Imaging Salt/sediment Interfaces with Three-component VSP data, Using Ray-based Interferometry-like Processes

This thesis addresses the fundamental problem of determining the radial and lateral structure of the earth's interior using body wave observations. My approach is a cautious one, involving detailed analysis of a substantial data set in which I attempt to isolate the contributions from radial and lateral structure in both the upper and lower mantles. This is an elusive task, as I am concerned with the 2 or 3% fluctuations about standard earth models, which produce rather subtle effects on teleseismic signals. However, this is the level of precision to which the three dimensional structure of the earth must be determined if we are to map the dynamical and compositional configuration of the earth. Studies similar to those described here cannot be conducted on a detailed global basis, given the intrinsic limitations due to station and earthquake distribution, so I have repeatedly emphasized the qualitative implications of my results, as they probably provide a representative sampling of the subtle, but significant heterogeneity of the earth. The topics addressed in the following work appear unrelated at first glance, ranging from determination of the detailed shear velocity structure at the base the mantle to variations in attenuation and velocity structure of the upper mantle. However, the data set used throughout is largely the same, and this in itself indicates the need to consider all of the complexity discussed herein for future progress to be made in mapping the three dimensional structure of the earth with a high level of confidence. The first chapter of the thesis presents results of a waveform analysis of transversely polarized SH signals that propagate through the lowermost mantle. The waveforms of these phases show clear interference patterns due to interaction with a discontinuous shear velocity increase about 280 km above the core-mantle boundary. This discontinuity, which has not been detected previously, is manifested in signals sampling three widely separated portions of the lower mantle, and hence is a good candidate for a global radial earth structure. Very detailed inspection of the signals reveals evidence for lateral variations in the depth of the discontinuity, which provides a procedure by which to map the structure of the D region in detail. Analysis of the relative amplitudes of SH and ScSH signals reveals that the velocity gradient above the core boundary is consistent with the smoothly varying gradients in most gross earth models, but evidence for local high velocity gradients at the base of the mantle is detected in ScSV signals. Chapter II presents a travel time analysis of the same data set used in Chapter I, which was motivated by the observation of large amplitude and travel time anomalies in the S and ScS data. An emphasis is placed on isolating the portions of the S and ScS paths which are anomalous. A strong empirical case is made for the existance of localized regions with scale lengths of 1000 to 2000 km and 2% velocity anomalies within the lower mantle at depths from 1000 to 2700 km. The long period signals traversing these regions show as much as a factor of 2 amplitude enhancement or diminution. This result demonstrates that both amplitude and travel time anomalies are induced by lateral structure in the portion of the mantle assumed to be homogeneous in most seismological studies. The third chapter is an analysis of the influence of upper mantle variations in attenuation, velocity structure and receiver structure on the S and ScS signals analyzed in the lower mantle studies. These variations contaminate and complicate the interpretation of any data set used to study deeper earth structure. Along with evidence for very strong and abrupt variations in upper mantle properties, results are presented which indicate the inadequacy of assumptions that are frequently made about the nature of long period body-wave receiver functions.

Quantifying errors in travel time and cost by latent variables

Detailed seismic modeling and imaging of Earth's deep interior is providing key information about lower-mantle structures and processes, including heat flow across the core-mantle boundary, the configuration of mantle upwellings and downwellings, phase equilibria and transport properties of deep mantle materials, and mechanisms of core-mantle coupling. Multichannel seismic wave analysis methods that provide the highest-resolution deep mantle structural information include network waveform modeling and stacking, array processing, and 3D migrations of P- and S-wave seismograms. These methods detect and identify weak signals from structures that cannot be resolved by global seismic tomography. Some methods are adapted from oil exploration seismology, but all are constrained by the source and receiver distributions, long travel paths, and strong attenuation experienced by seismic waves that penetrate to the deep mantle. Large- and small-scale structures, with velocity variations ranging from a fraction of a percent to tens of percent, have been detected and are guiding geophysicists to new perspectives of thermochemical mantle convection and evolution.

