• Journal of the Korean Society of Hazard Mitigation
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• v.4 no.4 s.15
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• pp.43-54
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• 2004

The broadband receiver functions are developed from teleseismic P waveforms recorded at Wonju(KSRS), Inchon(IRIS), and Pohang(PHN), and are analyzed to examine the crustal structure beneath these stations. The teleseismic receiver functions are inverted in the time domain of the vertical P wave velocity structures beneath the stations. Clear P-to-S converted phases from the Moho interface are observed in teleseismic seismograms recorded at these stations. The crustal velocity structures beneath the stations are estimated by using the receiver function inversion method(Ammon et al., 1990). The general features of inversion results are as follows: (1) For the Inchon station, the Conrad discontinuity exists at 17.5 Km(SW) deep and the Moho discontinuity exists at 29.5 Km(NW) and 30.5 Km(SE, SW) deep. (2) The shallow crustal structure beneath Wonju station may be covered with a sedimentary rock of a 3 Km thickness. The average Moho depth is assumed about 33.0 Km, and the Conrad discontinuity may exist at 17.0 Km(NE) and 21.0 Km(NW) deep. (3) For Pohang station, the thickness of shallow sedimentary layer is a 3.0 Km in the direction of NE and NW. The Moho depth is 28.0 Km in the direction of the NE and NW. The Conrad discontinuity can be estimated to be existed at 21.0 Km deep for the NE and NW directions.

• Journal of the Korean GEO-environmental Society
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• v.20 no.5
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• pp.5-12
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• 2019

On November 15, 2017, a unpredictable liquefaction damage was occurred at the $M_L=5.4$ Pohang earthquake and after, many researches have been conducted in Korea. In Korea, where there were no cases of earthquake damage, it has been extremely neglectable in preparing earthquake risk maps and building earthquake systems that corresponded to prevention and preparation. Since it is almost impossible to observe signs and symptoms of drought, floods, and typhoons in advance, it is very effective to predict the impacts and magnitudes of seismic events. In this study, 14,040 borehole data were collected in the metropolitan area and liquefaction evaluation was performed using the amplification factor. Based on this data, liquefaction hazard maps were prepared for ground accelerations of 0.06 g, 0.14 g, 0.22 g, and 0.30 g, including 200years return period to 4,800years return period. Also, the correlation analysis between the earthquake acceleration and LPI was carried out to draw a real-time predictable liquefaction hazard map. As a result, 707 correlation equations in every cells in GIS map were proposed. Finally, the simulation for liquefaction risk mapping against artificial earthquake was performed in the metropolitan area using the proposed correlation equations.

• Journal of the Korean Geotechnical Society
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• v.28 no.3
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• pp.35-43
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• 2012

Following the companion paper (I. Comparisons with Well-known Seismic Code and Site Response Characteristics), several acceleration data recorded during recent earthquake events in Korea were analyzed to verify the suitability of the proposed two-parameters site classification system and the corresponding site coefficients. For all of rock-soil site pairs less than 30 km distant, response spectrums and corresponding site coefficients, $F_a$ and $F_v$, were determined. Unfortunately, some of data have an eccentric error, where the spectral acceleration of rock site is more amplified than that of soil site. The $F_a$ and $F_v$ for all of pairs except the pairs of error were compared with those in the current code and the proposed system. The $F_a$ and $F_v$ from the recorded motions show definitely different trend from that of the current code. In addition, the site coefficients from recorded motions at four 765 kV substation sites, which are several hundred meters distant, have a remarkably similar trend and absolute values to those in proposed two-parameters site classification system. Based on earthquake motions recorded in domestic areas including data from the four 765 kV substation sites, the two-parameters site classification and site coefficients are superior to the results obtained from the current Korean seismic code.

