• 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.

• Economic and Environmental Geology
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• v.47 no.1
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• pp.17-27
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• 2014

We investigated space-time patterns of Quaternary fault activity of the Yangsan fault zone using ESR ages in the Samnam-myeon region, Ulsan, Korea. Some of fault gouge zones consist of well-defined bands which added to the older gouge band, indicative of reactivation. During addition of new bands, the older gouge band was inactive, which represents the type I faulting mode. ESR analyses of each band of the gouge zone allow us to construct history of fault movement. The entire fault gouge zones were reactivated by type III faulting mode giving us ESR ages of the lastest reactivation. ESR dates show temporal clustering into active and inactive periods analogous to historic and paleoseismic fault activities. ESR ages and dates of fault movements indicate migration of fault activities along the Yangsan Fault Zone. Segments of the Quaternary faults in the study area are branched in the south of Sangcheon site. The earliest record of activity in segmented faults is recorded from the western segment to the northern segment. Before 750~850 ka ago, the fault gouge zone from the western segment to the northern segment were active. At 750~850 ka ago, the fault gouge zone from the eastern segment to the northern segment were active. During 630~660 ka and 480~540 ka only the northern segment was active. After 340 ka ago, the fault gouge zone from the western segment to the northern segment were active again.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.105-112
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• 2001

The purpose of this study is to assess the stability of tunnel for a high speed railway crossing the fault zone. The area where the tunnel crossed the fault zone can be unstable during construction and operation. Geotechnical investigations have been conducted to determine an optimum excavation method by obtaining the material properties around the fault zone and to check the stability of the tunnel. For the numerical analysis, the FLAC, numerical analysis code based on finite difference method, was utilized to analyze the behavior of the fault at three points having typical ground conditions. Based on the results of numerical analysis, the combinations of compaction grouting and LW grouting were determined as suitable methods for pre-excavation Improvement of the ground surrounding the tunnel opening. In conclusion, the stability of the tunnel construction for the high speed railway within the fault zone may be obtained by adopting the optimum excavation method and the reinforcement method. The numerical analysis based on FLAC program contains errors caused by assumptions used in numerical analysis, therefore constant monitoring with respect to the change of ground condition and groundwater is highly recommended to minimize the numerical error and the possibility of damage to tunnel.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.1275-1282
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• 2005

This paper deals with the numerical study for excavation crossing the fault zone and the change of support pattern in field. The numerical analyses by FLAC program were performed to evaluate the suitable support pattern influenced by the width of Fault Zone, considering rock mass condition(RMR classification). Based on the results, it is found that partial reinforcement or degrading support pattern is suitable, when the width of Fault is under 3m. But when the width of Fault is more than 6m(0.5D), extra support pattern for fault zone is acceptable. At field, this result is generally used as a guide in the construction of roadway tunnel, but it is also possible to vary this assessment along the condition of fault.

• The Journal of Engineering Geology
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• v.24 no.3
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• pp.323-332
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• 2014

The Nobi fault zone, which generated the 1891 Nobi Earthquake (M8.0), includes five or six faults distributed in and around Gifu and Aichi prefectures, Japan. Because large cities are located near the fault zone (e.g., Gifu and Nagoya), and because the zone will likely be reactivated in the future, relatively thorough surveys have been conducted on the 1891 Nobi earthquake event, examining the fault geometry, house collapse rate, and the magnitude and distribution of earthquake intensity and fault displacement. In this study, we calculated the earthquake slip along faults in the Nobi fault zone by applying a 3D numerical analysis. The analysis shows that a zone with slip displacements of up to 100 mm included all areas with house collapse rates of 100%. In addition, the maximum vertical displacement was approximately ${\pm}1700mm$, which is in agreement with the ${\pm}1400mm$ or greater vertical displacements obtained in previous studies. The analysis yielded a fault zone with slip displacements of > 30 mm that is coincident with areas in which house collapse rates were 60% of more. The analysis shows that the regional slip sense was coincident with areas of uplift and subsidence caused by the Nobi earthquake.

• Journal of Electrical Engineering and Technology
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• v.10 no.1
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• pp.102-108
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• 2015

This paper proposes a new fault isolation methodology for a smart protective device which plays an agent role on the smart grid distribution system with the distributed generation. It, by itself, determines accurately whether its protection zone is fault or not, identifies the fault zone and separates the fault zone through the exchange of fault information such as the current information and the voltage information with other protective devices using bi-directional communication capabilities on the smart grid distribution system. The heuristic rules are obtained from the structure and electrical characteristics determined according to the location of the fault and DG (Distributed Generation) when faults such as single-phase ground fault, phase-to-phase short fault and three-phase short fault occur on the smart grid distribution system with DG.

