Reflection shear‐wave data collected near the principal axes of azimuthal anisotropy

Geophysics ◽  
1990 ◽  
Vol 55 (2) ◽  
pp. 147-156 ◽  
Author(s):  
H. B. Lynn ◽  
L. A. Thomsen
Keyword(s):  
Reflection Coefficient ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Azimuthal Anisotropy ◽  
Display Time ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Reflection Amplitude ◽  
Principal Axes

The presence of vertically oriented fractures and/or unequal horizontal stresses has created an azimuthally anisotropic earth, in which shear‐wave (SH) data collected along the principal axes of the anisotropy display time and reflection amplitude anomalies. Amoco shot two crossing shear‐wave (SH) lines that were approximately parallel to the orthogonal principal axes of the azimuthal anisotropy. At the tie point, these crossing SH lines display a time‐variant mis‐tie. The tie point also displays reflection‐coefficient anomalies, attributable to azimuthally dependent shear‐wave velocities. Field mapping documented a set of fractures striking N69E which are approximately parallel to the line that exhibited greater traveltimes. Time‐variant mis‐ties and reflection coefficient anomalies are two of the seismic responses theoretically expected of an azimuthally anisotropic earth, i.e., one in which the shear‐wave velocity depends upon the polarization azimuth of the shear wave.

scholarly journals B mode ultrasonography and elastography in the evaluation of the pectineus muscle in dogs with hip dysplasia

2020 ◽  
Vol 44 (5) ◽  
pp. 1142-1149
Author(s):  
Pedro Paulo ROSSIGNOLI ◽  
Marcus Antônio Rossi FELICIANO ◽  
Bruno Watanabe MINTO ◽  
Marjury Cristina MARONEZI ◽  
Ricardo Andres Ramirez USCATEGUI ◽  
...  
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Hip Dysplasia ◽  
Tissue Stiffness ◽  
Sonographic Appearance ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Arfi Elastography ◽  
Healthy Dogs

The goal of this study was to describe and compare B mode and elastographic characteristics of the pectineus muscle of healthy dogs with dysplastic dogs. Thirty-one dogs (62 limbs) with hip dysplasia and 17 nondysplastic dogs (34 limbs) were evaluated. The hip dysplasia score was defined according to the Fédération Cynologique Internationale. Using B mode, echotexture and echogenicity of different regions of the pectineus muscle were evaluated. By means of ARFI elastography, qualitative (elastogram) and quantitative (shear wave velocity) tissue stiffness was assessed. B mode findings demonstrated a hyperechoic and heterogeneous pattern of the pectineus tissue in dogs with hip dysplasia, with compromised muscular delimitation and loss of its normal sonographic appearance, indicating the disease (P < 0.001). In the elastogram, it was observed that dogs with hip dysplasia showed less deformable pectineus muscle, with red colors (rigid). In quantitative evaluation, the different regions evaluated presented similar shear wave velocities; in dysplastic patients, shear wave velocities were higher compared to nondysplastic animals, with values higher than 2.85 m/s being strong indicators of the disease. Values of shear wave velocity were also influenced by the grade of dysplasia and age of the patients; however, there was no correlation with the depth of the evaluated area or body weight. It was concluded that pectineus muscle in dogs with hip dysplasia presents B mode and elastographic changes when compared to normal animals, demonstrating that these techniques might aid the evaluation of diseased dogs.

Mapping Fundamental-Mode Site Periods and Amplifications from Thick Sediments: An Example from the Jackson Purchase Region of Western Kentucky, Central United States

2021 ◽  
Author(s):  
Yichuan Zhu ◽  
Zhenming Wang ◽  
N. Seth Carpenter ◽  
Edward W. Woolery ◽  
William C. Haneberg
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Fundamental Mode ◽  
Site Response ◽  
Velocity Profiles ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Jackson Purchase ◽  
Western Kentucky