• Journal of the Korean Geotechnical Society
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• v.20 no.7
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• pp.127-140
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• 2004

Conventional methods for the assessment of liquefaction potential were primarily for areas of severe earthquake zones (M=7.5) such as North America and Japan. Detailed earthquake related researches in Korea started in 1997, including development of the seismic design standards for port and harbour structures, which was later completed in 1999. Because most contents in the guidelines were quoted through literature reviews from North America and Japan, which are located in strong earthquake region, those are not proper in Korea, a moderate earthquake region. This requires further improvement of the present guidelines. Considering earthquake hazard data in Korea, use of laboratory tests based on irregular earthquake motion appears to be effective to reflect the dynamic characteristics of soil more realistically than those using simplified regular loading. In this study, cyclic triaxial tests using irregular earthquake motions are performed with different earthquake magnitudes, relative densities, and fines contents. Assessment of liquefaction potential in moderate earthquake regions is discussed based on various laboratory test results. Effects of these components on dynamic behavior of soils are discussed as well. From the test results, screening limits and magnitude scaling factors to determine the soil liquefaction resistance strength in seismic design were re-investigated and proposed using normalized maximum stress ratios under real irregular earthquake motions.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.3
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• pp.875-888
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• 2013

The researches have recently progressed toward the use of the superelastic shape memory alloys (SMAs) to develop new smart control systems that reduce permanent deformation occurring due to severe earthquake events and that automatically recover original configuration. The superelastic SMA materials are unique metallic alloys that can return to undeformed shape without additional heat treatments only after the removal of applied loads. Once the superelastic SMA materials are thus installed at the place where large deformations are likely to intensively occur, the structural system can make the best use of recentering capabilities. Therefore, this study is intended to propose new buckling-restrained braced frames (BRBFs) with superelastic SMA bracing systems. In order to verify the performance of such bracing systems, 6-story braced frame buildings were designed in accordance with the current design specifications and then nonlinear dynamic analyses were performed at 2D frame model by using seismic hazard ground motions. Based on the analysis results, BRBFs with innovative SMA bracing systems are compared to those with conventional steel bracing systems in terms of peak and residual inter-story drifts. Finally, the analysis results show that new SMA bracing systems are very effective to reduce the residual inter-story drifts.

• 한국지구물리탐사학회:학술대회논문집
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• 2008.10a
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• pp.97-100
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• 2008

Mount Fuji is the focus of intense study because of its potential hazard signaled by seismic, geologic and historical activity. Based on extensive seismic data recorded in the vicinity of Mt. Fuji, coda quality factor ($Q_c^{-1}$) using a single scattering model hypothesis, and intrinsic and scattering quality factor $(Q_i^{-1}$ and $Q_s^{-1})$ using the Multiple Lapse Time Window Analysis (MLTW) method was measured. To focus the study on the magmatic structure below Mt. Fuji, to the data were separated into two groups: a near-Fuji region of rays traversing an area with radius 5 km around the summit (R < 5 km), and a far-Fuji region of rays beyond a radius of 20 km around the summit (R > 20 km). The results of the study have a small error range due to the large data sample, showing that all $Q^{-1}$ values in near-Fuji area are greater than those of far-Fuji area, and $Q_i^{-1}$ for both the near and far-Fuji area is higher than $Q_s^{-1}$ at high frequencies. The $Q_i^{-1}$ values of the near-Fuji area are lower than those of the other volcanic areas considered, while values of $Q_s^{-1}$ are not. The low $Q_i^{-1}$ for the volcanic region of near-Fuji suggests that the magmatic activity, or percent of partial melt, at Mt. Fuji is not as active as hot spot volcanoes such as Kilauea, Hawaii.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.1
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• pp.11-20
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• 2008

In probabilistic seismic analysis of nonlinear structural system, dynamic analysis is performed to obtain the distribution of the response estimate using input ground motion time histories which correspond to a given seismic hazard level. This study investigates the differences in the distribution of the responses and the failure probability according to input ground motion models. Two types of input ground motion models are considered: real earthquake records scaled to specified intensity level and artificial input ground motion fitted to design response spectrum. Simulation results fir a nonlinear SDOF system demonstrate that the spectrum matched input ground motion produces larger failure probability than those of scaled input ground motion due to biased responses. Such tendency is more remarkable in the site of soft soil conditions. Analysis results show that such difference of failure probability is due to the conservative estimation of design response spectrum in the range of long period of ground motion.

