• Title, Summary, Keyword: 활성단층

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Numerical Analysis of Stress Regimes in and around Inactive and Active Fault Zones (비활성 그리고 활성 단층지역 내부와 주변에서의 응력장에 대한 수치적 분석)

  • Jeong, Woo-Chang;Song, Jai-Woo
    • Journal of the Korean Society of Hazard Mitigation
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    • v.1 no.1
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    • pp.117-125
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    • 2001
  • This paper presented the analysis of stress regimes in and around inactive and active fault zones. The stress regime in the vicinity of an existing inactive fault zone is dependent on the orientation of the fault with respect to the current stress field and the contrast between the elastic properties of the faulted rock and those of the surrounding rock. In the analysis of stress regimes around an active fault zone, if the yielding stress is exceeded during loading, the localized shearing in a fault zone will result in weakness with mean stresses in the fault becoming lower than those in the surrounding rock. It can be expected that such stress gradients will induce fluid flow towards the faults zone.

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Recent progress in studies on the characteristics of surface rupture associated with large earthquakes (대규모 지진에 수반된 지표파열특성에 관한 최근 연구동향)

  • Choi, Jin-Hyuck;Kim, Young-Seog;Klinger, Yann
    • Journal of the Geological Society of Korea
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    • v.53 no.1
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    • pp.129-157
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    • 2017
  • In given active faults, to explore the location, timing, and size of large paleo-earthquakes is the most essential work to examine characteristics of future large earthquakes, which can be facilitated for seismic hazard assessment and loss mitigation. During the last 20 years, many studies have been conducted for mapping of earthquake surface ruptures and/or active faults, which is greatly indebted to the advances in remote sensing techniques. In particular, based on fault geometry and slip distribution, many studies have tried to understand the effects of fault inheritances on coseismic rupture dynamics as well as temporal and spatial rupture history over multiple earthquake cycle. These studies commonly indicate that seismogenic-scale fault segmentation plays a key role in earthquake rupture behavior and fault evolution. This implies that paleoseismological investigations should be carried out based on fault segmentation in order to infer earthquake recurrence characteristics in a given active fault. Here, after brief reviewing of general concepts, materials/methods, and history/trend of the study on earthquake surface ruptures and active faults, we introduce major results of the most recent studies. Finally, we suggest a possible segmentation system of the Yangsan fault in southeast Korea based on previous paleoseismological studies, and discuss research strategies for further active fault researches in Korea and its associated seismic hazard assessment.

Evaluation on Geological Structures to Secure Long-term Safety of Nuclear Facility Sites (원자력시설물 부지의 장기적 안전성 확보를 위한 지질구조 평가)

  • Jin, Kwangmin;Kim, Young-Seog
    • Economic and Environmental Geology
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    • v.51 no.2
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    • pp.149-166
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    • 2018
  • Many large earthquakes have continuously been reported and resulted in significant human casualties and extensive damages to properties globally. The accident of Fukushima nuclear power plant in Japan was caused by a mega-tsunami, which is a secondary effect associated with the Tohoku large earthquake (M=9.0, 2011. 3. 11.). Most earthquakes occur by reactivation of pre-existing active faults. Therefore, the importance of paleoseismological study have greatly been increased. The Korean peninsula has generally been considered to be a tectonically stable region compared with neighboring countries such as Japan and Taiwan, because it is located on the margin of the Eurasian intra-continental region. However, the recent earthquakes in Gyeongju and Pohang have brought considerable insecurity on earthquake hazard. In particular, this region should be secure against earthquake, because many nuclear facilties and large industrial facilities are located in this area. However, some large earthquakes have been reported in historic documents and also several active faults have been reported in southeast Korea. This study explains the evaluation methods of geological structures on active fault, fault damage zone, the relationship between earthquake and active fault, and respect distance. This study can contribute to selection of safe locations for nuclear facilities and to earthquake hazards and disaster prevention.

Gravity Field Interpretation and Underground Structure Modelling as a Method of Setting Horizontal and Vertical Zoning of a Active Fault Core (활성단층의 3차원적인 규모를 결정하기 위한 중력장 데이터의 해석 및 지각구조 모델링: 양산단층에서의 예)

  • Choi, Sungchan;Kim, Sung-Wook;Choi, Eun-Kyeong;Lee, Young-Cheol;Ha, Sangmin
    • Economic and Environmental Geology
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    • v.54 no.1
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    • pp.91-103
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    • 2021
  • In order to estimate the vertical and horizontal structural in the Yangsan fault core line (Naengsuri area, Pohang), we carried out gravity field measurements and interpretation procedures such as Euler deconvolution method and curvature analysis in addition to the forward modelling technique (i.e. IGMAS+). We found a prominent gravity difference of more than 1.5 mGal across the fault core. This indicates a distinct density difference between the western and eastern crustal area across the Yangsan fault line. Comparing this gravity field interpretation with other existent geologic and geophysical survey data (e.g. LiDAR, trenching, electric resistivity measurements), It is concluded that (1) the prominent gravity difference is caused by the density difference of about 0.1 g/㎤ between the Bulguksa Granite in the west and the Cretaceous Sandstone in the east side, (2) the fault core is elongated vertically into a depth of about 2,000 meters and extended horizontally 3,000 meters to the NNE direction from Naengsuri area. Our results present that the gravity field method is a very effective tool to estimate a three -dimensional image of the active fault core.