ABSTRACT V S 30 is currently used as a key proxy to parameterize site response in engineering design and other applications. However, it has been found that VS30 is not an appropriate proxy, because it does not reliably correlate with site response. Therefore, the VS30-based National Earthquake Hazards Reduction Program site maps may not capture regional site responses. In earthquake engineering, site resonance, which can be characterized by the fundamental mode with a site period (Tf) and its associated peak amplification (A0), is the primary site-response concern. Mapping Tf and A0 is thus essential for accurate regional seismic hazard assessment. We developed a 3D shear-wave velocity model for the Jackson Purchase Region of western Kentucky, based on shear-wave velocity profiles interpreted from seismic reflections and refractions, mapped geologic units, and digital-elevation-model datasets. We generated shear-wave velocity profiles at grid points with 500 m spacing from the 3D model and performed 1D linear site-response analyses to obtain Tf and A0, which we then used to construct contour maps for the study area. Our results show that Tf and A0 maps correlate with the characteristics of regional geology in terms of sediment thicknesses and their average shear-wave velocities. We also observed a strong dependency of A0 on bedrock shear-wave velocities. The mapped Tf and A0 are consistent with those estimated from borehole transfer functions and horizontal-to-vertical spectral ratio analyses at broadband and strong-motion stations in the study area. Our analyses also demonstrate that the depth to bedrock (Zb) is correlated to Tf, and the average sediment shear-wave velocity (VS-avg) is correlated to A0. This implies that Zb and VS-avg may be considered as paired proxies to parameterize site resonance in the linear-elastic regime.

Shear‐wave logging to enhance seismic modeling

Geophysics ◽  
1991 ◽  
Vol 56 (12) ◽  
pp. 2129-2138 ◽  
Author(s):  
M. A. Payne
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Field Data ◽  
Compressional Wave ◽  
Oil Sand ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Amplitude Versus Offset ◽  
Amplitude Versus

In an effort to understand better the amplitude variation with offset for reflections from an oil sand and the sensitivity of the AVO response to shear‐wave velocity variations, I studied synthetic and field gathers collected from an onshore field in the Gulf of Mexico basin. A wave‐equation‐based modeling program generated the synthetic seismic gathers using both measured and estimated shear‐wave velocities. The measured shear‐wave velocities came from a quadrupole sonic tool. The estimated shear‐wave velocities were obtained by applying published empirical and theoretical equations which relate shear‐wave velocities to measured compressional‐wave velocities. I carefully processed the recorded seismic data with a controlled‐amplitude processing stream. Comparison of the synthetic gathers with the processed field data leads to the conclusion that the model containing the measured shear‐wave velocities matches the field data much better than the model containing the estimated shear‐wave velocities. Therefore, existing equations which relate shear‐wave velocities to compressional‐wave velocities yield estimates which are not sufficiently accurate for making quantitative comparisons of synthetic and field gathers. Even small errors in the shear‐wave velocities can have a large impact on the output. Such errors can lead to an incomplete and perhaps inaccurate understanding of the amplitude‐versus‐offset response. This situation can be remedied by collecting shear‐wave data for use in amplitude‐versus‐offset modeling, and for building databases to generate better shear‐wave velocity estimator equations.

ULTRASONIC SHEAR‐WAVE VELOCITIES IN ROCKS SUBJECTED TO SIMULATED OVERBURDEN PRESSURE AND INTERNAL PORE PRESSURE

Geophysics ◽  
1965 ◽  
Vol 30 (1) ◽  
pp. 117-121 ◽  
Author(s):  
B. S. Banthia ◽  
M. S. King ◽  
I. Fatt
Keyword(s):  
Hydrostatic Pressure ◽  
Pore Pressure ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Overburden Pressure ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
The Matrix ◽  
Internal Pore

Change in shear‐wave velocity for four dry sedimentary rocks has been studied as a function of the variation of both external hydrostatic pressure and internal pore pressure in the range 0 to 2,500 psi. The experimental method employs a beam of ultrasonic energy passing through a liquid in which a copper‐jacketed parallel‐sided slab of rock is rotated. The shear‐wave velocity is calculated from the laws of refraction and reflection of waves at a liquid‐solid boundary applied to the angle at which minimum energy is transmitted. The variation of shear‐wave velocity with pressure has been found to be a function of net overburden pressure, [Formula: see text], where [Formula: see text] hydrostatic pressure on the jacketed sample, [Formula: see text] pore pressure and n = a pressure‐dependent factor less than unity. The values of n at several differential pressures were chosen to yield a smooth curve passing through the displaced data points when the shear‐wave velocities were plotted as a function of net overburden pressure. Using the n values so obtained, the matrix compressibility [Formula: see text] for two of the sandstones has been calculated from the relation [Formula: see text]. The bulk compressibility [Formula: see text] for these two rocks had previously been obtained experimentally as a function of differential pressure. The values obtained for the matrix compressibility are in the range expected from a knowledge of the grain and cementing materials for these sandstones.

