SCATTERING OF SHEAR WAVES BY SPHERICAL OBSTACLES

Geophysics ◽  
1959 ◽  
Vol 24 (2) ◽  
pp. 209-219 ◽  
Author(s):  
Leon Knopoff
Keyword(s):  
Diffraction Pattern ◽  
Poisson’S Ratio ◽  
Wave Length ◽  
Shear Waves ◽  
Scattered Wave ◽  
Phase Shifts ◽  
The Other ◽  
Poisson's Ratio ◽  
S Waves

The problem of the scattering of plane S waves by a perfectly rigid, infinitely dense sphere is formulated. Calculations are made for the case in which the medium outside the sphere has a Poisson’s ratio of [Formula: see text]. The range of sizes of obstacles used in the calculations includes radii very small compared with the wave length and radii comparable to the wave length. The scattered wave motions include a P mode and two S modes. One of the S modes has a formal correspondence to the SH mode of plane seismology; the other corresponds to the SV mode. At large distances from the obstacle the scattered P and S fields are computed together with the phase shifts in time occurring in all the components. For small obstacles, the scattered azimuthal S component is circularly symmetric; the scattered meridional S component diffraction pattern is generally elongated in the direction of propagation; the scattered P component is generally broadside to the direction of propagation.

scholarly journals Relative amplitudes of P and S waves as a mantle reconnaissance tool

1969 ◽  
Vol 59 (3) ◽  
pp. 1189-1200
Author(s):  
John R. McGinley ◽  
Don L. Anderson
Keyword(s):  
Travel Time ◽  
Upper Mantle ◽  
Poisson’S Ratio ◽  
Basin And Range ◽  
The Other ◽  
Poisson's Ratio ◽  
P Waves ◽  
S Waves ◽  
High Attenuation ◽  
Short Period

abstract The unified magnitude, the ratio of the amiplitudes of S to P waves, and travel-time residuals were compiled from published data for the five Seismological Observatories, TFO, UBO, BMO, WMO and CBO. Using one of the stations as a reference, a relative measure of the above quantities was calculated for each of the other stations for each of a number of earthquakes. The stations in the Basin and Range Province are consistent with a markedly higher attentuation of P waves and a high attenuation of S relative to P when compared to the other stations. This latter observation indicates a high Poisson's ratio in the mantle under the Basin and Range. The delay times to these stations are also consistent with the high Poisson's ratio and with a low-velocity upper mantle. The ratio of the amplitudes of long-period S waves to short-period P waves varies by a factor of 4 among these stations. BMO, in eastern Oregon, has a high S/P amplitude ratio compared to other stations and a travel-time residual that is comparable to the observatories in the mid-continent. This may be another example of a seismic “window” into the upper mantle that is generated by underthrusting of the oceanic lithosphere.

Seismic wave velocity investigation at The Geysers‐Clear Lake geothermal field, California

Geophysics ◽  
1982 ◽  
Vol 47 (5) ◽  
pp. 819-824 ◽  
Author(s):  
Harsh K. Gupta ◽  
Ronald W. Ward ◽  
Tzeu‐Lie Lin
Keyword(s):  
Wave Velocity ◽  
Poisson’S Ratio ◽  
Poisson Ratio ◽  
Volcanic Field ◽  
P Wave ◽  
Poisson's Ratio ◽  
Clear Lake ◽  
Seismic Wave Velocity ◽  
S Waves ◽  
The Geysers

Analysis of P‐ and S‐waves from shallow microearthquakes in the vicinity of The Geysers geothermal area, California, recorded by a dense, telemetered seismic array operated by the U.S. Geological Survey (USGS) shows that these phases are easily recognized and traced on record sections to distances of 80 km. Regional average velocities for the upper crust are estimated to be [Formula: see text] and [Formula: see text] for P‐ and S‐waves, respectively. Poisson’s ratio is estimated at 23 locations using Wadati diagrams and is found to vary from 0.13 to 0.32. In general, the Poisson’s ratio is found to be lower at the locations close to the steam production zones at The Geysers and Clear Lake volcanic field to the northeast. The low Poisson ratio corresponds to a decrease in P‐wave velocity in areas of high heat flow. The decrease may be caused by fracturing of the rock and saturation with gas or steam.