Research on Earthquake Occurrence Characteristics Through the Comparison of the Yangsan-ulsan Fault System and the Futagawa-Hinagu Fault System (양산-울산 단층계와 후타가와-히나구 단층계의 비교를 통한 지진발생특성 연구)

  • Lee, Jinhyun;Gwon, Sehyeon;Kim, Young-Seog
    • The Journal of the Petrological Society of Korea
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    • v.25 no.3
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    • pp.195-209
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    • 2016
  • The understanding of geometric complexity of strike-slip Fault system can be an important factor to control fault reactivation and surface rupture propagation under the regional stress regime. The Kumamoto earthquake was caused by dextral reactivation of the Futagawa-Hinagu Fault system under the E-W maximum horizontal principal stress. The earthquakes are a set of earthquakes, including a foreshock earthquake with a magnitude 6.2 at the northern tip of the Hinagu Fault on April 14, 2016 and a magnitude 7.0 mainshock which generated at the intersection of the two faults on April 16, 2016. The hypocenters of the main shock and aftershocks have moved toward NE direction along the Futagawa Fault and terminated at Mt. Aso area. The intersection of the two faults has a similar configuration of ${\lambda}$-fault. The geometries and kinematics, of these faults were comparable to the Yansan-Ulsan Fault system in SE Korea. But slip rate is little different. The results of age dating show that the Quaternary faults distributed along the northern segment of the Yangsan Fault and the Ulsan Fault are younger than those along the southern segment of the Yansan Fault. This result is well consistent with the previous study with Column stress model. Thus, the seismic activity along the middle and northern segment of the Yangsan Fault and the Ulsan Fault might be relatively active compared with that of the southern segment of the Yangsan Fault. Therefore, more detailed seismic hazard and paleoseismic studies should be carried out in this area.

Discussions on the September 2016 Gyeongju Earthquakes (2016년 9월 경주지진 소고(小考))

  • Lee, Kiehwa
    • Geophysics and Geophysical Exploration
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    • v.20 no.3
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    • pp.185-192
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    • 2017
  • A sequence of earthquakes with the main shock $M_L$ 5.8 occurred on September 12 2016 in the Gyeongju area. The main shock was the largest earthquakes in the southern part of the Korean peninsula since the instrumental seismic observation began in the peninsula in 1905 and clearly demonstrated that the Yangsan fault is seismically active. The mean focal depth of the foreshock, main shock, and aftershock of the Gyeongju earthquakes estimated by the crustal model of single layer of the Korean peninsula without the Conrad discontinuity turns out to be 12.9 km, which is 2.8 km lower than that estimated based on the IASP91 reference model with the Conrad discontinuity. The distribution of the historical and instrumental earthquakes in the Gyeongju area indicates that the Yangsan fault system comprising the main Yangsan fault and its subsidiary faults is a large fracture zone. The epicenters of the Gyeongju earthquakes show that a few faults of the Yangsan fault system are involved in the release of the strain energy accumulated in the area. That the major earthquakes of Gyeongju earthquakes occurred not on the surface but below 10 km depth suggests the necessity of the study of the distribution of deep active faults of the Yangsan fault system. The magnitude of maximum earthquake of the Gyeongju area estimated based on the earthquake data of the area turns out to be 7.3. The recurrence intervals of the earthquakes over magnitudes 5.0, 6.0 and 7.0 based on the earthquake data since 1978, which is the most complete data in the peninsula, are estimated as 80, 670, and 5,900 years, respectively. The September 2016 Gyeongju earthquakes are basically intraplate earthquakes not related to the Great East Japan earthquake of March 11 2011 which is interplate earthquake.

Basic Concepts and Geological Applications of LiDAR (LiDAR 기법의 기본원리와 지질학적 적용)

  • Kim, Hyun-Tae;Kim, Young-Seog;We, Kwang-Jae
    • The Journal of Engineering Geology
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    • v.24 no.1
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    • pp.123-135
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    • 2014
  • Earthquakes can cause serious loss of life and significant property damage. Thus, the study of active faults is important in evaluating future fault activity and hazards caused by future earthquake events. Structural mapping and the tracing of active faults are the primary steps in studies of active faults. Until now, active faults in South Korea have been mapped using aerial photography, satellite images, and low-quality DEMs. Lineament analysis as a means of identifying active faults is relatively difficult in Korea due to geological characteristics (weak tectonic activity) and dense vegetation cover. In this paper, we introduce the basic concept of the LiDAR technique (a new prospective remote sensing method) and a data analysis method that can overcome these problems. This paper will contribute to a better understanding of the airborne LiDAR technique and its application to South Korea. Some preliminary results from Korean and USA LiDAR data show the usefulness of this technique for tracing lineaments, active faults, and terraces in South Korea.