• Proceedings of the Korea Information Processing Society Conference
• /
• 2016.04a
• /
• pp.390-393
• /
• 2016

지진 활동의 결과로 발생하는 피해를 감소시키기 위해 지층의 단층구조를 파악하는 것이 중요하다. 지층 탄성파 데이터를 공간자료구조를 활용하여 분석하고 효율적인 공간정보를 생산하는 시스템 개발과 관련된 연구를 제안한다. 공간자료구조는 방대한 탄성파 데이터를 지층을 이루는 암석층을 공간데이터로 저장하고, 분석하여 단층대를 이루는 공간을 검색 가능하게 한다. 검색된 단층가능 구간은 전문가의 판단을 통해 주변의 다른 단층구간과 다양한 요소들과 결합하여 지진 활동 연구에 중요한 판단 자료로 사용될 수 있다. 최근의 불안정한 지진활동 피해에서도 알 수 있듯이, 단층대의 확인 작업은 다양한 지상/지하 구조물의 안정성에 중요한 역할을 하는 자료가 된다.

• Journal of the Korean Geophysical Society
• /
• v.2 no.3
• /
• pp.155-168
• /
• 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
• /
• v.28 no.4
• /
• pp.645-660
• /
• 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
• /
• v.23 no.3
• /
• pp.217-225
• /
• 2013

We carried out geometrical, kinematic, and geomechanical analyses on a lineament (the Imgok fault) near Gangneung, observed in ASTER images and aerial photographs, and field surveys. Earthquake focal mechanism solutions, used to estimate the present-day stress state, revealed that the direction of maximum compression is approximately N$70^{\circ}$E and that the stress condition is in favor of either strike-slip or reverse movement on the fault. The strike of the fault is not ideal for slip under the present-day stress field and thus the fault has a low slip tendency. However, the fault may be able to slip if the frictional coefficient (${\mu}$), representing the resistance of the fault to slip, is sufficiently low (e.g., ${\mu}$ < 0.25).

• The Journal of Engineering Geology
• /
• v.17 no.4
• /
• pp.673-680
• /
• 2007

The seismic source parameters of the Odaesan earthquake on 20 January 2007, including focal depth, focal mechanism, magnitude, and source characteristics, are analysed using seismic moment tensor inversion. The Green's function for different 3 crust models representing the southern Korean Peninsula are used. Final results show that the event, considering 6 seismic moment tensor elements, is caused by the typical strike slip fault with nearly NNE strike. The focal depth is estimated to be about 11km and 6 seismic moment tensor elements with 7.2% CLVD value shows typical double couple seismic source. The consistent characteristics of the strike and epicenter of the event with Odaesan fault imply that Odaesan earthquake is mainly caused by movement of the Odaesan fault.

• Economic and Environmental Geology
• /
• v.56 no.3
• /
• pp.293-300
• /
• 2023

The Shape Preferred Orientation (SPO) method has been used to analyze the orientation of fault motion, which is utilized as basic data for fault kinematics studies. The rigid grains, which as quartz, feldspar, and rock fragments, in the fault gouge are arranged in the P-shear direction through rigid body rotation by a given shear stress. Using this characteristic, the fault motion can be estimated from the SPO inversely. Recently, a method for securing precision and reliability by measuring 3D-SPO using X-ray CT images and examining the shape of a large number of particles in a short time has been developed. As a result, the SPO method analyzes the orientation of thousands to tens of thousands of particles at high speed, suggests the direction of fault motion, and provides easy accessibility and reliable data. In addition, the shape information and orientation distribution data of particles, which are by-products obtained in the SPO analysis process, are expected to be used as basic data for conducting various studies such as the local deformation of fault rocks and the fault generation mechanism.

• The Journal of the Petrological Society of Korea
• /
• v.23 no.2
• /
• pp.75-103
• /
• 2014