<p>Seismic anisotropy across the Hikurangi subduction zone measured from shear-wave splitting exhibits strong lateral changes over distances of about 250 km. Teleseismic S-phases show trench-parallel fast polarisations with increasing delay times across the forearc and arc region. In the arc region, delay times reach up to 4.5 s, one of the largest delay times measured in the world. Such large delay times suggest strong anisotropy or long travel paths through the anisotropic regions. Delay times decrease systematically in the backarc region. In contrast, local S-phases exhibit a distinct change from trench-parallel fast orientations in the forearc to rench-perpendicular in the backarc, with average delay times of 0.35 s. In the far backarc, no apparent anisotropy is observed for teleseismic S-phases. The three different anisotropic regions across the subduction zone are interpreted by distinct anisotropic domains at depth: 1) In the forearc region, the observed "average" anisotropy (about 4%) is attributed to trench-parallel mantle flow below the slab with possible contributions fromanisotropy in the slab. 2) In the arc region, high (up to 10%) frequency dependent anisotropy in the mantle wedge, ascribed to melt, together with the sub-slab anisotropy add up to cause the observed high delay times. 3) In the far backarc region, the mantle wedge dynamic ends. The apparent isotropy must be caused by different dynamics, e.g. vertical mantle flow or small-scale convection, possibly induced by convective removal of thickened lithosphere. The proposed hypothesis is tested using anisotropicwave propagation in two-dimensional finite difference models. Large-scale models of the subduction zone (hundreds of kilometres) incorporating the proposed anisotropic domains of the initial interpretation result in synthetic shear-wave splittingmeasurements that closely resemble all large-scale features of real data observations across the central North Island. The preferred model constrains the high (10%) anisotropy to the mantle wedge down to about 100 kmunder the CVR, bound to the west by an isotropic region under the western North Island; the slab is isotropic and the subslab region has average (3.5%) anisotropy, down to 300 km. This model succeeds in reproducing the constant splitting parameters in the forearc region, the strong lateral changes across the CVR and the apparent isotropy in the far backarc region, as well as the backazimuthal variations. The influence of melt on seismic anisotropy is examined with different small-scale (tens of kilometres) analytical modelling approaches calculating anisotropy due to melt occurring in inclusions, cracks or bands. Conclusions are kept conservative with the intention not to over-interpret the data due to model complexities. The models show that seismic anisotropy strongly depends on the scale of inclusions and wavelengths. Frequency dependent anisotropy for local and teleseismic shear-waves, e.g. for frequency ranges of 0.01-1Hz can be observed for aligned inclusions on the order of tens of meters. To test the proposed frequency dependence in the recorded data, two different approaches are introduced. Delay times exhibit a general trend of -3 s/Hz. A more detailed analysis is difficult due to the restricted frequency content of the data. Future studies with intermediate frequency waves (such as regional S-phases) are needed to further investigate the cause of the discrepancy between local and teleseismic shear-wave splitting. An additional preliminary study of travel time residuals identifies a characteristic pattern across central North Island. Interpretation highlights the method as a valuable extension of the shear-wave splitting study and suggests a more detailed examination to be conducted in future.</p>

An improved method for noninvasive measurement of the local velocity of arterial pulse wave propagation by an echo-tracking-based ultrasound system is described. A data acquisition image interface was programmed in the ultrasound machine simultaneously to record M-mode ultrasound signals at two locations of a given distance apart along an artery. The selections of measurement sites, separation, and time resolution were performed on the control interface. The temporal sampling frequency could be as high as 10 kHz. The displacements of the blood vessel wall along the time axis were calculated from the M-mode signals by cross-correlation of the radio-frequency data and the distension waveforms were obtained. The temporal separation of the feet of the distension curves from the two measurement locations was derived to give the travel time of the pulse wave. Measurements were made in vivo on human carotid arteries. The pulse wave velocities measured from four volunteers were from 4.1 to 7.2 m/s with coefficients of variation from 5.9 to 29.5%. Some of the factors contributing to the variation in measured values of the velocity are discussed. The method is simple to implement and should be suitable for clinical research into local pulse wave velocity.

