• Proceedings of the Korean Nuclear Society Conference
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• 2004.10a
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• pp.1379-1380
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• 2004

• Journal of the Earthquake Engineering Society of Korea
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• v.4 no.3
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• pp.99-105
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• 2000

한반도 동남부 지역에서 발생하고 관찰된 약진 또는 중진의 자료를 이영하여 이 지역의 Q값과 지진원의 특성인 모서리 주파수 (fc), 응력강하량(Δ$\delta$) 및 모멘크규모 (Mw)를 산정하였다. 가속도 스펙트럼의 경사와 관련된 x의 통계학적 분포로부터 추정한 Q의 95% 신뢰범위는 1656~2454 이다. 1998년 1월 18일 울산 앞바다 지진과 1997년 6월 26일 경주지진의 지진원 요소를 구한 결과 fc 는 각각 4.22Hz , 2.94Hz, Δ$\delta$는 각각 106.8 bar, 106.2 bar, Mw는 각각 3.9, 4.0으로 추정되었다. 제한된 자료수로 인하여 이들의 통계학적 성질을 충분히 규명하지는 못하였지만 다른 연구자들의 기존결과와 유사한 값을 보인다. 본 연구의 결과는 강진동 모사에 직접 이용이 가능하며, 이 지역에 위치한 원자력 발전소 내진 안전성 검토에도 이용될 수 있다.

• Journal of the Korean GEO-environmental Society
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• v.12 no.4
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• pp.53-63
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• 2011

Selection or generation of appropriate input ground motion is very important in performing a dynamic analysis. In Korea, it is a common practice to use recorded strong ground motions or artificial motions. The recorded motions show non-stationary characteristics, which is a distinct property of all earthquake motions, but have the problem of not matching the design response spectrum. The artificial motions match the design spectrum, but show stationary characteristics. This study generated ground motions that preserve the non-stationary characteristics of a real earthquake motion, but also matches the design spectrum. In the process, an impulse function-based algorithm that adjusts a given time series in time domain such that it matches the target response spectrum is used. Application of the algorithm showed that it can successfully adjust any recorded motions to match the target spectrum and also preserve the non-stationary characteristics. The modified motions are used to perform a series of nonlinear site response analyses. It is shown that the results using the adjusted motions result in more reliable estimates of ground vibration. It is thus recommended that the newly adjusted motions be used in practice instead of original recorded motions.

• Tunnel and Underground Space
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• v.16 no.6 s.65
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• pp.486-494
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• 2006

The horizontal to vertical (H/V) ratio technique in spectral domain is a common useful technique to estimate empirical site transfer function. The technique, originally proposed by Nakamura, is proposed to analyse the surface waves in the micrortremor records. The purpose of this paper is to estimate spectral ratio using observed data at the seismic stations distributed within Southern Korean Peninsula from the Fukuoka earthquake including 11 aftershocks. The results show that most of the stations have fairly good amplification characteristics in low frequency band. However, some of the seismic stations show one (resonant frequency specific to the site) or several local peaks of amplification factors with narrow high frequency band. Even though the site amplification characteristics are important information, we should be careful to analyse the observed ground motions from the seismic stations which have several very high amplification peaks for the deconvolution of seismic source and attenuation parameters.

• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.1
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• pp.27-34
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• 2009

Site amplification should be considered in order to estimate Soil-Structure Interaction (SSI), seismic source and attenuation parameters with a greater degree of reliability. The horizontal to vertical (H/V) ratio technique, originally proposed by Nakamura (1989), has been applied to analyze the surface waves in microtremor records. Recently, its application has been extended to the shear wave energy of strong motion in order to study the site transfer function. The purpose of this paper is to estimate the H/V spectral ratio using the observed data from 9 seismic stations distributed within the Southern Korean Peninsula, from the Odesan earthquake (2007/01/20). The results show that most of the stations have more stable amplification characteristics in a low frequency band than in a high frequency band. However, each seismic station showed its own characteristic resonant frequency and low and high frequency. The resonant frequency at each station should be estimated carefully, because the quality of seismic data is dependent on the resonant frequency. It can be obtained more reliable results of seismic source and attenuation parameters, if seismic ground motions which deconvolved from site transfer function is used. The site amplification data from this study can be used to generally classify the sites within the Southern Korean Peninsula.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.5
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• pp.39-45
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• 2008

