• Journal of the Korean earth science society
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• v.24 no.4
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• pp.361-368
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• 2003

We have investigated the electric resistivity structure of the fault zone located in the Hongseong area where a big earthquake with M 5.0 occurred in 1978. Usually, Electric and Electromagnetic methods are broadly operated in the field of engineering works since these methods are effective to understand the distribution of geological weak zones - fault or fracture zones. We have conducted the dipole-dipole array resistivity method and MT(magnetotelluric) method and interpreted the resistivity distribution of the fault zone with the aid of various inversion methods. An MT survey was performed at 18 points along a 2.9 km survey line perpendicular to the fault line and a magnetic dipole source was used to enhance the S/N ratio in the high frequency. A Electric dipole-dipole array resistivity survey with the dipole length of 50 meters was carried out perpendicular to the fault. In view of two survey results, the fault marks the boundary between two opposite resistivity structures, especially the low resistivity zone is exhibited deeply through the prospective fault line. The result that the low resistivity zone is located at the center of the fault zone corresponds with the fact that the fault zone of the Hongseong area is active. We expect these results to provide basic information about the physical properties of fault zones in Korea.

• Journal of the Korean Geophysical Society
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• v.2 no.3
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• pp.217-224
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• 1999

Although faults can be found by geological surveys, the surface traces of faults are not easily discovered by traditional geological surveys due to alluvia. In and around faults and fracture zones, the electrical resistivity appears to be lower than that of the surroundings due to the content of groundwater and clay minerals. Therefore, electrical resistivity surveys are effective to search buried faults and fracture zones. The dipole-dipole array electrical resistivity surveys, which could show the two dimensional subsurface electrical resistivity structure, were carried out in two areas, Yongdang-ri, Woongsang-eup, Yangsan-si, Kyungsangnam-do and Malbang-ri, Woedong-eup, Kyungju-si, Kyungsangpook-do. The one was next to the Dongrae Fault and the other near the Ulsan Fault was close to the region in which debatable quaternary fault traces had been found recently. From each measured data set, the electrical resistivity cross-section was obtained using the inversion program the reliability of which was analyzed using analytic solutions. A low resistivity zone was found in the inverted cross-section from the Yongdang-ri area survey data, and two low resistivity zones were found in that from the Malbang-ri area survey data. They were almost vertical and were 15∼20 m wide. Accounting the shape and the very low resistivity values of those zones (<100 Ωm)in the inverted section, they were interpreted as fracture zones although they should be proven by trenching. The reliability of the interpretation might be improved by adding some more parallel resistivity survey lines and interpreting the results in 3 and/or adding other geophysical survey.

• Journal of the Korean GEO-environmental Society
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• v.17 no.4
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• pp.39-46
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• 2016

The final stability analysis of the tunnel structure is generally evaluated by performing site monitoring to determine whether or not the measured value through the convergence after the completion of excavation in the face. When the ground conditions are so poor, the reinforcement around the tunnel was applied for enhancing the stability of tunnels. For the additional tunnel crown collapse or excessive displacement have occurred under construction, correlation analysis were performed for the comparison construction and numeric analyses. In this paper, we investigated the collapse types, tunnel collapse were mostly occurs at the crown and they were analyzed because of the geological conditions in the collapse zone. And also, it was analyzed as being correlated in the crown of tunnel exists a fault fracture zone which extends to the surface part. Thus, in case of ground conditions such as fault fracture zone with a tunnel extending from the crown to the surface, the behavior is larger than the behavior predicted by numerical method.

• Tunnel and Underground Space
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• v.29 no.3
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• pp.197-213
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• 2019

We simulated the fault reactivation experiment conducted at 'Main Fault' intersecting the low permeability clay formations of Mont Terri Underground Research Laboratory in Switzerland using TOUGH-FLAC simulator. The fluid flow along a fault was modelled with solid elements and governed by Darcy's law with the cubic law in TOUGH2, whereas the mechanical behavior of a single fault was represented by creating interface elements between two separating rock blocks in FLAC3D. We formulate the hydro-mechanical coupling relation of hydraulic aperture to consider the elastic fracture opening and failure-induced dilation for reproducing the abrupt changes in injection flow rate and monitoring pressure at fracture opening pressure. A parametric study was conducted to examine the effects of in-situ stress condition and fault deformation and strength parameters and to find the optimal parameter set to reproduce the field observations. In the best matching simulation, the fracture opening pressure and variations of injection flow rate and monitoring pressure showed good agreement with field experiment results, which suggests the capability of the numerical model to reasonably capture the fracture opening and propagation process. The model overestimated the fault displacement in shear direction and the range of reactivated zone, which was attributed to the progressive shear failures along the fault at high injection pressure. In the field experiment results, however, fracture tensile opening seems the dominant mechanism affecting the hydraulic aperture increase.