• Economic and Environmental Geology
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• v.21 no.2
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• pp.131-137
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• 1988

Geological and electrical resistivity surveys were carried out to investigate subsurface geology and geologic structure of the Bonghwajae area in the Okchon zone. Pseudosections of the apparent electrical resistivity distribution along the three survey lines were obtained by using dipole-dipole electrode array method, and models of subsurface geology and geologic structure by using two dimensional finite difference method. The Bonghwajae fault zone exists around Bonghwajae area in the north-south direction, and is a boundary between Okchon Group and Choson Supper Group. Metabasite and hornblende gabbro intruded along the Bonghwajae fault zone remaining two fracture zones with low resistivity value of 20 ohm-m and widths of about 100m and 70-300m. They strike nearly N-S and dip westward with a high angle of $60-70^{\circ}$. Sochangri fault with a width of about 160m exists between Jisogori and Bonghwajae, by which Bonghwajae fault zone is displaced about 1km in the east-west direction. Hornblende gabbro whose electrical resistivity value is in the range of 5000-8000 ohm-m intruded the metabasite of 2000-4500 ohm-m after the Sochangri fault had formed. Great Limestone Group is widely distributed in the east of Bonghwajae fault zone, and interbeds so called Yongam formation of graphitic black slate with an extremely low electrical resistivity value of 2 ohm-m.

• Economic and Environmental Geology
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• v.45 no.5
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• pp.487-502
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• 2012

This paper is focused on mineral compositions, microstructures and distributional characters of remained grains in the fault rocks collected from a fault developed in Yongdang-ri, Yangbuk-myeon, Gyeongju City, Korea, using X-ray diffraction (XRD), optical microscope, laser grain size analysis and fractal dimension analysis methods. The exposed fault core zone is about 1.5 meter thick. On the average, the breccia zone is 1.2 meter and the gouge zone is 20cm thick, respectively. XRD results show that the breccia zone consists predominantly of rock-forming minerals including quartz and feldspar, but the gouge zone consists of abundant clay minerals such as chlorite, illite and kaolinite. Mineral vein, pyrite and altered minerals commonly observed in the fault rock support evidence of fault activity associated with hydrothermal alteration. Fractal dimensions based on box counting, image analysis and laser particle analysis suggest that mineral grains in the fault rock underwent fracturing process as well as abrasion that gave rise to diminution of grains during the fault activity. Fractal dimensions(D-values) calculated by three methods gradually increase from the breccia zone to the gouge zone which has commonly high D-values. There are no noticeable changes in D-values in the gouge zone with trend being constant. It means that the bulk-crushing process of mineral grains in the breccia zone was predominant, whereas abrasion of mineral grains in the gouge zone took place by continuous fault activity. It means that the bulk-crushing process of mineral grains in the breccia zone was predominant, whereas abrasion of mineral grains in the gouge zone took place by continuous fault activity. Mineral compositions in the fault zone and peculiar trends in grain distribution indicate that multiple fault activity had a considerable influence on the evolution of fault zones, together with hydrothermal alteration. Meanwhile, fractal dimension values(D) in the fault rock should be used with caution because there is possibility that different values are unexpectedly obtained depending on the measurement methods available even in the same sample.

• Journal of Electrical Engineering and Technology
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• v.3 no.2
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• pp.192-198
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• 2008

This paper proposes a FRTU-based intelligent fault distance determination strategy in which each FRTU is able to avoid multiple estimations and reduce the level of estimation error by utilizing heuristic rules driven by voltage and current information collected by 1:1 communication with other FRTUs from the same zone in a ubiquitous-based distribution system. In the proposed method, each FRTU, at first, determines a fault zone and a fault path on the faulted zone based on the proposed heuristic rules which use its current data and the voltage data of its neighboring FRTUs as input data. Next, it determines the fault distance from its position based on the fault current estimated from the current data of the neighboring FRTUs. Finally, in order to prove the effectiveness of the proposed method, the diverse fault cases are simulated in several positions of the typical distribution system using the EMTP.

• Journal of the Korean Society of Hazard Mitigation
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• v.1 no.1 s.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.