VSP measurement of shear‐wave velocities in consolidated and poorly consolidated formations

Geophysics ◽  
1992 ◽  
Vol 57 (12) ◽  
pp. 1583-1592 ◽  
Author(s):  
John O’Brien
Keyword(s):  
Shear Wave ◽  
Poisson’S Ratio ◽  
Mode Conversion ◽  
Shear Waves ◽  
Vertical Motion ◽  
Seismic Source ◽  
Poisson's Ratio ◽  
The Arctic ◽  
Wave Velocities ◽  
Shear Wave Velocities

Mode conversion in the subsurface can generate shear waves with sufficient amplitude so that they can be used to measure shear‐wave propagation effects. Significant mode conversion can occur even at near vertical incidence if there is sufficient contrast in Poisson’s ratio across the interface. This can be exploited to measure shear‐wave velocities in the underlying section in the course of vertical seismic profile (VSP) acquisition. The technique is effective even in poorly consolidated formations with low shear‐wave velocities where sonic waveform logging fails. Where shear‐wave velocity data are available from sonic waveform logs, the VSP data can be used to verify the wireline data and to calibrate these data to seismic frequencies. The technique is illustrated with a case study from the North Slope, Alaska, in which several shear‐wave events are observed propagating downward through the subsurface. The seismic source is a vertical‐motion vibrator; shear waves are generated via mode conversion in the subsurface and also radiated from the source at the surface, and they are observed with both far‐ and near‐source offsets. The shear‐wave events are strong even on the near‐offset data, which is attributed to the contrast in Poisson’s ratio at the interfaces where mode conversion occurs. The technique is not limited to the hard surfaces of the Arctic and should work in any well, either land or marine, that penetrates shallow interfaces where mode conversion can occur.

scholarly journals Femur Auxetic Meta-Implants with Tuned Micromotion Distribution

Materials ◽  
2020 ◽  
Vol 14 (1) ◽  
pp. 114
Author(s):  
Naeim Ghavidelnia ◽  
Mahdi Bodaghi ◽  
Reza Hedayati
Keyword(s):  
Mechanical Properties ◽  
Poisson’S Ratio ◽  
Bone Growth ◽  
Contact Region ◽  
Stress Shielding ◽  
Local Stress ◽  
Local Strain ◽  
The Other ◽  
Poisson's Ratio ◽  
Ratio Distribution

Stress shielding and micromotions are the most significant problems occurring at the bone-implants interface due to a mismatch of their mechanical properties. Mechanical 3D metamaterials, with their exceptional behaviour and characteristics, can provide an opportunity to solve the mismatch of mechanical properties between the bone and implant. In this study, a new porous femoral hip meta-implant with graded Poisson’s ratio distribution was introduced and its results were compared to three other femoral hip implants (one solid implant, and two porous meta-implants, one with positive and the other with a negative distribution of Poisson’s ratio) in terms of stress and micromotion distributions. For this aim, first, a well-known auxetic 3D re-entrant structure was studied analytically, and precise closed-form analytical relationships for its elastic modulus and Poisson’s ratio were derived. The results of the analytical solution for mechanical properties of the 3D re-entrant structure presented great improvements in comparison to previous analytical studies on the structure. Moreover, the implementation of the re-entrant structure in the hip implant provided very smooth results for stress and strain distributions in the lattice meta-implants and could solve the stress shielding problem which occurred in the solid implant. The lattice meta-implant based on the graded unit cell distribution presented smoother stress-strain distribution in comparison with the other lattice meta-implants. Moreover, the graded lattice meta-implant gave minimum areas of local stress and local strain concentration at the contact region of the implants with the internal bone surfaces. Among all the cases, the graded meta-implant also gave micromotion levels which are the closest to values reported to be desirable for bone growth (40 µm).

