• 대한토목학회논문집
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• 제41권6호
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• pp.687-695
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• 2021

최근 국내에서 큰 규모의 지진이 발생하게 되면서 내진설계의 중요성이 크게 증가하였다. 내진설계기준에서는 중요구조물 또는 특수구조물에 대해서는 동적시간이력해석을 수행하도록 규정하고 있다. 이러한 중요 또는 특수 구조물의 내진해석 및 설계에 있어 합리적 설계 입력 지진파를 결정하는 것은 해석 및 설계의 신뢰도를 확보하는데 매우 중요한 요소이다. 내진설계기준에서 합리적 설계 지진파는 해당 지역(단층)의 특성을 반영하면서 동시에 내진 성능 수준별 설계응답스펙트럼을 만족해야 한다. 이러한 요구조건은 해당 지역(단층)에서 계측됐던 실 지진파를 설계응답스펙트럼에 상응하게 수정하여 부분적으로 만족시킬 수 있다. 본 연구에서는 하모닉웨이브릿변환(Harmonic Wavelet Transform)을 이용하여 실 계측 지진파를 기반으로 설계응답스펙트럼에 상응하게 지진파시간이력 수정·생성 하는 방법을 제안하였다. 제안한 기법의 적용성 검토를 위해 경주(2016년)와 포항(2017년)에서 발생했던 각 규모 5.8과 5.4의 지진에 제안된 기법을 적용하여 설계응답스펙트럼에 상응한 지진파시간이력을 수정·생성 하였다

• Geomechanics and Engineering
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• 제8권3호
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• pp.377-390
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• 2015

The governing equations of wave propagation in one dimension of elastic continuum materials are investigated by taking the influence of the initial stress into account. After a short review of the theory of elastic wave propagation in a rock mass with an initial stress, results indicate that the initial stress differentially influences P-wave and S-wave propagation. For example, when the initial stress is homogeneous, for the P-wave, the initial stress only affects the magnitude of the elastic coefficients, but for the S-wave, the initial stress not only influences the elastic coefficients but also changes the governing equation of wave propagation. In addition, the P-wave and S-wave velocities were measured for granite samples at a low initial stress state; the results indicate that the seismic velocities increase with the initial stress. The analysis of the previous data of seismic velocities and elastic coefficients in rocks under ultra-high hydrostatic initial stress are also investigated.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2006년도 학술발표회 논문집
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• pp.25-32
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• 2006

We present a imaging method of seismic sources by time reversal propagation of seismic waves. Time-reversal wave propagation is actively used in medical imaging, non destructive testing and waveform tomography. Time-reversal wave propagation is based on the time-reversal invariance and the spatial reciprocity of the wave equation. A signal is recorded by an array of receivers, time-reversed and then back-propagated into the medium. The time-reversed signal propagates back into the same medium and the energy refocuses back at the source location. The increasing power of computers and numerical methods makes it possible to simulate more accurately the propagation of seismic waves in heterogenous media. In this work, a staggered-grid finite-difference solution of the elastic wave equation is employed for the wave propagation simulation. With numerical experiments, we show that the time-reversal imaging will enable us to explore the spatio-temporal history of complex earthquake.

• 한국전산구조공학회논문집
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• 제22권1호
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• pp.45-52
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• 2009

본 논문에서는 파랑하중과 지진하중 하에서의 방파제 설계와 관련한 해석에 대한 하나의 설계지침을 제시하였다. 이를 위해서 파랑하중 중 쇄파대내에서 일어날 수 있는 충격파랑하중을 정량적으로 하나의 모델에 대해 제안된 식에 의해 산출 해 보았다. 널리 사용되는 모리슨 방정식에 의한 파력과 쇄파력으로 야기되는 충격하중을 산술적으로 합하는 방식으로 계산해보았다. 결과적으로 충격하중이 크지 않아, 일반적으로 쇄파파력산정에 있어서 오차범위가 큰 불규칙파의 쇄파대내의 파력공식인 고다식을 사용하는 것은 큰 문제가 없다는 가정을 할 수 있었다. 이에 파랑하중의 경우 항만구조물에 사용되는 고다식을 이용하여 방파제 구조물의 거동을 해석해 보았다. 지진하중의 경우 단주기, 장주기, 인공지진파에 의한 수치해석을 수행하여 방파제의 거동을 해석하였다. 방파제의 설계에 있어서 중요한 것은 설치해역에 적합한 방파제를 선택하는 문제이며 다음으로는 파랑하중과 지진하중의 중요도를 판단하는 것이라 판단된다. 모델을 선정하여 계산해본 결과 파랑하중에 의한 구조물의 거동과 지진하중에 의한 거동이 같은 정도의 구조적인 변화를 나타내는 것으로 판단되어 방파제 설계 시 두 하중을 같은 비중으로 다루어야 할 것으로 판단되어 진다. 방파제 설계의 주요 항목으로 파랑하중과 지진하중이 동시에 중요하다는 점을 제시하였다.

