• The Journal of Engineering Geology
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• v.3 no.3
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• pp.231-239
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• 1993

This paper presents a result on the determination of velocity distribution by a tomographic inversion of crosshole seismic traveltimes in transversely isotropic(aniso tropic) media. The crosshole traveltimes used in this study are synthetic ones computed by ray tracing for some models having isotropic and transversely isotropic velocity distributions. The traveltimes are inverted by a general ART and ansotropic ART which considers the transversely isotropic effect during inver sion. The aniotropic ART gives accurate velodty distributions of transversely isotropic and isotropic models, while the isotropic ART determines accurate velocities only for the isotropic model but inaccurate for the transversely isotropic one. Therefore, the anisotropic ART may be used in case where no information is known on the isotropy or transverse isotropy of a survey area.

• Geophysics and Geophysical Exploration
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• v.10 no.4
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• pp.393-398
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• 2007

Seismic traveltime tomography technique was conducted at a site composed of black shale. It is well known that black shale has strong anisotropic property. Therefore, the anisotropic property of black shale has to be considered to obtain the appropriate subsurface velocity model by an inversion process. To estimate the anisotropic constant of the velocity of the black shale in the survey area, the relation between the velocity, which is calculated by the straight ray path and the first arrival time, and the angle of the ray propagation was examined. The elliptically shaped relation was found and it reveals that the black shale contains the anisotropic property of velocity. It was also noticed that the horizontal velocity is faster than the vertical velocity. When the estimated anisotropic constant was applied in the process of the velocity inversion for three sets of field data, we could obtain the appropriate velocity structures of the site that is consistent with the result of the geological survey.

• Geophysics and Geophysical Exploration
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• v.13 no.4
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• pp.307-314
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• 2010

Although conventional seismic data processing is based on the assumption that the media are isotropic, the subsurface is often anisotropy in shale formation or carbonate with cracks and fractures. This paper presents the anisotropic parameter and seismic modeling in transversely isotropic media with a vertical symmetry axis using seismic physical modeling. The experiment was successfully carried out with VTI media, laminated bakelite material, using contact transducer of p and s-wave transmission. The variation of velocities with angle of incidence was clearly shown in anisotropic material. Comparing these velocities with the calculated phase velocities, the (P) and (S)-wave velocity observed in anisotropic material was a very good agreement with the calculated values. Anisotropic parameter ${\varepsilon}$, ${\delta}$, ${\gamma}$ was estimated by using Lame's constant calculated from the observed velocity. For the purpose of testing (S)-wave polarization, a birefringence experiment was carried out. The higher velocity was associated with the polarization parallel to the fracture, and the lower velocity was associated with the polarization perpendicular to the fracture.

• Geophysics and Geophysical Exploration
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• v.10 no.4
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• pp.229-240
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• 2007

In this study, seismic anisotropic tomography algorithm was developed for imaging the seismic velocity anisotropy of the subsurface. This algorithm includes several inversion schemes in order to make the inversion process stable and robust. First of all, the set of the inversion parameters is limited to one slowness, two ratios of slowness and one direction of the anisotropy symmetric axis. The ranges of the inversion parameters are localized by the pseudobeta transform to obtain the reasonable inversion results and the inversion constraints are controlled efficiently by ACB(Active Constraint Balancing) method. Especially, the inversion using the Fresnel volume is applied to the anisotropic tomography and it can make the anisotropic tomography more stable than ray tomography as it widens the propagation angle coverage. The algorithm of anisotropic tomography is verified through the numerical experiments. And, it is applied to the real field data measured at limestone region and the results are discussed with the drill log and geological survey data. The anisotropic tomography algorithm will be able to provide the useful tool to evaluate and understand the geological structure of the subsurface more reasonably with the anisotropic characteristics.

• Geophysics and Geophysical Exploration
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• v.2 no.3
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• pp.137-141
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• 1999

In order to estimate the anisotropy of the medium, we deployed a series of 120-sources in a borehole, and simultaneously recorded 3-component seismic data at 5 locations on the surface. We have tried to estimate the directional velocities by comparing the first arrivals at different receivers. For that purpose, the receiver statics must be corrected prior to pick the first arrivals. However, in an IVSP with a limited number of receiver points, it may not possible to estimate a reliable receiver statics, therefore, instead of using individual first arrival times, we tried to estimate the move-out velocity at each records. From this analysis, we have found that there exists a measurable amount of difference in directional velocities, and confirmed that the velocity anisotropy agrees with the results of the previous studies conducted in this area.

