THE MEASUREMENT OF SHEAR‐WAVE VELOCITIES IN SOLIDS USING AXIALLY POLARIZED CERAMIC TRANSDUCERS

A double mode conversion obtained by critical‐angle reflection allows the velocity of shear‐wave propagation to be determined using longitudinally polarized ceramic discs. This method provides a simple and convenient method of obtaining high‐frequency shear waves of predeterminable polarization in the laboratory. Elastic constants of brass and Pyrex obtained with this method are in excellent agreement with those measured by the PnSP method of Hughes. This mode conversion technique, unlike the PnSP method, can be used on anisotropic materials of noncylindrical geometries.

Download Full-text

DETERMINATION OF THE ELASTIC CONSTANTS OF AN ISOTROPIC SOLID USING A “PLATE” VELOCITY MEASUREMENT

Geophysics ◽

10.1190/1.1439830 ◽

1966 ◽

Vol 31 (5) ◽

pp. 984-986 ◽

Cited By ~ 4

Author(s):

Ernest A. Kaarsberg

Keyword(s):

Shear Wave ◽

Elastic Constants ◽

High Frequency ◽

Velocity Measurement ◽

Infinite Plate ◽

Wave Velocities ◽

Shear Wave Velocities ◽

Plate Velocity ◽

Isotropic Solid

From the longitudinal and shear wave velocities measured in a solid, all of its elastic constants can be determined. Jamieson and Hoskins (1963) have shown how shear wave velocities can be measured in solids with an arrangement which converts high frequency longitudinal wave pulses from axially polarized ceramic transducers into shear wave pulses. This note illustrates how such elastic constants can also be determined with the aid of longitudinal “infinite plate” velocities.

Download Full-text

Near-surface shear-wave velocities and quality factors derived from high-frequency surface waves

The Leading Edge ◽

10.1190/tle32060612.1 ◽

2013 ◽

Vol 32 (6) ◽

pp. 612-618 ◽

Cited By ~ 14

Author(s):

Jianghai Xia ◽

Chao Shen ◽

Yixian Xu

Keyword(s):

Surface Waves ◽

Shear Wave ◽

High Frequency ◽

Quality Factors ◽

Surface Shear ◽

Near Surface ◽

Wave Velocities ◽

Shear Wave Velocities ◽

Surface Shear Wave

Download Full-text

Smooth Crustal Velocity Models Cause a Depletion of High-Frequency Ground Motions on Soil in 2D Dynamic Rupture Simulations

Bulletin of the Seismological Society of America ◽

10.1785/0120200311 ◽

2021 ◽

Author(s):

Yihe Huang

Keyword(s):

Shear Wave ◽

High Frequency ◽

Ground Motions ◽

Velocity Model ◽

Dynamic Rupture ◽

Ground Acceleration ◽

Velocity Models ◽

Wave Velocities ◽

Shear Wave Velocities ◽

Crustal Velocity

ABSTRACT A depletion of high-frequency ground motions on soil sites has been observed in recent large earthquakes and is often attributed to a nonlinear soil response. Here, I show that the reduced amplitudes of high-frequency horizontal-to-vertical spectral ratios (HVSRs) on soil can also be caused by a smooth crustal velocity model with low shear-wave velocities underneath soil sites. I calculate near-fault ground motions using both 2D dynamic rupture simulations and point-source models for both rock and soil sites. The 1D velocity models used in the simulations are derived from empirical relationships between seismic wave velocities and depths in northern California. The simulations for soil sites feature lower shear-wave velocities and thus larger Poisson’s ratios at shallow depths than those for rock sites. The lower shear-wave velocities cause slower shallow rupture and smaller shallow slip, but both soil and rock simulations have similar rupture speeds and slip for the rest of the fault. However, the simulated near-fault ground motions on soil and rock sites have distinct features. Compared to ground motions on rock, horizontal ground acceleration on soil is only amplified at low frequencies, whereas vertical ground acceleration is deamplified for the whole frequency range. Thus, the HVSRs on soil exhibit a depletion of high-frequency energy. The comparison between smooth and layered velocity models demonstrates that the smoothness of the velocity model plays a critical role in the contrasting behaviors of HVSRs on soil and rock for different rupture styles and velocity profiles. The results reveal the significant role of shallow crustal velocity structure in the generation of high-frequency ground motions on soil sites.

Download Full-text

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

Geophysics ◽

10.1190/1.1443226 ◽

1992 ◽

Vol 57 (12) ◽

pp. 1583-1592 ◽

Cited By ~ 4

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.

Download Full-text