• Korean Journal of Mineralogy and Petrology
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• v.36 no.1
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• pp.55-72
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• 2023

This study aims to identify the fault zone architecture and geometric and kinematic characteristics of the Yeongdeok Fault, based on the geometry and kinematic data of various structural elements obtained by detailed field survey and anisotropy of magnetic susceptibility (AMS) of the fault rocks. The Yeongdeok Fault extends from Opo-ri, Ganggu-myeon, Yeongdeok-gun to Gilgok-ri, Maehwa-myeon and Bangyul-ri, Giseong-myeon, Uljin-gun, and cuts various rock types from the Paleo-proterozoic to the Mesozoic with a range of 4.6-5.0 km (4.77 km in average) of right-lateral offset or forms the rock boundaries. The fault is divided into four segments based on its geometric features and shows N-S to NNW strikes and dips of an angle of ≥ 54° to the east at most outcrops, even though the outcrops showing the westward dipping (a range of 54°-82°) of fault surface increase as it goes north. The Yeongdeok Fault shows the difference in the fault zone architecture and in the fault core width ranging from 0.3 to 15 m depending on the bedrock type, which is interpreted as due to differences in the physical properties of bedrock such as ductility, mineral composition, particle size, and anisotropy. Combining the results of paleostress reconstruction and AMS in this and previous studies, the Yeongdeok Fault experienced (1) sinistral strike-slip under NW-SE maximum horizontal principle stress (σ_Hmax) and NE-SW minimum horizontal principle stress (σ_Hmin) in the late Cretaceous to early Cenozoic, and then (2) dextral strike-slip under NE-SW maximum horizontal principle stress (σ_Hmax) and NW-SE minimum horizontal principle stress (σ_Hmin) in the Paleogene. It is interpreted that the deformation caused by the Paleogene dextral strike-slip movement was the most dominant, and the crustal deformation was insignificant thereafter.

• Journal of the Korean Geophysical Society
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• v.2 no.3
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• pp.155-168
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• 1999

The paleoseismological importance of the Yangsan fault zone was examined by historical earthquake data, aerial photograph, and trench survey of the area. Occurrences of great earthquakes during the historical time indicate that the Yangsan and/or Ulsan fault have been active during the late Quaternary and generated historical events. Geomorphological evidences of the recent fault activity are clearly shown both in the northern segment (Yugye-ri, Tosung-ri and Naengsu-ri areas) and in the southern segment (Eonyang to Tongdosa areas) of the Yangsan fault. The main Yangsan fault is characterized by fault gouges and NNE-SSW lineaments. The reverse faulting in the Yugye-ri area generated about three-mater displacement of the lower terrace deposits. On the other hand, a major strike-slip movement with a minor component of 5-12 m vertical displacement was identified by the offset of the higher terrace surface in the Eonyang area.

• The Journal of Engineering Geology
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• v.9 no.1
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• pp.59-68
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• 1999

To clarify the geological structure of Yangsan fault around Sangchon-ri in the southern part of Kyungsang Basin the resistivity (dipole-dipole profiling) and VLF surveys carried out on the four profiles, crossing the inferred trace of the fault. The resistivity contrast across the fault is clearly shown on the profiles: higher resistivity and lower resistivity on the east and west, respectively. It is most likely from the uplift of the granitic bedrock on the east park due to the strike-fault raulting with vertical movement. The zero-crossing points of VLF anomalies, associated with near-surface fracture zone, are found to well correlate with the resistivity boundaries from the dipole-dipole profiling. Consequently, southern segment of Yangsan fault (at Sangchon-ri area) is interpreted to be vertically developed strike-slip fault with a difference more than 10m depth of basement rock at both sides.