Maine seismic experiment: A study of shear waves

1965 ◽  
Vol 55 (2) ◽  
pp. 425-439
Author(s):  
Ziro Suzuki
Keyword(s):  
Lower Crust ◽  
Poisson’S Ratio ◽  
Shear Waves ◽  
Poisson's Ratio ◽  
Apparent Velocity ◽  
Continuous Change ◽  
S Wave ◽  
Complicated Structure ◽  
Velocity Change ◽  
Seismic Experiment

Abstract Shear waves recorded at five stations in the Maine Seismic Experiment of 1961 are studied to find a possible velocity distribution. Possibilities in various cases are examined based on time, apparent velocity and amplitude, and compared with the results from P. Flat layer models are rejected and the continuous velocity change is the only possible case except for some more complicated structure. The range of possible distribution of S velocity and Poisson's ratio are obtained. The P and S wave crustal models cannot be reconciled with a constant Poisson's ratio. The Poisson's ratio is 0.255-0.27 at the surface and is constant or slightly decreasing up to 15 km deep. Beyond 20 km it increases continuously with depth up to 0.30-0.32 at the bottom of the crust. This implies the continuous change in material in the lower crust.

Effect of fluids and frequencies on Poisson’s ratio of sandstone samples

Geophysics ◽  
2016 ◽  
Vol 81 (2) ◽  
pp. D183-D195 ◽  
Author(s):  
Lucas Pimienta ◽  
Jérôme Fortin ◽  
Yves Guéguen
Keyword(s):  
Frequency Dependence ◽  
Poisson’S Ratio ◽  
Poisson's Ratio ◽  
Fluid Viscosity ◽  
S Wave ◽  
Standard Samples ◽  
Frequency Dependent ◽  
S Waves ◽  
Fontainebleau Sandstone ◽  
Dry Conditions

Poisson’s ratio [Formula: see text] is an important parameter when interpreting measured geophysical and seismic data. For an isotropic medium, it directly relates to the ratio of P- and S-wave velocities. We have measured [Formula: see text] as a function of pressure and frequency in fluid-saturated sandstones. The method of measuring [Formula: see text] was first tested as a function of pressure and frequency using standard samples. The phase shift [Formula: see text] between radial and axial strains was also measured. For all standard samples, such as the linear viscoelastic Plexiglas, the data indicated that [Formula: see text] correlated with [Formula: see text] and related to a dissipation on [Formula: see text]. Then, [Formula: see text] and [Formula: see text] were measured as a function of pressure and frequency for two dry and fluid-saturated Fontainebleau sandstone samples. Under dry conditions, no frequency dependence and very small pressure dependence were observed. Unusual behaviors were observed under fluid-saturated conditions. In particular, [Formula: see text] of one sample indicated a frequency-dependent bell-shaped dispersion under water and glycerin saturation that correlated with peaks in [Formula: see text]. Plotting the measurements as a function of apparent frequency (i.e., normalizing by the fluid viscosity) indicated a good fit between the water- and glycerin-saturated measurements. The bell-shaped dispersion in [Formula: see text] that was observed for one particular sandstone held for all effective pressures. These variations fully correlated with the peaks of [Formula: see text] observed. Our results can be interpreted using fluid flow and effective medium theories in the case of a porous microcracked rock. Drained/undrained and relaxed/unrelaxed transitions have frequency and magnitude of variations that are consistent with the measurements. The rock sample microcrack density strongly affects this frequency dependence. The inferred [Formula: see text] ratio at low effective pressures also indicates a large frequency-dependent bell-shaped dispersion. The parameter [Formula: see text] is a clear indicator of the frequency-dependent dissipation of [Formula: see text] and relates to the attenuation of P- and S-waves.

DETERMINATION OF THE PHYSICAL PROPERTIES OF COMPLEXLY CONSTRUCTED MEDIA USING NEAR-SURFACE CROSSWELL METHOD

2019 ◽  
pp. 13-20 ◽  
Author(s):  
H. Guliyev ◽  
Kh. Aghayev ◽  
F. Mehraliyev ◽  
E. Ahmadova
Keyword(s):  
Physical Properties ◽  
Poisson’S Ratio ◽  
Seismic Anisotropy ◽  
Water Saturation ◽  
Shear Waves ◽  
Practical Importance ◽  
Poisson's Ratio ◽  
High Porosity ◽  
Reservoir Pressure ◽  
Near Surface

