• Journal of the Korean earth science society
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• v.27 no.5
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• pp.539-547
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• 2006

The activity of the seismic wave propagation around the cavity is investigated for the exact inversion of the crosshole tomography data, in order to understand the possibility of the existence inside the underground cavity. It is found that the adequate frequency range for the tunnel investigation is about 2 kHz to 5 kHz, and the grid space should be set up to 1/10 of the wavelength. The propagation of the seismic wave near the cavity may go through or detour the cavity according to the seismic velocity inside the cavity. The detouring wave propagates with the seismic velocity of mother rock in spite of the velocity of inside of the cavity. The smaller the velocity difference is between the mother rock and cavity, the more frequent penetration of the seismic wave through the cavity appears.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.06a
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• pp.151-156
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• 2007

In December 2006, 2D surface streamer and Ocean Bottom Seismometer (OBS) data were acquired in the Ulleung basin in Korea where strong Bottom Simulating Reflectors (BSR) were shown as a result of 2D and 3D multichannel (MCS) reflection survey. The aim of this study is to provide another reliable source for estimating P wave velocity around BSR depth using OBS data in addition to velocity information from 2D surface seismic data. Four OBSs were deployed and four 20-km shot lines which pass two OBSs respectively were designed. To derive P wave velocity profile, interactive interval velocity analysis using ${\tau}$-p trajectory matching method (Kumar, 2005) was used for OBS data and semblance analysis was used for surface data. The seismic profiles cross the OBS instruments in two different directions yield recordings for four different azimuths. This raised the confidence for the results. All velocity profiles in the vicinity of BSR depth of four OBS sites show almost definite velocity changes which we could consider as upper BSR and free gas layer. Making comparison between velocity from OBS and that from 2D seismic semblance velocity analysis gives consistency in result.

• Journal of the Korean Geophysical Society
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• v.6 no.2
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• pp.99-105
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• 2003

Rayleigh waves which has more than 70% of the total seismic energy is the principal component of ground roll. Frequency component of a surface wave has a different propagation velocity, that is, phase velocity, which results in a different wavelength called dispersion. Rayleigh wave is one of the most common ways to use the dispersive properties of surface waves. MASW is a seismic method to evaluate shear-wave velocity information of the ground.

• Tunnel and Underground Space
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• v.28 no.3
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• pp.232-246
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• 2018

In this study, the relationship between in situ seismic wave velocities and RMR (rock mass rating) was investigated in a test bed for the examination of the basis of rock classification (RMR) based on seismic wave velocity. The seismic wave velocity showed a monotonous increase with depth. It was also found that there was no systematic correlation between the seismic wave velocity (Vp) and other parameters (RQD, joint spacing, UCS, rock core Vp, and RMR) collected at the same depth of the same borehole. However, correlative relation was observed among RMR, RQD, and joint spacing. On the other hand, when all the data in the borehole (three holes) are examined without considering the depth, Vp still shows no correlation with RMR parameters (e.g., correlative coefficient for uniaxial compressive strength and joint spacing are 0.039 and 0.091, respectively), but Vp shows weak correlative relation with RMR and RQD (correlative coefficient for RQD and RMR are 0.193 and 0.211, respectively). Thus, it is found that it is difficult to deduce physical properties of rock mass directly from seismic wave velocities, but the seismic wave velocity can be used as a tool to approximate rock mass properties because of weaker correlation between Vp and RMR with RQD. In addition, the velocity value of for soft and moderate rocks suggested by widely used construction standards is slower than that of the observed velocity, implying that the standards need to be examined and revised.

• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.291-296
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• 2006

The aspect of wave propagation around cavity was investigated for the exact inversion of crosshole tomography data in order to understand the possibility of the existence of underground cavity. We found that the adequate frequency range for the tunnel investigation was about 2kHz to 5kHz, and the grid space was set up to 1/10 length of wavelength. The propagation of the seismic wave near the cavity may go through or detour the cavity according to the seismic velocity of inside of cavity. The detouring wave propagates with the seismic velocity of mother rock in spite of the velocity of inside of cavity. The smaller the velocity difference between the mother rock and cavity, the more frequent penetration of the seismic wave through the cavity was appeared.

• Journal of the Earthquake Engineering Society of Korea
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• v.28 no.5
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• pp.249-255
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• 2024

Strong ground motions at specific sites can cause severe damage to structures. Understanding the influence of site characteristics on the dynamic response of structures is crucial for evaluating their seismic performance and mitigating the potential damage caused by site effects. This study investigates the impact of the average shear wave velocity, as a site characteristic, on the seismic response of low-to-medium-rise reinforced concrete buildings. To explore them, one-dimensional soil column models were generated using shear wave velocity profile from California, and nonlinear site response analyses were performed using bedrock motions. Nonlinear dynamic structural analyses were conducted for reinforced concrete moment-resisting frame models based on the regional information. The effect of shear wave velocity on the structural response and surface ground motions was examined. The results showed that strong ground motions tend to exhibit higher damping on softer soils, reducing their intensity, while on stiffer soils, the ground motion intensity tends to amplify. Consequently, the structural response tended to increase on stiffer soils compared to softer soils.