• The Journal of the Petrological Society of Korea
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• v.4 no.2
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• pp.144-152
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• 1995

The Jangsan Quartzite of the Joseon Supergroup and the foliated granite (so-called granitlc gneiss of presumed Precambrian age) of the Yeongnam massif are in direct contact at Cheondong-ri area, 6 km @SE of Danyang. sllthough it has been thought traditionally that the Jangsan Quartzite overlies unconformably the f&ted granite, it is difficult to interpret the contact as an unconformity smce the basal conglomerate in- the lower part of the Jangsan Quartzite does not have any clast of the foliated granite, Rather, recent structural studies of this area indlcate that the contact is a ductile shear zone. However, the sense and age of the shear movement are still problematic. Our mesoscopic and microscopic studies of &tre Cheondong-11 semi-brittle shear zone involving foliated cataclasite and phyllonite, which is a pa& of the Ogdong fault, indlcate a top-to-the northeast shearing, i.e., dextral strike slip. We also performed Pb-Pb dating for the age-unknown foliated granite, since the age of deformed granite ccarr emtrain the maximum age of deformation. The whole rock and feldspar Pb isotape data for the foliated granite and a micaceous xenolith define an isoc chron age of $2.16{\pm}0.15$ Ga ($2{\sigma}$;MSWD=4.4) which is interpreted as the emplacement age of the granite. This early Proterozoic age agrees with those of Precambrian igneous activity In the Yeongnam massif reported previously. The obtaiPrfid gge confirms the traditional idea about the age of the foliated granite and indicates that other methd(s) should be employed to constrain the age of the shear movement.

• 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.

• The Journal of Engineering Geology
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• v.13 no.1
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• pp.107-127
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• 2003

After detailed geological mapping, structural and fracture-density data were collected and analyzed in the vicinity of Cheonseong and Jeongjok Mts., Gyeongsangnam-do. A extensive dextral strike-slip fault (Beopgi Fault) Parallel to Yangsan and Dongrae Faults, a dextral-transtensional-NW fault, and a few intermittent faults have been found in the study area. Based on strike and frequency, fracture system has been divided into three sets such as NNE-trending J1 ($NS-40^{\circ}E$), WNW-trending J2 ($N50^{\circ}-80^{\circ}W$), and ENE-trending J3 ($N60^{\circ}-90^{\circ}E$). According to analysis of fracture density, it is revealed as follows: (a) Jl is the combination of Y-, P-, and R-shear fractures due to the dextral strike-slip of the Beopgi Fault. (b) J2 is the preexisted fracture zone conducting the intrusion of granite. Two tensional fractures dipping to NNE and SSW respectively have been induced by intrusion of granite and followed crustal uplift. (c) J3 is the tensional fracture developed between Yangsan and Dongrae Faults having NNE trend and dextral strike-slip sense. This study aims to reduce environmental impact and insure stability of underground facilities and tunnels.

• The Journal of the Petrological Society of Korea
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• v.25 no.3
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• pp.231-240
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• 2016

Three Quaternary faults have been revealed in marine terraces nearby the Homigot and the Gurongpo in the southeastern offshore of Korean Peninsula. The Hajung fault cuts the $4^{th}$ marine terraces and the Guman fault the $2^{nd}$, respectively. The Hajung fault strikes $N55^{\circ}$ to $45^{\circ}W$ and dips $40^{\circ}$ to $45^{\circ}NE$ with reverse-displacement of 180cm vertically. There are four sets of colluvial sediment strata that would be produced by faulting and indicate four times of fault movements during MIS 7 and MIS 5c. The Guman fault site consists of three sets of reverse faults that strike $N80^{\circ}E$ to $N70^{\circ}W$ and dip $25^{\circ}{\sim}35^{\circ}SE$ to $30^{\circ}SW$ with vertical displacement of 9~18 cm. The Guman faulting occurred during 80 ka (MIS 5a) to 71 ka (MIS 4) but it extends only to the lowest bed, the pebble sand bed, lay just on the unconformity, and not to the upper. Considering the attitude of the faults, we inferred that the Hajung fault was activated under the ENE-WSW compression during MIS 7 to MIS 5c and the Guman under N-S trending compression during MIS 5a. Using the OSL age dating results, we reconfirmed that the $2^{nd}$ terrace is correlated to MIS 5a and the $4^{th}$ terraces to MIS 7.