scholarly journals Investigation of fabric evolution using bidirectional shear wave velocity measurements

2019 ◽  
Vol 92 ◽  
pp. 03008
Author(s):  
Kazem Fakharian ◽  
Farzad Kaviani Hamedani ◽  
Iman Parandian ◽  
Morteza Jabbarpour Aghdam
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Velocity Measurements ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Fabric Evolution ◽  
Undrained Conditions

In order to characterise fabric evolution, continuous bidirectional shear wave velocity measurements are performed in vertical and horizontal directions (V&H) on triaxial soil specimens during shearing in which two horizontal piezo-electrics were mounted on samples using a new measurement technique. The specimens are prepared by wet tamping method and then subjected to strain-controlled compressional shearing under drained and undrained conditions. The shear wave velocities of all drained specimens initially increased as the loading commenced and then converged to a unique state in both horizontal and vertical directions. The shear wave velocity of undrained specimens on the other hand, for both horizontal and vertical directions initially decreased due to the rising of the excess pore water pressure and then gradually approached a unique shear wave velocity like drained specimens. The fabric condition or stiffness in V&H directions of all the examined drained and undrained specimens at critical state are found to be unique.

Shear-Wave Velocity of Surficial Geologic Sediments in Northern California: Statistical Distributions and Depth Dependence

2005 ◽  
Vol 21 (1) ◽  
pp. 161-177 ◽  
Author(s):  
Thomas L. Holzer ◽  
Michael J. Bennett ◽  
Thomas E. Noce ◽  
John C. Tinsley
Keyword(s):  
Shear Wave ◽  
San Francisco ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
San Francisco Bay ◽  
Geometric Mean ◽  
Depth Dependence ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Coefficients Of Variation

Shear-wave velocities of shallow surficial geologic units were measured at 210 sites in a 140-km2 area in the greater Oakland, California, area near the margin of San Francisco Bay. Differences between average values of shear-wave velocity for each geologic unit computed by alternative approaches were in general smaller than the observed variability. Averages estimated by arithmetic mean, geometric mean, and slowness differed by 1 to 8%, while coefficients of variation ranged from 14 to 25%. With the exception of the younger Bay mud that underlies San Francisco Bay, velocities of the geologic units are approximately constant with depth. This suggests that shear-wave velocities measured at different depths in these surficial geologic units do not need to be normalized to account for overburden stress in order to compute average values. The depth dependence of the velocity of the younger Bay mud most likely is caused by consolidation. Velocities of each geologic unit are consistent with a normal statistical distribution. Average values increase with geologic age, as has been previously reported. Velocities below the water table are about 7% less than those above it.

scholarly journals Evaluation of the possibilities of shear wave elastography for differentiation of lymphomatous and reactive changes of superficial lymph nodes

2020 ◽  
Vol 15 (1) ◽  
pp. 59-64
Author(s):  
E. V. Kovaleva ◽  
T. Yu. Danzanova ◽  
G. T. Sinyukova ◽  
E. A. Gudilina ◽  
P. I. Lepedatu ◽  
...  
Keyword(s):  
Differential Diagnosis ◽  
Lymph Nodes ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Ultrasound Elastography ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Reactive Changes ◽  
Hodgkin's Lymphomas