This paper considers the effect of continuous convection from small sources of buoyancy on the properties of the environment when the region of interest is bounded. The main assumptions are that the entrainment into the turbulent buoyant region is at a rate proportional to the local mean upward velocity, and that the buoyant elements spread out at the top of the region and become part of the non-turbulent environment at that level. Asymptotic solutions, valid at large times, are obtained for the cases of plumes from point and line sources and also periodically released thermals. These all have the properties that the environment is stably stratified, with the density profile fixed in shape, changing at a uniform rate in time at all levels, and everywhere descending (with ascending buoyant elements).The analysis is carried out in detail for the point source in an environment of constant cross-section. Laboratory experiments have been conducted for this case, and these verify the major predictions of the theory. It is then shown how the method can be extended to include more realistic starting conditions for the convection, and a general shape of bounded environment. Finally, the model is applied quantitatively to a variety of problems in engineering, the atmosphere and the ocean, and the limitations on its use are discussed.

This paper discusses the application of one of the Discrete Mathematics materials, namely Graph Theory, in determining the fastest route from Subang City, more precisely from Subang Pusakanagara, Subang to Cirebon City. The fastest path is the route taken by considering the minimum travel time from one place to another. There are various ways to determine the minimum travel path, but the goal is the same, namely to find a travel path with the minimum travel time. The research process begins with formulating a problem using Graph Theory with the help of the Google Maps application and the experiences of the researchers. This Google Maps application is very useful when traveling long distances but want to use the path with minimal travel time. After formulating the problem, it is continued with the implementation of the Weighted Average Method and ends with the Floyd Warshall Algorithm. The result of this study is to find the fastest path from the starting point, namely Subang Pusakanagara to the end point, namely Cirebon City.

Velocity anisotropy caused by fine layering has a strong effect on the travel paths at large vertical offsets in crosshole seismic data. This effect must be considered in seismic waveform tomography, so that the inversion procedure can match the waveforms in real data. In this paper, we propose to properly take into account this anisotropic effect in two stages. First, we invert for the anisotropy parameter simultaneously with the (horizontal) velocity in travel time tomography. Then we incorporate this estimated anisotropy parameter model in the waveform simulation during waveform tomography, to refine the velocity image. When considering this anisotropic effect, far-offset data are properly used in the inversion, then both travel time and waveform tomography may have a better ray coverage, producing a velocity image with a higher resolution.

Understanding of three-dimensional separation around ships on straight course or under maneuvering is important for developing next generation ships with improved performance in extreme maneuvers. The separation causes vortex-dominated flows in which the vortex breakdowns at sufficiently high drift angles. The object of this study is to identify and analyze the vortical structures and instabilities around high-speed Delft catamaran and validate URANS and DES solver CFDShip-IowaV4 in collaboration with NATO AVT 183 (Reliable Prediction of Separated Flow Onset and Progression for Air and Sea Vehicles). The computations are performed at wide ranges of Froude numbers (Fr) and drift angels (B). The CFD results are compared to EFD data provided from different facilities including BSHC, INSEAN and Delft. The data included motions, integral variables, wave profile and SPIV measurements. Three sets of CFD simulations are performed: (1) hull free to heave and pitch with 0.3<Fr<0.77 and 0<B<30 with URANS, (2) hull fixed at dynamic heave and pitch conditions with Fr=0.4, 0.5 and B=6, 9 with DES, (3) hull fixed at even keel condition with Fr=0.5 and B=6 with DES, and (4) hull free to heave and pitch with Fr=0.3 and B=24 with URANS and DES. Hydrodynamic forces, moments and motions for B=0 are compared to the experimental results from different facilities. In general, good agreement between experiments conducted at the Delft and INSEAN facilities, and CFD are achieved at B=0 with forces and motions errors less than 13%D. Although there is a good agreement on the force between CFD and BSHC experiments, the motions show large error with more than 30%D for heave and pitch. The difference in the experimental results could be attributed to the difference in non-dimensional depth in the experiment. For 0<B<10, CFD results are compared to the BSHC experimental results. The error for forces (X, Y) and moment (N) are less than 10%D. However, the error for the motions is 28%D and 36%D for heave and pitch respectively. The flow field around the catamaran is analyzed, including detailed study on vortex structures and wave elevations. This information is used to design the grid for DES simulations for cases (2), (3), and (4). The local mean velocity components are compared to the SPIV results from the INSEAN facility. Verification study shows oscillatory convergence for X and Y while monotonic divergence for N. The mean errors of the local velocity components are all less than 5%D. Although the LES was activated in the vortex regions, the turbulence was not fully resolved. Also, the verification and validation studies of forces and moments on demihulls, motions and wave…

