• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1999.04a
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• pp.35-40
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• 1999

In order to know the characteristics of attenuation of coda wave in the Kyungsang Sedimentary Basin quality factor for coda wave or coda Q is estimated from the earthquake data recorded in the KIGAM microearthquake network. The single scattering model for coda wave generation is adopted in estimating coda Q. Coda Q appears to be largely dependent on the normalized time(a) which is the ratio of elapsed time to S-wave travel time. In the present study coda Q(Qc) is estimated in the range of a=1.5-3.Q and expressed in terms of frequency(f). The deduced function in the range of 1 to 25 Hz is Qc=36.8283 f1.15095 to represent the strong dependence of coda Q on frequency. It is found that the difference of Qc between U-D N-S and E-W components is negligible, This face supports the back-scattering theory that coda were originates from scattered waves by randomly distributed heterogeneities in the crust. On the other hand it is observed that the coda Q increases with depth.

• Economic and Environmental Geology
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• v.32 no.4
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• pp.379-384
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• 1999

In order to know the characteristics of attenuation of coda wave in the Kyungsang Sedimetary Basin, quality faclity factor for coda wave (coda Q) is estimated from the earthquake data recorded in the KIGAM local seismic network. Thesingle scattering model for coda wave generation is adopted is adopted in estimating coda Q. In the present study, coda Q(Qc)is estimated in the range of $\alpha$=1.5~3.0, where $\alpha$ denotes the normalized time to S-wave travel time and expressed in terms of frequency (f). The deduced function in the range of 1 to 25 Hz is Qc=36.8283$f^{1.15095}$ which represents the strong dependence of coda Q on frequency. It is found that the difference of Qc between U-D, N-S, and E-W components is negligible. This fact suports the back scattering therory that coda wave originates from scattered waves by randomly distributed heterogenities in the crust On the other hand, it is observed that the coda Q increases with increasing epicentral distence. This observation suggests that QC increases with depth.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.6
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• pp.428-434
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• 2014

In this study, we examined the applicability of coda wave interferometry (CWI) technique, which was developed to characterize seismic waves, to detect and evaluate change in the velocity of ultrasonic waves in concrete due to acoustoelastic effect. Ultrasonic wave measurements and compressive loading tests were conducted on a concrete specimen. The measured wave signals were processed with CWI to detect and evaluate the relative velocity change with respect to the stress state of the specimen. A phase change due to the acoustoelastic effect of concrete was clearly detected in the late-arriving coda wave. This shows that the relative velocity change of ultrasonic waves in concrete due to the acoustoelastic effect can be evaluated successfully and precisely using CWI.

• Journal of the Korean GEO-environmental Society
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• v.10 no.7
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• pp.135-141
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• 2009

For more reliable estimation of soil-structure interaction and seismic source and attenuation properties, site amplification function should be considered. This study use the Nakamura's method (1989) for estimating site amplification though various methods for the same purpose have been proposed. This method was originally applied to the surface waves of background noise and therefore there are some limitation for applications to general wave energy. However, recently this method has been extended and applied to the S wave energy successfully. This study applied the method to the coda wave energy which is equivalent to the backscattered S wave energy. We used more than 60 observed ground motions from 5 earthquakes which occurred recently, with magnitude range from 3.6 to 5.1 Each station showed characteristic site amplification property in low-, high- and resonance frequency ranges. In the case of comparing these results to those from S wave energy, lots of information to the site classification work can be gained. Moreover, removal of site amplification can give us more reliable seismic source parameters.

• Journal of the Korean earth science society
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• v.37 no.1
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• pp.40-51
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• 2016

The problem has been pointed out that the domestic design response spectrum does not reflect site amplification, particularly in the high frequency bands, including the fact that site specific response spectrum from the observed ground motions appears relatively higher than design response spectrum. Among various methods, this study applied H/V spectral ratio of ground motion for estimating site amplification. This method, originated from S waves and Rayleigh waves, recently has been extended to Coda waves and background noise for estimating site amplification. For limited time of periods, 4 electric substation sites had operated seismic stations at two separate locations (bedrock and borehole) within each substation site. H/V spectral ratio of S wave, Coda wave, and background noise, was applied to 36 accelerations of 3 macro earthquakes (Odaesan, Jeju and Gongju earthquakes), larger than magnitude 3.4. observed simultaneously at each bedrock location within 4 electric substation sites. Site amplifications at the bedrock location of 4 sites were compared among S wave, Coda wave energy, and background noise, and then compared to the previous results from the borehole location data. The site classification was also tried using resonancy frequency information at each site and location. The results suggested that all the electric substation sites showed similar site amplification patterns among S wave, Coda wave, and background noise. Each station showed its own characteristics of site amplification property in low, high and specific resonance frequency ranges. Comparison of this study to other results using different method can give us much more information about dynamic amplification of domestic sites characteristics and site classification.

