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Earthquake Wave Propagation Using Staggered-grid Finite-difference Method in the Model of the Antarctic Region (엇격자 유한차분법을 이용한 극지해역 지진파 모델링)

  • Oh, Ju-Won;Min, Dong-Joo;Lee, Ho-Yong;Park, Min-Kyu
    • Journal of the Korean earth science society
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    • v.32 no.6
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    • pp.640-653
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    • 2011
  • We simulate the propagation of earthquake waves in the continental margin of Antarctica using the elastic wave modeling algorithm, which is modified to be suitable for acoustic-elastic coupled media and earthquake source. To simulate the various types of earthquake source, the staggered-grid finite-difference method, which is composed of velocity-stress formulae, can be more appropriate to use than the conventional, displacement-based, finite-difference method. We simulate the elastic wave propagation generated by earthquakes combining 3D staggered-grid finite-difference algorithm composed of displacement-velocity-stress formulae with double couple mechanisms for earthquake source. Through numerical tests for left-lateral strike-slip fault, normal fault and reverse fault, we could confirm that the first arrival of P waves at the surface is in a good agreement with the theoretically-predicted results based on the focal mechanism of an earthquake. Numerical results for a model made after the subduction zone in the continental margin of Antarctica showed that earthquake waves, generated by the reverse fault and propagating through the continental crust, the oceanic crust and the ocean, are accurately described.

Calcifying Aponeurotic Fibroma - A Case Report - (석회화 건막 섬유종 - 증례 보고 -)

  • Paik, Seung-Sam;Jang, Ki-Seok;Han, Hong Xiu;Kim, Hyung-Jong;Roh, Won-Il;Lee, Seong-Pil;Lee, Kwang-Hyun
    • The Journal of the Korean bone and joint tumor society
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    • v.9 no.2
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    • pp.233-237
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    • 2003
  • Calcifying aponeurotic fibroma is a benign, aggressive fibrous tumor seen in childhood or adolescence that most commonly affects the palm. We report our experience in treating calcifying aponeurotic fibroma in the hand of fifteen-year-old boy. He was presented with a recurrent mass in hypothenar area of his left hand. He had a history of local excision of the mass 7 years ago in local clinic. The palpable mass was hard, tender and movable. The simple X-ray revealed multifocally scattered microcalcifications in the mass. The excised mass showed the features of dense fibrotic soft tissue tumor with multiple small whitish calcifications. The microscopic sections showed a lobulated and a poorly circumscribed proliferation of dense fibrous tissue, containing islands of metaplastic chondroid differentiation with prominent calcification. The recommended treatment of this lesion is wide excision allowing for sparing of functional or vital structures, but high recurrence rate as this case has been reported to be more than 50 percent.

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A Survey on the Oral Health in Accordance with The Oral Health Behavior of Children in Kindergarten (유치원 아동들의 구강보건행태에 따른 구강건강실태 연구)

  • Lee, YunHui;Jwa, SuKyung;Choi, MiSung
    • Journal of the Korean Society of Radiology
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    • v.7 no.6
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    • pp.419-426
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    • 2013
  • This study was performed in order to suggest the basic informations about the proper oral health babits for kindergarten children, through the investigation of the oral health survey and their oral haelth behaviors. 213 of kindergarten children age 6 were surveyed who has lived at Daegu city and the examined data were analysed by use of spss 18.0 ver.program. The children who had performed the toothbrushing for 3 or 4 times a day, were estimated as high level in voluntary under taking of toothbrushing. It revealed that the low of the caries experience rate in the group of the sabiects who performed toothbrushing at every after meals. On the other hands, both the caries experience index of children who had perfomed toothbrushing with the rolling method and the dental plague index of children who had performed the toothbrushing just the morning time of the oral examination day, wer reveealed as high scores, due to the lack of the abilities to perform the toothbrusing with the proper method. It was needed to educate children for practical performing the toothbrush as well as for traning it with the right way, in order to promote the oral health for kindergarten children.