• Journal of the Earthquake Engineering Society of Korea
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• v.2 no.4
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• pp.41-52
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• 1998

The Dongnae Fault in the southeastern part of the Korean Peninsular is not a single fault but a complex fault zone composed of numerous minor faults. In order to deduce the paleostress tensor evolving the Dongnae Fault, we measured 329 faults in outcrops around the fault zone and analyzed the geometries of them. Most of them are steeply dipping(>65˚) and fall into three groups striking N10E, N30E and N70E. More than one half of them show the rakes less than 30˚ Paleostress tensor analysis using the collected fault data has been conducted with the Angelier's direct inversion method and the Choi's method. As result, four different principal paleostress axes each of which subtends an independent tectonic event are found. They are; (1) NNE-SSW compression and ESE-WNW extension (Event I), (2) NNE-SSW extension (Event II), (3) ESE-WNW extension (Event III) and (4) ENE-WSW compression and NNW-SSE extension (Event IV) in chronology. Therefore, the tectonic movement around the Dongnae Fault was firstly governed by strike-slip faulting related to Event I. Afterward, normal faults were formed by Event II and Event III. Finally, the dextral strike-slip faults along the major trace of the Dongnae Fault were formed in NNE direction related to Event IV.

• Proceedings of the Mineralogical Society of Korea Conference
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• 2003.05a
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• pp.84-85
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• 2003

