• Geophysics and Geophysical Exploration
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• v.11 no.3
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• pp.230-241
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• 2008

Characteristics of transfer responses for arrays like triangle, hexagon and semicircle were investigated. To characterize the site near Izmit city with ambient noise measurement, dispersion curves of surface waves were derived with using array technique like F-K, High resolution F-K, MSPAC and H/V ratio was calculated. Also, MASW was surveyed to get the high frequency part of dispersion curves. The transition from fundamental mode to first high mode of surface waves for dispersion curve was observed. Dispersion curve of fundamental mode of ambient noise and first higher mode of MASW was used in inversion to get S-wave velocity structure of subsurface. None-unique problem of results of surface wave inversion was solved with comparison of result of refraction tomography performed with first arrivals of MASW data.

• Journal of the Korean Geotechnical Society
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• v.31 no.11
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• pp.25-31
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• 2015

Elastic behavior of the railway roadbed which supports the repeating dynamic loads of the train is mainly affected by the shear modulus of the upper roadbed. Therefore, shear wave velocity estimation of the uniformly compacted roadbed can be used to estimate the elastic behavior of the railway roadbed. The objective of this study is to suggest the relationship between the dynamic cone penetration index (DCPI) and the shear wave velocity ($V_s$) of the upper roadbed in order to estimate the shear wave velocity by using the dynamic cone penetration test (DCPT). To ensure the reliability of the relationship, the dynamic cone penetration test and the measurement of the shear wave velocity are conducted on the constructed upper roadbed. As a method for measurement of the shear wave velocity, cross hole is used and then the dynamic cone penetration test is performed at a center point between the source and the receiver of the cross hole. As a result of the correlation of the dynamic cone penetration index and the shear wave velocity at the same depths, the shear wave velocity is estimated as a form of involution of the dynamic cone penetration index with a determinant coefficient above 0.8. The result of this study can be used to estimate both the shear wave velocity and the strength of the railway roadbed using the dynamic cone penetrometer.

• Economic and Environmental Geology
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• v.44 no.3
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• pp.229-238
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• 2011

S-wave, which provides lithology and pore fluid information, plays a key role in estimating gas-hydrate saturation. In general, P- and S-wave velocities increase in the presence of gas-hydrate and the P-wave velocity decreases in the presence of free gas under the gas-hydrate layer. Whereas there are very small changes, even slightly increases, in the S-wave velocity in the free gas layer because S-wave is not affected by the pore fluid when propagating in the free gas layer. To verify those velocity properties of the BSR (bottom-simulating reflector) depth in the gas-hydrate prospect area in the Ulleung Basin, P- and S-wave velocity profiles were derived from multi-component ocean-bottom seismic data which were acquired by Korea Institute of Geoscience and Mineral Resources (KIGAM) in May 2009. OBS (ocean-bottom seismometer) hydrophone component data were modeled and inverted first through the traveltime inversion method to derive P-wave velocity and depth model of survey area. 2-D multichannel stacked data were incorporated as an initial model. Two horizontal geophone component data, then, were polarization filtered and rotated to make radial component section. Traveltimes of main S-wave events were picked and used for forward modeling incorporating Poisson's ratio. This modeling provides S-wave profiles and Poisson's ratio profiles at every OBS site. The results shows that P-wave velocities in most OBS sites decrease beneath the BSR, whereas S-wave velocities slightly increase. Consequently, Poisson's ratio decreased strongly beneath the BSR indicating the presence of a free gas layer under the BSR.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.5
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• pp.340-346
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• 1999

Minimum reflection and backward radiation methods on liquid/solid interrace were used to determine the velocity dispersion relation of acoustical surface wave for brass and aluminum substrates and copper/stainless steel nickel/brass, and nickel/aluminum layered substrates. Dispersion data agreed to dispersion characteristics of a generalized Lamb wave. The difference between velocities determined by two phenomena was closely related to the dispersion characteristics. This correspondence was explained by considering the generation mechanism of surface waves and the concept of group velocity.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.5
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• pp.291-296
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• 2006

The residual stress in shot-peened Al 7075 alloy was evaluated using surface acoustic wave (SAW). Shot peening was conducted to produce a variation in the residual stress with the depth below the surface under a shot velocity of 30 m/s. The SAW velocity was measured from the V(z) curve using a scanning acoustic microscopy (SAM). The Vickers hardness profile from the surface showed a significant work hardening near the surface layer with a thickness of about 0.25 mm. As the residual stress became more compressive, the SAW velocity increased, whereas as the residual stress became more tensile, the SAW velocity decreased. The variation in the SAW velocity through the shot peened surface layer was in good agreement with the distribution of the residual stress measured by X-ray diffraction technique.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.4
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• pp.259-269
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• 1999