Mesozoic Gold-Silver Mineralization in South Korea: Metallogenic Provinces Reestimated to the Geodynamic Setting (남한의 중생대 금-은광화작용: 지구동력학적 관점에서 재검토된 금-은광상구)

  • Choi, Seon-Gyu;Park, Sang-Joon;Kim, Sung-Won;Kim, Chang-Seong;Oh, Chang-Whan
    • Economic and Environmental Geology
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    • v.39 no.5 s.180
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    • pp.567-581
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    • 2006
  • The Au-Ag lode deposits in South Korea are closely associated with the Mesozoic granitoids. Namely, the Jurassic deposits formed in mesozonal environments related to deep-seated granitoids, whereas the Cretaceous ones were developed in porphyry-related environments related to subvolcanic granitoids. The time-space relationships of the Au-Ag lode deposits in South Korea are closely related to the changing plate motions during the Mesozoic. Most of the Jurassic auriferous deposits (about $165{\sim}145$ Ma) show fluid characteristics typical of an orogenic-type gold deposits, and were probably generated in a compressional to transpressional regime caused by an orthogonal to oblique convergence of the Izanagi Plate into the East Asian continental margin. On the other hand, strike-slip faults and caldera-related fractures together with subvolcanic activity are associated with major strike-slip faults reactivated by a northward (oblique) to northwestward (orthogonal) convergence, and probably have played an important role in the formation of the Cretaceous Au-Ag lode deposits (about $110{\sim}45$ Ma) under a continental arc setting. The temporal and spatial distinctions between the two typical Mesozoic deposit styles in South Korea probably reflect a different thermal episodes (i.e., late orogenic and post-orogenic) and ore-forming fluids related to different depths of emplacement of magma due to regional changes in tectonic environment.

Stratigraphy of the Central Sub-basin of the Gunsan Basin, Offshore Western Korea (한국 서해 대륙붕 군산분지 중앙소분지의 층서)

  • Kim, Kyung-min;Ryu, In-chang
    • Economic and Environmental Geology
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    • v.51 no.3
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    • pp.233-248
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    • 2018
  • Strata of the Central sub-basin in the Gunsan Basin, offshore, western Korea were analyzed by using integrated stratigraphy approach. As a result, five distinct unconformity-bounded units are recognized in the basin: Sequence I (Cretaceous or older(?)), Sequence II (Late Cretaceous), Sequence III (late Late Cretaceous or younger(?)), Sequence IV (Early Miocene or older(?)), Sequence V (Middle Miocene). Since the late Late Jurassic, along the Tan-Lu fault system wrench faults were developed and caused a series of small-scale strike-slip extensional basins. The sinistral movement of wrench faults continued until the Late Cretaceous forming a large-scale pull-apart basin. However, in the Early Tertiary, the orogenic event, called the Himalayan Orogeny, caused basin to be modified. From Late Eocene to Early Miocene, tectonic inversion accompanied by NW strike folds occurred in the East China. Therefore, the late Eocene to Oligocene was the main period of severe tectonic modification of the basin and Oligocene formation is hiatus. The rate of tectonic movements in Gunsan Basin slowed considerably. In that case, thermal subsidence up to the present has maintained with marine transgressions, which enable this area to change into the land part of the present basin.

Movement History of the Yangsan Fault based on Paleostress Analysis (고응력 분석을 통한 양산단층의 구조운동사)

  • 장천중;장태우
    • The Journal of Engineering Geology
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    • v.8 no.1
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    • pp.35-49
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    • 1998
  • To interpret the movement historv of the Yangsan fault, the paleostresses were analyzed from about 1,000 striated small faults and 330 extension joints which were measured from 37 sites near and along the strike of the Yangsan fault from Yangsan-si, Kyeongsangnam-do to the Shinkwang-myeon, Kyeongsangbuk-do. Six sequential tectonic events have boen established as followings: (I) NW-SE extension, (Il) ENE-WSW compression and NNW-SSE extension, (III) NW-SE compression, (W) ENE-WSW extension, (V) E-W comoression and N-S extension, and (VI) NNE-SSW compression and(VI) NNE-SSWextension. The movement history of the Yangsan fault rnrning in NNE direction were inteepreted based on these six sequential stress fields. The initial feature of the Yangsan fault was formed at the first stage with the development of extension fractures by tectonic event (I) of NW-SE extension. The fault was acted continuously with a right-1ateral strike-slip movement by tectonic event( II) closely related to event( I). The movements had been continued until the Late Miocene. This age was the most active period in faulting. The left-lateral strike-slip movement was followed by subsequent tectonic events (ffi) and (IV). The activity of the Yangsan fault was suspended temporarily by compression of tectonic event (V) which was perpendicular to the strike of the fault. This period might be very short and the magnitude of the tectonic was also small. In the last stage, the fault acted with slight extension or right-lateral moveenent by tectonic event (VI).