In case when the upper part of the medium has complex geological structure and geodynamic processes occur in it, the necessity of these data increases in projecting of the object under construction. Purpose. Studying of acoustic, elastic and anisotropic properties of the upper part of section of complicatedly constructed geological media. Methodology. Seismic observations are conducted in shallow wells in the areas of construction objects located in various seismogeological conditions by NSCW (Near-Surface Cross Well testing) method. Field seismic records are processed. Kinematic and dynamic parameters of pressure and differently polarized shear waves are determined. Thin-layered one-dimensional models of physical properties of the medium are created and interpreted on the basis of nonlinear theory of elastodynamics. Results. It is determined that the medium with high porous, water saturated rocks and anomalous high reservoir pressure has anomalous low value of velocities and gradient of their increase with depth. When this medium was re-examined after deep piles were built there, the overestimated seismic velocities are obtained, which is explained by a decrease in the section of anomalously high reservoir pressure and, accordingly, the porosity of the rocks after piles were built. When the hollowness is increased in unsaturated pebble rocks, the negative value of Poisson's ratio is obtained on the standard method. Seismic anisotropy related with the direction of the grains packing of the rocks is revealed on velocities of shear waves. The change of property of rocks on depth is manifested clearer on frequencies of waves than on their amplitudes. Scientific novelty. The elasticity moduli of the 3rd order are determined which are more sensible to variability of nonlinear elastic properties of rocks of the medium than the moduli of the 2nd order. The values of Poisson's ratio are recalculated for one and the same rocks located in different conditions of rock pressure on the basis of nonclassical theory of deformation. Practical importance. The obtained results can be applied to study the media characterized by complex seismogeological hydrodynamic conditions with clay-sandy rocks of high porosity and water saturation.

SONIC DETERMINATION OF THE ELASTIC PROPERTIES OF ICE

1947 ◽  
Vol 25a (2) ◽  
pp. 88-95 ◽  
Author(s):  
T. D. Northwood
Keyword(s):  
Rayleigh Wave ◽  
Young’S Modulus ◽  
Elastic Properties ◽  
Elastic Waves ◽  
Poisson’S Ratio ◽  
Young's Modulus ◽  
The Other ◽  
Poisson's Ratio ◽  
Wave Velocities

By measuring the velocity of various types of elastic waves in a solid it is possible to deduce Young's modulus and Poisson's ratio. Longitudinal, extensional, and Rayleigh wave velocities were measured in ice, the first by resonance in a rod and the other two by a pulsing technique. The value obtained for Young's modulus was 9.8 × 1010 dynes per cm.2 and for Poisson's ratio was 0.33.

scholarly journals Experiments on the diffraction of cathode rays.—II

1928 ◽  
Vol 119 (783) ◽  
pp. 651-663 ◽  
Keyword(s):  
Thin Film ◽  
Diffraction Pattern ◽  
Discharge Tube ◽  
Photographic Plate ◽  
Wave Length ◽  
The Other ◽  
X Rays ◽  
Spark Gap ◽  
De Broglie Waves ◽  
Considerable Length

§ 1. The following paper is an account of further experiments which have been made on the lines of those described in these ' Proceedings ’ (vol. 117, p. 600), and largely with the same apparatus. A beam of cathode rays passing normally through a very thin film of metal was found to produce a pattern of concentric rings on a photographic plate about 30 cm. away. These could be explained as a diffraction pattern due to the de Broglie waves of the electron, the atoms of the metal crystals being the diffracting system. In the present paper several points of uncertainty are cleared up, and the work extended to other cases. § 2. As mentioned in a note at the end of the previous paper, the discrepancy of 6 per cent, between the values of the crystal constants of aluminium and gold determined by X-rays, and those found by applying the de Broglie theory to the diffraction rings formed by the cathode rays, has now been explained. It was due to an error in the measurement of the energy of the cathode rays, and hence their wave-length. The energy was measured by a spark-gap connected in parallel with the discharge tube. In the earlier measurements a considerable length of leads and a rectifying valve were included with the discharge tube, and it now appears that an appreciable fraction of the potential fall occurred in these. When two spark-gaps were used, one connected as before, and the other directly across the discharge, there was 1-2 mm. difference in the readings. The following table shows the values of P, the voltage; D, the diameter of the ring corresponding to reflection from the (2, 0, 0) plane; and D√P (1 + P e /1200 m 0 c 2 ), which latter quantity should be constant for any one metal on the de Broglie theory (see previous paper, p. 603). The factor in brackets is the relativity correction, and in the experiments in question never differs from unity by more than 3 per cent.

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