In many engineering applications (e.g. helicopters, turbines, compressors), lifting surfaces experience unsteady motion or are perturbed by unsteady incoming flows. Horizontal axis wind turbine rotors experience large time dependent variations in angle-of-attack as a result of control input angles, blade flapping, structural response and wake inflow. In addition, the blade sections encounter substantial periodic variations in local velocity and sweep angle. Thus, the unsteady aerodynamic behaviour of the blade sections must be properly understood to enable accurate predictions of the air loads and aero elastic response of the rotor system.

The propagation time stability of an acoustic path traveling from the ocean surface to the bottom is predicted by a ray-path analysis. The sound-velocity profile as a function of horizontal distance is derived from towed thermistor-chain data, with a representative stable structure assumed between the thermistor-chain data and the bottom. The fluctuations of travel time at various points along the ship track due to sound-velocity profile variations are predicted by calculating the ray path travel time. The spectrum of these fluctuations shows a slope of K−3, where K is the spatial wavenumber, for K in the region of 2×10−4&amp;lt;K &amp;lt;2×10−3. Measurement noise due to the 0.05°C resolution of the thermistor-chain data exceeds the predicted travel-time fluctuation for K&amp;gt;2×10−3.

A longer, wider and more complicated change in the travel path is put forward to adapt to the rapidly increasing expansion of metropolises in the field of urban travel. Urban travel requires higher levels of sustainable urban transport. Therefore,this paper explores the circuity characteristics of urban travel and investigates the temporal relationship between time and travel circuity and the spatial relationship between distance and travel circuity to understand the efficiency of urban travel. Based on Guangzhou Taxi-GPS big data, travel circuity is considered in this paper to analyze the circuity spatial distribution and strength characteristics of urban travel in three types of metropolitan regions, including core areas, transition areas and fringe areas. Depending on the different attributes of the three types, the consistency and dissimilar characteristics of travel circuity and influencing factors of travel circuity in metropolises are discussed. The results are shown as follows: (1) by observing the temporal andspatial distribution of travel circuity, it can be found that peaks and troughs change with time, and travel circuity of transition areas is higher than other areas during the peak period. When travelling in these three regions, travel circuity spatial distribution is consistent, which is the core-periphery distribution. When travelling among these three regions, travel circuity spatial distribution is distinct; (2) by analyzing the relationship between time and distance of travel and travel circuity, it can be seen that the shorter the travel time or travel distance, the greater the travel circuity, resulting in a lower travel efficiency; (3) the influence of six factors, including population, road and public transportation, on travel circuity is significant. Whether it is the origin point or destination point, when its location is closer to the city center and the station density of grid is lower, the travel circuity is higher.