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The Geodynamic Evolution of the Chugaryeong Fault Valley in a View Point of Paleomagnetism (고지자기학적 관점에서 본 추가령단층곡의 생성과 진화)

  • 이윤수;민경덕;황재하
    • Economic and Environmental Geology
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    • v.34 no.6
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    • pp.555-571
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    • 2001
  • The dynamic evolution of the Chugaryeong fault valley is studied by paleomagnetic works on 163 samples at 16 sites from Late Cretaceous and Quaternary volcanic rocks in the valley. Conglomerate test and stepwised thermal/alternating field demagnetization indicate that all the characteristic directions are of primary origin. Paleomagnetic pole ponsition(216.8$^{\circ}$E/7l .6$^{\circ}$N; dp=7.1$^{\circ}$, dm=10.0$^{\circ}$) for the upper par of the Jijangbong Volcanic Complex Is indistinguishable from the coeval retference pole position from the Gyeongsang Basin, which further substanciates the reliability of the Paleomagnetic data. This indicates the study area has not undergone any tectonic rotation since Late Cretaceous by uy significant reactivation of the Chugaryeong fault valley. The Quaternary pole position (134.2$^{\circ}$E/86.5$^{\circ}$N; $A_{95}$=7.1 $^{\circ}$) from the Jeongog Basalt reflects the present geocentric axial dipole field for the area, supporting the above conclusion. Unlike the upper part, paleomasnelic directions of the lower part of the Jijangbong Volcanic Complex show random distrinution between sites. We interpret that the early stage of the volcanic activity was created by sinistral strike slip motion of the Chugaryeong fault during early Late Cretaceous. The creation and evolution of the Chugaryeong fault valley emphasize the significance of the kinematic FR (folding ruler) model in east Asia.

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Fracture Developing History and Density Analysis based on Grid-mapping in Bonggil-ri, Gyeongju, SE Korea (경주시 봉길리 지역의 단열발달사 및 단열밀도 해석)

  • Jin, Kwang-Min;Kim, Young-Seog
    • The Journal of Engineering Geology
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    • v.17 no.3
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    • pp.455-469
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    • 2007
  • The study area, Bonggil-ri, Gyeongju, SE Korea, is composed of Cretaceous sedimentary rocks, and Tertiary igneous rocks and dykes. A research on fracture developing history and density distribution was carried out on well exposed Tertiary granites. The fractures developed in this area have the following sequence; NW-SE trending duo-tile shear bands (set a), NNW-SSE trending extensional fractures (set d), WNW-ESE trending extensional or normal fractures (set b), NE-SW trending right-lateral fractures (set c), WNW-ESE trending reverse fault reactivated from normal faults (set e) and NW-SE trending left-lateral faults reactivated from shear bands (set a) under brittle condition. According to the result of fracture density analysis, the fracture density in this area depends on rock property rather than rock age, and also higher fracture density is observed around fault damage zones. However, this high fracture density may also be related to the cooling process associated with dyke intrusion as well as rock types and fault movement. Regardless of the reason of the high fracture density, high fracture density itself contributes to fluid flow and migration of chemical elements.

Interpretation of Paleostress using Geological Structures observed in the Eastern Part of the Ilgwang Fault (일광단층 동편에서 관찰되는 지질구조를 이용한 고응력사 해석)

  • Kim, Taehyung;Jeong, Su-Ho;Lee, Jinhyun;Naik, Sambit Prasanajit;Yang, Wondong;Ji, Do Hyung;Kim, Young-Seog
    • The Journal of Engineering Geology
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    • v.28 no.4
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    • pp.645-660
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    • 2018
  • In the southeastern part of the Korean Peninsula, huge fault valleys, including the Yangsan and Ulsan faults, are recognized. These NNE-SSW trending lineaments are called as a whole Yangsan Fault System. However, this fault system is relatively poorly studied except the Yangsan and Ulsan faults. This study deduced the paleostress history based on the mutual cross-cutting relationships between geologic structures developed in the granite body near the Ilgwang fault, which is compared with previous studies. In the study area, four lineaments parallel to the Ilgwang fault are recognized, and three of them show evidences of faulting. In each lineament, both slip-senses of left-lateral and right-lateral are recognized. It indicates that these faults consistently underwent multiple deformations of inversion along the faults. The inferred paleostress directions based on the mutual cross-cutting relationships of the geological structures are as follows: 1) Tensile fractures developed in the late Cretaceous under the ENE-WSW direction of compressive stress, 2) NW-SE trending maximum horizontal principal stress generated conjugate strike-slip faults, and 3) selective reactivations of some structures were derived under the compression by the NE-SW trending principal stress.