소백산육괴의 동부에 분포하는 영양-울진지역의 선캠브리아기 변성암류는 평해층, 기성층, 원남층, 평해화강편마암, 하다우백질화강편마암 등으로 구성되어 있다(김옥준 외, 1963). 그러나, 최근 김남훈 외(2001, 2002)은 야외조사연구와 암석학적 및 지구화학적 연구를 통하여 주로 변성화산암류로 기재되었던 기성층은 변성화산암류가 아니라 평해층과 원남층에서 산출되는 화강암질편마암과 각섬암 기원의 변성암류가 연성전단변형을 받아 형성된 압쇄암 내지 초압쇄암으로 되어 있고, 기존의 기성층은 변성화산암류와 같이 성분상으로 구분되는 별개의 층이 아닌 구조적으로 만들어진 연성전단대의 중심부일 가능성을 시사한 바가 있다. 본 연구는 연성전단대의 연장성 및 연성전단대 형성과 관련된 지구조운동의 특성을 파악하고, 중첩된 변형구조들의 선후관계로부터 영양-울진지역 선캠브리아기 변성암류에 대한 변형작용사를 규명하기 위해 기성층의 분포지를 중심으로 이 지역 선캠브리아기 변성암류에 대한 상세한 야외지질조사를 실시하였다. 그 결과, 예천(북후면-평은면)지역을 통과하여 봉화 부근에서 동북동-서남서 방향이 동-서 방향으로 전환하여 장군봉지역까지 연장되는 것으로 알려져 있는 우수 주향 이동성 예천전단대(KIGAM, 1995; 강지훈 외 1997; 강지훈, 2000; 강지훈과 김형식, 2000)는 영양-울진지역까지 연장됨이 확인된다. 또한, 영양-울진지역의 선캠브리아기 변성암류에는 연성전단변형 이전에 적어도 한 번의 습곡작용과 이후에 적어도 두 번의 습곡작용이 인지된다. 각 변형단계별 특징적인 구조요소를 요약하면 다음과 같다. D1 변형: 편마면 내지 편리(S0)가 습곡되어 형성된 F1 습곡은 동-서 방향의 준 수평적인 습곡축을 갖는 뿌리 없는 등사습곡 형태로 인지된다. 양 날개부의 S0 엽리는 F1 습곡축면(S1)으로 완전히 전위된 하나의 엽리(S0-1)로 나타나고, S0-1 엽리는 이 지역의 광역엽리로 인지된다. S0-1 광역엽리는 구성암류의 대상 분포 방향과 유사한 서북서 주향에 북쪽으로 중각 경사하는 집중된 방향성을 보이며 분산되어 나타난다. D2 변형: 변형구조로는 신장선구조, 압쇄구조면, 비대칭습곡 등으로 인지된다. 신장선구조는 S0-1 엽리면상에서 주로 신장된 석영(집합체)과 장석(집합체)들의 정향배열에 의해 정의되고, S0-1 엽리의 주향 방향으로 저각으로 침강하는 집중된 방향성을 보이며 분산되어 나타난다. 신장선구조에 평행하고 S0-1 엽리에 수직한 단면에서는 상부-동쪽-이동의 우수주향 이동성 연성 전단운동감각을 지시하는 구조요소들이 다량 관찰된다. 연성전단변형에 의해 형성된 압쇄구조면은 전단엽리와 압쇄엽리에 각각 해당하는 C면과 S면 등이 인지된다. 전단엽리 C면은 S0-1 광역엽리와 거의 일치하고, 압쇄엽리 S면은 F2 비대칭습곡의 축면엽리와 거의 일치한다. S0-1 엽리를 습곡시키는 F2 비대칭습곡은 S0-1 엽리를 전단면으로 하여 상부-동쪽-이동 전단운동에 의해 형성된 밀착습곡 형태로 인지된다. F2 습곡축은 북동 방향으로 중각 내지 저각 침강하고 F1 습곡축과는 65$^{\circ}$-75$^{\circ}$ 범위의 사이각을 이룬다. F2 습곡축면은 동북동 주향에 북쪽으로 중각으로 경사하고 F1 습곡축면과는 20$^{\circ}$-40$^{\circ}$ 범위의 사이각을 이룬다. D3 변형. S0-1 엽리와 압쇄구조면 등을 습곡시키는 F3 습곡은 준 수평적인 습곡축과 습곡축면을 갖는 개방 횡와습곡의 형태로 인지된다. D4 변형: F4 습곡은 비대칭 공역성 킹크습곡, 공역성 충상단층에 수반되어 나타나는 드래그습곡, 대칭 개방 직림습곡 등의 다양한 습곡 형태로 인지된다. 이들 F4 습곡의 축면엽리는 일반적으로 동-서 주향에 남쪽과 북쪽으로 경사한다. 그 경사각은 비대칭 공역성 킹크습곡(저각), 드래그습곡(중각), 대칭 개방 직립습곡(고각) 순으로 고각을 이룬다. F4 습곡축은 동쪽과 서쪽으로 저각 침강하는 집중된 방향성을 보인다. 공역성 충상단층은 동-서 주향에 남쪽과 북쪽으로 경사하는 단층면과 상부가 북쪽과 남쪽으로 충상하는 운동상을 보인다. 드래그습곡의 축면엽리는 이러한 공역성 충상단층운동의 전단압축방향에 수직으로 발달한다. 이러한 D4 변형구조는 남-북 방향의 압축 지구조 환경하에서 형성된 것으로 고찰된다.

• The Korean Journal of Petroleum Geology
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• v.1 no.1 s.1
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• pp.15-27
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• 1993

Seismic reflection profiles from the eastern continental margin of Korea delineate three major Neogene sedimentary basins perched on the shelf and slope regions: Pohang-Youngduk, Mukho and Hupo basins. The stratigraphic and structural analyses demonstrate that the formation and filling of these basins were intimately controlled by two phases of regional tectonism: transtensional and subsequent contractional deformations. In the Oligocene to Early Miocene, back-arc opening of the East Sea induced extensional shear deformation with dextral strike-slip movement along right-stepping Hupo and Yangsan faults. During the transtensional deformation, the Pohang-Youngduk Basin was formed by pull-apart opening between two strike-slip faults; in the northern part, block faulting caused to form the Mukho Basin between basement highs. As a result of the back-arc closure, the stress field was inverted into compression at the end of the Middle Miocene. Under the compressive regime, two episodes (Late Miocene and Early Pliocene) of regional deformation led to the destruction and partial uplift of the basin-filling sequences. In particular, during the second episode of compressive deformation, the Hupo fault was reactivated with an oblique-slip sense, which resulted in an opening of the Hupo Basin as a half-graben on the downthrown fault block.