Flow rate measurements are a common topic for process monitoring in chemical engineering and food industry. To achieve the requested low uncertainties of 0:1% for flow rate measurements, a precise measurement of the shear layers of such flows is necessary. The Laser Doppler Velocimeter (LDV) is an established method for measuring local flow velocities. For exact estimation of the flow rate, the flow profile in the shear layer is of importance. For standard LDV the axial resolution and therefore the number of measurement points in the shear layer is defined by the length of the measurement volume. A decrease of this length is accompanied by a larger fringe distance variation along the measurement axis which results in a rise of the measurement uncertainty for the flow velocity (uncertainty relation between spatial resolution and velocity uncertainty). As a unique advantage, the laser Doppler profile sensor (LDV-PS) overcomes this problem by using two fan-like fringe systems to obtain the position of the measured particles along the measurement axis and therefore achieve a high spatial resolution while it still offers a low velocity uncertainty. With this technique, the flow rate can be estimated with one order of magnitude lower uncertainty, down to 0:05% statistical uncertainty. 1 And flow profiles especially in film flows can be measured more accurately. The problem for this technique is, in contrast to laboratory setups where the system is quite stable, that for industrial applications the sensor needs a reliable and robust traceability to the SI units, meter and second. Small deviations in the calibration can, because of the highly position depending calibration function, cause large systematic errors in the measurement result. Therefore, a simple, stable and accurate tool is needed, that can easily be used in industrial surroundings to check or recalibrate the sensor. In this work, different calibration methods are presented and their influences to the measurement uncertainty budget of the sensor is discussed. Finally, generated measurement results for the film flow of an impinging jet cleaning experiment are presented.

view Abstract Citations (66) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Velocity Fields around Rich Clusters of Galaxies Villumsen, J. V. ; Davis, M. Abstract The authors study the nature of the velocity field around large clusters in Ω = 1 cosmological N-body simulations that have initial conditions which produce large-scale structure reasonably consistent with observations. The purpose is to test the accuracy of the spherical infall models commonly used to measure the mass of the Virgo supercluster and to characterize the nature of the deviations from simple spherical infall. The use of a spherical model for the Virgocentric flow as a measure of Ω is shown to be subject to large systematic and random errors. A much better test is to use a local criterion, noting that local peculiar velocity tracks the direction and amplitude of the local peculiar gravitational force extremely well. Publication: The Astrophysical Journal Pub Date: September 1986 DOI: 10.1086/164521 Bibcode: 1986ApJ...308..499V Keywords: Computational Astrophysics; Galactic Clusters; Many Body Problem; Velocity Distribution; Boundary Value Problems; Cosmology; Gravitational Effects; Mass Distribution; Virgo Galactic Cluster; Astrophysics; COSMOLOGY; GALAXIES: CLUSTERING; NUMERICAL METHODS full text sources ADS | data products SIMBAD (2)

Using seismic body and surface waves, the velocity structure of the Earth's mantle is determined with the emphasis on regions of anomalous variations (so-called ‘discontinuities’). In the upper mantle, the interpretation of Rayleigh and Love wave dispersion curves yields shear velocity profiles with discontinuities at depths 350 km and 700 km, and a low-velocity zone extending to 350km. In the lower mantle P-velocity profile is determined from dt/dΔ measurements using large aperture seismic array and travel times from Long Shot nuclear explosion for the Japan-Kuriles-Aleutian-Montana path. The velocity structure shows anomalous gradients or ‘discontinuities’ at depths 700, 1200 and 1900km, indicating that the lower mantle is not homogeneous. Lateral variations of the velocity structures are investigated. For the upper mantle studies the Earth is divided into three regions: oceanic areas, continental shields, and tectonic zones. Pure path phase velocities of Love waves are extracted from the composite dispersion data. The pure path shear velocity profiles obtained from these data are characterized by lower velocities under the oceans in the uppermost portion of the mantle. Shields have the highest velocities. These velocity differences are interpreted in terms of temperature variations. At a depth of 110 km the temperature of the oceanic mantle is higher (by 100–500° C depending on the temperature coefficient of the velocity) than that of the mantle under the shields. The presence of lateral heterogeneities in the mantle is demonstrated qualitatively by the differences of dt/dΔ vs Δ curves for two separate paths. Undulations of the geoid as determined from satellite observations are investigated for determining the sources of the anomalies. It is concluded that the main sources of lateral density variations must be in the mantle at depths greater than about 100km.