• 한국지진공학회논문집
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• 제23권3호
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• pp.191-199
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• 2019

To calculate proper seismic design load and seismic design category, the exact site class for construction site is required. At present, the average shear-wave velocity for multi-layer soil deposits is calculated by the sum of shear-wave velocities without considering of vertical relationship of the strata. In this study, the transfer function for the multi-layered soil deposits was reviewed on the basis of the wave propagation theory. Also, the transfer function was accurately verified by the finite element model and the eigenvalue analysis. Three methods for site period estimation were evaluated. The sum of shear-wave velocities underestimated the average shear-wave velocities of 526 strata with large deviations. The equation of Mexican code overestimated the average shear-wave velocities. The equation of Japanese code well estimated the average shear-wave velocities with small deviation.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2005년도 제7회 특별심포지움 논문집
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• pp.3-9
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• 2005

In order to obtain more reliable data for the information on the ground, a new site Investigation method is proposed, in which seismic waves (S-waves) generated by the Swedish Ram Sounding Test (SRS) are used. It is indicated that the energy transferred from the hammer to the rod in SRS's is much more stable, compared to SPT's. A series of SRS with measurements of seismic waves at the ground surface were carried out to clarify the characteristics of seismic wave propagation in the ground. As the results of comparison between seismic S-wave amplitudes and $N_d$ (blow count for 20 cm penetration in SRS), it was found that amplitudes of S-waves generated by SRS correlate well with $N_d$. The amplitude of the S-wave is thought to be more adequate parameter for the soil strength and rigidity than $N_d$.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 1999년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall
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• pp.91-98
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• 1999

In this study a modified ground strain model is developed for an equivalent earthquake load and is applied to the seismic analysis of buried pipelines, The ground strain can be obtained using the ratio of a maximum ground velocity to a wave propagation velocity. To reflect soil conditions and seismic characteristics the wave propagation velocity is evaluated by a proposed dispersion curve based on wave energy distribution. In order to verify the procedures the observed earthquake data and the results of this study are compared. For the application of an equivalent earthquake load to the seismic analysis the buried pipelines are modeled using the beam theory. the results of the analyses are compared with those of a dynamic analysis code and those obtained from the response displacement method. Finally various parametric studies considering different soil conditions and seismic loads are examined.

• Geomechanics and Engineering
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• 제23권4호
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• pp.327-338
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• 2020

The role of precise prediction of subsurface fluids and discrimination among them cannot be ignored in reservoir characterization and petroleum prospecting. A suitable rock physics model should be build for the extraction of valuable information form seismic data. The main intent of current work is to present a rock physics model to analyze the characteristics of seismic wave propagating through a cracked porous rock saturated by a three phase fluid. Furthermore, the influence on wave characteristics due to variation in saturation of water, oil and gas were also analyzed for oil and water as wet cases. With this approach the objective to explore wave attenuation and dispersion due to wave induce fluid flow (WIFF) at seismic and sub-seismic frequencies can be precisely achieved. We accomplished our proposed approach by using BISQ equations and by applying appropriate boundary conditions to incorporate heterogeneity due to saturation of three immiscible fluids forming a layered system. To authenticate the proposed methodology, we compared our results with White's mesoscopic theory and with the results obtained by using Biot's poroelastic relations. The outcomes reveals that, at low frequencies seismic wave characteristics are in good agreement with White's mesoscopic theory, however a slight increase in attenuation at seismic frequencies is because of the squirt flow. Moreover, our work crop up as a practical tool for the development of rock physical theories with the intention to identify and estimate properties of different fluids from seismic data.

• 한국지반신소재학회논문집
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• 제19권1호
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• pp.55-63
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• 2020

본 연구에서는 다층으로 구성된 깊은 토사지반 내 박스구조물에 대하여 지진하중이 작용할 때 동적거동 특성을 규명하기 위하여 진동대를 이용한 축소모형시험과 유효응력을 고려한 내진해석을 수행하였다. 입력지진파는 장주기파(Hachinohe), 단주기파(Ofunato)와 인공지진파 및 최근 경주 및 포항지역에서 발생한 실지진파 등 5개의 지진파를 사용하여 하부지반에서 작용시켰다. 모형실험 및 수치해석 분석결과, 지진하중 작용시 박스구조물에 발생하는 변위는 연직방향이 수평방향에 비해 크게 발생하였으며, 기초지반 하부의 과잉간극수압 증가가 변위를 유발하는 것으로 확인하였다. 또한, 실지진파에 비해 인공지진파 작용시 지반 및 지중구조물의 동적거동이 크게 나타났다.

• Ocean and Polar Research
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• 제29권1호
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• pp.9-31
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• 2007

Most seismic sea waves in the East Sea originate from earthquakes occurring near the Japanese west coast. While the waves propagate in the East Sea, they are deformed by refraction, diffraction and scattering. Though the Boussinesq equation is most applicable for such wave phenomena, it was not used in numerical modelling of seismic sea waves in the East Sea. To examine characteristics of seismic sea waves in the East Sea, numerical models based on the Boussinesq equation are established and used to simulate recent tsunamis. By considering Ursell parameter and Kajiura parameter, it is proved that Boussinesq equation is a proper equation for seismic sea waves in the East Sea. Two models based on the Boussinesq equation and linear wave equation are executed with the same initial conditions and grid size ($1min{\times}1min$), and the results are compared in various respects. The Boussinesq equation model produced better results than the linear model in respect to wave propagation and concentration of wave energy. It is also certified that the Boussinesq equation model can be used for operational purpose if it is optimized. Another Boussinesq equation model whose grid size is $40sec{\times}30sec$ is set up to simulate the 1983 and 1993 tsunamis. As the result of simulation, new propagation charts of 2 seismic sea waves focused on the Korean east coast are proposed. Even though the 1983 and 1993 tsunamis started at different areas, the propagation paths near the Korean east coast are similar and they can be distinguished into 4 paths. Among these, total energy and propagating time of the waves passing over North Korea Plateau(NKP) and South Korea Plateau(SKP) determine wave height at the Korean east coast. In case of the 1993 tsunami, the wave passing over NKP has more energy than the wave over SKP. In case of the 1983 tsunami, the huge energy of the wave passing over SKP brought about great maximum wave heights at Mukho and Imwon. The Boussinesq equation model established in this study is more useful for simulation of seismic sea waves near the Korean east coast than it is the Japanese coast. To improve understanding of seismic sea waves in shallow water, a coastal area model based on the Boussinesq equation is also required.