• 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.

• 한국지구과학회:학술대회논문집
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• 2002.02a
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• pp.36-36
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• 2002

• The Journal of the Petrological Society of Korea
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• v.28 no.4
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• pp.347-357
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• 2019

The main fault zone of the Yangsan Fault, located in the southeastern part of the Korean peninsula, is newly found at the Cheonjin-ri, Dudong-myeon, Ulju-gun, Ulsan, Korea. About 100 wide fault zone exposed along the Guryangcheon stream strikes N-S and dips over 70° toward east. The main fault zone is composed of N-S-striking gouge and breccia layers and enclosed lenses. Striations on the subvertical fault surfaces mainly indicate dextral slip, but moderate-angle minor reverse faults showing top-tothe-west shearing transect the foliated high-angle gouge and breccia layers. These indicate that the dextral slip along the fault, which is interpreted as the main movement of the fault, was followed by reverse slip. The fault zone is composed of N-S-striking gouge layers and enclosed, fractured lenses. Locally distributed NE-SW- to E-W-striking fault gouge layers with fractured lenses show asymmetric folds, indicating progressive dextral movement. Therefore, the exposed fault zone has a high internal complexity due to the combined effects of NNE-SSW-trending dextral shearing and E-W-trending shortening by compression. In addition, around main boundary fault between the western volcanic rocks and eastern sedimentary rocks offsets the overlying Quaternary fluvial conglomerate. This is a good example that understanding of internal structures of main fault zone (or fault core), such as the Yangsan Fault, plays an important role to study the Quaternary activity and to find the active fault.

• Journal of the Korean earth science society
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• v.43 no.1
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• pp.151-164
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• 2022

According to the records of historical and instrumental earthquakes, the southeastern part of the Korean Peninsula is considered the highest seismic activity area. Owing to recent reports of numerous Quaternary faults along the Yangsan and Ulsan fault zones, paleoseismological studies are being actively conducted in these areas. The study area is located in the central part of the Ulsan fault zone, where the largest number of active faults have been reported. Based on lineament and geomorphic analysis using LiDAR images and aerial photographs, fault-related landforms showing topographic relief were observed and a trench survey was conducted. The trench length 20 m, width 5 m, depth 5 m is located approximately 300 m away to the northeast from the previously reported Malbang fault. From the trench section, we interpreted the geometric and kinematic characteristics of the fault based on the deformed features of the Quaternary sedimentary layers. The attitude of the reverse fault, N26°W/33°NE, is similar to those of the reported faults distributed along the Ulsan fault zone. Although a single apparent displacement of approximately 40 cm has been observed, the true displacement could not be calculated due to the absence of the slickenline on the fault plane. Based on the geochronological results of the cryogenic structure proposed in a previous study, the most recent faulting event has been estimated as being earlier than the late Wurm glaciation. We interpreted the thrust fault system of the study area as an imbrication structure based on the previous studies and the fault geometry obtained in this additional trench. Although several previous investigations including many trench surveys have been conducted, they found limited success in obtaining the information on fault parameters, which could be due to complex characteristics of the reverse fault system. Additional paleoseismic studies will contribute to solving the mentioned problems and the comprehensive fault evolution.

• Economic and Environmental Geology
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• v.54 no.3
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• pp.389-397
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• 2021

Moryang Fault is geomorphologically observed as a linear fault valley from Angang through Moryang, Duckhyun and Wondong to Gimhae, and contacts with Yangsan Fault, being obliquely away to the east, at Angang disrict. The fault valley appears a V-shape feature with a width from 100 to 300 m, and has fragmental zones of the fault along the valley on a small scale. Nine fault-outcrop localities were found along the nine-kilometers valley between Daehyun-ri, Gyeongju, and Baenaemi-gogae, Yangdong-ri, Ulsan. The fault strikes the North-North-East to the Northeast and dips to the Northwest with high angles, and reveals it had been undergone predominantly sinistral reverse fault movement sense, left-lateral and right-lateral strike-slip sense in bedrocks. However, after unconsolidated sediments, there was the top-up-to-the-east dextral reverse fault movement.

• 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.