• The Journal of Engineering Geology
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• v.25 no.4
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• pp.485-498
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• 2015

Structural analysis for a large-scale fault in Maegok-dong, Ulsan, was carried out based on filed-works to investigate the geometric and kinematic characteristics of the fault as well as its Quaternary slip. As results, a series of repeated stratigraphy, minor faults, fracture zones, and deformation band clusters are observed over a distance of about 100 m in the first studied site consisting of sedimentary rocks, which may indicate the damage zone of a large-scale fault in this site. In the second site, mainly composed of granitic clastic rocks, a large-scale thrust fault is expected based on low-angle dipping faults showing branched and/or merged patterns. Age of the last slip on this fault was restrained as after 33,275 ± 355 yr BP based on radiocarbon dating for organic material included in the gouge zone. Dimension of fault damage zone, dominant sense of slip, and age of the slip event associated with the fault suggest that these structures have a close relationship with the Ulsan Fault and/or Yeonil Tectonic Line, which are well-known large-scale neotectonic structural features around the study area. Therefore, it is necessary to study the characteristics of the faults in detail based on structural geology and paleoseismology in order to ensure seismic and geologic stability of the buildings under construction, and to prevent geologic hazards in this area.

• Geomechanics and Engineering
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• v.33 no.5
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• pp.477-486
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• 2023

In the studies on fault dislocation of tunnel, existing literatures are mainly focused on the problems caused by normal and reverse faults, but few on strike-slip faults. The paper aims to research the deformation and failure mechanism of a tunnel under strike-slip faulting based on a model test and test-calibrated numerical simulation. A potential faulting hazard condition is considered for a real water tunnel in central Yunnan, China. Based on the faulting hazard to tunnel, laboratory model tests were conducted with a test apparatus that specially designed for strike-slip faults. Then, to verify the results obtained from the model test, a finite element model was built. By comparison, the numerical results agree with tested ones well. The results indicated that most of the shear deformation and damage would appear within fault fracture zone. The tunnel exhibited a horizontal S-shaped deformation profile under strike-slip faulting. The side walls of the tunnel mainly experience tension and compression strain state, while the roof and floor of the tunnel would be in a shear state. Circular cracks on tunnel near fault fracture zone were more significant owing to shear effects of strike-slip faulting, while the longitudinal cracks occurred at the hanging wall.

• Journal of the Korean Geophysical Society
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• v.1 no.1
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• pp.31-40
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• 1998

Gravimetric and magnetic surveys were conducted in order to reveal near-surface structures such as basements, faults, and fracture zones in an area near Angang, where the Yangsan fault is believed to pass through. Along two lines approximately perpendicular to the strike of the major fault, gravity and magnetic data were measured at 67 stations with a 15 m interval and at 296 stations with a 3 m interval, respectively. Average depth to the magnetic basement is estimated using the spectral analysis method to be 8.5 and 10.0 m along lines located to the east and the west of the Hyeongsan river, respectively. Average value of reduced gravity on the east line is higher than that on the west by the amount of 1.71 mGal, which indicates that the basement rocks are more severely fractured in the western part. Forward gravity modeling along the east line indicates that a fracture zone extends westward from a fault located 210 m west of the eastern end. Density and depth to the bottom of the fracture zone are estimated to be 2.44 g/cm3 and 70 m, respectively. The gravity model study also indicates presence of a small graben, 190 m wide and 3.5 m deep on an average, on the basement surface. The earth surface above the graben is approximately 44 cm lower than the nearby surface. This indicates that the graben might have been formed by recent fault movements.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.04a
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• pp.66-73
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• 2001

Yangsan fault in the southeastern part of Korean peninsula has been locally reactivated along a prexisted fault during the late Pleistocene time. Geomorphological evidence of the reactivation is revealed at the northern segment(Yugye-ri, Tosung-ri areas) of the Yangsan fault. The reactivation is distinctively characterized by fault gouge and fracture zone with high frequency in the Yugye-ri area. Obique slip separation of the area is about three meters of the middle terrace. The cumulative vertical displacement is recognized after the formation of the middle terrace. Age of the reactivated faulting is constrained to during the formation of dissected valley deposits. Average vertical slip based on paleo-event is inferred to about 0.5-0.7 meter in this area.

• Journal of the Korean Geophysical Society
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• v.3 no.3
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• pp.141-152
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• 2000

In the vicinity of the Antarctic-Scotia plate boundary off Elephant Island(EI), geophysical data(multichannel seismic and gravity data) reveal rapid structural variation of the Shackleton Fracture Zone(SFZ) along its strike. The SFZ ridge terminates in front of the Antarctic Peninsula margin, whereas the transform fault of the SFZ continues farther southeast near EI and the width of the SFZ broadens toward the southeast. Accordingly, the SFZ transform fault changes its morphology along its strike as (1) a graben structure along the high Shackleton ridge in Drake Passage, (2) a half-graben structure in oceanic crust just southeast of the Antarctic-Scotia plate boundary, and (3) splay faults deforming the margin of EI. Two phases of tectonic deformation are clearly observed along the transform fault. Major extensional deformation had formed a large-scale half-graben during roughly about $10{\sim}20$ Ma when Drake Passage had opened. And then, the Shackleton fault has been reactivated with reverse sense, which has been caused by recent convergence between Antarctic and Scotia plates due to westward movement of the Scotia plate since 6 Ma.

• 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.