Elastic wave velocity measurement technique such as impact-echo method and ultrasonic pulse velocity method has been successfully used to evaluate the moduli and strength of concrete. However, estimation results obtained by the NDT methods do not agree well with real things because longitudinal wave velocity is influenced by various factors. In this paper, among several factors influencing P-wave velocity, the influence of moisture content in concrete was investigated through the experiment. Test results show that longitudinal wave velocity is significantly affected by the moisture content of concrete, i.e., the lower moisture content. the lower velocity. Moisture content influences rod-wave velocity measured by impact-echo method stronger than ultrasonic pulse velocity measured by transmission method. During drying process with ages. the difference of increasing rate between longitudinal wave velocity and compressive strength of concrete is gradually increased. Therefore, to establish more accurate relationship between longitudinal wave velocity and strength, the difference of the increasing rate should be considered.

• Journal of the Korean earth science society
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• v.23 no.6
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• pp.507-513
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• 2002

To delineate the relationship between dynamic elastic modulus and lithologies, suspension PS logging was applied to Yuseong granite, Paldang banded gneiss, and Sabuk sedimentary rock. P and S wave velocities were also measured for these lithologies. In addition, uniaxial strength and Poisson’s ratio were measured in a laboratory for Yuseong granite and Paldang banded gneiss. In laboratory measurements, P and S wave velocities in Paldang banded gneiss were higher than those in Yuseong granite whereas Poisson’s ratio in Paldang banded gneiss was lower than that in Yuseong granite. This implies that P and S wave velocities correlate reversely with Poisson’s ratio. The dynamic Young modulus obtained from suspension PS logging was high compared to the dynamic bulk modulus and the dynamic shear modulus.

• Journal of the Korean Geophysical Society
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• v.8 no.2
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• pp.67-74
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• 2005

Two-dimensional S-wave velocity sections from SH-wave refraction tomography and surface wave dispersions were obtained by inverting traveltimes of first arrivals and surface wave dispersions, respectively. For the purpose of comparison, a P-wave velocity tomogram was also obtained from a P-wave refraction profiling. P and Rayleigh waves generated by vertical blows on a plate with a sledgehammer were received by 100- and 4.5-Hz geophones, respectively. SH-waves generated by horizontal blows on both sides of a 50 kg timber were received by 8 Hz horizontal geophones. The shear-wave signals were enhanced subtracting data of left-side blows from ones of the right-side blows. Shear-wave velocities from tomography inversion of first-arrival times were compared with ones from inverting dispersion curves of Rayleigh waves. Although the two velocity sections look similar to each other in general, the one from the surface waves tends to have lower velocities. First arrival picking of SH waves is troublesome since P and PS-converted waves arrive earlier than SH waves. Application of the surface wave method, on the other hand, is limited where lateral variation of subsurface tructures is not mild.

• Geophysics and Geophysical Exploration
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• v.9 no.1
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• pp.108-113
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• 2006

Urban conditions, such as existing underground facilities and ambient noise due to cultural activity, restrict the general application of conventional geophysical techniques. At a tunnelling site in an urban area along an existing railroad, we used the refraction microtremor (REMI) technique (Louie, 2001) as an alternative way to get geotechnical information. The REMI method uses ambient noise recorded by standard refraction equipment and a linear geophone array to derive a shear-wave velocity profile. In the inversion procedure, the Rayleigh wave dispersion curve is picked from a wavefield transformation, and iteratively modelled to get the S-wave velocity structure. The REMI survey was carried out along the line of the planned railway tunnel. At this site vibrations from trains and cars provided strong seismic sources that allowed REMI to be very effective. The objective of the survey was to evaluate the rock mass rating (RMR), using shear-wave velocity information from REMI. First, the relation between uniaxial compressive strength, which is a component of the RMR, and shear-wave velocity from laboratory tests was studied to learn whether shear-wave velocity and RMR are closely related. Then Suspension PS (SPS) logging was performed in selected boreholes along the profile, in order to draw out the quantitative relation between the shear-wave velocity from SPS logging and the RMR determined from inspection of core from the same boreholes. In these tests, shear-wave velocity showed fairly good correlation with RMR. A good relation between shear-wave velocity from REMI and RMR could be obtained, so it is possible to estimate the RMR of the entire profile for use in design of the underground tunnel.

• Journal of Korean Ophthalmic Optics Society
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• v.4 no.1
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• pp.37-43
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• 1999

Ocular lens failure can be verified by measuring the elastic wave velocity diffraction patterns of monochromatic wave applied with elastic wave were detected using optical heterodyne method. The elastic wave velocity was measured by analysing the diffraction patterns. According to measured results of the longitudinal elastic wave velocity of the middle index-refraction and high index-refraction lens are 6588.5575 m/s and 3973.53 m/s, respectively.