Stratigraphic response to tectonic evolution of sedimentary basins in the Yellow Sea and adjacent areas (황해 및 인접 지역 퇴적분지들의 구조적 진화에 따른 층서)

  • Ryo In Chang;Kim Boo Yang;Kwak won Jun;Kim Gi Hyoun;Park Se Jin
    • The Korean Journal of Petroleum Geology
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    • v.8 no.1_2 s.9
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    • pp.1-43
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    • 2000
  • A comparison study for understanding a stratigraphic response to tectonic evolution of sedimentary basins in the Yellow Sea and adjacent areas was carried out by using an integrated stratigraphic technology. As an interim result, we propose a stratigraphic framework that allows temporal and spatial correlation of the sedimentary successions in the basins. This stratigraphic framework will use as a new stratigraphic paradigm for hydrocarbon exploration in the Yellow Sea and adjacent areas. Integrated stratigraphic analysis in conjunction with sequence-keyed biostratigraphy allows us to define nine stratigraphic units in the basins: Cambro-Ordovician, Carboniferous-Triassic, early to middle Jurassic, late Jurassic-early Cretaceous, late Cretaceous, Paleocene-Eocene, Oligocene, early Miocene, and middle Miocene-Pliocene. They are tectono-stratigraphic units that provide time-sliced information on basin-forming tectonics, sedimentation, and basin-modifying tectonics of sedimentary basins in the Yellow Sea and adjacent area. In the Paleozoic, the South Yellow Sea basin was initiated as a marginal sag basin in the northern margin of the South China Block. Siliciclastic and carbonate sediments were deposited in the basin, showing cyclic fashions due to relative sea-level fluctuations. During the Devonian, however, the basin was once uplifted and deformed due to the Caledonian Orogeny, which resulted in an unconformity between the Cambro-Ordovician and the Carboniferous-Triassic units. The second orogenic event, Indosinian Orogeny, occurred in the late Permian-late Triassic, when the North China block began to collide with the South China block. Collision of the North and South China blocks produced the Qinling-Dabie-Sulu-Imjin foldbelts and led to the uplift and deformation of the Paleozoic strata. Subsequent rapid subsidence of the foreland parallel to the foldbelts formed the Bohai and the West Korean Bay basins where infilled with the early to middle Jurassic molasse sediments. Also Piggyback basins locally developed along the thrust. The later intensive Yanshanian (first) Orogeny modified these foreland and Piggyback basins in the late Jurassic. The South Yellow Sea basin, however, was likely to be a continental interior sag basin during the early to middle Jurassic. The early to middle Jurassic unit in the South Yellow Sea basin is characterized by fluvial to lacustrine sandstone and shale with a thick basal quartz conglomerate that contains well-sorted and well-rounded gravels. Meanwhile, the Tan-Lu fault system underwent a sinistrai strike-slip wrench movement in the late Triassic and continued into the Jurassic and Cretaceous until the early Tertiary. In the late Jurassic, development of second- or third-order wrench faults along the Tan-Lu fault system probably initiated a series of small-scale strike-slip extensional basins. Continued sinistral movement of the Tan-Lu fault until the late Eocene caused a megashear in the South Yellow Sea basin, forming a large-scale pull-apart basin. However, the Bohai basin was uplifted and severely modified during this period. h pronounced Yanshanian Orogeny (second and third) was marked by the unconformity between the early Cretaceous and late Eocene in the Bohai basin. In the late Eocene, the Indian Plate began to collide with the Eurasian Plate, forming a megasuture zone. This orogenic event, namely the Himalayan Orogeny, was probably responsible for the change of motion of the Tan-Lu fault system from left-lateral to right-lateral. The right-lateral strike-slip movement of the Tan-Lu fault caused the tectonic inversion of the South Yellow Sea basin and the pull-apart opening of the Bohai basin. Thus, the Oligocene was the main period of sedimentation in the Bohai basin as well as severe tectonic modification of the South Yellow Sea basin. After the Oligocene, the Yellow Sea and Bohai basins have maintained thermal subsidence up to the present with short periods of marine transgressions extending into the land part of the present basins.

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