• Tunnel and Underground Space
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• v.19 no.5
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• pp.432-439
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• 2009

For more reliable estimation of seismic source, attenuation properties and dynamic ground property, site amplification function should be considered. Among various estimation methods, this study used the Nakamura's method (1989) for estimating site amplification characteristics. This method was originally applied to the surface waves of background noise and therefore there are some limitations in applying to general wave energy. However, recently this method has been extended and applied to the S wave energy successfully. This study applied the method to S wave and Coda wave energy, which is equivalent to the backscattered S wave energy. We used more than 60 observed ground motions from 5 earthquakes which were occurred recently, with magnitude range from 3.6 to 5.1. Each station showed characteristic site amplification property in low-, high- and resonance frequencies. Some of the stations showed as high as 4 times of site amplification in the range of specific frequencies, which may imply abnormal small scale geologic strata below the station or development of various trapped modes in the basin structure. Moreover, removal of site amplification can give us more reliable seismic source and attenuation parameters, addition to the seismic hazard estimation.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.05a
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• pp.37-42
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• 2005

We analyzed spectral attenuation of coda waves and estimated coda Q values in the crust of the Korean peninsula. 574 NS-component seismograms registered by the Korea Meteorological Administration (KMA) and Korea Institute of Geology, Mining and Materials (KIGAM) seismic networks with epicentral distances less than 100 km and sampling rate greater than 80 Hz were selected for this study. We estimated coda Q values using the single isotropic scattering model at center frequencies of 1.5, 3, 6, 9, 12, 15, and 18 Hz with 20 s time window starting from double of the S-wave arrival times. Estimated coda Q value at 1 Hz ($Q_0$) and n value range 50 to 250 and 0.5 to 1.0, respectively, and they are well correlated with the regional geology in the Korean peninsula. The $Q_0$ values in western Korea agree well with those of eastern China.

• Smart Structures and Systems
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• v.17 no.1
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• pp.73-89
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• 2016

The stress dependence of ultrasonic wave velocity is known as the acoustoelastic effect. This effect is useful for stress monitoring if the acoustoelastic coefficient of a subject medium is known. The acoustoelastic coefficients of metallic materials such as steel have been studied widely. However, the acoustoelastic coefficient of concrete has not been well understood yet. Basic constituents of concrete are water, cement, and aggregates. The mix proportion of those constituents greatly affects many mechanical and physical properties of concrete and so does the acoustoelastic coefficient of concrete. In this study, influence of the water-cement ratio (w/c ratio) and the fine-coarse aggregates ratio (fa/ta ratio) on the acoustoelastic coefficient of concrete was investigated. The w/c and the fa/ta ratios are important parameters in mix design and affect wave behaviors in concrete. Load-controlled uni-axial compression tests were performed on concrete specimens. Ultrasonic wave measurements were also performed during the compression tests. The stretching coda wave interferometry method was used to obtain the relative velocity change of ultrasonic waves with respect to the stress level of the specimens. From the experimental results, it was found that the w/c ratio greatly affects the acoustoelastic coefficient while the fa/ta ratio does not. The acoustoelastic coefficient increased from $0.003073MPa^{-1}$ to $0.005553MPa^{-1}$ when the w/c ratio was increased from 0.4 to 0.5. On the other hand, the acoustoelastic coefficient changed in small from $0.003606MPa^{-1}$ to $0.003801MPa^{-1}$ when the fa/ta ratio was increased from 0.3 to 0.5. Finally, it was also found that the relative velocity change has a linear relationship with the stress level of concrete.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.497-500
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• 2007

탄성파 코다 파는 두 수진기에서 기록된 탄성파 자료의 상호상관으로부터 두 신호에 대한 순간응답을 구하고 이로부터 지층정보를 구하는데 이용된다. 여기에서는 인공합성 탄성파 자료와 가스 하이드레이트 현장자료에 적용하여 상호상관 모음도와 가상음원 모음도 (virtual source)를 구하고자 하였다. 인공합성자료는 해저면 탄성파 탐사법 (ocean bottom seismic)을 모델로 이용하여 인공합성 탄성파 단면도를 제작하였으며, 탄성파 코다 파를 살펴보기 위해 인공 OBS 자료 중 첫 번째 트레이스를 가상음원으로 정하고 모든 음원 모음도와 상호상관으로 가상응원 단면도를 제작하였다. 현장자료 적용으로는 해저면 기인 고진폭 반사파인 BSR (bottom simulating reflection)을 포함하고 있는 자료를 선정하여 상호상관 단면도와 가상음원 단면도를 제작하였다. 중합단면도상에 나타난 가스 분출지역은 상호상관 단면도에서도 나타났으며, 중합단면도상 BSR부분은 vs 단면도에서 강한 반사파를 보여줌을 알 수 있었다.

• The Journal of Engineering Geology
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• v.23 no.4
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• pp.435-445
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• 2013

Since design response spectrum does not reflect local soil characteristics, site specific response spectrum of observed ground motions appears relatively higher than design response spectrum at high frequency range. These problems have been pointed out from the domestic seismic design industry. Among various estimation methods, this study used the method H/V ratio of ground motion for estimating site amplification. This method has been extended to background noise, Coda waves and S waves recently for estimating site amplification. This study applied this method to the background noise and Coda wave energy. This study analysed more than 267 background noises from 15 macro earthquakes including main Fukuoka earthquake (2005/03/20, M=6.5) and then compared to results from S waves, at 8 main domestic seismic stations. The results showed that most of the domestic seismic stations gave similar results to those from S waves. Each station showed its own characteristics of site amplification property in low, high and specific resonance frequency ranges. Comparison of this study to other studies using different method can give us much information about dynamic amplification of domestic sites characteristics and site classification.