• Korean Journal of Remote Sensing
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• v.37 no.6_2
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• pp.1901-1922
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• 2021

Since most large earthquakes occur by reactivation of preexisting active faults, it is important to understand the locations and characteristics of active faults in terms of earthquake hazard research and earthquake disaster prevention. Recently, several remote sensing techniques are broadly used for lineament analysis performed prior to field surveys in active fault surveys. The aim of this paper is introducing simple principles and application examples of each remote sensing technique (satellite remote sensing, airborne remote sensing, InSAR, LiDAR) widely used for active fault investigation. This paper also explains the analytical methods for the slope break generated by fault activity based on GIS and the horizontal displacement of the strike-slip fault. In discussion, we would like to discuss the problems and solutions on making DEM based on aerial photography, and a new developed technique (RRIM) to overcome the problems of DEM based on aerial LiDAR. Understanding remote sensing techniques used for active fault investigation and utilizing appropriate methods depending on the situation and limitations of each remote sensing technique are important for effective active fault investigation.

• Korean Journal of Mineralogy and Petrology
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• v.33 no.4
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• pp.349-359
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• 2020

The Ulsan Fault Zone (UFZ) of NNW trend is developed in the Gyeongsang Basin, the southeastern part of the Korean Peninsula, and the Quaternary faults have been found around the UFZ. The faults generally thrust the Bulguksa igneous rocks of Late Cretaceous-Early Tertiary upon the Quaternary deposits or are developed within the Quaternary deposits. They mainly show the reverse-slip sense of top-to-the west movement. The lines connecting the their outcrop sites show a zigzag-form which is similar to the orientation of their fault surfaces which show the various trends, like (W)NW, N-S, (E)NE, ENE trends. The E-W trending dextral strike(-slip) fault is found in the Quaternary deposits of the Singye-ri valley. It cuts the N-S trending reverse fault and are cut by the N-S trending thrust fault again. Two types of at least two times of Quaternary tectonic movements related to the formation of neotectonic fault zone in the Singye-ri valley are considered from such the geometric and kinematic characteristics of Quaternary faults. One is the reverse faulting of N-S trend by the E-W directed 1st compression and associated the strike-slip tear faulting of E-W trend, and then the thrust faulting of N-S trend by the E-W directed 2nd compression. The other is the reverse faulting of N-S trend, and then the dextral strike-slip faulting of E-W trend by the NW-SE directed compression, and then the thrust faulting of N-S trend. In this paper is suggested the development history of Singye-ri neotectonic fault zone on the basis of the various orientations of Quaternary fault surfaces around the UFZ, and the zigzag-form connecting line of their outcrop sites, and the compressive arc-shaped lineaments which convex to the west reported recently in the Yangsan Fault Zone.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.28 no.2
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• pp.289-295
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• 2010

Yangsan fault system is a large fault more than 170km and one of the important structures Geologically that has been create recently in the Korean Peninsula. Debates have been made incessantly and widely throughout the Yangsan fault system because it's a lot of earthquake record. In this study, GPS data that was received from Yangsan GPS station in were processed by the Precise Point Positioning and the movement velocity was calculated by the statistical process about the results, where is the fault zone. The results showed that Yangsan is moving by azimuth angle of $126^{\circ}$ and the velocity of 49mm/year. It is respected that this results will be utilized in basic data about geophysics.

• Journal of The Geomorphological Association of Korea
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• v.25 no.3
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• pp.89-103
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• 2018

This study presents results of analysis on fault-related landforms and the Quaternary fluvial landforms, which are important evidences for active faulting by identifying surface deformation, around the Ulsan Fault Zone. In addition, this study suggests lineament map and inferred active fault-line map based on analyzing linearity and continuity of these landforms and by compiling location information of existing active faults. We convince that quantitative tectonic-geomorphological analysis are an effective method for active faults tracking, in particular, considering the conditions of relatively low seismicity and surface ruptured-events in the Korean Peninsula compared to plate boundary active areas. However, research on active fault in South Korea is just an infant stage since the 1990s and requires accumulation of research achievements on development and application of various fault analysis techniques, analysing and standardizing linear structures.