The source parameters of 85 events ($1.6\;{\leq}\;M_L\;{\leq}\;4.9$) that occurred in and around the Korean Peninsula during 2006 and 2007 were analyzed by an iterative spectral fitting procedure. The data set consists of 487 S-wave trains on three-component seismograms recorded at broadband seismograph stations in the southern part of the Korean Peninsula. Moment magnitudes for each event were determined using spectral analyses of the seismograms, and the results were compared with the variation in corner frequencies with hypocentral distance. Corner frequencies have a tendency to decrease with increases in hypocentral distance, and the decrease is smaller the larger the moment magnitude. We define the measured corner frequency on a displacement spectrum as the apparent corner frequency. Although it was reported that the distance dependency of the corner frequency was found in some regions, such as the eastern Canadian Shield and the Baltic Shield, the origin of the phenomenon is not certain yet.

• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.5
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• pp.23-29
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• 2009

On December 13, 1996, an earthquake with local magnitude (M$_L$) 4.5 occurred in the Yeongwol area of South Korea. The epicenter was 37.2545$^{\circ}$N and 128.7277$^{\circ}$E, which is located inside the Okcheon Fold Belt. The waveform inversion analysis was carried out to estimate source parameters of the event according to the filtering bandwidth of seismic data. Using 0.02$\sim$0.2 Hz filtering bandwidth, focal depth and seismic moment were estimated to be 6 km and 1.3$\times$10$^{16}$ N$\cdot$m, respectively. This seismic moment corresponds to the moment magnitude (M$_W$) 4.7. The focal mechanism by the waveform inversion and P wave first motion polarity analysis is a strike slip faulting including a small thrust component, and the direction of P-axis is ENE-WSW. The moment magnitude estimated by spectral analysis was 4.8, which is similar to that estimated by waveform inversion. Average stress drop was estimated to be 14.3 MPa.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05d
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• pp.352-358
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• 1996

원자력발전소의 지진에 대한 절대안전성을 확보하기 위하여 설치된 지진감시설비망에 과도진동이 유발되는 사례가 자주 발생하여, 이에 대한 원인을 분석하고 대책을 강구하는 연구를 수행하였다. 현재 울진1,2호기 배관상에 설치되어 있는 가속도계 및 응답스펙트럼기록기에 작업자의 실수로 인한 인위적인 충격이나 배관진동에 의해 과도한 진동이 발생할 수 있다는 개연성을 밝혀 내고 이러한 지진감시설비의 개선 및 적합한 설치장소에 대하여 의견을 제시할 수 있는 계기를 마련하였다.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.1
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• pp.57-66
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• 2008

An experimental study was performed to evaluate seismic reduction performance and applicability of 3-dimensional floor isolation system to the main control room of nuclear power plant. A friction pendulum system(FPS) and air spring were designed and fabricated for 3-dimensional floor isolation system. Two kind of the partial experimental model of a main control room attached to the FPS and air spring were tested on the shaking table. The experimental model consisted of a control panel, a $2.5m{\times}2.5m$ access floor, four FPS and air springs. The artificial time histories based on the vertical and horizontal floor response spectrums(OBE, SSE) of the main control room were used as the earthquake input signals in the test. Compared to non-isolated system, the seismic response of experimental models using 3-dimensional floor isolation system were shown considerable seismic reduction performance.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.6
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• pp.509-516
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• 2014

Accuracy of seismic response evaluated by a capacity spectrum method (CSM) is generally known to be less than that by Incremental dynamic analysis (IDA). In this paper, a procedure for IDA based seismic fragility curves for steel moment resisting frames was suggested. This study compares seismic fragility curves using the suggested method (IDA method) with those using a CSM and intends to verify the validity of the IDA method. The shapes of both seismic fragility curves are similar in slight and moderate damage states. However, in the case of extensive and complete damage states, the fragility curves obtained from the IDA method presents a more steep slope due to less variation (or uncertainties). This is due to the fact that the IDA method can properly capture the structural response beyond yielding rather than the CSM.