• Geomechanics and Engineering
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• v.3 no.3
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• pp.189-206
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• 2011

Amplification based on empirical relations is widely used for seismic microzonation of urban centers. Amplifications are used to represent the site effects of a particular soil column. Many empirical correlations are available to estimate the amplification of seismic waves. These correlations are based on the ratio of shear wave velocity of foundation/rock to soil velocity or 30 m equivalent shear wave velocity ($Vs^{30}$) and are developed considering deep soil data. The aim of this work is to examine the applicability of available amplification relations in the literature for shallow engineering bedrock sites by carrying out site response studies. Shear wave velocity of thirteen sites having shallow engineering bedrock have been selected for the study. In these locations, the depth of engineering bedrock (> 760 ${\pm}$ 60 m/s) is matched with the drilled bore hole. Shear wave velocity (SWV) has been measured using Multichannel Analysis of Surface Wave survey. These sites are classified according to the National Earthquake Hazards Reduction Program (NEHRP) classification system. Amplifications for an earthquake are arrived for these sites using empirical relations and measured SWV data. Site response analysis has been carried out in SHAKE using SWV and using synthetic and real earthquake data. Amplification from site response analysis and empirical relations are compared. Study shows that the amplification arrived using empirical relations does not match with the site response amplification. Site response amplification is much more than empirical values for same shear wave velocity.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.03b
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• pp.109-116
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• 2000

Rippability refers to the ease of excavation by construction equipment. Since it is related to rock quality in terms of hardness and fracture density, which may be measured by seismic refraction surveys, correlations have been made between rippability and seismic P wave velocities. The 1-channel signal enhancement seismograph(Bison, Model 1570C) was used to measure travel time of the seismic wave through the ground, from the source to the receiver. The seismic velocity measurement was conducted with 153 lines at 5 rock slopes of Chungbuk Youngdong area. Schmidt rebound hardness test were conducted with 161 points on rock masses and the point load test also on 284 rock samples. The uniaxial compressive strength and seismic wave velocity of 60 rock specimens were measured in laboratory. These data were used to evaluate the rock quality of 5 rock slopes.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.442-451
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• 2008

The evaluation of field degree of consolidation on soft clays has been an important problem in geotechnical areas. Monitoring either settlements or pore water pressures has been widely applied in the filed, but occasionally they have some problems. This study addresses the suggestion and application of another method for evaluating the degree of consolidation using shear wave velocities. A research site where soft clay layers were consolidated by surcharging loads was chosen. Laboratory tests were performed to determine the relation between shear wave velocity and effective stress. Field seismic tests were conducted several times during the consolidation of the clay layers. The tests results show that the shear wave velocity increased significantly as clays consolidated. The shear wave velocities at each field stress states were derived from the laboratory results and the degree of consolidation was evaluated by comparing the shear wave velocities obtained by laboratory and field seismic methods. In most stress states, the degree of consolidation evaluated using the shear wave velocity matched well with that obtained from field settlement record, showing the potential of applying the method using shear waves in the evaluation of field degree of consolidation on soft clay deposits.

• Journal of the Korean Geotechnical Society
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• v.24 no.10
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• pp.33-43
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• 2008

In this study, for the purpose of evaluating the shear wave velocity in core zone, cross-hole test, down-hole test, MASW (Multi-channel Analysis of Surface Wave), and seismic reflection survey were carried out on the crest of the existing 'Y' dam. The results of field tests were compared one another. Furthermore, the field test results were compared with the result by the Sawada's empirical recommendation method. The purpose of this study is to compare the results of four kinds of field tests for evaluation of shear wave velocity in core zone of existing dam, to verify applicability of the empirical method which was recommended by Sawada and Takahashi, and to recommend a reasonable method for evaluation of shear wave velocity which is needed to evaluate tile maximum shear modulus of core zone. From the results of four kinds of field tests such as cross-hole test, down-hole test, MASW, and seismic reflection survey, it was found that the shear wave velocity distributions were similar within 18 m in depth and the results obtained by MASW and seismic reflection survey were almost the same by 30 m in depth. For evaluation of shear wave velocity in core zone of the existing dam, in consideration that it is not easy to bore the hole ill the core zone of existing dam, surface surveys such as MASW and seismic reflection method are recommended as realistic methods. On condition that it is impossible to conduct the field test and it is preliminary investigation, it is recommended that Sawada's low bound empirical equation be used.