• Journal of the Korean earth science society
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• v.33 no.7
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• pp.637-644
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• 2012

The Seoul metropolitan area is densely populated with 40 percent of Korean people and quite weak to the seismic hazard. According to the analysis of historical documents, the largest earthquake occurred in this area is MMI VIII-IX acompanying with a large shaking, collapse of stone walls, collapse of houses, and many casualties. Two times of damaging earthquakes occurred in the first century (A.D. 27, 89), and there was a long quiet period of about 1430 years. Another big earthquakes re-occurred three times in the 16-17 century (1518, 1613, 1692) and then a quiet period has continued to the present time. Just after Seoul earthquake in 1518, aftershocks occurred almost 19 days consecutively and many triggered earthquakes occurred not only in Seoul metropolitan area but also in Hwanghae province, northern Korea. It indicates that the largest potential earthquake in and around Seoul is MMI VIII-IX with a long occurrence period of about 1400-1500 years.

• Tunnel and Underground Space
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• v.26 no.5
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• pp.339-347
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• 2016

The world's first underground repository for low- and intermediate- level radioactive waste (SFR1) has been in operation since 1988. SFR1 can accommodate $1,000m^3$ of radioactive waste per year with 4 chambers and 1 silo with a total capacity of $63,000m^3$ of radioactive waste. With extended operation time of 10 of the 12 nuclear power reactors and dismantling of the other 2 nuclear reactors, more nuclear waste need to be disposed in the future. Therefore, Swedish Nuclear Fuel and Waste Management Company (SKB) submitted a license application for a repository extension (SFR3) that consists of 6 additional rock chambers with a capacity of $108,000m^3$ of radioactive waste and for accommodating 9 boiling water reactor tanks. In this study, plans for the extension SFR3 are presented with the geological, geomechanical and hydrogeological issues to be considered.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.165-165
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• 2011

내진 설계규정이 적용되기 이전에 시공되어 사용 중인 교량의 경우 지진 발생시 교각의 파괴 또는 구조적 피해는 교량 전체 시스템의 붕괴를 초래하므로 지진하중에 대하여 피해를 최소화해야 한다. 이를 위해 내진설계규정이 적용되기 이전의 교량 또는 지진취약지역으로 분류된 곳의 교량, 사회적 중요도가 높은 교량에 대해 교각의 내진성능보강을 실시하고 있다. 2007년 말 국토해양부가 관리하고 있는 11,940개 교량 중 지진 발생시 피해가 우려되는 1,342개(일반국도 682개, 고속국도 600개) 교량에 대해 2006년부터 내진보강이 착수되었고 2009년에는 확대 추진하여 일반국도 80개교, 고속국도 100개교에 대한 보강을 실시하였다. 이와 같이 확대 추진되고 있는 정책에 반해, 내진보강 기술 및 제품이 부족하고 새로운 내진보강재 개발이 불가피해지고 있는 것이 현실이다. 소성영역에서의 횡방향 철근은 지진 시 종방향 철근의 좌굴과 콘크리트의 압축강도저하를 방지하며, 전단보강철근으로도 중요한 역할을 하여 교각의 전단강도를 증가시킨다. 그러나 이러한 횡방향 철근은 초기 설계에 의한 시공이 종료된 후 기존의 성능을 증가시키기 위하여 철근량을 증가하거나 단면의 변화를 주기에는 매우 어려운 일이다. 따라서 내진성능을 위한 단면력 증가를 위하여 다양한 재료의 보강재와 형식이 사용되고 있다. 본 연구에서는 원형교각 모델의 구조해석을 이용해 내진성능평가를 선행한 후 실험체를 제작, Helical Bar를 보강하여 준정적 실험을 통해 내진보강성능을 평가하였다. 압축설계강도 $f_{ck}=240kgf/cm^2$를 기준으로 교량등급 2등교인 일반적인 도로교의 1/4축소모형을 설계, 기초부는 $1,200{\times}600{\times}600$ (mm)으로 철근과 콘크리트로 구성하였으며, 기둥부는 직경 400mm, 높이 1,250mm 크기의 철근콘크리트 원형 교각 실험체를 제작하였다. 제작된 실험체는 총 3개로, 분류는 무보강 일반 실험체, Helical Bar 직경에 따른 분류, 보강간격에 따른 분류로 나누어진다.