• Journal of the Korean Geophysical Society
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• v.3 no.1
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• pp.49-56
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• 2000

As a part of geophysical studies on segmentation of the Ulsan fault, walkaway refraction seismic data were measured at 17 stations near National Road 7 between Kyungju and Ulsan. Seismic anisotropy was analyzed in the offset range of 1-48 m. The average refraction velocity of 1787 m/s indicates the refractor is the upper boundary of weathered basement. P-wave anisotropy is computed to be 0.056 in average, which may serve as a weak evidence that the strike of major geologic structure coincide with the inferred fault direction. In the south of the province boundary between Kyungsangnam-do and Kyungsangbuk-do, the velocity anisotropy is normal in that P-wave velocity in the strike direction is faster than the one measured in the dip direction. On the contrary, it appears that the fault strikes in many directions or that fractures may be developed better in the dip direction in the northern par. Such a difference in anisotropic pattern is believed to be a seismic evidence indicating that a segmentation boundary of the Ulsan fault locates near the province boundary.

• Tunnel and Underground Space
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• v.18 no.3
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• pp.214-218
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• 2008

Dynamic fracturing of anisotropic granite was investigated by SHPB (Split Hopkinson Pressure Bar). Energy absorption during the test and maximum stress were increased as strain rate increased. Maximum stresses in every direction were dependent on the strain rate but not so sensitive to anisotropy. Elastic wave velocity was decreased as strain rate increased and dependent on strain rate in every direction. Especially, elastic wave velocity decreased more rapidly in a strong rock.

• The Journal of Engineering Geology
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• v.11 no.2
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• pp.215-227
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• 2001

The Okchon Formation and the Mesozoic granite of the Boeun, Chungbuk are compared in terms of seismic wave velocities estimated from the field experiment, and seismic wave velocities in 3-D measured from the rock specimen. P-wave velocity for the field data ranges from 861 m/s (Guryongsan-2 Formation) to 2697m/s (Bulguksa Granite). P-wave anisotropy also ranges from 46% (Changri Formation) to 81% (Bulguksa Granite), with an average value of 68.5%. P-wave velocities for the rock specimens from Guryongsan-1, Guryongsan-2, Changri, and Munjuri Formations are greater than 5000m/s. S-wave velocities for those specimens are approximately 3500m/s, which is 3-5 times grater than the ones estimated from the field experimental data. P-wave anisotropy for the specimens from Bulguksa Granite and Guryongsan-1 Formation exceeds 60%, which is compared to 30% for the other specimens. This value is much smaller than average P-wave anisotropy (69.5%) for the field data. It is suggested that velocity difference, associated with the propagation direction, is much greater for the field data than for the specimens.

• Journal of the Korean Wood Science and Technology
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• v.29 no.1
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• pp.22-30
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• 2001

Composites with various layer constructions involving the ratio of S/P were produced from wood strands(S) and particles(P) (Cryptomeria japonica D.Don) to measure various Young's moduli and anisotropy by ultrasonics. As a result, static Young's moduli of composites were almost same as dynamic Young's moduli obtained from natural frequency. However, these were smaller than those evaluated from ultrasonic wave propagation velocity. The differences between propagation velocity of the parallel(${\parallel}$) and perpendicular(${\bot}$) in-plane direction resulted in a tendency of anisotropy. The tendency of anisotropy was larger in three-layer constructions than in seven-layer constructions. The differences of strand surface layers showed larger values than those of particle surface layers. Also, composites with higher weight ratio of strand had a tendency to propagate rapidly in each direction. In contrast to these results, the propagation velocity in the thickness direction had a tendency to propagate rapidly in composites with particle surface layers and the lower weight ratio of strand.

• Geophysics and Geophysical Exploration
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• v.20 no.1
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• pp.25-32
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• 2017

We present a 3D SH-wave velocity model of the crust and uppermost mantle and seismic radial anisotropy beneath East Asia. The SH-wave velocity structure model was built using Love-wave group-velocity dispersion data from earthquake data recorded at broadband seismic networks of Korea, Japan, and China. Love-wave group-velocity dispersion curves were obtained by using the multiple filtering technique in the period range of 3 to 150 s for 3,369 event-station pairs. The inverted model using these data sets provides a crust and upper mantle SH-wave velocity structure down to 100 km depth. At 10 ~ 40 km depths SH-wave velocity beneath the East Sea is higher than beneath the Japanese island region. We estimated the Moho beneath the East Sea to be between 10 ~ 20 km depth, while Moho beneath the Korean Peninsula at around 35 km based on the depth where high-velocity anomalies are detected. We estimated the lithosphere-asthenosphere boundary beneath the East Sea to be at around 50 km based on the depth where strong low-velocity anomalies are observed. Widespread low-velocity anomalies are found between 50 ~ 100 km depth in the study region. Positive radial anisotropy ($V_{SV}$ > $V _{SH}$) is observed down to 35 km depth, while negative radial anisotropy ($V_{SV}$ > $V _{SH}$) is observed for deeper depth.