocity maps show the interesting features around the Merapi Volcano which generally agree with the previous studies. Merapi-Lawu Anomaly (MLA) is emerged as a relatively low anomaly in our group velocity maps.

  3. The preliminary results: Seismic ambient noise Rayleigh wave tomography around Merapi volcano, central Java, Indonesia

    NASA Astrophysics Data System (ADS)

    Trichandi, Rahmantara; Yudistira, Tedi; Nugraha, Andri Dian; Zulhan, Zulfakriza; Saygin, Erdinc

    2015-04-01

    Ambient noise tomography is relatively a new method for imaging the shallow structure of the Earth subsurface. We presents the application of this method to produce a Rayleigh wave group velocity maps around the Merapi Volcano, Central Java. Rayleigh waves group velocity maps were reconstructed from the cross-correlation of ambient noise recorded by the DOMERAPI array which consists 43 broadband seismometers. In the processing stage, we first filtered the observation data to separatethe noise from the signal that dominated by the strong volcanic activities. Next, we cross-correlate the filtered data and stack to obtain the Green's function for all possible station pairs. Then we carefully picked the peak of each Green's function to estimate the dispersion trend and appliedMultiple Filter Technique to obtain the dispersion curve. Inter-station group velocity curvesare inverted to produceRayleigh wave group velocity maps for periods 1 to 10 s. The resulted Rayleigh group velocity maps show the interesting features around the Merapi Volcano which generally agree with the previous studies. Merapi-Lawu Anomaly (MLA) is emerged as a relatively low anomaly in our group velocity maps.

  4. Ambient seismic noise tomography of Jeju Island, South Korea

    NASA Astrophysics Data System (ADS)

    Lee, S. J.; Rhie, J.; Kim, S.; Kang, T. S.; Kim, Y.

    2015-12-01

    Jeju Island, formed by Cenozoic basaltic eruptions, is an island off the southern coast of the Korean Peninsula. This volcanic island is far from the plate boundaries and the fundamental cause of the volcanic activity in this region is not understood well. To understand the origin of the island, resolving the detailed seismic velocity structures is crucial. Therefore, we applied ambient noise tomography to study the velocity structures of the island. Continuous waveform data recorded at 20 temporary and 3 permanent broad-band seismic stations are used. The group and phase velocity dispersion curves of the fundamental mode Rayleigh waves are extracted from cross-correlograms for 253 station pairs by adopting multiple filter technique. The fast marching method and the subspace method are jointly applied to construct 2-D group and phase velocity maps for periods ranging between 1 and 15 s. 1-D shear wave velocity models and their uncertainties are estimated by the Bayesian technique. The optimal number of the layers are determined at the end of the burn-in period based on the Bayesian Information Criteria (BIC). Final 3-D velocity model of the island is constructed by compiling 1-D models. In our 3-D model, a distinct low velocity anomaly appears beneath Mt. Halla from surface to about 6 km depth. The surficial extent of the anomaly is more or less consistent with the surface geologic feature of the third-stage basaltic eruption reported by previous studies but the vertical extension of the anomaly is not well constrained. To improve the velocity model, especially enhance the vertical resolution of the anomaly, we will apply joint analysis of the surface wave dispersions and teleseismic receiver functions. The improved model will provide more information to infer the tectonic or volcanic implications of the anomaly and unravel the origin of the strange volcanic island in South Korea.

  5. Trans-dimen