The Quaternary faults are extensively observed along major inherited fault zones (i.e. Yangsan Fault System, Ulsan Fault, Yeonil Tectonic Line, Ocheon Fault System) in SE Korea. Their geometry and kinematics provide a very useful piece of information about the Quaternary crustal deformation and stress field in and around Korean Peninsula. Using magnetic fabrics (AMS), we attempted to determine the slip senses of Jinti, Mohwa, Suseongji2, and Wangsan faults and then interpreted the fabric development process of fault gouge and the characteristics of stress field during the Quaternary. All the magnetic fabrics of the faults, except the Wangsan Fault, consistently indicate a dominant reverse-slip sense with weak strike-slip component. Most of the oblate fabrics are nearly parallel to the fault surface and the anisotropy degrees generally increase in proportion to the oblatenesses. These results suggest that the fabrics of the fault gouges resulted from a progressive deformation due to continuous simple shear during the last reactivation stage as reverse faulting. It is also interpreted that the pre-existing fabrics were overwhelmed and obliterated by the re-activated faulting. Paleostress field calculated from the fault slip data indicates an ENE-WNW compressive stress, which is in accord with those determined from previous fault tectonic analysis, focal mechanism solution, and hydraulic fracturing test in and around Korean Peninsula.

• Journal of the Korean earth science society
• /
• v.43 no.1
• /
• pp.188-198
• /
• 2022

Some deep faults do not reach the ground surface and are seldom recognized. Gokgang Fault area in the east of the Heunghae area of the Pohang basin has been selected to confirm the feasibility of the Horizontal-to-Vertical Spectral Ratio (HVSR) approach to identify blind faults. Densely spaced microtremor data have been acquired along two lines in the study area and processed to obtain resonance frequencies. An empirical relationship between the resonance frequency and the bedrock depth was proposed using borehole data available in the study area. Resonance frequencies along two lines were then converted to bedrock depths. The resulting depth profiles show significant lateral variations in the bedrock depth. As expected, considerable variation in the resonance frequency is observed near the Gokgang fault. The depth profiles also present additional significant variations in the resonance frequencies and the bedrock depths. The feature is presumably related to a blind fault that is previously unknown. Therefore, this case study confirms the feasibility of the HVSR technique to identify faults otherwise not recognized on the surface.

• Economic and Environmental Geology
• /
• v.54 no.6
• /
• pp.743-752
• /
• 2021

The three-dimensional distribution of the fault was evaluated using gravity field interpretation such as curvature analysis and Euler deconvolution in the Seoul-Gyeonggi region where the Chugaryeong fault zone was developed. In addition, earthquakes that occurred after 2000 and the location of faults were compared. In Bouguer anomaly of Chugaryeong faults, the Pocheon Fault is an approximately 100 km fault that is extended from the northern part of Gyeonggi Province to the west coast through the central part of Seoul. Considering the frequency of epicenters is high, there is a possibility of an active fault. The Wangsukcheon Fault is divided into the northeast and southwest parts of Seoul, but it shows that the fault is connected underground in the bouguer anomaly. The magnitude 3.0 earthquake that occurred in Siheung city in 2010 occurred in an anticipated fault (aF) that developed in the north-south direction. In the western region of the Dongducheon Fault (≒5,500 m), the density boundary of the rock mass is deeper than that in the eastern region (≒4,000 m), suggesting that the tectonic movements of the western and eastern regions of the Dongducheon Fault is different. The maximum depth of the fracture zone developed in the Dongducheon Fault is about 6,500 m, and it is the deepest in the research area. It is estimated that the fracture zone extends to a depth of about 6,000 m for the Pocheon Fault, about 5,000 m for the Wangsukcheon Fault, and about 6,000 m for the Gyeonggang Fault.

• The Journal of Engineering Geology
• /
• v.26 no.3
• /
• pp.393-401
• /
• 2016

In the present study, fault attitudes and the locations of appearance of faults in tunnel faces were predicted by analyzing the trajectory of the maximum longitudinal displacement immediately before the appearance of faults through three-dimensional finite element analysis. A total of 28 fault attitude models were used in the analysis. Those faults that have drives with dip appear first in the upper part of tunnel faces as tunnel excavation progresses and their maximum longitudinal displacement shows a tendency to move from the middle part to the upper part of tunnel faces. Those faults that have drives against dip appear first in the lower part of tunnel faces as tunnel excavation progresses and their maximum longitudinal displacement shows a tendency to move from the middle part or middle upper part to the lower part of tunnel faces. In addition, when the dip of faults is larger the maximum longitudinal displacement moves from the left upper part toward the wall part in the case of drive with dip models and from the left lower part toward the wall part in the case of drives against dip models. Therefore, it was indicated that the attitudes of faults distributed ahead of tunnel faces and the locations where faults appear in tunnel faces can be predicted by analyzing the longitudinal displacement trajectory of tunnel faces following excavation.