Objective: to evaluate the possibilities of ultrasound elastography for differentiation of reactive and lymphomatous superficial lymph nodes (LN).Materials and methods. The prospective study included 138 patients with enlarged superficial LN. Based on a previous histological examination, patients were divided into two groups: 1st group (n = 108) – patients with non-Hodgkin’s lymphomas and Hodgkin’s lymphoma; 2nd (n = 30) – patients with reactive (inflammatory) changes in superficial LN. All patients underwent ultrasound elastography of the enlarged LN using ARFI technology.Results. According to the results of ultrasound elastography, the average, minimum, and maximum shear wave velocities for enlarged LN in lymphoma (1st group) were 2.616 ± 0.684; 1.980 ± 0.557 and 3.351 ± 0.987 m / s, respectively; for LN with reactive changes (2nd group) – 1.704 ± 0.223; 1.414 ± 0.209 and 2.027 ± 0.261 m / s, respectively. Thus, the average, minimum, and maximum values of shear wave velocities significantly different between the groups (p ˂0.001). The cut off values of the average shear wave velocity in the differential diagnosis of lymphoma and hyperplasia are determined at the level of 2.05 m / s, with a sensitivity of 88.5 %, specificity of 100 %, and AUC of 0.942 (p ˂0.001).Conclusion. Ultrasound elastography demonstrated statistically significant differences in shear wave velocity in the enlarged superficial LN in lymphoma and in inflammatory processes that can be used as a preliminary non-invasive differential diagnosis of enlarged superficial LN in these conditions. 

A further comparison of shear-wave velocities

1982 ◽  
Vol 19 (4) ◽  
pp. 506-507 ◽  
Author(s):  
T. J. Larkin ◽  
P. W. Taylor
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Laboratory Apparatus ◽  
Wave Source ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Seismic Tests ◽  
Sample Disturbance

In a previous paper by the same authors the values of the shear-wave velocity in natural soils found from laboratory tests were compared with wave velocities measured in situ. Dynamic free-vibration torsion tests were carried out in the laboratory on undisturbed 150 × 75 mm soil samples. Downhole seismic tests were performed at the site to measure the velocity of propagation of low strain shear waves from a surface wave source. Differences between laboratory and field values of the shear-wave velocity were considered to be due to sample disturbance. Further work has established that, provided system compliance in the laboratory apparatus is allowed for, laboratory and field values agree reasonably well. The test results are analysed again with account being taken of the stiffness of the laboratory apparatus.

scholarly journals The influence of acute physical effort on liver stiffness estimation using Virtual Touch Quantification (VTQ). Preliminary results.

2016 ◽  
Vol 18 (2) ◽  
pp. 151 ◽  
Author(s):  
Mariana M Gersak ◽  
Erich Sorantin ◽  
Jana Windhaber ◽  
Sorin M Dudea ◽  
Michael Riccabona
Keyword(s):  
Blood Flow ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Liver Blood Flow ◽  
Liver Stiffness ◽  
Physical Effort ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
The Mean

Aim: Food intake and acutely decompensated cardiac failure may impair liver stiffness estimations, mainly because these methods are influenced by liver blood flow variation encountered in these conditions. It is well known that also during physical effort liver blood flow changes, due to the redistribution of blood flow mainly to the skeletal muscles. The aim of this study is to assess the change of liver shear- wave velocities immediately after cessation of an acute physical effort. A secondary aim was to find the proper timing for accurate liver stiffness estimation after physical exhaustion. Material and methods: Liver shear-wave velocities were measured using virtual touch quantification (VTQ) in seven apparently healthy volunteers, in fasting conditions. All subjects underwent a complete abdominal ultrasound study, including the liver VTQ. Then, all subjects performed a spiroergometry and thereafter, another series of three liver shear-wave velocity measurements were performed: immediately after spiroergometry, five min, and ten min after spiroergometry, respectively. Results: Before spiroergoemetry, the mean liver shear-wave velocity was 1.05±0.12 m/sec. Immediately after spiroergometry, mean liver shear-wave velocities increased significantly, measuring 1.34±0.16 m/sec (p <0.01). The mean liver shear-wave velocities at five and ten minutes after exhausting were 1.23±0.14 m/sec and 1.05±0.11 m/sec respectively. Conclusions: Liver stiffness estimation using VTQ was influenced by acute physical exercise in our study group. Despite the small number of subjects, the preliminary results show that if patients had done physical effort before VTQ elastography, they should rest at least ten minutes before reliable liver stiffness estimations can be performed.

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